Risk of Norovirus Transmission during Air Travel

Krista Kornylo MPH, David K. Kim MD, Marc‐Alain Widdowson VetMB, MS, George Turabelidze MD, PhD, Francisco M. Averhoff MD, MPH
DOI: http://dx.doi.org/10.1111/j.1708-8305.2009.00344.x 349-351 First published online: 1 September 2009

Abstract

Background During October 2006, an outbreak of norovirus gastroenteritis sickened 200 (59%) of the 379 passengers and 26 (18%) of the 144 crew members on a riverboat. In November 2006, CDC was notified that a group of ill passengers had boarded a commercial flight from St Louis, Missouri, to Atlanta, Georgia. A recent study demonstrated probable norovirus transmission from eight symptomatic flight attendants to passengers on board an aircraft during an international flight; however, there are no published reports of transmission of norovirus on flights of short duration.

Methods We investigated the risk of norovirus transmission on a short flight as part of an outbreak response. Using a standardized questionnaire, we conducted interviews of passengers and flight attendants who were on the flight. We collected information on traveler demographics and illness before, during, and after the flight. We also collected information about potential onboard risk factors for norovirus transmission, such as proximity and contact with ill appearing persons during the flight, as well as use of onboard lavatories and hand hygiene.

Results We were able to complete questionnaires for 50 (56%) of the 89 passengers on the flight and 2 (67%) of the 3 flight attendants. Two (5%) of 42 possible secondary cases were identified. These two passengers neither sat in proximity to an index‐case passenger during the flight nor reported use of an onboard lavatory.

Conclusions Although onboard transmission cannot be excluded, likelihood of norovirus transmission on a short flight when ill travelers do not have episodes of vomiting or diarrhea appears minimal.

Norovirus is a highly contagious virus, with no antiviral drug therapy or vaccine, which commonly causes acute onset of diarrhea, vomiting, nausea, and abdominal cramps in humans.1–3 Its modes of transmission include consumption of contaminated food or water, direct contact with an infected person, contact with fomites, and aerosolized vomitus particles. A recent study demonstrated probable norovirus transmission from eight symptomatic flight attendants to passengers on board an aircraft during an international flight; 4 however, there are no published reports of transmission of norovirus on flights of short duration.

During October 2006, an outbreak of norovirus gastroenteritis sickened 200 (59%) of the 379 passengers and 26 (18%) of the 144 crew members on a riverboat.5 Passengers experiencing vomiting or diarrhea were advised to postpone their air travel home until their symptoms resolved. On November 2, CDC was notified that a group of ill passengers had boarded a commercial flight from St Louis, Missouri, to Atlanta, Georgia on October 23 (total cabin time including boarding and taxiing: around 2.5 h). We attempted to ascertain if there was norovirus transmission from ill riverboat passengers to other travelers during the flight and, if so, determine the risk factors for transmission during the flight.

Methods

Using a standardized questionnaire, 3 weeks after the flight, we conducted telephonic interviews of passengers and flight attendants who were on the flight. This investigation was part of an outbreak response and did not require institutional review board approval. We collected information on traveler demographics and illness before, during, and after the flight. We also collected information about potential onboard risk factors for norovirus transmission, such as proximity and contact with ill appearing persons during the flight, as well as use of onboard lavatories and hand hygiene.4,6,7

We defined an index case as illness in a riverboat passenger who had vomiting (≥ 1 episode) and/or diarrhea (≥ 3 loose stools in a 24‐h period) within 3 days before boarding the flight. We defined a possible secondary case as illness in a passenger or flight attendant on the flight who did not travel on the riverboat and developed vomiting or diarrhea within 72 hours after the flight, had no known contact with another person with similar symptoms in the week before onset, and had no known etiology for his or her symptoms. We did not collect clinical specimens for norovirus testing because the investigation took place 3 weeks after the flight.

Results

We were able to complete questionnaires for 50 (56%) of the 89 passengers on the flight and 2 (67%) of the 3 flight attendants. No contact information was available for 38 passengers and 1 passenger refused the interview. One flight attendant was not contacted.

Eight riverboat passengers were on board the flight; of these, five (63%) had illness that met the case definition for being an index case. None of the index‐case passengers reported episodes of vomiting or diarrhea during the flight; one passenger did have bouts of diarrhea immediately before and immediately after the flight, and another reported use of the onboard lavatory. The five index‐case passengers were seated in rows 11, 12, and 29 (Figure 1).

Figure 1

Aircraft configuration and the location of index and suspect secondary cases during the flight (n = 89).

Only 2 (5%) of the 42 passengers contacted met the criteria for a possible secondary case. These two passengers neither sat in proximity to an index‐case passenger during the flight (Figure 1) nor reported use of an onboard lavatory.

Discussion

Our investigation found little evidence of in‐flight norovirus transmission on board a short commercial flight with symptomatic index passengers. However, we lacked contact information for a substantial proportion of the passengers and were thus not able to include them in our study. Also, two of five index‐case passengers (row 29) had very few passengers seated around them and information was only available on 2 out of 10 passengers seated within two rows. Because the two potential secondary case passengers were not tested for norovirus, had no epidemiologic link to the index cases, were seated several rows away, and did not use the rest room, we do not attribute their illness to norovirus transmitted from the index‐case passengers, although we cannot rule out the possibility that inapparent transmission did occur on this flight.

A recent investigation suggested probable norovirus transmission from eight symptomatic flight attendants to passengers on board an aircraft during an international flight, but was linked to inapparent contamination of rest‐room facilities.4 Compared with the international flight, this flight was of much shorter duration, index‐case passengers were minimally symptomatic during the flight, and contact with other passengers and flight crew was limited. Norovirus transmission risk on a commercial flight is likely greater when episodes of vomiting or diarrhea occur on board and with longer duration of flight; longer flights may result in greater use of lavatories among both ill and non‐ill passengers, increasing the possibility of norovirus transmission. This investigation provides reassuring additional data that, in the absence of in‐flight episodes of vomiting and diarrhea, norovirus is not likely easily transmitted in airplanes.

Declaration of interests

The authors state they have no conflicts of interest to declare.

Acknowledgments

We thank Anandi Sheth, Manoj Menon, and Gwen Ewald for their assistance with the interviews.

This study/report was supported in part by an appointment to the Applied Epidemiology Fellowship Program administered by the Council of State and Territorial Epidemiologists (CSTE) and funded by the Centers for Disease Control and Prevention (CDC) Cooperative Agreement U60/CCU007277.

Footnotes

  • This paper was presented as a poster at the International Society of Travel Medicine Conference in Vancouver, Canada on May 21, 2007.

References

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