Estimation of health care costs for work
AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 52:195–201 (2009)
Estimation of Health-Care Costs for
Work-Related Injuries in the Mexican
Institute of Social Security
Fernando Carlos-Rivera, MScE,1 Guadalupe Aguilar-Madrid, MD, Dr PH,2
´mez-Montenegro, MHA,1 Cuauhte
´moc A. Jua
´rez-Pe
´rez, MD, MSc,2
Pablo Anaya Go
2
´nchez-Roma
´n, MD, MSc,
Francisco Rau
´l Sa
Jaqueline E.A. Durcudoy Montandon, MSc,2 and Vı
´ctor Hugo Borja-Aburto, MD, PhD2
Background Data on the economic consequences of occupational injuries is scarce in
developing countries which prevents the recognition of their economic and social
consequences. This study assess the direct heath care costs of work-related accidents in the
Mexican Institute of Social Security, the largest health care institution in Latin America,
which covered 12,735,856 workers and their families in 2005.
Methods We estimated the cost of treatment for 295,594 officially reported occupational
injuries nation wide. A group of medical experts devised treatment algorithms to quantify
resource utilization for occupational injuries to which unit costs were applied. Total costs
were estimated as the product of the cost per illness and the severity weighted incidence of
occupational accidents.
Results Occupational injury rate was 2.9 per 100 workers. Average medical care cost per
case was $2,059 USD. The total cost of the health care of officially recognized injured
workers was $753,420,222 USD. If injury rate is corrected for underreporting, the cost for
formal injured workers is 791,216,460. If the same costs are applied for informal workers,
approximately half of the working population in Mexico, the cost of healthcare for
occupational injuries is about 1% of the gross domestic product.
Conclusions Health care costs of occupational accidents are similar to the economic
direct expenditures to compensate death and disability in the social security system in
Mexico. However, indirect costs might be as important as direct costs. Am. J. Ind. Med.
52:195–201, 2009. ß 2008 Wiley-Liss, Inc.
KEY WORDS: costs; occupational accidents; IMSS; Mexico
INTRODUCTION
1
RAC Salud Consultores, Mexico City, Mexico
Instituto Mexicano del Seguro Social, Unidad de Investigacio¤ n en Salud en el Trabajo,
Mexico City, Mexico
Contract grant sponsors: Fondo de Fomento a la Investigacio¤ n; Instituto Mexicano del
Seguro Social; Contract grant number: 2005/2/I/353.
*Correspondence to: V|¤ctor Hugo Borja-Aburto, Coordinacio¤ n de Salud en el Trabajo,
Centro Me¤dico Nacional Siglo XXI, Av. Cuauhte¤ moc 330, Edif. C, 1er piso, Col. Doctores,
06725 Me¤ xico, D.F., Me¤ xico. E-mail: [email protected]
2
Accepted 28 October 2008
DOI 10.1002/ajim.20666. Published online in Wiley InterScience
(www.interscience.wiley.com)
2008 Wiley-Liss, Inc.
International indirect estimates have reported that workrelated diseases and accidents represent a public health
problem in most developing countries [Leigh et al., 1999;
Giuffrida et al., 2002; Concha-Barrientos et al., 2005].
However, the lack of reliable and systematized data on workrelated accidents and illnesses make it difficult to show
the significant economic and social consequences of this
problem in Latin American and other developing countries.
For many countries official incidence data of occupational
196
Carlos-Rivera et al.
injuries show rates below developed countries, what erroneously indicate that this is not a problem in those countries.
This lack of information diminishes the priority of occupational health and so begins a vicious circle. Work and health
authorities, as well as business operators do not make
decisions, and workers and the general public do not demand
improvements in working conditions to reduce risks and
prevent those accidents and illnesses [Nuwayhid, 2004]. The
present study is an effort to estimate direct heath-care costs
for occupational accidents in Mexico, as an example of the
experience in developing countries.
Workers’ compensation plans in Mexico, called occupational risks insurance, are mandatory for all workers in the
formal sector of the economy. Occupational risks insurance
provides health care for the worker in the case of his/her
incurring some accident or disease associated with the
exercise of his/her work, or an in-transit accident that may
occur to and from the worker’s home and workplace.
Similarly, the employer is covered with respect to shortand long-term economic obligations (subsidies, aid, global
indemnizations, and pensions) that are established by the
Mexican Federal Work Law [Ley Federal del Trabajo, 2002].
The Mexican Institute Social Security (IMSS) Law
establishes that occupational risks insurance provisions
should be fully covered by employer insurance quota
payments. The formula for this premium recognizes and
rewards those who invest in prevention, and sets greater
financial contributions for companies registering higher
insurance claims. Therefore, accurate data are required to
classify enterprises and estimate the financial burden.
Although this insurance contemplates an important healthcare expenses component for workers experiencing occupational accidents or diseases, actuarial valuations have
basically taken into account the expenditure for indemnification for work-related disabilities and deaths, because IMSS
accounting systems do not separate health-care cost by
insurance branch. The balance for 2005 was an apparent net
surplus of approximately one-third of 1.8 billion USD
quota paid by employers [IMSS Report to the Federal
Executive Branch and the Congress, 2005–2006]. The
present study is an effort to estimate direct heath-care costs
for occupational accidents and diseases for IMSS insured
workers, as an example of the experience in developing
countries.
METHODS
In order to quantify health-care costs, we carried out a
study from the perspective of the health-services provider
(IMSS) in which the variable of interest comprises direct
medical costs for the year 2005. To determine health-care
costs, it was necessary, on the one hand, to obtain the number
and cases of work-related injuries, and on the other hand, to
estimate their health-care costs.
Incidence of Occupational Injuries
The incidence of work-related injuries and illnesses in
the year 2005 was obtained from the Occupational Health
Information System [IMSS, Statistical Memory, [Memoria
Estadı´stica], 2005]. This registry includes all injuries
recognized as work-related accidents by occupational
physicians, after they receive health care at IMSS owned
and operated hospitals and clinics. Total temporary disability
is paid at 100% of the salary since the first day of the
accident until return to work, 1 year maximum, or a pension
for permanent disability is granted. Previous reports have
shown that 30% of occupational accidents are not
registered [Salinas-Tovar et al., 2004]. Since occupational
diseases are not as easily recognized as accidents are, only a
few of them are declared and included in the registry. The
incidence of occupational diseases (about 5,000 cases
per year, basically traditional diseases: hearing loss and
pneumoconiosis) obtained from these official reports was so
low that this problem deserves special attention. Therefore,
we decided not to include occupational illnesses in this report
because this would underestimate the care cost of these
diseases.
Occupational injuries were coded according to the
World Health Organization’s International Disease Classification Version 10 (WHO-IDC-10, 1995) and listed according to their frequency. We organized injuries into similar
injury-type diagnostic groups (contusions, wounds, luxations, fractures, etc.) and anatomic region groups (head, neck,
thoracic organ, pelvic organ, etc.) according to the frequency
of the event in the worker population. This way, we
constituted 27 different injury groups that included 79% of
the cases reported in the occupational health statistics.
The remaining 21% of the cases were grouped as ‘‘other
diagnoses.’’ For the total cost estimation, ‘‘other diagnoses’’
were assigned the average cost of diagnostic groups.
Care Cost Estimation
A pilot study showed that consultation-derived medical
files did not provide sufficient information for estimating the
resources employed. Thus, to estimate the frequency of
resource use by diagnosis, we resorted to the opinion of a
panel of experts composed of IMSS medical specialists, with
whom we constructed treatment algorithms for each disease.
To the resources that these experts reported employing,
we applied the medical-care unit costs published by IMSS for
the main medical resources utilized in 2005 [Unit Costs;
Diario Oficial de la Federacio´n, 2004]. In the case of
drugs, we used acquisition costs published on the IMSS
transparency web page according to bids effected in the year
2005 [Transparency Portal (Portal Transparencia) IMSS,
2005].
Costs of Work-Related Injuries
Medical costs included the following headings: outpatient specialty consultations (OSC); laboratory and imaging studies; drugs; surgery (SURG); rehabilitation; use of
ambulances; primary care-level consultations, and occupational health consultations (OHC).
To determine medical resources for each diagnostic
group, the panels of experts defined the usual treatment
algorithms at IMSS and later, resources employed. These
panels of experts comprised 82 IMSS physicians in the Valley
of Mexico, where they cared for 20% of injured workers.
In the first study stage algorithms described typical
treatment for each diagnosis according to its level of
complexity or severity (e.g., see Fig. 1). For a single identical
general diagnosis, various scenarios can be presented
according to resources utilization necessary for medical care
according to the severity and complications of his/her illness,
that is, required the use of other services such as surgical
interventions (SURG), in addition to hospitalization days
(HOSP) and a greater number of ambulatory rehabilitation
(AR) sessions, in comparison with patients not requiring
surgery.
In the second stage of the study and from the treatment
algorithms, we constructed databases with this information,
and unit costs were divided by cost centers, by heading, and
by event. In the case of headings, we included the following
cost centers: consultations; hospital bed days; imaging
examinations; laboratory examinations; surgical intervention, and minor procedures carried out in the consultory,
while we classified the following by event: emergencies
(EMERG); consultations; hospitalizations (HOSP); surgery
(SURG); and intensive care unit (ICU). In addition to these,
there are the following cost centers that comprise part of the
two previous centers: rehabilitation, drugs, and OHC.
In the third study stage, we estimated costs taking as
reference medical resources utilization for the treatment of
each diagnosis, differentiating this according to the level of
complexity. Likewise, the panels of specialists defined the
197
proportion of cases in each diagnostic group according to the
complexity of each illness to be used to weight cases within
each diagnostic group. Once the amount of each medical
resource utilized in the care of the patient in each scenario
was determined, these amounts were multiplied by unit costs,
and a total cost weighted by the complexity of each patient in
the diagnostic groups was obtained.
The formula employed for calculating the per-patient
total cost was
n
X
Cjx ¼
Qjxi Pi
x¼1
where Cjx is the cost for patient ‘‘j’’ with complexity ‘‘x,’’ Qjxi
the amount utilized for medical resource care ‘‘i’’ used by
patient ‘‘j’’ with complexity ‘‘x,’’ and Pi the unit cost of
medical service ‘‘i.’’
In a fourth stage, the cost of each diagnosis was
multiplied by the number of incident cases, and the sum of
all these cases represents the total health-care cost of
occupational accidents in the year 2005 at IMSS.
To broad the explanation of the methods, we included an
example of an exposed tibial fracture. Figure 1 displays the
treatment algorithm defined by the experts to identify the
frequency of services utilization in the medical-care process
from the patient’s admittance to the emergency room to his/
her hospital discharge and getting back to work after an
occupation health physician certification. According to
the panel of experts, there are three main types of tibial
fracture, based on the number of surgeries per patient: mild,
moderate, and severe (for one, two, and three procedures,
respectively). Table I shows the total cost and the patient
proportional distribution according to severity for tibial
fractures. The expected costs for mild, moderate, and severe
exposed tibial fractures were $6,867 USD, $10,098 USD, and
$13,362 USD, respectively. Finally, the total cost for each
fracture type is weighted by the frequency mentioned by the
experts (30% mild, 63% moderate, and 7% severe); this result
FIGURE 1. Treatment algorithm of exposed tibia fracture. Mexican Institute of Social Security (IMSS), 2005. EMERG, Emergency
consultation; SURG, Surgery; HOSP, Hospitalization; HR,Hospital rehabilitation; OSC, Outpatient specialist consultation; AR, Ambulatory
rehabilitation; OHC,Occupational health consultation.Note:Numbersbetween parenthesesindicatethefrequencyofeach resource.
198
Carlos-Rivera et al.
TABLE I. Cost Estimation of Exposed Tibial Fracture, Mexican Institute of Social Security (IMSS), 2005
Patient type according to resources utilization frequency
Parameters included in the expected-costs model
Mild (30%)
Frequency of medical resources utilization
Moderate (63%)
Severe (7%)
Unit cost (USD)
Frequency
Total cost (USD)
Frequency
127
1,857
364
7
100
18
2
1
10
10
4
3
254
1,857
3,637
72
401
54
2
2
13
13
4
3
254
3,714
4,728
94
401
54
2
3
16
16
4
3
254
5,571
5,819
116
401
54
7
40
7
28
110
0
2
9
12
0
79
65
337
110
6,867
20
2
9
16
149
79
65
450
110
10,098
50
2
11
18
373
79
80
506
110
13,362
Emergency consultations (EMERG)
Surgical interventions (SURG)
Days of hospitalization (HOSP)
Hospital rehabilitation (HR) sessions
Out-patient specialty consultations (OSC)
Specialty consultation procedures (bandaging, removal
of surgical stitches, splint, or cast removal)
Ambulatory rehabilitation (AR) sessions
Occupational health consultation (OHC)
Clinical analyses practiced
Radiodiagnostic studies
Drugs
Average per-patient expected cost of exposed tibial fracture
Total cost (USD)
Frequency
Total cost (USD)
Details may not add up to totals due rounding.
is applied to the expected per-patient calculated cost for an
exposed tibial fracture, which in this case was $9,357 USD
(Table II). Likewise, in this table we present the distribution
by severity and the expected costs for two other different
conditions.
RESULTS
In the year 2005, IMSS insured 12,735,856 workers
(30% of the working population) against occupational
injuries from 802,107 companies; of these workers,
373,239 received medical care for occupational risks
(2.9/100 workers). Of these latter workers, 79% were
classified as occupational accidents, 19% as commuting
accidents, and the remaining 2% as occupational diseases.
Of these occupational injuries, 1,367 were fatal and
13,450 generated permanent disabilities. In addition,
occupational accidents caused a loss of 7,868,180 workdays
due to temporary disability. The economic provisions to
compensate for temporary loss of the ability to work and
indemnification for work-related permanent disabilities and
deaths raised 578 million USD [IMSS, Statistical Memory,
EOIT, 2005].
Table III shows health-care total costs for occupational
accidents, separated from commuting or in-transit accidents,
by 29 diagnostic groups incidence. Average medical cost
of occupational accidents was $2,059 USD per case, with
important variations ranging from $225 USD for simple
contusions to $38,250 for flame-related burns treatment.
Simple contusions were the most frequent injuries—
79,544 cases per annum—but exhibited the lowest cost.
Occupational accidents caused 2,384 hand and or finger
amputations, with $3,156 USD per-case cost. Likewise,
ocular injuries are similar in cost and incidence, but
cause more disability. Finally, the highest average cost is
represented by flame-related burns, with an average per-case
cost of $38,250 USD and an incidence of 201 workers
per year. The three most expensive cost centers for occupational injuries were surgery, which comprised the 37.3% of
the total costs, followed by hospital stay and by OSC with
30.1% and 12.0% of the total costs, respectively.
TABLE II. Examples of Estimation of Expected Costs for Different Conditions
Mild
Conditions
Simple contusion
Spinal column/disc hernia
Exposed tibial fracture
a
Moderate
%
Cost per case
%
Cost per case
100
50
30
225
723
6,867
50
63
6,049
10,098
Severe
%
7
Expected costa
Cost per case
$ USD
13,362
225
3,386
9,357
The expect cost was calculated as the summatory of the products of the proportion of patients in each severity condition and their associated cost.
Costs of Work-Related Injuries
199
TABLE III. Total Costs of Occupational Accidents Ordered by Incidence, Mexican Institute of Social Security (IMSS), 2005
Injury
Simple contusions
Spinal column/disc hernia
Contaminated wounds
Luxations/sprains of the ankle
Contaminated wounds of the hand
Closed fracture of the wrist and hand
Sequelae of ankle and foot sprains and fractures
Interphalangial/hand/fingers
Sequelae of knee sprain and trauma
Hand fracture sequelae
Shoulder luxations
Sequelae of knee sprain and trauma
Distal radial fracture
Closed fracture and luxation of the ankle
Exposed wrist fracture
Electricity-related burns
Closed tibial fracture
Abdomen/thorax/thoracic abdominal trauma
Amputation of hand, fingers/multiple
Ocular/orbital injury
Closed humerus fracture
Spinal column/spondylolisthesis
Exposed tibial fracture
Crushing/hand
Hemothoracic injury
Flame-related burns
Crushing/upper extremites
Other injuries
Total
Number of
occupational
accidents
Number of
commuting
accidents
Average cost
per case
($, USD)
Occupational
accidents
costs ($, USD)
Costs for
commuting
accidents ($, USD)
Total costs
($, USD)
79,544
22,843
19,759
18,948
14,468
11,994
8,508
7,248
5,989
5,560
4,881
4,857
4,091
3,582
2,999
2,830
2,813
2,511
2,384
2,097
1,326
1,139
938
297
216
201
54
63,518
295,594
20,021
1,156
3,239
11,730
3,239
1,013
4,438
1,225
2,035
623
873
1,496
1,040
828
253
29
1,003
547
24
133
640
141
334
10
50
3
2
14,228
70,353
225
3,386
2,263
466
2,463
768
4,178
679
3,903
5,955
864
3,384
4,243
5,301
2,655
21,103
4,295
9,872
3,156
3,485
4,281
7,585
9,357
2,981
842
38,250
5,252
2,059
17,871,852
77,345,663
44,718,014
8,829,292
35,636,781
9,211,248
35,550,000
4,923,475
23,373,891
33,110,312
4,216,579
16,437,566
17,358,528
18,987,992
7,961,118
59,720,352
12,080,361
24,788,504
7,522,886
7,307,679
5,675,962
8,639,884
8,772,329
885,378
181,809
7,688,226
283,626
130,771,875
629,851,181
4,498,295
3,914,179
7,330,414
5,465,886
7,978,127
777,792
18,543,502
832,127
7,944,032
3,708,367
754,164
5,062,919
4,412,825
4,389,184
672,232
611,975
4,307,051
5,399,965
75,734
463,482
2,739,529
1,069,555
3,127,628
29,811
42,086
114,750
10,505
29,292,926
123,569,040
22,370,147
81,259,842
52,048,428
14,295,178
43,614,908
9,989,040
54,093,502
5,755,602
31,317,923
36,818,678
4,970,742
21,500,485
21,771,353
23,377,176
8,633,350
60,332,327
16,387,412
30,188,469
7,598,620
7,771,161
8,415,491
9,709,440
11,899,957
915,189
223,895
7,802,975
294,131
160,064,801
753,420,222
OA, occupational accident; ITA, in commuting accident; USD, U.S. dollars.
Details may not add up to totals due rounding.
DISCUSSION
This study estimated the magnitude of the direct cost
of health care of occupational injuries at IMSS. However,
before we generalize the results nationwide, we must
recognize some limitations derived from the use of official
records to estimate incidence and the employed methodology
for cost calculation.
Since consultation-derived medical files did not provide
sufficient information for estimating treatment algorithms,
we resorted to the opinion of a panel of experts composed of
IMSS medical specialists. However, participating physicians
from the Valley of Mexico, with whom we constructed
treatment algorithms for each disease, might not accurately
represent the treatment algorithms provided by physicians
and the actual treatment received by patients nationwide.
However, it is worth to notice that most practicing physicians
at IMSS are formed in the same institution and follow
standards set by central authorities. Drugs and equipments
are bought based on central guidelines, and physicians are not
allowed to prescribe drugs out of a pre-established list. This
could reduce uncertainties but does not completely eliminate
possible bias on treatment estimates.
Another limitation is that occupational diseases were not
included in these estimates. The reporting system for
occupational diseases is particularly weak because of the
difficulty to relate the cause of the disease to the working
environment. Therefore, the misattribution of occupational
illness to other sources can be more important than occupational accidents. However, the contribution of occupational
200
Carlos-Rivera et al.
illnesses to the total medical cost can be very high [Leigh
et al., 2003].
The medical-care costs presented in this work are
conservative estimates if compared with those carried out in
other countries. This underestimation can originate from the
low incidence of recognized occupational accidents and
diseases at IMSS and due to lower unit costs of care in
Mexico. The work-related injuries rate for 2005 was 2.9 per
100 workers, a number lower than that reported in U.S. and
Canada and about half of that reported in Chile and Spain
[International Labour Organization [ILO], Statistics, 2003
and 2007].
The injury-type classification process must take great care
to avoid cross-over subsidies between branches where it is
difficult to separate expenditures since health care is provided
to their beneficiaries in various insurance branches, such as
occupational injuries, common disease and maternity, voluntary insurance, and health care for retired worker. If we correct
for the 30% misclassification found in a recent report [SalinasTovar et al., 2004], the number of work-related injures would
be 384,272 cases. Taking into account the average cost per
case calculations of the present study, the corrected cost would
be $ 791,216,460 USD.
It is noteworthy that the costs of injuries reported herein
cannot be employed directly for estimating the costs of
injuries occurring outside the work environment. The group
of medical experts participating in the advisory panels who
defined the proportion of patients according to the severity
of each diagnostic group referred that in general terms,
occupational injuries are considered as injuries with a
greater risk of infection; thus, they should be managed
more carefully. Nonetheless, on the other hand, workers are
relatively healthier than the general population, and special
management was not considered, for example, adult patients
with co-morbidities such as diabetes and high blood pressure
submitted to surgery.
The average cost of work-related injuries reported
here is about half of the median health care of cost of 4,377
reported in a Canadian cohort [Alamgir et al., 2008].
This estimation demonstrates the high cost of health care
for work-related injuries and the need to include them in
any income–expense balance in a social security system,
especially if financial incentives for prevention programs are
considered. Cost appraisal data for commuting accidents are
important for consideration, given that these are not included
in occupational risk insurance-premium calculations. The
cost of these commuting accidents represents 16% of the total
cost.
The estimated health-care expenditures of occupational
injuries at IMSS for 753 million USD and the costs for
economic provisions to compensate for loss of the
ability to work for 578 million USD for indemnification for
work-related disabilities and deaths comprise only two
components of the total occupational-injury costs. Indirect
costs might be as important as or more important than direct
costs [Weil, 2001]. Indirect costs include loss of productivity,
pain, and suffering-associated, as well as out-of-pocket
expenses contracted by the family concerning patient home
care. Conservative estimates suggest an indirect-to-direct
cost ratio of 1:1 [Dorman, 1999]. There are many variations
of the proportion of the costs but usually the proportion of
indirect costs is much bigger than direct costs [Ha¨ma¨la¨inen
et al., 2006; Brown et al., 2007].
At IMSS direct health-care costs of occupational
accidents are completely covered by the premium paid by
the employer. However, indirect costs are not directly
compensated for by the social security system, but borne
by workers, their families, employers, the public health
system, and taxpayers. The fact that employers and
social security institutions bear only a portion of total costs
has implications in the appreciation of its true magnitude, the
economic and social impact that occupational accidents and
diseases represent for health-care institutions, the society,
and the country.
IMSS covers most of the formal sector of the economy.
However, the informal sector has grown rapidly during the
last decades so that above figures solely reflect the reality of
occupational accidents in 30% of the workers [Sa´nchezRoma´n et al., 2006]. If we apply the rates of the population
covered by IMSS to the total workforce, assuming similar
occupational risks, we can estimate that 1.4 million workrelated injuries occur each year in the country. The healthcare expenditure under this occupational accidents and
diseases is borne by the workers, public health system, and
finally, the taxpayers. If similar direct cost could be applied,
then health care and indemnification for work-related
disabilities and deaths would be close to 1% of the NGP.
This figure is similar to that reported in Costa Rica in 1995 by
the National Insurance Institute (Instituto Nacional de
Seguros), which exclusively administers occupational risks
and covers 56% of the country’s work force (EAP) and 84.3%
of the salaried population.
Estimations from Bolivia and Panama yielded a cost
equivalent to 9.8–11% of the GNP, respectively (OPS-OMS,
1998 Informe; OPS-OMS, 1999 124.a Sesio´n; OPS-OMSS,
Regional Worker Health Plan, 2001), 124th Executive
Committee Session). Likewise, in the U.S. Leigh and
collaborators in 1992 estimated that occupational illness
and injury costs represented 3% of the GNP [Leigh et al.,
1997]. Similarly, a study conducted by the Universidad
Pompeu Fabra [2001] in Spain reported that the total cost for
occupational accidents and diseases represented >1.7% of
the GNP [Cost Approximation of Work Claims in Spain,
2002]. Finally, for the European Agency for Occupational
Safety and Health at Work (EU-OSHA) estimated cost of
occupational accidents varied from 1% to 3% of the GNP,
without including disability compensation costs [EU-OSHA,
2002].
Costs of Work-Related Injuries
201
ACKNOWLEDGMENTS
de trabajo y a´rea de promocio´n de los trabajadores. Me´xico, D.F.:
Divisio´n Te´cnica de Informacio´n en Estadı´stica en Salud. ST-5; 2006.
We gratefully thank the team of specialist who
developed the treatment algorithms and the staff from the
participating hospitals: Hospitales de Traumatologı´a y
Ortopedia Victorio de la Fuente, Lomas Verdes, Pestalozzi,
and Unidad de Medicina Familiar No. 1 from the Instituto
Mexicano del Seguro Social.
Leigh JP, Markowitz SB, Fahs M, Shin CH, Landrigan PJ. 1997.
Occupational injury and illness in the United States; Estimates of costs,
morbidity, and mortality. Arch Intern Med 157:1557–1568.
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Estimation of Health-Care Costs for
Work-Related Injuries in the Mexican
Institute of Social Security
Fernando Carlos-Rivera, MScE,1 Guadalupe Aguilar-Madrid, MD, Dr PH,2
´mez-Montenegro, MHA,1 Cuauhte
´moc A. Jua
´rez-Pe
´rez, MD, MSc,2
Pablo Anaya Go
2
´nchez-Roma
´n, MD, MSc,
Francisco Rau
´l Sa
Jaqueline E.A. Durcudoy Montandon, MSc,2 and Vı
´ctor Hugo Borja-Aburto, MD, PhD2
Background Data on the economic consequences of occupational injuries is scarce in
developing countries which prevents the recognition of their economic and social
consequences. This study assess the direct heath care costs of work-related accidents in the
Mexican Institute of Social Security, the largest health care institution in Latin America,
which covered 12,735,856 workers and their families in 2005.
Methods We estimated the cost of treatment for 295,594 officially reported occupational
injuries nation wide. A group of medical experts devised treatment algorithms to quantify
resource utilization for occupational injuries to which unit costs were applied. Total costs
were estimated as the product of the cost per illness and the severity weighted incidence of
occupational accidents.
Results Occupational injury rate was 2.9 per 100 workers. Average medical care cost per
case was $2,059 USD. The total cost of the health care of officially recognized injured
workers was $753,420,222 USD. If injury rate is corrected for underreporting, the cost for
formal injured workers is 791,216,460. If the same costs are applied for informal workers,
approximately half of the working population in Mexico, the cost of healthcare for
occupational injuries is about 1% of the gross domestic product.
Conclusions Health care costs of occupational accidents are similar to the economic
direct expenditures to compensate death and disability in the social security system in
Mexico. However, indirect costs might be as important as direct costs. Am. J. Ind. Med.
52:195–201, 2009. ß 2008 Wiley-Liss, Inc.
KEY WORDS: costs; occupational accidents; IMSS; Mexico
INTRODUCTION
1
RAC Salud Consultores, Mexico City, Mexico
Instituto Mexicano del Seguro Social, Unidad de Investigacio¤ n en Salud en el Trabajo,
Mexico City, Mexico
Contract grant sponsors: Fondo de Fomento a la Investigacio¤ n; Instituto Mexicano del
Seguro Social; Contract grant number: 2005/2/I/353.
*Correspondence to: V|¤ctor Hugo Borja-Aburto, Coordinacio¤ n de Salud en el Trabajo,
Centro Me¤dico Nacional Siglo XXI, Av. Cuauhte¤ moc 330, Edif. C, 1er piso, Col. Doctores,
06725 Me¤ xico, D.F., Me¤ xico. E-mail: [email protected]
2
Accepted 28 October 2008
DOI 10.1002/ajim.20666. Published online in Wiley InterScience
(www.interscience.wiley.com)
2008 Wiley-Liss, Inc.
International indirect estimates have reported that workrelated diseases and accidents represent a public health
problem in most developing countries [Leigh et al., 1999;
Giuffrida et al., 2002; Concha-Barrientos et al., 2005].
However, the lack of reliable and systematized data on workrelated accidents and illnesses make it difficult to show
the significant economic and social consequences of this
problem in Latin American and other developing countries.
For many countries official incidence data of occupational
196
Carlos-Rivera et al.
injuries show rates below developed countries, what erroneously indicate that this is not a problem in those countries.
This lack of information diminishes the priority of occupational health and so begins a vicious circle. Work and health
authorities, as well as business operators do not make
decisions, and workers and the general public do not demand
improvements in working conditions to reduce risks and
prevent those accidents and illnesses [Nuwayhid, 2004]. The
present study is an effort to estimate direct heath-care costs
for occupational accidents in Mexico, as an example of the
experience in developing countries.
Workers’ compensation plans in Mexico, called occupational risks insurance, are mandatory for all workers in the
formal sector of the economy. Occupational risks insurance
provides health care for the worker in the case of his/her
incurring some accident or disease associated with the
exercise of his/her work, or an in-transit accident that may
occur to and from the worker’s home and workplace.
Similarly, the employer is covered with respect to shortand long-term economic obligations (subsidies, aid, global
indemnizations, and pensions) that are established by the
Mexican Federal Work Law [Ley Federal del Trabajo, 2002].
The Mexican Institute Social Security (IMSS) Law
establishes that occupational risks insurance provisions
should be fully covered by employer insurance quota
payments. The formula for this premium recognizes and
rewards those who invest in prevention, and sets greater
financial contributions for companies registering higher
insurance claims. Therefore, accurate data are required to
classify enterprises and estimate the financial burden.
Although this insurance contemplates an important healthcare expenses component for workers experiencing occupational accidents or diseases, actuarial valuations have
basically taken into account the expenditure for indemnification for work-related disabilities and deaths, because IMSS
accounting systems do not separate health-care cost by
insurance branch. The balance for 2005 was an apparent net
surplus of approximately one-third of 1.8 billion USD
quota paid by employers [IMSS Report to the Federal
Executive Branch and the Congress, 2005–2006]. The
present study is an effort to estimate direct heath-care costs
for occupational accidents and diseases for IMSS insured
workers, as an example of the experience in developing
countries.
METHODS
In order to quantify health-care costs, we carried out a
study from the perspective of the health-services provider
(IMSS) in which the variable of interest comprises direct
medical costs for the year 2005. To determine health-care
costs, it was necessary, on the one hand, to obtain the number
and cases of work-related injuries, and on the other hand, to
estimate their health-care costs.
Incidence of Occupational Injuries
The incidence of work-related injuries and illnesses in
the year 2005 was obtained from the Occupational Health
Information System [IMSS, Statistical Memory, [Memoria
Estadı´stica], 2005]. This registry includes all injuries
recognized as work-related accidents by occupational
physicians, after they receive health care at IMSS owned
and operated hospitals and clinics. Total temporary disability
is paid at 100% of the salary since the first day of the
accident until return to work, 1 year maximum, or a pension
for permanent disability is granted. Previous reports have
shown that 30% of occupational accidents are not
registered [Salinas-Tovar et al., 2004]. Since occupational
diseases are not as easily recognized as accidents are, only a
few of them are declared and included in the registry. The
incidence of occupational diseases (about 5,000 cases
per year, basically traditional diseases: hearing loss and
pneumoconiosis) obtained from these official reports was so
low that this problem deserves special attention. Therefore,
we decided not to include occupational illnesses in this report
because this would underestimate the care cost of these
diseases.
Occupational injuries were coded according to the
World Health Organization’s International Disease Classification Version 10 (WHO-IDC-10, 1995) and listed according to their frequency. We organized injuries into similar
injury-type diagnostic groups (contusions, wounds, luxations, fractures, etc.) and anatomic region groups (head, neck,
thoracic organ, pelvic organ, etc.) according to the frequency
of the event in the worker population. This way, we
constituted 27 different injury groups that included 79% of
the cases reported in the occupational health statistics.
The remaining 21% of the cases were grouped as ‘‘other
diagnoses.’’ For the total cost estimation, ‘‘other diagnoses’’
were assigned the average cost of diagnostic groups.
Care Cost Estimation
A pilot study showed that consultation-derived medical
files did not provide sufficient information for estimating the
resources employed. Thus, to estimate the frequency of
resource use by diagnosis, we resorted to the opinion of a
panel of experts composed of IMSS medical specialists, with
whom we constructed treatment algorithms for each disease.
To the resources that these experts reported employing,
we applied the medical-care unit costs published by IMSS for
the main medical resources utilized in 2005 [Unit Costs;
Diario Oficial de la Federacio´n, 2004]. In the case of
drugs, we used acquisition costs published on the IMSS
transparency web page according to bids effected in the year
2005 [Transparency Portal (Portal Transparencia) IMSS,
2005].
Costs of Work-Related Injuries
Medical costs included the following headings: outpatient specialty consultations (OSC); laboratory and imaging studies; drugs; surgery (SURG); rehabilitation; use of
ambulances; primary care-level consultations, and occupational health consultations (OHC).
To determine medical resources for each diagnostic
group, the panels of experts defined the usual treatment
algorithms at IMSS and later, resources employed. These
panels of experts comprised 82 IMSS physicians in the Valley
of Mexico, where they cared for 20% of injured workers.
In the first study stage algorithms described typical
treatment for each diagnosis according to its level of
complexity or severity (e.g., see Fig. 1). For a single identical
general diagnosis, various scenarios can be presented
according to resources utilization necessary for medical care
according to the severity and complications of his/her illness,
that is, required the use of other services such as surgical
interventions (SURG), in addition to hospitalization days
(HOSP) and a greater number of ambulatory rehabilitation
(AR) sessions, in comparison with patients not requiring
surgery.
In the second stage of the study and from the treatment
algorithms, we constructed databases with this information,
and unit costs were divided by cost centers, by heading, and
by event. In the case of headings, we included the following
cost centers: consultations; hospital bed days; imaging
examinations; laboratory examinations; surgical intervention, and minor procedures carried out in the consultory,
while we classified the following by event: emergencies
(EMERG); consultations; hospitalizations (HOSP); surgery
(SURG); and intensive care unit (ICU). In addition to these,
there are the following cost centers that comprise part of the
two previous centers: rehabilitation, drugs, and OHC.
In the third study stage, we estimated costs taking as
reference medical resources utilization for the treatment of
each diagnosis, differentiating this according to the level of
complexity. Likewise, the panels of specialists defined the
197
proportion of cases in each diagnostic group according to the
complexity of each illness to be used to weight cases within
each diagnostic group. Once the amount of each medical
resource utilized in the care of the patient in each scenario
was determined, these amounts were multiplied by unit costs,
and a total cost weighted by the complexity of each patient in
the diagnostic groups was obtained.
The formula employed for calculating the per-patient
total cost was
n
X
Cjx ¼
Qjxi Pi
x¼1
where Cjx is the cost for patient ‘‘j’’ with complexity ‘‘x,’’ Qjxi
the amount utilized for medical resource care ‘‘i’’ used by
patient ‘‘j’’ with complexity ‘‘x,’’ and Pi the unit cost of
medical service ‘‘i.’’
In a fourth stage, the cost of each diagnosis was
multiplied by the number of incident cases, and the sum of
all these cases represents the total health-care cost of
occupational accidents in the year 2005 at IMSS.
To broad the explanation of the methods, we included an
example of an exposed tibial fracture. Figure 1 displays the
treatment algorithm defined by the experts to identify the
frequency of services utilization in the medical-care process
from the patient’s admittance to the emergency room to his/
her hospital discharge and getting back to work after an
occupation health physician certification. According to
the panel of experts, there are three main types of tibial
fracture, based on the number of surgeries per patient: mild,
moderate, and severe (for one, two, and three procedures,
respectively). Table I shows the total cost and the patient
proportional distribution according to severity for tibial
fractures. The expected costs for mild, moderate, and severe
exposed tibial fractures were $6,867 USD, $10,098 USD, and
$13,362 USD, respectively. Finally, the total cost for each
fracture type is weighted by the frequency mentioned by the
experts (30% mild, 63% moderate, and 7% severe); this result
FIGURE 1. Treatment algorithm of exposed tibia fracture. Mexican Institute of Social Security (IMSS), 2005. EMERG, Emergency
consultation; SURG, Surgery; HOSP, Hospitalization; HR,Hospital rehabilitation; OSC, Outpatient specialist consultation; AR, Ambulatory
rehabilitation; OHC,Occupational health consultation.Note:Numbersbetween parenthesesindicatethefrequencyofeach resource.
198
Carlos-Rivera et al.
TABLE I. Cost Estimation of Exposed Tibial Fracture, Mexican Institute of Social Security (IMSS), 2005
Patient type according to resources utilization frequency
Parameters included in the expected-costs model
Mild (30%)
Frequency of medical resources utilization
Moderate (63%)
Severe (7%)
Unit cost (USD)
Frequency
Total cost (USD)
Frequency
127
1,857
364
7
100
18
2
1
10
10
4
3
254
1,857
3,637
72
401
54
2
2
13
13
4
3
254
3,714
4,728
94
401
54
2
3
16
16
4
3
254
5,571
5,819
116
401
54
7
40
7
28
110
0
2
9
12
0
79
65
337
110
6,867
20
2
9
16
149
79
65
450
110
10,098
50
2
11
18
373
79
80
506
110
13,362
Emergency consultations (EMERG)
Surgical interventions (SURG)
Days of hospitalization (HOSP)
Hospital rehabilitation (HR) sessions
Out-patient specialty consultations (OSC)
Specialty consultation procedures (bandaging, removal
of surgical stitches, splint, or cast removal)
Ambulatory rehabilitation (AR) sessions
Occupational health consultation (OHC)
Clinical analyses practiced
Radiodiagnostic studies
Drugs
Average per-patient expected cost of exposed tibial fracture
Total cost (USD)
Frequency
Total cost (USD)
Details may not add up to totals due rounding.
is applied to the expected per-patient calculated cost for an
exposed tibial fracture, which in this case was $9,357 USD
(Table II). Likewise, in this table we present the distribution
by severity and the expected costs for two other different
conditions.
RESULTS
In the year 2005, IMSS insured 12,735,856 workers
(30% of the working population) against occupational
injuries from 802,107 companies; of these workers,
373,239 received medical care for occupational risks
(2.9/100 workers). Of these latter workers, 79% were
classified as occupational accidents, 19% as commuting
accidents, and the remaining 2% as occupational diseases.
Of these occupational injuries, 1,367 were fatal and
13,450 generated permanent disabilities. In addition,
occupational accidents caused a loss of 7,868,180 workdays
due to temporary disability. The economic provisions to
compensate for temporary loss of the ability to work and
indemnification for work-related permanent disabilities and
deaths raised 578 million USD [IMSS, Statistical Memory,
EOIT, 2005].
Table III shows health-care total costs for occupational
accidents, separated from commuting or in-transit accidents,
by 29 diagnostic groups incidence. Average medical cost
of occupational accidents was $2,059 USD per case, with
important variations ranging from $225 USD for simple
contusions to $38,250 for flame-related burns treatment.
Simple contusions were the most frequent injuries—
79,544 cases per annum—but exhibited the lowest cost.
Occupational accidents caused 2,384 hand and or finger
amputations, with $3,156 USD per-case cost. Likewise,
ocular injuries are similar in cost and incidence, but
cause more disability. Finally, the highest average cost is
represented by flame-related burns, with an average per-case
cost of $38,250 USD and an incidence of 201 workers
per year. The three most expensive cost centers for occupational injuries were surgery, which comprised the 37.3% of
the total costs, followed by hospital stay and by OSC with
30.1% and 12.0% of the total costs, respectively.
TABLE II. Examples of Estimation of Expected Costs for Different Conditions
Mild
Conditions
Simple contusion
Spinal column/disc hernia
Exposed tibial fracture
a
Moderate
%
Cost per case
%
Cost per case
100
50
30
225
723
6,867
50
63
6,049
10,098
Severe
%
7
Expected costa
Cost per case
$ USD
13,362
225
3,386
9,357
The expect cost was calculated as the summatory of the products of the proportion of patients in each severity condition and their associated cost.
Costs of Work-Related Injuries
199
TABLE III. Total Costs of Occupational Accidents Ordered by Incidence, Mexican Institute of Social Security (IMSS), 2005
Injury
Simple contusions
Spinal column/disc hernia
Contaminated wounds
Luxations/sprains of the ankle
Contaminated wounds of the hand
Closed fracture of the wrist and hand
Sequelae of ankle and foot sprains and fractures
Interphalangial/hand/fingers
Sequelae of knee sprain and trauma
Hand fracture sequelae
Shoulder luxations
Sequelae of knee sprain and trauma
Distal radial fracture
Closed fracture and luxation of the ankle
Exposed wrist fracture
Electricity-related burns
Closed tibial fracture
Abdomen/thorax/thoracic abdominal trauma
Amputation of hand, fingers/multiple
Ocular/orbital injury
Closed humerus fracture
Spinal column/spondylolisthesis
Exposed tibial fracture
Crushing/hand
Hemothoracic injury
Flame-related burns
Crushing/upper extremites
Other injuries
Total
Number of
occupational
accidents
Number of
commuting
accidents
Average cost
per case
($, USD)
Occupational
accidents
costs ($, USD)
Costs for
commuting
accidents ($, USD)
Total costs
($, USD)
79,544
22,843
19,759
18,948
14,468
11,994
8,508
7,248
5,989
5,560
4,881
4,857
4,091
3,582
2,999
2,830
2,813
2,511
2,384
2,097
1,326
1,139
938
297
216
201
54
63,518
295,594
20,021
1,156
3,239
11,730
3,239
1,013
4,438
1,225
2,035
623
873
1,496
1,040
828
253
29
1,003
547
24
133
640
141
334
10
50
3
2
14,228
70,353
225
3,386
2,263
466
2,463
768
4,178
679
3,903
5,955
864
3,384
4,243
5,301
2,655
21,103
4,295
9,872
3,156
3,485
4,281
7,585
9,357
2,981
842
38,250
5,252
2,059
17,871,852
77,345,663
44,718,014
8,829,292
35,636,781
9,211,248
35,550,000
4,923,475
23,373,891
33,110,312
4,216,579
16,437,566
17,358,528
18,987,992
7,961,118
59,720,352
12,080,361
24,788,504
7,522,886
7,307,679
5,675,962
8,639,884
8,772,329
885,378
181,809
7,688,226
283,626
130,771,875
629,851,181
4,498,295
3,914,179
7,330,414
5,465,886
7,978,127
777,792
18,543,502
832,127
7,944,032
3,708,367
754,164
5,062,919
4,412,825
4,389,184
672,232
611,975
4,307,051
5,399,965
75,734
463,482
2,739,529
1,069,555
3,127,628
29,811
42,086
114,750
10,505
29,292,926
123,569,040
22,370,147
81,259,842
52,048,428
14,295,178
43,614,908
9,989,040
54,093,502
5,755,602
31,317,923
36,818,678
4,970,742
21,500,485
21,771,353
23,377,176
8,633,350
60,332,327
16,387,412
30,188,469
7,598,620
7,771,161
8,415,491
9,709,440
11,899,957
915,189
223,895
7,802,975
294,131
160,064,801
753,420,222
OA, occupational accident; ITA, in commuting accident; USD, U.S. dollars.
Details may not add up to totals due rounding.
DISCUSSION
This study estimated the magnitude of the direct cost
of health care of occupational injuries at IMSS. However,
before we generalize the results nationwide, we must
recognize some limitations derived from the use of official
records to estimate incidence and the employed methodology
for cost calculation.
Since consultation-derived medical files did not provide
sufficient information for estimating treatment algorithms,
we resorted to the opinion of a panel of experts composed of
IMSS medical specialists. However, participating physicians
from the Valley of Mexico, with whom we constructed
treatment algorithms for each disease, might not accurately
represent the treatment algorithms provided by physicians
and the actual treatment received by patients nationwide.
However, it is worth to notice that most practicing physicians
at IMSS are formed in the same institution and follow
standards set by central authorities. Drugs and equipments
are bought based on central guidelines, and physicians are not
allowed to prescribe drugs out of a pre-established list. This
could reduce uncertainties but does not completely eliminate
possible bias on treatment estimates.
Another limitation is that occupational diseases were not
included in these estimates. The reporting system for
occupational diseases is particularly weak because of the
difficulty to relate the cause of the disease to the working
environment. Therefore, the misattribution of occupational
illness to other sources can be more important than occupational accidents. However, the contribution of occupational
200
Carlos-Rivera et al.
illnesses to the total medical cost can be very high [Leigh
et al., 2003].
The medical-care costs presented in this work are
conservative estimates if compared with those carried out in
other countries. This underestimation can originate from the
low incidence of recognized occupational accidents and
diseases at IMSS and due to lower unit costs of care in
Mexico. The work-related injuries rate for 2005 was 2.9 per
100 workers, a number lower than that reported in U.S. and
Canada and about half of that reported in Chile and Spain
[International Labour Organization [ILO], Statistics, 2003
and 2007].
The injury-type classification process must take great care
to avoid cross-over subsidies between branches where it is
difficult to separate expenditures since health care is provided
to their beneficiaries in various insurance branches, such as
occupational injuries, common disease and maternity, voluntary insurance, and health care for retired worker. If we correct
for the 30% misclassification found in a recent report [SalinasTovar et al., 2004], the number of work-related injures would
be 384,272 cases. Taking into account the average cost per
case calculations of the present study, the corrected cost would
be $ 791,216,460 USD.
It is noteworthy that the costs of injuries reported herein
cannot be employed directly for estimating the costs of
injuries occurring outside the work environment. The group
of medical experts participating in the advisory panels who
defined the proportion of patients according to the severity
of each diagnostic group referred that in general terms,
occupational injuries are considered as injuries with a
greater risk of infection; thus, they should be managed
more carefully. Nonetheless, on the other hand, workers are
relatively healthier than the general population, and special
management was not considered, for example, adult patients
with co-morbidities such as diabetes and high blood pressure
submitted to surgery.
The average cost of work-related injuries reported
here is about half of the median health care of cost of 4,377
reported in a Canadian cohort [Alamgir et al., 2008].
This estimation demonstrates the high cost of health care
for work-related injuries and the need to include them in
any income–expense balance in a social security system,
especially if financial incentives for prevention programs are
considered. Cost appraisal data for commuting accidents are
important for consideration, given that these are not included
in occupational risk insurance-premium calculations. The
cost of these commuting accidents represents 16% of the total
cost.
The estimated health-care expenditures of occupational
injuries at IMSS for 753 million USD and the costs for
economic provisions to compensate for loss of the
ability to work for 578 million USD for indemnification for
work-related disabilities and deaths comprise only two
components of the total occupational-injury costs. Indirect
costs might be as important as or more important than direct
costs [Weil, 2001]. Indirect costs include loss of productivity,
pain, and suffering-associated, as well as out-of-pocket
expenses contracted by the family concerning patient home
care. Conservative estimates suggest an indirect-to-direct
cost ratio of 1:1 [Dorman, 1999]. There are many variations
of the proportion of the costs but usually the proportion of
indirect costs is much bigger than direct costs [Ha¨ma¨la¨inen
et al., 2006; Brown et al., 2007].
At IMSS direct health-care costs of occupational
accidents are completely covered by the premium paid by
the employer. However, indirect costs are not directly
compensated for by the social security system, but borne
by workers, their families, employers, the public health
system, and taxpayers. The fact that employers and
social security institutions bear only a portion of total costs
has implications in the appreciation of its true magnitude, the
economic and social impact that occupational accidents and
diseases represent for health-care institutions, the society,
and the country.
IMSS covers most of the formal sector of the economy.
However, the informal sector has grown rapidly during the
last decades so that above figures solely reflect the reality of
occupational accidents in 30% of the workers [Sa´nchezRoma´n et al., 2006]. If we apply the rates of the population
covered by IMSS to the total workforce, assuming similar
occupational risks, we can estimate that 1.4 million workrelated injuries occur each year in the country. The healthcare expenditure under this occupational accidents and
diseases is borne by the workers, public health system, and
finally, the taxpayers. If similar direct cost could be applied,
then health care and indemnification for work-related
disabilities and deaths would be close to 1% of the NGP.
This figure is similar to that reported in Costa Rica in 1995 by
the National Insurance Institute (Instituto Nacional de
Seguros), which exclusively administers occupational risks
and covers 56% of the country’s work force (EAP) and 84.3%
of the salaried population.
Estimations from Bolivia and Panama yielded a cost
equivalent to 9.8–11% of the GNP, respectively (OPS-OMS,
1998 Informe; OPS-OMS, 1999 124.a Sesio´n; OPS-OMSS,
Regional Worker Health Plan, 2001), 124th Executive
Committee Session). Likewise, in the U.S. Leigh and
collaborators in 1992 estimated that occupational illness
and injury costs represented 3% of the GNP [Leigh et al.,
1997]. Similarly, a study conducted by the Universidad
Pompeu Fabra [2001] in Spain reported that the total cost for
occupational accidents and diseases represented >1.7% of
the GNP [Cost Approximation of Work Claims in Spain,
2002]. Finally, for the European Agency for Occupational
Safety and Health at Work (EU-OSHA) estimated cost of
occupational accidents varied from 1% to 3% of the GNP,
without including disability compensation costs [EU-OSHA,
2002].
Costs of Work-Related Injuries
201
ACKNOWLEDGMENTS
de trabajo y a´rea de promocio´n de los trabajadores. Me´xico, D.F.:
Divisio´n Te´cnica de Informacio´n en Estadı´stica en Salud. ST-5; 2006.
We gratefully thank the team of specialist who
developed the treatment algorithms and the staff from the
participating hospitals: Hospitales de Traumatologı´a y
Ortopedia Victorio de la Fuente, Lomas Verdes, Pestalozzi,
and Unidad de Medicina Familiar No. 1 from the Instituto
Mexicano del Seguro Social.
Leigh JP, Markowitz SB, Fahs M, Shin CH, Landrigan PJ. 1997.
Occupational injury and illness in the United States; Estimates of costs,
morbidity, and mortality. Arch Intern Med 157:1557–1568.
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