Risk of influenza transmission in a hospital emergency department during the week of highest incidence

Objectives.

To estimate the risk of influenza transmission in patients coming to a hospital emergency department during the week of highest incidence and to analyze factors associated with transmission.

Methods.

Retrospective observational analysis of a cohort of patients treated in the emergency room during the 2014–2015 flu season. The following variables were collected from records: recorded influenza diagnosis, results of a rapid influenza confirmation test, point of exposure (emergency department, outpatient clinic, or the community), age, sex,

flu vaccination or not, number of emergency visits, time spent in the waiting room, and total time in the hospital. We compiled descriptive statistics and performed bivariate and multivariate analyses by means of a Poisson regression to estimate

relative risk (RR) and 95% CIs.

Results.

The emergency department patients had a RR of contracting influenza 3.29 times that of the communityexposed population (95% CI, 1.53–7.08, P=.002); their risk was 2.05 times greater than that of outpatient clinic visitors (95% CI, 1.04–4.02, P=.036). Emergency patients under the age of 15 years had a 5.27 greater risk than older patients (95% CI, 1.59–17.51; P=.007). The RR of patients visiting more than once was 11.43 times greater (95% CI, 3.58–36.44; P<.001). The risk attributable to visiting the emergency department risk was 70.5%, whereas risk attributable to community exposure was 2%.

Conclusions.

The risk of contracting influenza is greater for emergency department patients than for the general population or for patients coming to the hospital for outpatient clinic visits. Patients under the age of 15 years incur greater risk.