The SEEDs of two gastrointestinal diseases: Socioeconomic, environmental, and demographic factors related to cryptosporidiosis and giardiasis in Massachusetts☆
Introduction
Cryptosporidiosis and giardiasis are widely recognized as potentially waterborne infections (Steiner et al., 1997). Over the period from 1999 to 2002, there were nearly 13,000 laboratory-confirmed cases of cryptosporidiosis (Hlavsa et al., 2005a) and over 80,000 giardiasis cases in the United States (Hlavsa et al., 2005b). Cryptosporidiosis is responsible for over 1000 annual hospitalizations, while giardiasis induces over 5000 annual hospitalizations (Mead et al., 1999; MMWR, 2007). These diseases, in rare instances, can also cause death (Mead et al., 1999), especially among the frailest populations. Despite efforts to improve sanitation and public health infrastructure, these gastrointestinal infections still pose a significant public health threat (Marshall et al., 1997).
The biology of these parasites and biological mechanisms of infection are well documented (O’Donoghue, 1995; Adam, 2001; Griffiths, 1998). Recent research has shown that incidence rates of gastrointestinal infections may be related to drinking water source (Furtado et al., 1998). Factors that may contribute to contamination of drinking water sources with pathogens include farm runoff and heavy rainfall (Sischo et al., 2000; Kistemann et al., 2002). Incidence of gastrointestinal infections vary spatially and temporally (Chui et al., 2006). CDC data suggest that the reported rates of cryptosporidiosis and giardiasis vary widely by state and by season (Steiner et al., 1997; Hlavsa et al., 2005a; Dietz and Roberts, 2000; Lee et al., 2002).
Spatial and temporal variations in reported rates of laboratory-confirmed cryptosporidiosis and giardiasis cases in Massachusetts have also been demonstrated by Naumova et al. (2000). There was also an association between drinking water source and incidence rates of these infections. Some variability may be attributed to variability in reporting practices. As a logical extension of the Naumova et al. (2000) paper, we hypothesize that certain town-level socioeconomic, demographic, and environmental factors may affect the reported rates of these infections. This observed spatial variability in incidence rates may be due to the real underlying variability in disease incidence, differences in reporting, or both. Differences in reporting of disease may be associated with better access to health care or different rates of testing for these parasites based on certain characteristics. For example, in general, the wealthy tend to utilize health care services more than the poor (Lasser et al., 2006).
Cryptosporidiosis and giardiasis are reportable diseases in the United States and in Massachusetts. However, current-state surveillance data do not provide specific socioeconomic and demographic information on individuals who contracted these reportable diseases. We utilized town/city-level socioeconomic, demographic, and environmental proxies in place of individual-level, case-specific data. This approach has been widely used and publicized in many public health studies and can provide insight as to the environmental factors that may act as distal causes of disease. Examples include studies of social epidemiology and overall health status (Xu, 2006; Pickett and Pearl, 2001), chronic diseases (Diez-Roux et al., 1997), cancer (Sanderson et al., 2006), and infectious diseases (Aral et al., 2005; Koopman and Longini, 1994). In one recent study, negative health outcomes across the lifespan were more likely to occur in areas of high socioeconomic inequality than in areas where wealth was distributed more uniformly (Krieger et al., 2005). For example, AIDS incidence was found to be related to economic deprivation in a study of Massachusetts block groups (Zierler et al., 2000).
Section snippets
Methods
We applied an ecological approach to investigate the basic relationships between socioeconomic, demographic, and environmental indicators at the town/city level and town-specific information on cryptosporidiosis and giardiasis. We used the Massachusetts reportable diseases surveillance data for the period 1992–2002 and also derived a set of socioeconomic, demographic, and environmental proxies from the 1990 and 2000 US Census databases at the town/city level. As of June 2007, there were 351
Results
In 2002, the reported incidence of cryptosporidiosis in Massachusetts (1.2 per 1,00,000 person-years) was comparable to the national cryptosporidiosis incidence (1.0 per 1,00,000 person-years) (Hlavsa et al., 2005a). For giardiasis, the 2002 reported rate in Massachusetts (14.6 per 1,00,000 person-years) was nearly twice as high as the overall national rate (7.4 per 1,00,000 person-years) (Hlavsa et al., 2005b).
Discussion
In Massachusetts, distal measures thought to influence person-to-person transmission of gastrointestinal infection were found to be associated with cryptosporidiosis in particular. After controlling for population size, population density remained significantly associated with the presence of a reported case of cryptosporidiosis or giardiasis. This suggests that individuals living in densely populated communities may have a greater propensity to contract these infections than individuals living
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Funding sources: National Institute of Environmental Health Sciences (R01ES013171), the National Institute of Allergy and Infectious Diseases (R01 AI434315), and the US Environmental Protection Agency (EPA) (Grant # 48-C-02-042).