Mucus prevents hand sanitizers from quickly killing the flu

Sticky mucus may thwart alcohol-based hand sanitizers’ ability to fight the flu.

Flu viruses encased in mucus drops from infected people’s spit can withstand the alcohol in hand sanitizers for more than two minutes, researchers report September 18 in mSphere. Researchers dotted volunteers’ fingers with either mucus or saline solution containing the flu virus, then measured how long it took to inactivate the virus in both wet and dry samples.

A five-microliter drop — about the size of a pinhead — of mucus-coated flu virus took more than half an hour to dry, almost twice as long as saline. Drying time was important because previous studies tested sanitizers’ killing ability on dry viruses, and didn’t account for mucus’s moistening power.

A hand sanitizer containing 31 percent alcohol inactivated flu viruses in saline solution within 20 seconds. And in already dried mucus, that process took just under eight seconds. But moist mucus shielded flu viruses from alcohol, keeping the viruses viable for up to 2 minutes and 39 seconds, Ryohei Hirose, an infectious disease researcher at the Kyoto Prefectural University of Medicine in Japan, and his colleagues found. That may be long enough for health care workers to unwittingly transfer virus-infected mucus from one person to another.

The team didn’t test whether rubbing the sanitizer over the skin causes the alcohol to penetrate the mucus and kill viruses faster, Hirose says. Rubbing might help, he acknowledged. But there’s already an easy way to kill flu viruses: Washing hands with plain water or with soap killed viruses within 30 seconds, even when the mucus was still wet.