Mycobacterium tuberculosis specimen contamination revisited: the role of laboratory environmental control in a pseudo-outbreak

OBJECTIVE: To investigate suspected pseudooutbreaks of Mycobacterium tuberculosis (MTB) during August 1994 and July 1995 among patients who did not have clinical findings consistent with tuberculosis. DESIGN: Retrospective and prospective surveys of all clinical and laboratory data using standard epidemiological tools and DNA fingerprinting. SETTING: A university-affiliated community hospital. PATIENTS: Those with positive MTB cultures during periods when we noted that the number of MTB positive cultures greatly outnumbered the usual monthly average (retrospective analysis, 1994) and patients with positive MTB cultures without clinical findings consistent with tuberculosis (prospective survey, 1995). RESULTS: Epidemiological and molecular studies revealed specimen cross-contamination in the laboratory due to a faulty exhaust hood. Improvement in laboratory ventilation and change of the implicated hood prevented further specimen contamination. CONCLUSIONS: The identification of positive MTB cultures from patients without clinical evidence of tuberculosis should be a signal to suspect laboratory contamination and implement control measures. These should include a thorough epidemiological investigation, DNA fingerprint analysis, and an environmental inspection (Infect Control Hosp Epidemiol 1998;19:101-105). The resurgence in tuberculosis (TB) has led to an increased number of specimens processed for Mycobacterium tuberculosis (MTB) detection.1,2 Even transient increases in the volume of testing may overload the capabilities of some facilities, enhancing the likelihood of procedural lapses or equipment malfunction. Carryover of organisms from positive to negative specimens during batch processing may occur, and episodes of cross-contamination involving conventional and radiometric methodologies have been reported.3-6 The rate of sample contamination or false-positive samples has been quoted as 0.4% to 3.5%.6-8 In many studies, contamination was confirmed by phage typing and unusual antimycobacterial susceptibility patterns.3,9,1o More recently, the standard MTB DNA fingerprinting methodology From the Division of Infectious Diseases, the Department of Medicine (Drs. Segal-Maurer, Urban, and Rahal) , the Department of Nursing (Ms. Burns and Ms. Lim) , the Department of Pathology, Microbiology Laboratory (Dr Lavie) , the New York Hospital Medical Center of Queens, Flushing, New York; and the Department of Medicine (Drs. Segal-Maurer and Rahal) and Microbiology (Dr Urban) , Cornell University Medical College, the Public Health Research Institute, Tuberculosis Center (Dr Kreiswirth) , New York City, New York. The authors thank the infection control nurses and the microbiology and engineering departments for their cooperation during the investigation, as well as the administrative staff for their prompt response. The authors also thank Mitchell Gayer for his technical expertise. This work was presented in part at the Sixth Annual Meeting of the Society for Healthcare Epidemiology of America, Washington, DC, April 21-23, 1996. Abstract 33. Address reprint requests to Sorana Segal-Maurer, MD, Division of Infectious Diseases, New York Hospital Medical Center of Queens, 56-45 Main St, Flushing, NY 11355. 97-OA-026. Segal-Maurer S, Kreiswirth BN, Burns JM, Lavie S, Lim M, Urban C, Rahal JJ. Mycobacterium tuberculosis specimen contamination revisited: the role of laboratory environmental control in a pseudo-outbreak. Infect Control Hosp Epidemiol 1998; 19: 10 1-105. This content downloaded from 157.55.39.171 on Sat, 25 Jun 2016 06:01:34 UTC All use subject to http://about.jstor.org/terms 102 INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY February 1998 using the insertion sequence IS6110 has proven useful, in conjunction with traditional epidemiological investigation techniques, in identifying sources of contamination!'" Recent reports linking pseudooutbreaks with laboratory contamination have postulated reagent tubing contamination and contact between reagent containers and specimens.7,9,10," This is the first reported pseudo-outbreak in which faulty laboratory ventilation caused specimen crosscontamination with MTB.