Symptoms, Infection Duration, and Hemagglutinin Inhibition Antibody Response in Influenza A Infections.

<bold>Background: </bold>Many influenza studies assume that symptomatic and asymptomatic cases have equivalent antibody responses.<bold>Methods: </bold>This study examines the relationship between influenza symptoms and serological response. Influenza-positive index cases and household members in Managua, Nicaragua, during 2012-2017 were categorized by symptom status.<bold>Results: </bold>Antibody response was assessed using hemagglutination inhibition assays (HAI). Among 510 cases, 74.5% had ≥4-fold increase in HAI antibodies, and 75.3% had febrile illness. In a logistic regression model, febrile cases had 2.17 times higher odds of a ≥4-fold titer rise compared to asymptomatic cases (95% confidence interval, 1.02-4.64).<bold>Conclusions: </bold>Studies relying on serological assays may not generalize to asymptomatic infections. [ABSTRACT FROM AUTHOR]