Pseudo-outbreak of multidrug-resistant Mycobacterium tuberculosis associated with presumed laboratory processing contamination.

An investigation prompted by six positive cultures for multidrug-resistant Mycobacterium tuberculosis during a 7-week period found that an unusual resistance pattern, temporal proximity of laboratory processing, and identical DNA fingerprints supported the theory of cross-contamination. Laboratory processing procedures included specimen batching and multi-use vials of buffer solution. Processing procedures were changed and no additional cases of suspected cross-contamination have been observed.