Salmonella typhi: the laboratory as a reservoir of infection.

As a part of educational and proficiency exercises thousands of students and laboratory personnel have been exposed to Salmonella typhi. In a retrospective study 24 cases of laboratory-acquired typhoid fever in the United states during a 33-month period were identified; laboratory-acquired cases represented only 2.4% of all typhoid cases but 11.2% of the sporadic cases. Twenty-one of the 24 cases occurred when S. typhi was voluntarily introduced into the laboratory for educational proficiency testing or research purposes. Twelve patients were exposed to S. typhi when working with it as an unknown organism; another five were merely present in the laboratory. Obvious breaks in technique were found to be the cause of infection for only seven of the 24 patients, although infection of the others implies that breaks in technique occurred. Laboratory-acquired typhoid fever may severe as a marker for other less severe laboratory-acquired infections; these data suggest that such infections could be common.