Risk underestimated

Viruses survive longer in droplets with bacteria

Bacteria from the lungs protect flu viruses. As a Lausanne research team showed in an experiment, droplets containing flu viruses remain infectious for longer if certain bacteria from our respiratory tract are also present in the droplet. This finding helps to explain why viruses spread so easily from person to person, wrote the Swiss Federal Institute of Technology in Lausanne (EPFL) in a press release on Wednesday.

The new findings were published in the "Journal of Virology". For their experiment, the EPFL researchers produced droplets similar to those produced when sneezing. Some of these droplets contained only influenza viruses, others also contained bacteria such as streptococci and staphylococci.

Virus survives in bacterial droplets for several hours
They placed these droplets on a surface and allowed them to dry in normal room air. After half an hour, the virus was almost completely dead in the droplets without bacteria. In the droplets with bacteria, the infectious viral load was a hundred times higher at the same time. The virus was able to survive in them for several hours. Similar results were obtained in a second experiment in which the effect was measured in suspended droplets.

Microscopic examinations showed that the droplets with the bacteria were flatter than those without. According to the researchers, this accelerates the evaporation process and thus leads to faster crystallization of the salt in the droplets, allowing the viruses to live longer.

Researchers: "Risk of infection is probably underestimated"
Previous models for predicting the spread of a virus in a closed room do not take this effect into account. "This means that they probably underestimate the risk of infection," says first author Shannon David.