Investigation of Cross-contamination in a Mycobacterium Tuberculosis Laboratory Using Epidemiological Data and Spoligotyping

Objective: To investigate possible pseudo-outbreak of Mycobacterium tuberculosis (MTB) during a two week period July 2-15th 2005, as suggested by an increase in incidence of newly diagnosed patients with tuberculosis. Many of them had negative – smears for AFB and only one positive-MTB culture. Methodology: Retrorespective surveys of all medical and laboratory data using standard epidemiological tools and DNA fingerprinting in King Khalid University Hospital, Riyadh, Saudi Arabia. Results: A total of 22 samples representing 20 individual patients were examined. Epidemiological and laboratory analysis of these samples revealed that 14 were identified as presumed false-positive reports due to laboratory cross-contamination. In a further 5 cases, patients were diagnosed clinically as having tuberculosis and were defined as cases of possible cross-contamination. The source was a patient with both clinical and radiographic evidence of TB and was the only one who was smear and culture positive for TB. Molecular analysis and epidemiological studies revealed that specimen patching and multi-use vials of buffer solution were the source of cross-contamination. Conclusions: This investigation strongly supports the idea that M.tuberculosis grown from smear-negative specimens from patients without clinical evidence of tuberculosis should be analyzed by rapid and reliable strain differentiation techniques, such as spoligotyping, to help rule-out laboratory contamination.