Bat-associated Rabies: Reassessing the Risk of Bedroom Exposure

Abstract

Source: De Serres G, Skowronski DM, Mimault P, et al. Bats in the bedroom, bats in the belfry: reanalysis of the rationale for rabies postexposure prophylaxis. Clin Infect Dis. 2009;48:1493–1499; doi: 10.1086/598998Canadian researchers sought to determine the necessity of postexposure rabies prophylaxis (RPEP) for individuals exposed to a bat but without knowledge of direct contact — eg, bat seen in the room of a sleeping child, no evidence of a bite, and bat not available for testing. To estimate the proportion of the population with bat exposure annually, a random-digit-dial telephone survey of residents in Quebec was conducted from January through March 2007.Participants were asked whether they or their child had been in the presence of a bat; if so, additional questions sought details related to bat exposure and intervention. Exposure was classified as direct contact if there was recognized physical contact with a bat. Household exposure in the absence of recognized physical contact was divided into three categories including bedroom exposure, bedroom access (bat found elsewhere in the house with a door open to allow bat access to the individual while sleeping), and other exposure circumstances.From a telephone survey of 14,453 households (63% of those eligible) involving 36,445 individuals, only four individuals reported direct contact with a bat without a known bite in the previous 12 months. Another 152 reported indoor proximity to a bat without known contact. These exposures included bedroom exposures in 34, bedroom access in 41, and other types in 77. None of the four with direct contact and none of the 34 with bedroom exposure sought medical advice but two (5%) of the 41 who reported bedroom access to bats sought medical advice and both received RPEP.The total exposed without direct contact (152) was used as a proportion of the population of Quebec (7.6 million) to estimate the expected number of exposures in the province (56,605). From 1990 through 2007 in Canada and the US, there were 36 individuals with bat-acquired rabies. Of these, 17 had no recognized physical contact; two reported bedroom exposure. Based on these figures, the system would need to treat 2.7 million people to prevent one case of rabies and the investigation and treatment would involve a huge outlay of personnel and a cost of $2 billion (in Canadian $) for biological products and virologic analyses alone. The authors’ most sensitive calculation assumed that all 17 of the rabies cases with no recognized physical contact had a bedroom bat exposure. Given this assumption, the system would need to treat 314,000 individuals to prevent one case of rabies acquired through bedroom exposure.The authors conclude that bedroom exposure to bats is fairly frequent in Quebec and contracting rabies from such an exposure is quite rare. Even recognizing the almost universal fatality from rabies, the low cost-benefit ratio suggests that current recommendations to consider RPEP after non-bite bedroom exposure should be reconsidered.Dr Shane has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.De Serres and colleagues present compelling evidence to reconsider the liberal approach toward RPEP when evidence of bites is lacking. Despite the inherent limitations of a population-based survey and potential regional differences between Quebec and other areas where frequency of bat exposures may vary, the number needed to treat (NNT) analysis outlines the tremendous resources involved in RPEP. In an era of limited resources and reduced vaccine supply, a reconsideration of our liberal use of RPEP for bat exposures is warranted. (See also AAP Grand Rounds, July 2008;20:5.1)The June 2009 revision of the ACIP guidelines to reduce the number of doses of RPEP from five to four emanated from efforts to address a rabies vaccination shortage in 2007. Population-based evidence that levels of antibody following four and five doses of rabies vaccine were equivalent and absence of infection in those who received four versus five doses of RPEP provided the basis for these recommended modifications to the schedule.2,3 Although this reduction in doses for RPEP has the potential to reduce the expenditures calculated by the authors in their economic analysis, implementation of the reduced vaccination schedule is unlikely to have a significant impact on the total expenditures associated with RPEP. Human resources comprise the greatest expenditures required to evaluate each suspected exposure.4