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BACKGROUND: Previous studies have shown that measures of lower neighborhood socioeconomic status are correlated with higher rates of influenza-related hospitalization in New Haven County, CT. It is unknown whether this disparity also exists in other parts of the United States. FluSurv-NET conducts population-based surveillance for laboratory confirmed influenza-related hospitalizations among residents of over 70 counties in the 10 Emerging Infections Program states (California, Colorado, Connecticut, Georgia, Maryland, Minnesota, New Mexico, New York, Oregon, Tennessee) and four additional states (Ohio, Michigan, Rhode Island, Utah). We examined the distribution of FluSurv-NET cases across neighborhood poverty strata during two influenza seasons (October 1-April 30).
METHODS: During the 2010-2011 and 2011-2012 surveillance seasons, FluSurv-NET identified 8716 hospitalized influenza cases. Of these, 7932 (91%) were geocoded and linked to US Census data. We used census tract as the neighborhood unit. Poverty was measured according to the 2008-2012 American Community Survey as household income below the federally defined poverty level. We categorized neighborhoods by their percent of households in poverty (<5%, 5-<10%, 10-<19%, ≥20%) and calculated age adjusted (2000 US Standard Population) influenza-related hospitalization incidence overall and for each FluSurv-NET site stratified by neighborhood poverty status. Denominator data for incidence calculations came from the 2010 US Census.
RESULTS: For both seasons combined, the age adjusted cumulative incidence of influenza-related hospitalizations in high poverty (≥20%) neighborhoods was 43.4 per 100,000 population (95%CI: 42.3, 44.6), nearly twice the incidence in low poverty (<5%) neighborhoods (21.9 per 100,000, 95%CI: 20.8, 23.1). This relationship was observed in all 14 surveillance sites with the smallest disparity observed in Georgia (Standardized Rate Ratio (SRR) 1.3; 95%CI: 1.1, 1.7) and the greatest in Minnesota (SRR 3.4; 95%CI: 2.7, 4.3). Restricting the analysis to pediatric cases, the relationship also remained for the 13 surveillance sites with at least 10 cases aged <18 years. The SRR also varied by site for pediatric cases, ranging from 1.4 (95%CI: 1.0, 1.9) in Colorado to 5.0 (95%CI: 3.2, 7.8) in Minnesota.
CONCLUSIONS: High poverty neighborhoods consistently experienced greater influenza hospitalization rates than low poverty neighborhoods across all age groups, although the extent of this disparity varied by site. Studies have shown that neighborhood disadvantage and crowding correlate with lower resident health status. Linking geocoded surveillance data and US Census data can reveal vulnerable populations masked by conventional surveillance methods. Ongoing monitoring of area-based socioeconomic correlates of health may help target interventions where they are needed most.