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

Abstract

Molecular strain typing by restriction fragment length polymorphism analysis was used to demonstrate that two clusters ofMycobacterium tuberculosis cultures involving six patients resulted from cross-contamination in the mycobacteriology laboratory. Contaminated cultures were processed by the decontamination procedure and were read on the BACTEC instrument following acid-fast bacillus smear-positive specimens from patients with active tuberculosis. Investigation of these episodes suggested opportunities for modification of laboratory procedures to minimize cross-contamination and confirmed the adverse medical and public health consequences of false-positive cultures. Strain-typing results were used in decisions regarding patient care, including the curtailment of unnecessary treatment in one patient. Molecular strain typing appears to be a valuable means of identifying false-positive cultures of M. tuberculosis in selected settings.

Demonstration of homology between IS6110 of Mycobacterium tuberculosis and DNAs of other Mycobacterium spp.?

“…A standard methodology has now been agreed on internationally to enable results from different laboratories to be compared (22). This method has been applied to identifying cross-infection within the hospital environment (16) and crosscontamination in the laboratory (20). It has also been used to demonstrate routes of transmission to and from closed communities of intravenous-drug abusers and homeless men (4,10) and to define epidemiological relationships between strains in a wider context (11).…”

Molecular epidemiology of Mycobacterium tuberculosis strains isolated from patients in a human immunodeficiency virus cohort in Switzerland

“…Application of RFLP typing has been used to elucidate the event of secondary tuberculosis (TB; i.e., endogenous reactivation versus exogenous reinfection [31]). Apart from being an excellent tool for tracing cross-contamination in the laboratory (25), DNA fingerprinting has become the method of choice in demonstrating the transmission of TB in a large variety of settings such as hospitals (1,14), shelters for the homeless (2, 10), communities (12,24), and care institutions for patients infected with the human immunodeficiency virus (HIV) (3,8,9,27). Today, it is generally accepted that (i) HIV-positive individuals are more susceptible to infections and (ii) once they are infected with tubercle bacilli, these patients are at greater risk of a latent infection that rapidly progresses to a manifest one.…”

An Outbreak of Bronchoscopy-Related Mycobacterium tuberculosis Infections Due to Lack of Bronchoscope Leak Testing

“…Six patients were exposed to the contaminated bronchoscope but apparently did not develop infection with the outbreak strain, while the case status of another patient is undetermined because specimens were not obtained for culture. Rather than considering the initial bronchial washing culture findings as false-positives, which is appropriate during pseudo-outbreaks, 21,[25][26][27] we believe that true infection in these patients may have been masked or prevented by prompt initiation of four-drug antituberculous therapy, particularly when active infection developed in two individuals despite four-drug therapy.…”