ECCMID19: Some individuals shed flu virus before symptoms appear

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Research examining influenza transmission in a tertiary care hospital has discovered that a substantial proportion of patients and healthcare workers shed the flu virus before clinical symptoms appear. The findings, presented at the 29th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID; 13–16 April, Amsterdam, the Netherlands), suggest that current infection control measures might not be enough to protect healthcare workers and patients during routine care in hospitals.

Knowing whether individuals are infectious in the absences of symptoms is a major concern for infection control in hospitals. To investigate this issue in influenza, researchers tracked almost 700 healthcare workers and inpatients over two consecutive flu seasons at the University Hospital in Zurich (Switzerland), uncovering transmission clusters that were missed by routine surveillance.

The team tracked flu infection through nasal swabs collected daily and performed diagnostic multiplex PCR and RNA sequencing on specimens. Contacts between the study participants were traced and participants were asked to keep daily diaries recording any illness.

During the study 16 healthcare workers (from a total of 152) and 19 patients (from a total of 542) were diagnosed with influenza infection. Most of these individuals experienced influenza symptoms when their tests were positive, however, several remained asymptomatic despite testing positive for infection (13% of healthcare workers and 11% of inpatients). [usepro_private]

Importantly, 17% of influenza-positive swabs were collected on days the healthcare workers and patient did not report symptoms. In addition, among symptomatic individuals 14% of healthcare workers had positive influenza tests before symptoms developed.

Further analyses based on local and temporal proximity of healthcare workers and inpatients revealed at least seven clusters of potential transmission events among healthcare workers, among inpatients, or between healthcare workers and inpatients.

Stefan Kuster from the University Hospital and University of Zurich commented: “Our findings suggest that influenza infection in acute care is common and a significant proportion of individuals appear to shed influenza virus without harbouring any symptoms, making the spread of flu very difficult to control even with self-diagnoses and current infection control practices. Influenza vaccination is not perfect but remains the best tool we have to protect healthcare workers and their patients from severe illness.”

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Source: Tamò R, Böni J, Kouyos R et al. The TransFLU influenza transmission study in acute healthcare: attack rates, symptoms and transmission clusters. Presented at ECCMID (13–16 April, Amsterdam, the Netherlands). Presentation O1208 (Abstract 2292).  [/usepro_private]

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