Until now, most experts dealing with infectious diseases have said the flu virus spreads mainly by droplets formed when people with the flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby, or possibly be inhaled into the lungs.
A new study’s finding, however, is fueling even more concern during a flu season which has reached epidemic levels in some states, and has seen a much higher-than-normal number of cases in South Florida.
The study [1], which was funded by the U.S. Centers for Disease Control and Prevention (CDC) and the National Institutes of Health, provides new evidence that coughs and sneezes may not be necessary to fill the air with droplets of the flu virus. The flu’s potentially expanded airborne quality means the virus can spread more easily than previously thought.
‘Tiny Droplets’ Stay in the Air
“People with flu generate infectious aerosols (tiny droplets that stay suspended in the air for a long time) even when they are not coughing, and especially during the first days of illness,” explained Donald Milton, M.D., professor of environmental health at the University of Maryland School of Public Health and the study’s lead researcher, in a news release. “So when someone is coming down with influenza, they should go home and not remain in the workplace and infect others.”
Dr. Milton and his research team captured and examined samples of exhaled breath from 142 people with confirmed cases of influenza during natural breathing, prompted speech, spontaneous coughing, and sneezing. The team then assessed the infectivity, or the ability of a pathogen to establish an infection, from the captured influenza aerosols. The analysis showed that a significant number of patients shed infectious particles that can be transmitted through the air — without coughing or sneezing.
The study’s finding seems logical, says Sergio Segarra, M.D. [2], chief medical officer at Baptist Hospital of Miami [3] and an emergency physician, because of how easily the flu can spread based on previous studies.
People with the flu can spread it to others up to about six feet away, usually from coughs or sneezes, according to current guidelines from the CDC. Most healthy adults are able to infect other people beginning one day before symptoms develop, and up to five to seven days after becoming sick.
Transmission Via Breathing Seems ‘Logical’
“As with any study, you need other studies to verify its findings,” says Dr. Segarra. “But when you are looking at flu virus droplets that are so small — that spreading the virus by breathing in close proximity would be logical. That, in addition to the virus living up to 24 hours on surfaces, makes it that much worse.”
The United States is in the middle of a particularly nasty flu season, with nearly all states reporting high levels of severe flu, and hospitals swamped with cases. South Florida is seeing elevated cases, says Dr. Segarra. The flu season usually peaks around February.
“We’ve seen the flu much earlier and we’re seeing a lot more cases,” says Dr. Segarra, who estimates that local emergency departments are seeing rates of the flu that are twice as high as last year at this time. “If I was travelling on an airplane, I would wear a mask, and I’ve had the vaccine. I would wear it and bring hand sanitizers with me. It’s just too much out there and the vaccines could be only 30 to 40 percent effective.”
The study’s authors say their findings could be used to “improve mathematical models of the risk of airborne influenza transmission from people with symptomatic illness and to develop more effective public health interventions.”
Researchers from the University of Maryland, San Jose State University, Missouri Western State University and University of California at Berkeley contributed to the study.