Pathways To Flu Virus Exposure

A new study examines four flu exposure pathways and quantifies the risk posed by each pathway, which, the analysis found, varies based on changes in viral concentrations. The study appears in the September issue of the peer-reviewed journal Risk Analysis, published by the Society for Risk Analysis.

“Relative Contributions of Four Exposure Pathways to Influenza Infection Risk” calculates the risks involved with each kind of exposure in a setting where a person attends a bed-ridden individual ill with influenza. In examining ways of reducing the risk of preventing infections through each pathway, the study supports general advisories to cover coughs, wash hands frequently, and disinfect surfaces. The study also substantiates the benefits of caregivers using gloves and a filtering-facepiece respirator, if possible, when they are present in a confined room with an individual ill with influenza.

Researchers Dr. Mark Nicas of the University of California Berkeley’s School of Public Health, and Dr. Rachael M. Jones of the University of Illinois Chicago’s School of Public Health, used sophisticated modeling and examined available research to show infection rates in four pathways of exposure dealing with direct skin contact and inhalation of cough particles.

The relative likelihood of being infected by the different exposure routes were:

1. hand contact with contaminated surfaces, 31 percent;
2. inhaling small particles carrying virus when in the room, 17 percent;
3. inhaling relatively large particles carrying virus when three feet or closer to the infected person, 0.52 percent; and
4. close contact spraying of cough droplets carrying virus onto the membranes of the eyes, nostrils and lips, 52 percent.

Since incidents of infection were documented with each pathway, Nicas and Jones conclude, “Non-pharmaceutical interventions for influenza should simultaneously address potential exposure via hand contact to the face, inhalation, and droplet spray.” Thus, all four exposure pathways should be addressed when someone is sick, as it is difficult to know which one poses the most risk as virus concentrations change.