Incidence of Influenza in Healthy Adults and Healthcare Workers: A Systematic Review and Meta-Analysis

Abstract

BackgroundWorking in healthcare is often considered a risk factor for influenza; however, this risk has not been quantified. We aimed to systematically review evidence describing the annual incidence of influenza among healthy adults and healthcare workers (HCWs).Methods and FindingsWe searched OVID MEDLINE (1950 to 2010), EMBASE (1947 to 2010) and reference lists of identified articles. Observational studies or randomized trials reporting full season or annual influenza infection rates for healthy, working age adult subjects and HCWs were included. Influenza infection was defined as a four-fold rise in antibody titer, or positive viral culture or polymerase chain reaction.From 24,707 citations, 29 studies covering 97 influenza seasons with 58,245 study participants were included. Pooled influenza incidence rates (IR) (95% confidence intervals (CI)) per 100 HCWs per season and corresponding incidence rate ratios (IRR) (95% CI) as compared to healthy adults were as follows. All infections: IR 18.7 (95% CI, 15.8 to 22.1), IRR 3.4 (95% CI, 1.2 to 5.7) in unvaccinated HCWs; IR 6.5 (95% CI, 4.6 to 9.1), IRR 5.4 (95% CI, 2.8 to 8.0) in vaccinated HCWs. Symptomatic infections: IR 7.5 (95% CI, 4.9 to 11.7), IRR 1.5 (95% CI, 0.4 to 2.5) in unvaccinated HCWs, IR 4.8 (95% CI, 3.2 to 7.2), IRR 1.6 (95% CI, 0.5 to 2.7) in vaccinated HCWs.ConclusionsCompared to adults working in non-healthcare settings, HCWs are at significantly higher risk of influenza.

2012/13 influenza vaccine effectiveness against hospitalised influenza A(H1N1)pdm09, A(H3N2) and B: estimates from a European network of hospitals

“…A 2011 systematic review of the incidence of influenza in healthy adults and healthcare workers [14] calculated a pooled annual incidence of infection of 18.7 per 100 HCW per season in unvaccinated HCWs and 6.5 per 100 HCW per season in vaccinated HCWs. These estimates were significantly higher than the incidence rates in adults working in non-healthcare settings.…”

Understanding motivators and barriers of hospital-based obstetric and pediatric health care worker influenza vaccination programs in Australia

“…2 Direct patient contact, along with proximity to visitors and co-workers puts healthcare workers (HCWs) at a higher risk of influenza infection. 4,5 Vaccinating HCWs against influenza reduces the transmission of the virus in health care settings; decreases staff illness and absenteeism, and indirectly benefits patients by decreasing their chance of being infected. 6,7 As pregnant women and premature infants are at particular risk of severe influenza, vaccinating HCWs who care for them is especially important.…”

Pandemic influenza A(H1N1)pdm09: risk of infection in primary healthcare workers

“…8,9 However, while healthcare workers appear to be at greater risk of serologically confirmed infection, they do not appear to be more likely to experience symptomatic infection, possibly because of greater exposure to multiple strains of influenza, which may confer cross-protection and reduce symptom severity. 8 This may have implications for transmission of infection to vulnerable patients, and for healthcare worker vaccination policy. The design of this study allowed comparison of the proportions of asymptomatic and symptomatic infections.…”