Worrisome Persistence on Masks
Seasonality can also be potentially gauged in the laboratory. Most of the studies on environmental persistence of SARS-CoV-2 have been conducted using virus grown in tissue culture. But that, too, is an imperfect method.
Virus disseminated into the environment from naturally infected humans likely has different survival properties than virus grown in culture, said Relman.
In addition, many labs cannot, or fail to, control and vary relative humidity, the committee letter noted. The aerosol studies so far have used humidity levels of 50% to 65%, which is more favorable to decay, while respiratory fluid is more likely to protect against infectivity, and the 20%-to-40% wintertime indoor humidity in temperate regions is more favorable for virus survival.
Even with these caveats, the committee cited worrisome studies on SARS-CoV-2 survival.
In a study published April 2 online in The Lancet, Hong Kong researchers reported significant reductions in virus in culture starting with temperatures at 37°C (98.6°F) or above.
On surfaces at a room temperature of 22°C (71.6°F) with a relative humidity of 65%, there was no infectious virus on printing paper or tissue papers after just 3 hours. It took 4 days for an infectious level to break down on glass and money, and 7 days for stainless steel and plastic. But after 7 days, investigators found 0.1% of the original inoculum on the outside of a surgical mask.
“The persistence of infectious virus on PPE is concerning,” writes Relman, noting that more studies are needed to guide healthcare workers, especially on what might be used to disinfect personal protective equipment “when they cannot be discarded after single use.”
Chad Roy, PhD, a researcher from Tulane University National Primate Research Center in New Orleans, Louisiana, told Relman by phone that in experiments where the virus was suspended as an aerosol at a temperature of 23°C (73.4° F) and about 50% humidity, SARS-CoV-2 had a longer half-life than the influenza virus, SARS-CoV-1, monkeypox virus, and Mycobacterium tuberculosis.
“This result is also concerning, but quite preliminary,” writes Relman.
This article first appeared on Medscape.com.