Influenza Activity and Preterm Birth in the Atlanta Metropolitan Area: A Time-Series Analysis from 2010 to 2017.

Abstract

Annual influenza epidemics lead to substantial public health burden, and pregnant people are vulnerable to severe outcomes. Influenza during pregnancy is hypothesized to increase risk of adverse birth outcomes, but population-based epidemiologic evidence remains limited and inconsistent. We conducted a time-series analysis to estimate short-term associations between community-level seasonal influenza activity and daily counts of preterm births in Atlanta, United States from October 17th, 2010 to July 10th, 2017. We defined weekly influenza exposures four ways: (1) percent test-positive from virologic surveillance, (2) percent of patients with symptoms of influenza-like illness (ILI) in outpatient settings, (3) a composite measure of percent test-positive and ILI, and (4) influenza hospitalization rates. We used Poisson log-linear models to estimate associations, adjusting for time-varying confounders and ongoing at-risk pregnancies. We further examined associations by influenza type and exposure lags, and effect modification by maternal characteristics. We studied a total of 316,253 births. We found consistent positive associations between influenza activity and preterm birth across different exposure measures and exposure lags. An interquartile range increase in composite measure of ILI activity and percent test-positive was associated with a 1.014 (95% confidence interval: 1.001, 1.027) increase in preterm birth during the same week. In stratified analyses, associations were more pronounced among married, non-Black, and Hispanic pregnant people. Periods of high influenza activity were associated with increased risk of preterm birth.