Effectiveness of Public Health Measures in Mitigating Pandemic Influenza Spread: A Prospective Sero-Epidemiological Cohort Study

Background. Few studies have validated the effectiveness of public health interventions in reducing influenza spread in real-life settings. We aim to validate these measures used during the 2009 pandemic. Methods. From 22 June to 9 October 2009, we performed a prospective observational cohort study using paired serum samples and symptom review among 3 groups of Singapore military personnel. "Normal" units were subjected to prevailing pandemic response policies. "Essential" units and health care workers had additional public health interventions (eg, enhanced surveillance with isolation, segregation, personal protective equipment). Samples were tested by hemagglutination inhibition; the principal outcome was seroconversion to 2009 influenza A(H1N1). Results. In total, 1015 individuals in 14 units completed the study, with 29% overall seroconversion. Seroconversion among essential units (17%) and health care workers (11%) was significantly lower than that in normal units (44%) (P < .001). Symptomatic illness attributable to influenza was also lower in essential units (5%) and health care workers (2%) than in normal units (12%) (P = .06). Adjusted for confounders, unit type was the only significant variable influencing overall seroconversion (P < .05). From multivariate analysis within each unit, age (P < .001) and baseline antibody titer (P = .012) were inversely related to seroconversion risk. Conclusions. Public health measures are effective in limiting influenza transmission in closed environments.