Public health implications of the microbial pesticide Bacillus thuringiensis: an epidemiological study, Oregon, 1985-86.

Bacillus thuringiensis var. kurstaki (B.t.-k) is a microbial pesticide which has been widely used for over 30 years. Its safety for a human population living in sprayed areas has never been tested. Surveillance for human infections caused by B.t.-k among Lane County, Oregon residents was conducted during two seasons of aerial B.t.-k spraying for gypsy moth control. Bacillus isolates from cultures obtained for routine clinical purposes were tested for presence of Bacillus thuringiensis (B.t.). Detailed clinical information was obtained for all B.t.-positive patients. About 80,000 people lived in the first year's spray area, and 40,000 in the second year's area. A total of 55 B.t.-positive cultures were identified. The cultures had been taken from 18 different body sites or fluids. Fifty-two (95 percent) of the B.t. isolates were assessed to be probable contaminants and not the cause of clinical illness. For three patients, B.t. could neither be ruled in nor out as a pathogen. Each of these three B.t.-positive patients had preexisting medical problems. The level of risk for B.t.-k and other existing or future microbial pesticides in immunocompromised hosts deserves further study.