Influenza-related hospitalization of adults associated with low census tract socioeconomic status and female sex in New Haven County, Connecticut, 2007-2011

Objectives: To help guide universal influenza vaccination efforts in the United States, it is important to know which demographic groups are currently at highest risk of costly complications of influenza infection. Few studies have examined the relationship between hospitalization with influenza and either socioeconomic status (SES) or sex. We examined associations between census tract-level SES and sex and incidence of influenza-related hospitalizations among adults.

Design: Descriptive analysis of data collected by active population-based surveillance for persons >18 years old hospitalized with laboratory confirmed influenza during the 2007-2008 through 2010-2011 influenza seasons. Case residential addresses were geocoded and linked to data from the 2006-2010 American Community Survey to obtain census-tract level (neighborhood) SES measures. Census-tract level SES variables included measures of poverty, education, crowding, primary language, and median income. Four levels were created for each.

Setting: New Haven, County, Connecticut.

Sample: Entire New Haven County population >18 years old.

Main outcome measures: Age-adjusted incidence of influenza hospitalizations and relative risk by sex and by each of five SES measures.

Results: Crude and age-adjusted incidence progressively increased with decreasing neighborhood SES for each measure both overall and for each influenza season. Female incidence was higher than male for each age group, and female age-adjusted incidence was higher for each SES level and influenza season.

Conclusions: Female sex and lower neighborhood SES were independently and consistently associated with higher incidence of hospitalization of adults with influenza. If this is more broadly the case, these findings have implications for future influenza vaccination efforts. Analysis using census tract SES measures can provide additional perspective on health disparities.