Bat rabies in the United States and Canada from 1950 through 2007: human cases with and without bat contact.

BACKGROUND Since the 1980s, rare cases of rabies in humans in Canada and the United States have been almost exclusively caused by the bat-variant virus. METHODS We reviewed indigenously acquired cases of bat-variant rabies in humans in Canada and the United States from 1950 through 2007. RESULTS Of 61 cases identified, 5 occurred after organ transplantation and were excluded from further analysis. A bite was reported by 22 (39%) of the case patients, 9 (16%) had a direct contact (i.e., were touched by a bat) but no history of a bite, 6 (11%) found bats in their home (2 [4%] in the room where they slept) but reported no direct contact, and 19 (34%) reported no history of bat exposure whatsoever. With the exception of California (8 cases) and Texas (7 cases), no state or province had >3 cases. Of the case patients, 76% were men, and 40% were 10-29 years of age. The median incubation period was 7 weeks (<10 weeks in 72% of cases). The incidence of bat-variant rabies cases increased from 2.2 per billion person-years in 1950-1989 to 6.7 per billion person-years in 1990-2007. Of 36 case patients with bat rabies described since 1990, 16 had no history of direct bat contact; 2 (13%) of the 16 would have qualified for rabies postexposure prophylaxis on the basis of exposure criteria expanded in 1995 to include bats that were in the same room as a sleeping person. The incidence of rabies for this type of exposure was 0.6 cases per billion person-years. CONCLUSION The true preventable proportion of cases and the number needed to treat with rabies postexposure prophylaxis to prevent 1 case would be useful information to inform the current guidelines.