PRACTICAL ASPECTS OF THE IMPLEMENTATION OF THE SURVEILLANCE PROGRAM

5. PRACTICAL ASPECTS OF THE IMPLEMENTATION OF THE SURVEILLANCE PROGRAM

An antimicrobial resistance surveillance program should be based on the acquisition and reporting of reliable standardized, quality controlled, non- duplicative data. This objective may be achieved by obtaining appropriate speci- mens from the infected individual, by the successful identification and isolation of the causative organism, by the accurate determination of the antimicrobial susceptibility of the isolate and by transforming the data into useful information for action. The microorganisms, the antimicrobials, and the setting of the sur- veillance have to be chosen according to the criteria presented above but addi- tional decisions should be taken about the choice of specimens, method and duration of the surveillance program, indicator, and denominator. In the mean- time, if they do not exist, quality control programs should be implemented.

Case definition. Ideally, surveillance of antimicrobial resistance should involve the collection of both clinical and microbiological data. Therefore, the first step in setting up a surveillance program is to design a case definition. As usual, the case definition should serve as inclusion criteria and include infor- mation about time, place, and persons. Here are two examples of case defini- tions of infections and of the data to collect for key pathogens developed by WHO (2002).

Pneumonia: (a) clinical: febrile illness with purulent productive cough, rapid breathing in

children; (b) laboratory: isolation of S. pneumoniae or H. influenzae from sputum or blood; (c) appropriate specimens: sputum, blood (nasopharyngeal swabs may be used in children); (d) optimal sampling location and surveillance type: primary health care facility.

Urinary tract infection:

(a) clinical: frequency and dysuria or fever in presence of indwelling catheter or other focus of infection; (b) laboratory: isolation of E. coli from urine in significant numbers or blood; (c) appropriate specimen: urine (midstream or catheter specimen); (d) optimal sampling location: primary healthcare facility.

418 Hervé M. Richet Mode of surveillance. Surveillance may be defined as passive or active.

Passive surveillance is done when data are awaited and no attempts are made to seek reports actively from the primary data collector. Surveillance is said to

be active when reports are sought from the primary data collector on a regular basis. Active surveillance is the method of choice. Choice of specimens. A distinction should be made between specimens col- lected to diagnose an infection and those realized to detect colonization. The choice of the specimens to include depends on the objectives of the surveillance program. The types of specimens to include should be part of the case definition. Emerging resistance may present first in colonizing organisms.

Data to collect. Below is an example of minimum data set to collect for a specific organism according to WHO (2002). Recommended minimum data set for S. aureus:

(a) case-based data: unique identifier capable of cross linkage with laboratory data. Age or date of birth; gender; healthcare facility and care group; date of admission and of onset; presenting sign, symptoms; predisposing fac- tors (surgery, trauma, indwelling devices);

(b) laboratory-based data: unique identifier capable of cross-linkage with clini- cal data. Specimen date and type; method of identification, resistance to specified antimicrobials.

Microbiological representativeness. Colonies used for susceptibility test- ing should be representative of the culture as a whole. Expression of antimicrobial resistance data. Laboratories should use stan- dards for reporting quantitative resistance data (e.g., minimal inhibitory con- centrations or zone diameters) in ways that will detect decreased susceptibility. This is necessary because numerical antimicrobial test results reported non- quantitatively (e.g., as susceptible, intermediate, or resistant) may hide an emerging resistance character in microorganisms with a small decrease in susceptibility that may still be classified as susceptible.

Choice of the surveillance method. The measure of the incidence rate is the best way to conduct surveillance of antimicrobial resistance. Incidence quantifies the number of new cases of diseases in a population at risk during a specific time interval. The duration of surveillance should be based on the expected rate of the event under surveillance. Table 1 shows the estimate of sample size needed for documenting increasing antimicrobial frequencies. As an example, if 5% of isolates in a sample of 200 are resistant, an increase to 11% or more in a second sample will show a significant increase.

Numerator for surveillance. For reliable and accurate information, data should relate to a single episode of disease in each patient. Regarding surveil- lance of antimicrobial resistance, it is of the utmost importance to avoid

Types of Surveillance Data 419

Table 1. Estimate of sample size needed for documenting increasing antimicrobial resistance (WHO, 2002)

% of resistance detected % resistance (indicative of significant increase) in original sample

detectable in a second sample at sample size of

including duplicate results since a patient may have either consecutive cultures obtained from the same body site or cultures from different body sites yielding the same organism (e.g., urine and blood culture). Therefore, only the first pos- itive culture from the patient for each disease episode should be reported for surveillance purposes. However, there is a need for a clear definition of what represents a “disease episode.” Emerging resistance in an organism isolated previously from the same patient could count, according to a predefined case definition, as a new episode.

Denominator for surveillance. Whenever possible, rates should be expressed as incidence rates within a defined human population instead of using the number of isolates tested as denominators. This is important because the submission of microbiology specimens to the laboratory is inconsistent and varies broadly. Rates produced by using this method are of limited epidemiological relevance. In hospital settings, it is recommended to use the number of admissions and the number of days of hospitalization, which are particularly useful for inter- or intra- healthcare facility comparison.

Quality control program. Organizers of antimicrobial resistance programs should ensure that clinical laboratories providing data for the surveillance pro- gram have access to and routinely participate in pertinent training and profi- ciency testing programs with good performance and that they indicate in their reports the antimicrobial resistance testing methods they use (e.g., specific automated methods or manual techniques). Internal and external quality control should be performed.