Persistent tuberculosis or specimen contamination?

Kathy Trakas, Valentina Stosor, Stephen Dietrich, Laura Mosher, John R. Warren*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Cross-contamination during sequential processing of sputum specimens from different patients causes false-positive growth of Mycobacterium tuberculosis in culture. We describe an unusual case of cross-contamination in a 36-year-old man with acquired immunodeficiency syndrome and possible persistent tuberculosis. Culture with 1 of 3 sputum specimens was positive for rifampin-susceptible M tuberculosis. Review of processing revealed that his single culture-positive sputum specimen had followed a sputum specimen from another patient with active pulmonary tuberculosis that was positive in culture for M tuberculosis resistant to rifampin. Molecular strain typing by restriction fragment length polymorphism demonstrated the 2 isolates to be an identical strain of M tuberculosis. Agar proportion susceptibility testing of the rifampin-resistant isolate revealed low numbers of resistant organisms in a range of 1.5% to 3.3%. It was concluded that rifampin-susceptible organisms that constituted approximately 98% of the resistant isolate contaminated sputum from the patient with possible persistent tuberculosis. His culture result was, therefore, considered false positive, not an indication of tuberculosis.

Original languageEnglish (US)
Pages (from-to)902-903
Number of pages2
JournalArchives of Pathology and Laboratory Medicine
Issue number6
StatePublished - 2000

ASJC Scopus subject areas

  • Pathology and Forensic Medicine
  • Medical Laboratory Technology


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