Laboratory-Acquired Rocky Mountain Spotted Fever: The Hazard of Aerosol Transmission

Nine patients with laboratory-acquired Rocky Mountain spotted fever were seen during the period 1971 to 1976. Investigation of each case revealed either definite or probable exposure to an aerosol containing infectious rickettsiae; in no case was there evidence of parenteral exposure either by accidental self-inoculation or by tick bite. These illnesses are believed to represent infection acquired via the respiratory route. This report emphasizes the aerosol hazard of Rickettsia rickettsii in the laboratory and discusses the possibility of respiratory transmission of Rocky Mountain spotted fever in nature. The illness occurred only in personnel who had received either no vaccination or the primary series of the commercial (Lederle) vaccine against this infection. Other personnel who had received the primary series with multiple booster vaccinations demonstrated increased immunity as measured by humoral antibody titers and rickettsial antigen-induced lymphocyte transformation; no cases of clinical disease developed in these multiply-vaccinated personnel. (N Engl J Med 297:859–863, 1977) Rocky Mountain spotted fever, an infectious disease caused by Rickettsia rickettsii, is endemic throughout the continental United States. Transmission to human beings occurs through the bite of an infected arthropod, the dog tick, Dermacentor variabilis, in the eastern United States, or the wood tick, D. andersoni, in the western United States. Accidental selfinoculation of infectious material in both laboratory^1,2 and clinical³ settings can also occur. Although aerosol inoculation of monkeys provides a well studied animal model for the disease,^4,5 there are only three previously reported cases of laboratory-acquired disease for which a careful investigation failed to disclose.