Secondary attack rates from asymptomatic and symptomatic influenza virus shedders in hospitals: Results from the TransFLUas influenza transmission study. (6th March 2022)

• Record Type: Journal Article
• Authors: Tamò, Raphaël; Turk, Teja; Böni, Jürg; Kouyos, Roger D.; Schmutz, Stefan; Huber, Michael; Shah, Cyril; Bischoff-Ferrari, Heike A.; Distler, Oliver; Battegay, Edouard; Giovanoli, Pietro; Guckenberger, Matthias; Kohler, Malcolm; Müller, Rouven; Petry, Heidi; Ruschitzka, Frank; McGeer, Allison; Sax, Hugo; Weber, Rainer; Trkola, Alexandra; Kuster, Stefan P.
• Is Part Of: Infection control and hospital epidemiology. Volume 43:Number 3(2022)
• Page Start: 312
• Page End: 318
• Publication Date: 2022-03-06
• Subjects: Nosocomial infections -- Epidemiology -- Periodicals; Health facilities -- Sanitation -- Periodicals; Hospital buildings -- Sanitation -- Periodicals; Cross Infection -- Periodicals; Epidemiology -- Periodicals; Hospitals -- Periodicals; Infection Control -- Periodicals; 614.44
• DOI: 10.1017/ice.2021.112
• Languages: English
• ISSNs: 0899-823X

Abstract

Abstract: Objective: Nosocomial transmission of influenza is a major concern for infection control. We aimed to dissect transmission dynamics of influenza, including asymptomatic transmission events, in acute care. Design: Prospective surveillance study during 2 influenza seasons. Setting: Tertiary-care hospital. Participants: Volunteer sample of inpatients on medical wards and healthcare workers (HCWs). Methods: Participants provided daily illness diaries and nasal swabs for influenza A and B detection and whole-genome sequencing for phylogenetic analyses. Contacts between study participants were tracked. Secondary influenza attack rates were calculated based on spatial and temporal proximity and phylogenetic evidence for transmission. Results: In total, 152 HCWs and 542 inpatients were included; 16 HCWs (10.5%) and 19 inpatients (3.5%) tested positive for influenza on 109 study days. Study participants had symptoms of disease on most of the days they tested positive for influenza (83.1% and 91.9% for HCWs and inpatients, respectively). Also, 11(15.5%) of 71 influenza-positive swabs among HCWs and 3 (7.9%) of 38 influenza-positive swabs among inpatients were collected on days without symptoms; 2 (12.5%) of 16 HCWs and 2 (10.5%) of 19 inpatients remained fully asymptomatic. The secondary attack rate was low: we recorded 1 transmission event over 159 contact days (0.6%) that originated from a symptomatic case. No transmission event occurred in 61 monitored days of contacts with asymptomatic influenza-positive individuals. Conclusions: Influenza in acute care is common, and individuals regularly shed influenza virus without harboring symptoms. Nevertheless, both symptomatic and asymptomatic transmission events proved rare. We suggest that healthcare-associated influenza prevention strategies that are based on preseason vaccination and barrier precautions for symptomatic individuals seem to be effective.