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

BACKGROUND: Influenza 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. METHODS: The 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. RESULTS: Overall 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. CONCLUSION: Asymptomatic 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.