The role of hands and fomites in influenza transmission

Abstract

Seasonal influenza causes a considerable disease burden every year, while pandemic influenza occurs at irregular intervals and can lead to potentially devastating impacts worldwide. Understanding the transmission mechanisms and the relative importance of various transmission modes could help to better inform infection control and prevention interventions and strategies, especially during a new influenza pandemic, when the vaccine is not yet available and the antiviral medication supply is insufficient.

This thesis aims to explore the role of hands and fomites in influenza transmission and to inform better influenza control and prevention measures. I undertook a series of specific studies to assess the risk of influenza transmission via hands and fomites and to evaluate the effect of non-pharmaceutical interventions on influenza transmission with respect to the contact transmission of influenza.

First, I conducted an observational study and found that influenza virus RNA and infectious influenza viruses were detected on the naturally contaminated hands and personal objects of influenza patients. Influenza virus RNA could be transferred from the patients’ naturally contaminated hands to briefly used objects. Proper hand hygiene practice was effective in viable influenza virus removal from hands of influenza patients contaminated by their own cough.

Second, I analysed the data from two independent studies of the influenza contamination on mobile phones of laboratory-confirmed influenza cases in Hong Kong and in the United States. Influenza virus RNA was detected on more than a quarter of patients’ mobile phones, but few of them were culture-positive. More mobile phone influenza virus contamination was observed in younger adults.

Third, I conducted a longitudinal study to assess influenza virus occurrence on communal surfaces in a university campus covering periods of both during and outside influenza season. Influenza A virus RNA was detected before and during influenza season, while influenza B virus RNA was only detected during influenza season. However, no viable influenza virus could be cultured. The findings also suggested that the surface contamination was mainly due to surface touch behaviour rather than respiratory droplet deposition.

I reviewed the evidence on the effect of hand hygiene, and surface and object cleaning in influenza transmission prevention. Although mechanistic studies supported the potential effect of hand hygiene, meta-analysis results of randomized controlled trials did not provide evidence to support the protective effect of hand hygiene intervention on influenza transmission. Limited direct evidence supported the effect of surface and object cleaning intervention on influenza transmission prevention. The implications of these evidences for the inclusion of these interventions in influenza epidemic and pandemic preparedness planning are discussed.

Overall, my findings suggest that contaminated hands could play a considerable role in influenza transmission. The influenza virus contamination rate was higher on personal objects of influenza cases than that on communal objects, but the possibility of transmission of influenza via communal fomites could not be ruled out. Due to the mixed and combined transmission routes of influenza, any intervention alone may not be effective to interrupt the transmission of influenza. Further studies evaluating the efficacy of combinations of interventions are needed.