Rabies Risk Assessment of Exposures to a Bat on a Commercial Airliner — United States, August 2011

On August 5, 2011, a bat flew through the cabin of a commercial airliner minutes after takeoff during an early morning flight from Wisconsin to Georgia, potentially exposing the passengers and flight crew to rabies virus. Three days later, the Wisconsin Division of Public Health (WDPH) requested assistance from CDC to conduct a rabies risk assessment for the passengers, flight crew, and ground crew members associated with the flight. No one was determined to have been exposed to rabies virus based on Advisory Committee on Immunization Practices guidelines for rabies prevention (1). An environmental assessment of the Wisconsin airport found a rigorous animal control and incident documentation program and no evidence of bat infestation. Although none of the persons assessed required postexposure rabies prophylaxis in this incident, bats active in daylight or found in areas where they are not normally found (e.g., aboard an aircraft) can pose risks for rabies transmission, and public health officials should be prepared to respond to such occurrences.

At 6:45 a.m. on August 5, 2011, a commercial airliner carrying 50 passengers, two pilots, and one flight attendant departed Madison, Wisconsin, bound for Atlanta, Georgia. Shortly after takeoff, a bat flew from the rear of the aircraft through the cabin several times before being trapped in the lavatory (2). The pilots were notified, and the aircraft returned to the airport. All passengers disembarked to allow maintenance crew members to remove the bat from the aircraft. The bat avoided capture and flew out the cabin door, through the airport terminal, and was seen exiting the building through automatic doors. After a search of the aircraft cabin for additional bats, 15 passengers reboarded the aircraft; 35 remaining passengers made alternative arrangements. Because the bat was not captured, the rabies status of the animal was unknown.

Assessment of Potential Exposures

On August 8, WDPH was notified of a news report describing the aircraft incident involving the bat. WDPH requested assistance from CDC to conduct a multistate investigation, assessing the potential risk for rabies and the need for rabies postexposure prophylaxis among passengers, the flight crew, and ground crew members associated with the flight.

A risk assessment tool was created to evaluate potential contact with the bat or its saliva, rabies vaccination history, and any circumstances during the flight that might have reduced the alertness of passengers and prevented an accurate description of events. Because of difficulties obtaining an accurate passenger manifest, the risk assessment tool also inquired about passenger knowledge of other passengers' identities and potential bat contact on board the flight. A separate risk assessment tool was developed for crew members and ground crew members to assess potential exposure and any history of bat infestation on the airport grounds. Additionally, an evaluation was conducted of any environmental circumstances that might have contributed to the bat's ability to enter the airliner.

During this investigation, the airline's initial departure manifest could not be provided to public health officials because it was voided when the flight was rescheduled with 15 passengers. Consequently, reservation manifests and airline weight calculations were needed to determine the possible number of persons exposed. Airline officials provided CDC with the names of the 15 confirmed passengers who reboarded the flight and the 33 persons who had made prior reservations. However, weight and flight records confirmed that 50 passengers were on board when the aircraft initially departed from Madison, and, on questioning, four of the 33 persons with reservations reported not boarding the flight. Telephone numbers were available for 36 of the 50 passengers; two passengers were contacted using e-mail, and one was contacted using a social network. Travel agencies were contacted to facilitate telephone contact of the remaining identified passengers, and a press release was issued to seek contact with the remaining unidentified passengers. Information for one unidentified passenger not listed on the flight manifest was obtained from a family member aboard the flight. Five passengers remained unidentified.

In all, CDC interviewed 45 (90%) of the 50 passengers on board the initial flight and confirmed that none had physical contact with the bat or exposure to its saliva, and all were alert during the flight. The 45 passengers were residents of 11 states. They ranged in age from 2 to 63 years (mean: 41.2 years), and 24 (53%) were male. Two passengers reported having been vaccinated previously against rabies.

The airline conducted the risk assessment of the two pilots, one flight attendant, and 16 ground crew members associated with the flight. None of the airline personnel reported contact with the bat, bat saliva, or altered alertness during the incident.

Airport Environmental Assessment

Because 10 ground crew members reported previous bat sightings at the airport, on August 22, WDPH, the Wisconsin Department of Natural Resources, Public Health Madison & Dane County, and airport authorities conducted an environmental assessment of the airport to ascertain circumstances leading to the incident. The airport jetways, gates, and baggage handling areas were inspected. No bat droppings or other evidence of bats were seen. A review of airport animal incident records confirmed that few bats had been seen at the airport in previous years. Several measures were recommended to minimize the potential for exposure of passengers and airline personnel to bats, including using netting to cover crevices where bats might roost, extending and retracting the jetways at each gate before the first flight of the morning, and training airport employees on correct procedures for bat capture and submission for testing. No more bat sightings have been reported at the airport.

Reported by

James Kazmierczak, DVM, Jeffrey P. Davis, MD, Wisconsin Div of Public Health. Teal R. Bell, Karen Marienau, MD, Nicole J. Cohen, MD, Nina Marano, DVM, Div of Global Migration and Quarantine; Sergio Recuenco, MD, DrPh, Charles Rupprecht, VMD, PhD, Div of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases; Danielle Buttke, DVM, PhD, Danielle Tack, DVM, Michael L. Bartholomew, MD, EIS officers, CDC. Corresponding contributor: Danielle Buttke, dbuttke@cdc.gov, 770-488-3418.

Editorial Note

Since 2001, 15 (71%) of the 21 human rabies infections acquired in the United States were caused by rabies virus variants associated with bats (3). The major reservoirs of rabies in the United States are bats and wild mesocarnivores (e.g., raccoons, skunks, foxes, and coyotes). Approximately 6% of bats captured for testing in 2010 were infected with rabies virus (3,4). Although the prevalence in healthy bats that are not easily captured likely is much lower (4), a bat seen active during daylight hours or in an area where bats are not normally found, such as an aircraft cabin, should be tested for rabies as a public health precaution.

Worldwide, commercial air carriers transported approximately 2.5 billion passengers in 2009 and are expected to transport 3.3 billion by 2014 (5). As the number of airline passengers increases, transmission of infectious diseases before, during, and after a flight is an increasingly important public health concern. Transportation of animals, including exotic species, on aircraft has the theoretic potential for transmission of zoonotic pathogens. However, no air travel–associated zoonotic outbreaks resulting from direct animal-to-human transmission have been reported (6).

Among 42 reported cases of human rabies during 1995–2010 in the United States not associated with transplanted organs or tissues, 11 (26%) infections were among travelers to rabies-endemic countries and were related to direct contact with wildlife or a dog bite. None of the human rabies cases were attributed to exposure to rabies virus during travel on a public conveyance (7). Although human-to-human transmission of rabies virus can occur, only two documented cases of this type of transmission have been reported, other than cases associated with organ or tissue transplantation (8).

This investigation illustrates the unique challenges public health officials face when possible exposures to zoonotic pathogens occur in mass transit settings, particularly during air travel. Passenger reservation manifests can be inconsistent and provide limited contact information, necessitating other methods of communication to contact known and unknown travelers, including social networks, e-mail, press releases, and travel agencies. To date, five passengers on this flight remain unidentified.

Prevention strategies against rabies include public education regarding the risk for rabies virus transmission from bats and recommendations for overall avoidance of bats; however, aircraft present a unique environment in which avoidance might not be possible. Any potential human exposure to a bat should be investigated thoroughly and rapidly. A standard risk assessment in accordance with Advisory Committee on Immunization Practices recommendations (1) should be conducted, and the need for postexposure prophylaxis should be determined. Whenever possible, bats associated with potential exposure to humans or domestic animals should be collected and submitted for rabies diagnostic testing.

Acknowledgments

David Redell, Wisconsin Dept of Natural Resources; Timothy Butcher, Dane County Regional Airport, Madison; Beth Cleary, Public Health Madison & Dane County, Wisconsin. Leslie N. Sadeghi, Div of Global Migration and Quarantine; Richard Franka, DVM, PhD, Div of High-Consequence Pathogens and Pathology, National Center for Emerging and Zoonotic Infectious Diseases, CDC.

References

1. CDC. Human rabies prevention—United States, 2008: recommendations of the Advisory Committee on Immunization Practices. MMWR 2008;57(No. RR-3).
2. CNN iReport. Bat on a plane [Video]. Available at http://ireport.cnn.com/docs/DOC-647392. Accessed April 6, 2012.
3. Blanton JD, Palmer D, Dyer J, Rupprecht CE. Rabies surveillance in the United States during 2010. J Am Vet Med Assoc 2011;239:773–83.
4. CDC. Rabies. Atlanta, GA: US Department of Health and Human Services, CDC; 2011. Available at http://www.cdc.gov/rabies/bats/education/index.html. Accessed April 6, 2012.
5. International Air Transport Association. Industry expects 800 million more travelers by 2014—China biggest contributor [Press release]. Singapore: International Air Transport Association; February 14, 2011. Available at http://www.iata.org/pressroom/pr/pages/2011-02-14-02.aspx. Accessed April 11, 2012.
6. Mangili A, Gendreau MA. Transmission of infectious diseases during commercial air travel. Lancet 2005;365:989–96.
7. CDC. Human rabies. Atlanta, GA: US Department of Health and Human Services, CDC; 2011. Available at http://www.cdc.gov/rabies/location/usa/surveillance/human_rabies.html. Accessed April 6, 2011.
8. Fekadu M, Endeshaw T, Wondimagegnehu A, Bogale Y, Teshager T, Olson JG. Possible human-to-human transmission of rabies in Ethiopia. Ethiop Med J 1996;34:123–7.