Flying and Infection- a new study

Flying soon?  Worried about contagious diseases? 

This is an interesting article posted on Medscape

Localized Risk for Infection Transmission on Planes, Study Finds

The likelihood of airline passengers transmitting infectious diseases to one another is low, new data suggest. Although passengers seated within one row or two seats on either side of an infected individual have an 80% or higher chance of becoming infected, the likelihood was less than 3% for the remaining passengers, the researchers find.

“Transmission is limited to one row in front of or in back of an infectious passenger. This is more conservative than current public health guidance, calling for surveillance of passengers within two rows of an infectious passenger. Our simulations also indicate that an infectious flight attendant can generate several infections; thus, it is imperative that flight attendants not fly when they are ill,” the authors explain.

Vicki Stover Hertzberga, PhD, from the Nell Hodgson Woodruff School of Nursing, Emory University, Atlanta, Georgia, and colleagues published their findings online today in the Proceedings of the National Academy of Sciences.

More than a dozen documented cases of inflight transmission have occurred, and research on severe acute respiratory syndrome (SARS) and pandemic influenza (H1N1p) transmission on airplanes shows that air travel can help newly emerging infections and pandemics spread rapidly, the authors explain. However, the average risk for transmission of respiratory infections on commercial airline flights remains unknown.

To estimate the risk, the 10-member research team flew on 10 transcontinental flights that lasted between 211 and 313 minutes. Of those flights, seven had no unoccupied seats and the other flights had two, three, and 17 unoccupied seats. The researchers observed and recorded the actions and movements of 1540 passengers seated and 41 crew members working in the economy class cabin of single-aisle airplanes.

The investigators observed one passenger on one flight coughing moderately and none coughing severely. No crew members were seen coughing.

Infection Transmission Closely Linked to Movement of Passengers and Crew

Estimated infection transmission was closely linked to movement of passengers in the airplane, and the extent to which passengers moved varied according to where they were seated. More than one third (38%) of passengers remained in their seats for the duration of the flight, 38% left once, 13% left twice, and 11% left more than twice. Those who moved spent a median of 5.4 minutes out of their seats. The proportion of passengers who left their seat more than once was highest for passengers seated in an aisle seat (80%), followed by those in a middle seat (62%) and passengers in a window seat (43%).

Only half of the passengers visited a lavatory during the flight: 38% used it once, 9% used it twice, and 3% used it more than twice.

For passengers, the most frequent behaviors were waiting for, using, or leaving a lavatory (825 passengers; average time, 4.3 minutes) and checking the overhead storage bin (135 passengers; average time, 1 minute.)

Passengers waited for the front lavatory almost twice as long as they waited for the back lavatories (3.1 vs 1.7 minutes).

During an average flight (238 minutes of observation), each crew member was in contact with passengers for 67 minutes and spent an average of 155 minutes in the galley.

Of the 1296 passengers (84%) who had close contact with a passenger sitting beyond a 1-m radius from them as a result of movement, the median number of contacts was 44, and the median total duration of that contact was 47 person-minutes. For each individual contact, the median duration was 0.4 minutes.

The number of contacts fell the farther patients were seated from the aisle, with the greatest average number of contacts for passengers seated in aisle seats (n = 64), followed by those in middle (n = 58) and window seats (n = 12).

 Duration of contact was slightly higher for those seated near the front of the plane.

Influenza Transmission Model

The researchers developed a model in which they simulated direct influenza transmission occurring during a flight, using two scenarios and a transmission rate that has been used in previous transmission studies.

 In the first scenario, an index passenger was seated in a midcabin aisle seat. The 11 passengers sitting closest to the infectious passenger had a high likelihood of becoming infected (>0.80). For the remaining passengers, the probability of transmission was very low (<0.03). “On average, this manifests as 0.7 additional infected passengers per flight,” the authors write.

Simulations for other seats show an average of no more than two additional infected passengers per flight.

The second scenario involved an infectious crew member, and found an infectious crew member would infect an average of 4.6 passengers per flight. “A crew member is not likely to come to work while being extremely sick. Even if she or he came to work, she or he would be more likely to take medication to reduce or eliminate coughing,” the authors write. Therefore, the team used a lower transmission rate in this simulation than with the infected passenger.

In addition to running simulations, the researchers collected 228 samples from the air and hard surfaces and tested them for 18 common respiratory viruses. All samples tested negative, even though eight flights occurred during influenza season in the northern hemisphere.

 The researchers offer several explanations for case reports that have documented much higher transmission rates among airplane passengers. Some of those passengers may have been infected while waiting in the airport or while boarding or leaving the plane. Exposure could also have occurred from other sources before or after flying. Of five flights in these case reports, three were longer (9.5 – 14 hours), which would have resulted in “many more opportunities for transmission,” the researchers write. They add that their model assumes the main transmission route for influenza and SARS is by droplets, but that virus-laden particles that can travel larger distances may also be a significant vehicle for transmission.

The authors say their findings should not be extrapolated to short-hop domestic flights, international flights, or flights on other airlines. Passengers on short-hop flights may move around less, and those on longer international flights may move much more. “Our results also cannot be extrapolated from single-aisle cabins to double-aisle cabins commonly used for international flights. Different airlines will have different cabin-disinfection protocols and supervise their cabin-cleaning staff in different ways,” the researchers conclude.  Troy Brown, RN