Impact of pregnancy on observed sex disparities among adults hospitalized with laboratory‐confirmed influenza, FluSurv‐NET, 2010‐2012

INTRODUCTION: Previous FluSurv‐NET studies found that adult females had a higher incidence of influenza‐associated hospitalizations than males. To identify groups of women at higher risk than men, we analyzed data from 14 FluSurv‐NET sites that conducted population‐based surveillance for laboratory‐confirmed influenza‐associated hospitalizations among residents of 78 US counties. METHODS: We analyzed 6292 laboratory‐confirmed, geocodable (96%) adult cases collected by FluSurv‐NET during the 2010‐12 influenza seasons. We used 2010 US Census and 2008‐2012 American Community Survey data to calculate overall age‐adjusted and age group‐specific female:male incidence rate ratios (IRR) by race/ethnicity and census tract‐level poverty. We used national 2010 pregnancy rates to estimate denominators for pregnant women aged 18‐49. We calculated male:female IRRs excluding them and IRRs for pregnant:non‐pregnant women. RESULTS: Overall, 55% of laboratory‐confirmed influenza cases were female. Female:male IRRs were highest for females aged 18‐49 of high neighborhood poverty (IRR 1.50, 95% CI 1.30‐1.74) and of Hispanic ethnicity (IRR 1.70, 95% CI 1.34‐2.17). These differences disappeared after excluding pregnant women. Overall, 26% of 1083 hospitalized females aged 18‐49 were pregnant. Pregnant adult females were more likely to have influenza‐associated hospitalizations than their non‐pregnant counterparts (relative risk [RR] 5.86, 95% CI 5.12‐6.71), but vaccination levels were similar (25.5% vs 27.8%). CONCLUSIONS: Overall rates of influenza‐associated hospitalization were not significantly different for men and women after excluding pregnant women. Among women aged 18‐49, pregnancy increased the risk of influenza‐associated hospitalization sixfold but did not increase the likelihood of vaccination. Improving vaccination rates in pregnant women should be an influenza vaccination priority.