BACKGROUND: The relationship between socioeconomic status (SES) and Shiga toxin-producing E. coli (STEC) is not well understood. However, recent multiyear studies in Connecticut and New York City found that as CTP increased, age-adjusted rates of STEC decreased. To explore whether these findings are generalizable nationally, we obtained surveillance data from 2010-2014 on STEC including hospitalization status for the 10 FoodNet sites (CA, CO, CT, GA, MD, MN, NM, NY, OR, TN, catchment population 47.9 million). The dataset included geocoded case data linked to CTP level as measured by the 2010-2014 American Community Survey, and denominators based on the 2010 US Census.
METHODS: CTP level was categorized into 4 levels based on percentage of residents living below the federal poverty level: 0-<5%, 5-<10%, 10-<20%, and >20%. Age-adjusted 5-year incidence per 100,000 population by CTP was determined for O157 and nonO157 STEC separately and combined. The incidence by CTP of STEC and whether hospitalized was examined by demographic features, FoodNet site and surveillance year. Relative rates were calculated comparing incidence in census tracts with <20% below poverty (73.6% of the study population) to those with >20% below poverty (26.4% of the study population).
RESULTS: Overall, there were 5234 cases of STEC (45% O157); 1,375 (26%) were hospitalized. Because O157 and non-O157 STEC had a similar relationship with CTP, we combined them. Five-year incidence was 10.93 per 100,000 population. By increasing 4-category CTP, age-adjusted STEC incidence was 12.86, 13.69, 12.09 and 8.36 (RR <20%CTP [first three categories] vs >20%= 1.53, 95% CI 1.43,1.64, p<0.001). Relative age-adjusted STEC rates for the <20%CTP group compared to the >20%CTP group were >1.0 for each age group, by sex, for each FoodNet site, for each surveillance year and for non-Hispanic whites and blacks and for Hispanics. Relative age-adjusted hospitalization rates for the <20% CTP group compared to the >20% CTP group were generally higher than for all STEC relative rates.
CONCLUSIONS: Those living in lower poverty census tracts in the US have been at higher risk of STEC than those living in the highest poverty census tracts. This finding likely reflects different prevalence of risk factors by CTP rather than healthcare seeking or diagnostic bias as it applies to analysis limited to hospitalized cases. Research is needed to better understand exposure differences between people living in higher vs lower CTP to help direct prevention efforts. Current STEC prevention efforts should include all socioeconomic groups.