A statewide outbreak of Cryptosporidium and its association with the distribution of public swimming pools

Abstract

Summary In order to characterize the association between county-level risk factors and the incidence of Cryptosporidium in the 2007 Iowa outbreak, we used generalized linear mixed models with the number of Cryptosporidium cases per county as the dependent variable. We employed a spatial power covariance structure, which assumed that the correlation between the numbers of cases in any two counties decreases as the distance between them increases. County population size was included in the model to adjust for population differences. Independent variables included the number of pools in specific pool categories (large, small, spa, wading, waterslide) and pool-owner classes (apartment, camp, country club or health club, hotel, municipal, school, other) as well as the proportion of residents aged <5 years. We found that increases in the number of bigger pools, pools with more heterogeneous mixing (municipal pools vs. country club or apartment pools), and pools catering to young children (wading pools) are associated with more cases at the county level.

Cryptosporidium outbreaks associated with swimming pools

“…In Canada and the United States, the two most common species of Cryptosporidium associated with outbreaks in swimming pools are Cryptosporidium parvum and Cryptosporidium hominis (Hopkins et al 2013;Mathieu et al 2004;Health Canada 2004;Polgreen et al 2012;Boehmer et al 2009;Wheeler et al 2007;Causer et al 2006). Many studies report that pool-fouling was a risk factor for infection with Cryptosporidium (Hopkins et al 2013;Mathieu et al 2004;Health Canada 2004).…”

“…Cryptosporidium attacks persons of all ages; however, children are affected by the illness more often than adults or the elderly (Mathieu et al 2004;Polgreen et al 2012;Causer et al 2006). Polgreen et al (2012) reported that although subjects in the cases ranged from 0 to 88 years of age, about 47% of cases were observed among children under the age of 9 (Polgreen et al 2012).…”

“…Polgreen et al (2012) reported that although subjects in the cases ranged from 0 to 88 years of age, about 47% of cases were observed among children under the age of 9 (Polgreen et al 2012). Children have been reported to be the most important reservoir for Cryptosporidium even when they are asymptomatic (Bouzid et al 2013).…”

“…Having contact with children, daycare, or another infected person are associated with the illness (Mathieu et al 2004;Causer et al 2006), because a person coming in contact with children may be at risk of secondary infections. Although the gender distribution of infection was even among children, females were more impacted than males among adults (Polgreen et al 2012). This pattern may be explained by the common practice of mothers being involved in changing diapers and caring for sick children, resulting in a secondary infection.…”

“…In a statewide outbreak investigation carried out in Iowa, investigators found that smaller camp pools in comparison with larger camp pools were a risk factor for Cryptosporidium infection (Polgreen et al 2012). The reasons for this may be due to poor implementation control measures and lack of resources in a small camp pools compared with the larger ones (Health Canada 2004).…”