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A study confirms that the flu is spread by aerosols, not only by coughing, sneezing



Sick people can spread the flu to others with just breathing, according to a new study that shows how the virus can spread through air routes, and the cough and sneeze transmission function is lower than previously thought .

New details on how the flu spreads – a topic that in the past generated scientific controversy about what size respiratory droplets can contain viruses – occurs when the United States and other countries fight against a season of hard flu (see news story). related to CIDRAP News).

And the findings could fine-tune future recommendations about the non-pharmaceutical steps that people can take to reduce their risk of getting the flu. A research team led by the University of Maryland reported their findings yesterday in Proceedings of the National Academy of Sciences (PNAS) .

The machine & # 39; Gesundheit & # 39; analyzed patients' breathing

The team recruited volunteers with influenza illness on the College Park campus of the University of Maryland and the surrounding areas from December 2012 to March 2013. Of the 355 college-age people who examined , 142 were positive for the flu. Among those with influenza, the researchers obtained nasopharyngeal samples on days 1 to 3 after the onset of symptoms.

To measure the transmission, each participant sat in a chamber for 30 minutes with his face in a large metal cone, part of a "Gesundheit Machine" that captures and measures the influenza virus on exhaled breath. " Patients were also asked to cough, sneeze and say the alphabet three times.

In total, the researchers collected 218 samples from the nasopharynx and 218 breath sample sessions.

When the team analyzed the samples, they found that a significant number of patients routinely remove infectious viruses, not just RNA particles, into particles small enough to transmit them in the air.They were surprised to find that 11 (48%) of the 23 fine aerosol samples acquired when patients did not They were coughing had detectable viral RNA, and of those 8 contained infectious virus, suggesting that coughing is not a prerequisite to generate fine aerosol droplets

In the few sneezes captured by the Gesundheit machine, the researchers did not see larger numbers of viral RNA copies in coarse or fine aerosols, suggesting that sneezing is not as important a contribution as the virus through aerosols. .

Researchers: Stay home when you are sick!

Donald Milton, MD, MPH, who led the team and is a professor of environmental health at the School of Public Health at the University of Maryland, said in a press release that sick patients pollute the air around them, just by breathing, and not only by coughing or sneezing, especially during the first days of illness.

"Then, when someone gets the flu, they should go home and not stay in the wo. Dr. Sheryl Ehrman, a co-author of the study at the Engineering Faculty of San Jose State University, said in the statement The study findings suggest that surfaces should be kept clean and hands washed at all times, and avoiding coughing does not provide complete protection against the flu. "Staying at home and outside of public spaces could make a difference in the spread of the influenza virus, "he said.

Among other surprising findings, the team found an association between increased viral shedding in fine aerosol samples and influenza vaccination in both the current season as in the previous one, a finding that they say requires further study.

In addition, they saw that the thin aerosol release was significantly greater for men, who appeared to produce 3.2 more cough viruses than women, although women coughed more often than men.

Data confirm patterns seen by epi experts

Michael Osterholm, PhD, MPH, director of the Center for Research and Policy of Infectious Diseases at the University of Minnesota (CIDRAP), said the study confirmed the role he plays respiratory transmission in the spread of influenza, challenging the conventional belief that large droplets are the main carriers. CIDRAP publishes CIDRAP News.

"This confirms what the epidemiological data has shown over the years," he said, adding that infectious virus transmitters can hover in the air in any environment where someone is sick with the flu, be it a building, a metro, plane or a store.

Respiratory drops are like boulders that fall quickly over a short distance, while aerosols are like perfume that can be smelled in the fragrance department of a three-aisle store, Osterholm said.

He said the findings have practical implications on how to protect the public, health workers and other groups. For example, Osterholm said that the results of the study are likely to influence the debate on respiratory protection against influenza, for which N95 respirators have an advantage, since surgical masks do not adequately protect against aerosols.

See also:

January 18 PNAS Summary

January 18 Press Release from the University of Maryland


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