Study profiles another air-travel hazard: norovirus

Mar 31, 2010 (CIDRAP News) – To the general risks of airline travel today—overbookings, delays, and knee-crushing seats—passengers can now add another potential indignity: enduring and contracting the explosive vomiting and diarrhea of norovirus infection.

Using both epidemiology and microbiology, investigators from the Centers for Disease Control and Prevention (CDC) and the New Hampshire Department of Health and Human Services have concluded that norovirus caused the disruption of an October 2008 flight on which so many passengers became ill that the flight was aborted halfway through—and also a later wave of illness among passengers who were infected while on board.

Unlike in previous investigations, though, the greatest risk of becoming infected did not arise in the plane's heavily used restrooms. The riskiest places to be, it turns out, were seats immediately adjacent to the sick travelers or their close companions, or aisle seats, because the sick travelers walked by them.

"Although this investigation serves as an extreme example, it is possible that norovirus transmission occurs regularly on airplanes on a smaller scale," the authors warn in Clinical Infectious Diseases.

The problematic flight departed Boston on Oct 8, 2008, heading for Los Angeles and carrying among its passengers 35 members of a leaf-peeping tour group. (Four more members of the group had planned other routes home, while two had been hospitalized in the previous 2 days.)

Early in the flight, six tour-group members began vomiting into air-sickness bags. One, according to the paper, "had multiple episodes of diarrhea, with at least 1 occurring in the aisle of the first-class section. The soiled aisle was not cleaned until after completion of the flight."

The sick passengers walked back and forth to a bathroom to use it and to dispose of full air-sickness bags; eventually the bathroom became so fouled it was closed off by flight attendants. After several hours, the impact on the flight became so great that it was diverted to Chicago and cancelled. Four of the sick passengers were taken to a local emergency room; two were hospitalized. The remaining sick passengers along with the well ones were put up in a Chicago hotel and returned to Los Angeles the next day.

Because the sick passengers' symptoms closely matched those of a norovirus outbreak, the CDC launched an investigation, and eventually determined that 15 members of the tour group had been ill, with the peak day of illness occurring the day of the flight. Six who submitted stool samples were infected with an identical norovirus strain.

In a second phase of the investigation, the disease detectives found seven passengers who reported falling ill with matching symptoms on Oct 10 through 12, 2 to 4 days after the flight. One was lab-confirmed as having a norovirus infection, but the sample did not contain enough viral RNA to allow it to be matched to the outbreak strain.

Those most likely to have been infected during the flight turned out not to be passengers who had used the soiled bathroom; by happenstance, the CDC said, most of the passengers used the bathrooms before the tour-group members' symptoms began. Instead, those most at risk for infection were occupying aisle seats that the ill passengers walked past, or seats next to ill passengers and their close companions. Because some of those seats were next to people who did not fall ill on the flight, the CDC warned, it is possible that those who acquired the disease while in flight were infected via asymptomatic viral shedding by tour-group members whose symptoms had already resolved.

Norovirus outbreaks are a common risk in the confined quarters of cruise ships, but there have been only three previously described outbreaks of norovirus-like illness on aircraft. Nevertheless, the authors say, the risk of contracting norovirus on board a flight is probably significant, because of the prevalence of the disease in the population, the organism's ability to survive on surfaces, the difficulty of deep-cleaning aircraft, and the likelihood that travelers embarking on flights may have come from a high-risk environment such as a cruise ship.

The only way to reduce the risk, they say, may be to reinforce common—and commonly ignored—recommendations that sick travelers not be allowed to board planes or vessels. But since that policy relies on passengers' identifying themselves as sick—and would come with the extra costs of delays, airline surcharges, and hotel bills—they are unlikely to succeed without a broad commitment by the travel industry to reducing passengers' financial penalties for doing the right thing.

Kirking HL, Cortes J, Burrer S et al. Likely transmission of norovirus on an airplane, October 2008. Clin Infect Dis 2010 Mar 30 (early online publication) [Abstract]

See also:

Widdowson MA, Glass R, Monroe S, et al. Probable transmission of norovirus on an airplane. (Letter) JAMA 2005 Apr 20;293(15):1859-60. [Full text]

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