title: Persistent tuberculosis or specimen contamination?
abstract: 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.
authors.affiliation: Department of Pathology, Northwestern University Medical School, Chicago, IL 60611, USA.
authors.forename: K
authors.initials: K
authors.lastname: Trakas
authors.forename: V
authors.initials: V
authors.lastname: Stosor
authors.forename: S
authors.initials: S
authors.lastname: Dietrich
authors.forename: L
authors.initials: L
authors.lastname: Mosher
authors.forename: J R
authors.initials: JR
authors.lastname: Warren
mesh_terms: D017088:AIDS-Related Opportunistic Infections / Q000175:diagnosis* / Q000188:drug therapy; D000328:Adult; D000995:Antitubercular Agents / Q000627:therapeutic use; D003951:Diagnostic Errors; D004352:Drug Resistance, Microbial; D004359:Drug Therapy, Combination; D004866:Equipment Contamination; D005189:False Positive Reactions; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000254:growth & development / Q000302:isolation & purification*; D012150:Polymorphism, Restriction Fragment Length; D012293:Rifampin / Q000494:pharmacology; D013048:Specimen Handling / Q000592:standards*; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000188:drug therapy
chemical_list: D000995:Antitubercular Agents; D012293:Rifampin