924. Incidence of Symptomatic and Asymptomatic Influenza Among Healthcare Workers: A Multicenter Prospective Cohort Study

Abstract

BackgroundInfluenza is an important cause of viral nosocomial infections; however, the incidence of asymptomatic influenza among healthcare workers (HCWs) is poorly known. The objective was to estimate the cumulative incidence of asymptomatic and symptomatic influenza among HCWs.MethodsThe AFP (Asymptomatic Influenza Project, NCT02868658) multicenter prospective cohort study was conducted in 5 French university hospitals in Lyon (2 sites), Grenoble, Saint-Etienne, and Dijon. Each voluntary HCW was followed-up during the entire 2016–2017 influenza season with 3 visits for influenza diagnostic by PCR from nasal swabs and serology. The outcome was laboratory confirmed influenza (LCI) defined by an influenza detection by PCR, and/or influenza A seroconversion/significant increase in the anti-A antibodies titer against A/Hong-Kong/4801/2014, with the absence of seroconversion/significant increase in the level of anti-B/Brisbane/60/2008 antibodies; influenza A was indeed the only strain circulating this winter in the Lyon area. Asymptomatic cases presented no general or respiratory sign/symptom, paucisymptomatic LCI cases had those symptoms/signs but not conforming to clinical influenza, symptomatic LCI cases had temperature ≥37.8°C and cough or sore throat. Cumulative incidence was expressed per 100 HCWs.ResultsOverall 278 HCWs were analyzed, 84.2% were female, the mean age was 38 years, and influenza vaccination coverage in 2016–2017 was 45.3%. Globally, 62 HCWs had evidence of LCI. Among laboratory confirmed influenza cases, 67.7% (95% CI: 55.8%–79.7%, n = 42) were asymptomatic, 21.0% (95% CI: 10.5%–31.4%, n = 13) were paucisymptomatic, and 11.3% (95% CI: 3.2%–19.4%, n = 7) were symptomatic. Among HCWs, global cumulative influenza incidence was 22.3% (95% CI: 17.7%–27.5%). Cumulative incidence of asymptomatic influenza was 15.1% (95% CI: 10.9%–19.3%), it was 4.7% (95% CI: 2.2%–7.2%) for paucisymptomatic influenza, and 2.5% (95% CI: 0.1%–4.4%) for symptomatic influenza.ConclusionAsymptomatic influenza is frequent among HCWs, representing two-third of the influenza burden in this population. This highlights the importance of infection control measures among HCWs no presenting influenza symptoms.Disclosures All authors: No reported disclosures.