A striking increase in the numbers of cultures positive for Mycobacterium tuberculosis was noticed in a mycobacterial reference laboratory in Campinas, Sao Paulo State, Brazil, in May 1995. A contaminated bronchoscope was the suspected cause of the increase. All 91 M. tuberculosis isolates grown from samples from patients between 8 May and 18 July 1995 were characterized by spoligotyping and IS6110 fingerprinting. Sixty-one of the 91 isolates had identical spoligotype patterns, and the pattern was arbitrarily designated S36. The 61 specimens containing these isolates had been processed and cultured in a 21-day period ending on 1 June 1995, but only 1 sample was smear positive for acid-fast bacilli. The patient from whom this sample was obtained was considered to be the index case patient and had a 4+ smear- positive lymph node aspirate that had been sent to the laboratory on 10 May. Virtually all organisms with spoligotype S36 had the same IS6110 fingerprint pattern. Extensive review of the patients' charts and investigation of laboratory procedures revealed that cross-contamination of specimens had occurred. Because the same strain was grown from all types of specimens, the bronchoscope was ruled out as the outbreak source. The most likely source of contamination was a multiple-use reagent used for specimen processing. The organism was cultured from two of the solutions 3 weeks after mock contamination. This investigation strongly supports the idea that M. tuberculosis grown from smear-negative specimens should be analyzed by rapid and reliable strain differentiation techniques, such as spoligotyping, to help rule out laboratory contamination.374916919Tuberculosis notification update (1996) Weekly Epidemiol. Rec., 71, pp. 65-72Bauer, J., Thomsen, V.O., Poulsen, S., Andersen, A.B., False-positive results from cultures of Mycobacterium tuberculosis due to laboratory cross-contamination confirmed by restriction fragment length polymorphism (1997) J. Clin. Microbiol., 35, pp. 988-991Bhattacharya, M., Dietrich, S., Mosher, L., Siddiqui, F., Reisberg, B.E., Paul, W.S., Warren, J.R., Cross contamination of specimens with Mycobacterium tuberculosis: Clinical significance, causes, and prevention (1997) Microbiol. Infect. Dis., 109, pp. 324-330Braden, C.R., Templeton, G.L., Stead, W.W., Bates, J.H., Cave, M.D., Valway, S.E., Retrospective detection of laboratory cross-contamination of Mycobacterium tuberculosis cultures with use of DNA fingerprint analysis (1997) Clin. Infect. Dis., 24, pp. 35-40Dunlap, N.E., Harris, R.H., Benjamin W.H., Jr., Harden, J.W., Hafner, D., Laboratory contamination of Mycobacterium tuberculosis cultures (1995) Am. J. Respir. Crit. Care Med., 152, pp. 1702-1704Groenen, P.M.A., Bunschoten, A.E., Van Soolingen, D., Van Embden, J.D.A., Nature of DNA polymorphism in the direct repeat cluster of Mycobacterium tuberculosis: Application for strain differentiation by a novel typing method (1993) Mol. Microbiol., 10, pp. 1057-1065Jones W.D., Jr., Bacteriophage typing of Mycobacterium tuberculosis cultures from incidents of suspected laboratory cross-contamination (1988) Tubercle, 69, pp. 43-49Kamerbeek, J., Schouls, L., Kolk, A., Van Agterveld, M., Van Soolingen, D., Kuijper, S., Bunschoten, A., Van Embden, J., Simultaneous detection and strain differentiation of Mycobacterium tuberculosis for diagnosis and epidemiology (1997) J. Clin. Microbiol., 35, pp. 907-914MacGregor, R.R., Clark, L.W., Bass, F., The significance of isolating low numbers of Mycobacterium tuberculosis in culture of sputum specimens Chest, 68, pp. 518-523Maurer, J.R., Desmond, E.P., Lesser, M.D., Jones, W.D., False-positive cultures of Mycobacterium tuberculosis (1984) Chest, 86, pp. 439-442Murray, P.R., Mycobacterial cross-contamination with the modified BACTEC 460 TB system (1991) Diagn. Microbiol. Infect. Dis., 14, pp. 33-35Small, P.M., McClenny, N.B., Singh, S.P., Schoolnik, G.K., Tompkins, L.S., Mickelsen, P.A., Molecular strain typing of Mycobacterium tuberculosis to confirm cross-contamination in the mycobacteriology laboratory and modification of procedures to minimize occurrence of false-positive cultures (1993) J. Clin. Microbiol., 31, pp. 1677-1682Smith, W.B., Vance D.W., Jr., Specimen cross-contamination by a strain of Mycobacterium tuberculosis lacking nitrate reductase activity (1991) Diagn. Microbiol. Infect. Dis., 14, pp. 523-526Van Embden, J.D.A., Cave, M.D., Crawford, J.T., Dale, J.W., Eisenach, K.D., Gicquel, B., Hermans, P., Small, P.M., Strain identification of Mycobacterium tuberculosis by DNA fingerprinting: Recommendations for a standardized methodology (1993) J. Clin. Microbiol., 31, pp. 406-409Wurtz, R., Demarais, P., Trainor, W., McAuley, J., Kocka, F., Mosher, L., Dietrich, S., Specimen contamination in mycobacteriology laboratory detected by pseudo-outbreak of multidrug-resistant tuberculosis: Analysis by routine epidemiology and confirmation by molecular technique (1996) J. Clin. Microbiol., 34, pp. 1017-101
