Traditional definition of healthcare-associated influenza underestimates cases associated with other healthcare exposures in a population-based surveillance system

Abstract

Objective: To provide comprehensive population-level estimates of the burden of healthcare-associated influenza.

Design: Retrospective cross-sectional study.

Setting: US Influenza Hospitalization Surveillance Network (FluSurv-NET) during 2012-2013 through 2018-2019 influenza seasons.

Patients: Laboratory-confirmed influenza-related hospitalizations in an 8-county catchment area in Tennessee.

Methods: The incidence of healthcare-associated influenza was determined using the traditional definition (ie, positive influenza test after hospital day 3) in addition to often underrecognized cases associated with recent post-acute care facility admission or a recent acute care hospitalization for a noninfluenza illness in the preceding 7 days.

Results: Among the 5,904 laboratory-confirmed influenza-related hospitalizations, 147 (2.5%) had traditionally defined healthcare-associated influenza. When we included patients with a positive influenza test obtained in the first 3 days of hospitalization and who were either transferred to the hospital directly from a post-acute care facility or who were recently discharged from an acute care facility for a noninfluenza illness in the preceding 7 days, we identified an additional 1,031 cases (17.5% of all influenza-related hospitalizations).

Conclusions: Including influenza cases associated with preadmission healthcare exposures with traditionally defined cases resulted in an 8-fold higher incidence of healthcare-associated influenza. These results emphasize the importance of capturing other healthcare exposures that may serve as the initial site of viral transmission to provide more comprehensive estimates of the burden of healthcare-associated influenza and to inform improved infection prevention strategies.

Fig. 1.

Traditional definition of healthcare-associated influenza and additional preadmission healthcare exposures.Influenza-related hospitalizations with a positive test after day 3 were included in the traditional definition. Influenza-related hospitalizations with a positive test in the first 3 days of admission among patients directly transferred from a post-acute care facility or discharged from a non-influenza acute care hospitalization in the 7 days preceding the index admission were included in the additional preadmission healthcare exposure category. Cases meeting the traditional definition and those captured by the addition of the preadmission healthcare exposures were included in the expanded definition of healthcare-associated influenza. Note. HD, hospital day.

Fig. 2.

Proportion of influenza-related hospitalizations by type of healthcare exposure, FluSurv-NET, 2012–2019.Cases meeting the traditional definition and those captured by the additional preadmission healthcare exposures were included in the expanded definition of healthcare-associated influenza.Influenza-related hospitalizations with a positive test after hospital day 3 were included in the traditional definition.Influenza-related hospitalizations with a positive test in the first 3 days of admission in patients directly transferred from a post-acute care facility.Influenza-related hospitalizations with a positive test in the first 3 days of admission in patients discharged from a noninfluenza acute care hospitalization in the 7 days preceding index admission.

Fig. 3.

Proportion of influenza-related hospitalizations by traditional and expanded definitions of healthcare-associated influenza, FluSurv-NET, 2012–2019.

Fig. 4.

Incidence rate ratio of healthcare-associated influenza by type of preadmission healthcare exposure, FluSurv-NET, 2012–2019.