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Probable Transmission of Norovirus on an Airplane
To the Editor: Noroviruses are highly infectious and transmitted by multiple routes in closed settings,1 but in-flight transmission of norovirus has never been documented. After notification of acute gastrointestinal illness among crew members of an 8-hour international flight arriving in Philadelphia, Pa, from London on December 19, 2002, we investigated if passengers on the flight subsequently became ill and, if so, the means of transmission.
Methods
The airline gathered information from crew members on their illnesses and in-flight activities. Stool specimens were tested for norovirus by reverse transcription polymerase chain reaction. We mailed a questionnaire to all 191 passengers (86% of airplane capacity) to gather information about on-board exposures and occurrence of gastrointestinal illness, defined as vomiting, diarrhea with at least 3 episodes in 24 hours, or any diarrhea with either abdominal cramps or nausea between December 17 and 23, 2002. Probable norovirus illness was defined as gastroenteritis with onset 18 to 60 hours after disembarkation, excluding bloody diarrhea (which is inconsistent with norovirus infection). Differences in exposures of persons with and without probable norovirus gastroenteritis were assessed using Fisher exact test and Wilcoxon rank-sum test (STATA version 5.0; Stata Corp, College Station, Tex), with significance defined as P<.05. As a public health response, this investigation required no institutional review board approval.
Results
Eight of 14 crew members reported only diarrhea (n = 1), only vomiting (n = 5), or both symptoms (n = 2), with onset in-flight. Two were later hospitalized and provided stool samples in which identical norovirus sequences were detected. The ill crew members served passengers in economy class (n = 3), business class (n = 2), or both classes (n = 1), and 2 crew members had unspecified duties. All were removed from service upon illness onset and were seated in the rear of the airplane. No episode of diarrhea or vomiting outside of a restroom was reported.
Ninety-three (49%) of 191 questionnaires were returned (median response, 20 days after flight). Eight passengers reported gastroenteritis with onset between December 17 and 23, 2002 (Figure). Six reported illness 18 to 60 hours after disembarkation but 1 reported bloody diarrhea, resulting in 5 passengers (5.4%) with probable norovirus gastroenteritis. Of the respondents, 83 passengers (89%) provided complete information on class traveled, consumption of food, beverages, and ice, and number of visits to the airplane restrooms. Cases (n = 5) visited a restroom significantly more often than noncases (n = 78), with median visits of 3 vs 2, respectively (P = .006) (Table). No other significant difference was found. No passenger noticed soiling of restrooms with feces or vomitus or witnessed other persons vomiting.
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Figure. Reports of Gastrointestinal Illness Among Aircraft Passengers
*Meets case definition of nonbloody diarrhea with onset 18 to 60 hours after disembarkation.
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Table. Risk Factors for Illness Among Aircraft Passengers
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The small number of cases could have allowed a bias leading to a false association (eg, exaggeration by a disgruntled passenger); however, the association with restroom visits remained significant (P = .02) with reanalysis of the data excluding the case who reported the most restroom visits (4 visits).
Comment
This is the first study, to our knowledge, of probable transmission of norovirus on an aircraft. Spread of norovirus via airborne droplets of vomitus in closed settings is well documented,2-3 but during this flight limited transmission to passengers occurred despite 8 crew members on-board who had norovirus gastroenteritis. This suggests that airborne droplets will not circulate widely through an aircraft if vomiting is confined to toilets. Nonetheless, probable norovirus illness was reported by 5 passengers and was associated with visiting restrooms reported as clean by all respondents. This suggests inapparent environmental contamination with norovirus. The strain detected in the ill crew was also associated with environmental persistence on cruise ships during 2002.1 Contaminated areas are rarely successfully identified, hampering implementation of targeted control measures.
We had no layout of the plane or seating information; therefore, we were unable to collect information on use of specific restrooms. Contact was established too late to allow for stool collection from passengers and confirmation of transmission from crew by sequence comparison of detected noroviruses. Nonetheless, we believe transmission did occur. First, the clinical symptoms and postulated incubation period of the passenger illnesses fit criteria specific for norovirus disease.4 Second, 5 norovirus-like illnesses among 93 disembarked passengers within 3 days corresponds with more than 6 diarrheal episodes per person-year, 5 to 10 times baseline rates of diarrhea.5 Finally, the association with possibly contaminated restrooms is consistent with norovirus epidemiology but not with that of bacterial and parasitic agents. This association also suggests that passengers were infected on the plane and not in the short period while grouped before or after the flight.
Because norovirus infection is common and disembarked passengers disperse before becoming ill, in-flight transmission of norovirus is likely underreported. Strategies to control norovirus transmission during flight should include rapid sequestering of affected persons in areas with separate airspaces and lavatory facilities and paying particular attention to disinfection of all bathroom surfaces, even in the absence of obvious soiling.
Financial Disclosures: None reported.
Acknowledgment: We thank Claudia Chesley, BA, for editorial assistance, and staff from state health departments for their collaboration.
Marc-Alain Widdowson, VetMB
zux5{at}cdc.gov
Roger Glass, MD;
Steve Monroe, PhD;
R. Suzanne Beard, BS
Respiratory and Enteric Virus Branch
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, Ga
John W. Bateman, BA
New York Quarantine Station
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Jamaica, NY
Perrianne Lurie, MD
Division of Infectious Disease Epidemiology
Pennsylvania Department of Health
Harrisburg
Caroline Johnson, MD
Division of Disease Control
Philadelphia Department of Public Health
Philadelphia, Pa
1. Widdowson M-A, Cramer EH, Hadley L, et al. Outbreaks of acute gastroenteritis on cruise ships and on land: identification of a predominant circulating strain of norovirus—United States 2002. J Infect Dis. 2004;190:27-36.
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2. Chadwick PR, Walker M, Rees AE. Airborne transmission of a small round structured virus [letter]. Lancet. 1994;343:171.
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3. Marks PJ, Vipond IB, Carlisle D, Deakin D, Fey RE, Caul EO. Evidence for airborne transmission of Norwalk-like virus (NLV) in a hotel restaurant. Epidemiol Infect. 2000;124:481-487.
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4. Kaplan JE, Feldman R, Campbell DS, Lookabaugh C, Gary GW. The frequency of a Norwalk-like pattern of illness in outbreaks of acute gastroenteritis. Am J Public Health. 1982;72:1329-1332.
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5. Mead PS, Slutsker L, Dietz V, et al. Food-related illness and death in the United States. Emerg Infect Dis. 1999;5:607-625.
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Letters Section Editor: Robert M. Golub, MD, Senior Editor.
JAMA. 2005;293:1859-1860.
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