Prevalence of presumptive Bacillus anthracis in the human population examined by nasal swabs

Routine cultures may reveal presumptive Bacillus anthracis microorganisms in human samples. Our study of 1336 individuals showed the probability of encountering presumptively positive cultures using routine microbiologic examination was approximately 0.4% (5 individuals) when nasal swabs were examined for the following characteristics indicative of Bacillus anthracis: nonhemolytic ground-glass colonies retaining their shape when manipulated, nonmotile in testing media, and microscopically revealing spore-forming gram-positive rods. Confirmatory tests revealed that those cultures were of Bacillus nonanthracis microorganisms. The probability appears significantly high to suggest a need for the confirmatory tests to be available at the community laboratories. In addition, our study confirmed the Gramʹs staining method does not kill all the spores of the spore-forming gram-positive rods, necessitating special safety requirements.