Case study 1 – rat bites in Philadelphia: identifying the factors contributing to risk

Public Health Significance of Urban Pests 401 1993, whereas the lower population densities in urban areas do not. However, this is not to say that in urban environments where rodent control measures are inadequate and low levels of predation exist rodent population densities will not increase. Because the population growth of commensal rodents can be explosive, the potential exists for an increase in zoonotic diseases within those populations. Thus, to be effective and to pre- vent commensal rodent population densities from increasing, urban rodent control stra- tegies should not rely solely on public complaints. Another public health issue of great concern is bites inflicted by rats in urban environ- ments. T his threat to public health has medical, social and emotional dimensions Anderson, 1993. The continuing presence of commensal rats in and around many urban and rural residences in the United States results in reports of hundreds of rat bites each year. This number is said to be underreported by factor of at least ten Hirschhorn Hodge, 1999; Hirschhorn, 2005. Rats are often found in substandard dwellings where the density of buildings is very high and the construction design denies rats outdoor burrowing opportunities. In these situa- tions, rats colonize basements and kitchens, and attempt to coexist with their human occupants. Each rat bite has the potential to spread infection, and the ectoparasites asso- ciated with the rodent can spread additional infectious organisms. The following case study illustrates the identification of risk factors.

12.4.4.1. Case study 1 – rat bites in Philadelphia: identifying the factors contributing to risk

In this study Hirschhorn Hodge, 1999, investigators examined rat-bite reports of 622 urban victims. To determine risk factors, the study assessed demographic characteristics and environmental factors. Cases were divided into two groups by date: 1974–1984 and 1985–1996 Fig. 12.1. The study used United States Census Bureau data for Philadelphia, from 1980 and 1990. Each rat bite was investigated, and the following data were exami- ned from each case reported: characteristics of the victim, place and time, number of rat bites, circumstances of the bite, environmental conditions, and location of the bite on the victim. Rat-bite incidence was 2.12 bites per 100 000 people in the first period and decrea- sed by 54, to 1.39 bites per 100 000 people in the second period. Most bites were received in the home. Of all the rat bites reported, 67 occurred in sin- gle-family dwellings, 24 in multiple-family dwellings, and only 8 in laboratories and schools. About half the rat-bite victims lived in housing that was in poor repair. Rat bites also showed a seasonal pattern and were most likely to occur in the summer months bet- ween the hours of 0:00 and 6:00. Nearly 50 of the bites reported were received on the hands, 20 on the head and the remainder on other extremities. Nearly all victims were asleep when bitten, and the majority were in bed. Socioeconomic factors were important contributors to the risk of being bitten. Most victims were living in poverty, as defined by the United States Census Bureau. The typical rat-bite victim in Philadelphia was an impoverished child less than 5 years old Fig. 12.2, with many less than a year old, living in substandard housing in close proxi- mity to brown rat infestations. The rat bite was usually to the hands or head, and it occur- Commensal rodents 400 In addition to zoonoses, commensal rodent infestations in homes present other human health-related issues. Carrer, Maroni Cavallo 2001 reported that the presence of rodents in the home may contribute to increased levels of indoor allergens, causing aller- gic asthma and rhinoconjunctivitis. Other studies confirmed asthma attacks as being asso- ciated with the presence of rat and mouse allergens in the home Perry, Matsui Merriman, 2003; Cohn et al., 2004; also, see Chapter 1. It should also be recognized that the awareness of rats and mice in and around a dwelling can be a source of anxiety for its occupants WHO Regional Office for Europe, 1998; Battersby, Parsons Webster, 2002; Williams et al., 2005. Thus, the presence of rats and mice also affect mental health. In particular, in decaying urban areas, this can further stress people whose health status is already compromised by poverty and social exclusion Battersby, Parsons Webster, 2002. Rat bites in urban settings are also an important health concern and will be dis- cussed in subsection 12.4.4.1.

12.4.4. Public health risks in urban areas