As Flu Season Winds Down, New Study Highlights Inflight Transmission Risks

This flu season in the United States peaked in early February during week 5, according to a new flu situation update released by the Centers for Disease Control and Prevention (CDC). Despite steady declines in flu season indicators around the country since then, influenza activity remained high during week 10 ending March 10, 2018. Puerto Rico and 26 states continue to report widespread flu, according to the most recent FluView report, and hospitalization rates rose slightly from 86.3 laboratory-confirmed influenza-associated hospitalizations per 100,000 population during the previous week to a cumulative rate of 89.9 per 100,000. For Americans aged 65 and over, the hospitalization rate rose from 370.6 per 100,000 during week 9 to 386.2 per 100,000.

Although the CDC has reported that the proportion of influenza A and B viruses are nearly equal, influenza A viruses continue to cause the majority of hospitalizations. During week 10, 79% of hospitalizations were associated with influenza A viruses, and H3N2 was identified in more than 85% of hospitalized patients. Throughout the 2017-2018 flu season, the CDC has continued to recommend the flu vaccine for all individuals 6 months of age and older and prompt treatment with influenza antiviral medications such as Tamiflu for individuals who are severely ill with flu symptoms or at high risk for developing serious flu complications.

The National Center for Health Statistics, part of the US Department of Health and Human Services, recently released estimates for 15 selected health measures based on data from the National Health Interview Survey (NHIS) for January to September 2017. Included in that report is new data on the rate of flu vaccination during the past 12 months in adults ages 18 and older. For the third quarter of 2017, the highest rate of receipt of the flu vaccine occurred in adults aged 65 and older at 69%, nearly double the 34.8% rate in those aged 18 to 49. Adults aged 50 to 64 saw a 44.2% rate of flu vaccination. Public health officials hope that the development of a more effective universal flu vaccine will help to boost vaccination rates.

In other flu news, in a new study published in the journal PNAS, researchers studied inflight flu transmission among airline passengers. “Respiratory diseases are often spread within populations through close contact,” explained study author and Emory University professor Vicki Hertzberg, PhD, in a recent statement. “We wanted to determine the number and duration of social contacts between passengers and crew, but we could not use our regular tracking technology on an aircraft. With our trained observers, we were able to observe where and when contacts occurred on flights. This allows us to model how direct transmission might occur.”

By looking at the movements of passengers on 10 domestic flights in the United States, 8 of which were during flu season, the researchers constructed a dynamic-network model used to simulate direct influenza transmission during flight. They determined that passengers sitting 1 or 2 seats away from someone with the flu, or in a row in front of or behind someone with the flu, had an 80% risk of catching the virus. For remaining passengers, that risk dropped to 3%. “We found that direct disease transmission outside of the one-meter area of an infected passenger is unlikely,” said study author Howard Weiss, PhD.

Additionally, the researchers noted that passengers can also catch the flu from contaminated inflight surfaces such as tray tables, seat belts, and lavatory handles. “Passengers and flight crews can eliminate this risk of indirect transmission by exercising hand hygiene and keeping their hands away from their nose and eyes.”