Nosocomial transmission of a drug-sensitive W-variant Mycobacterium tuberculosis strain among patients with acquired immunodeficiency syndrome in Tennessee

Tuberculosis Patients Who Are A Potential Source for Unprotected Exposure in Health Care Systems: A Multicenter Case Control Study

Setting

Five health care systems in Texas.

Objective

To describe the epidemiology of inadequate isolation for pulmonary tuberculosis leading to tuberculosis (TB) exposures from confirmed TB patients and the patient factors that led to the exposures.

Design

A retrospective cohort and case-control study of adult patients with TB resulting in exposures (cases) vs those TB patients who did not result in exposures (controls) during January 2005 to December 2012.

Results

There were 335 patients with pulmonary TB disease, 199 cases and 136 controls. There was no difference between groups in age (46 ± 14.6 vs 45 ± 17 years; P > .05), race, or substance abuse. Cases were more likely to be transplant recipients (adjusted odds ratio [AOR], 18.90; 95% CI, 1.9-187.76), have typical TB chest radiograph (AOR, 2.23; 95% CI, 1.1-4.51), and have positive acid-fast bacilli stains (AOR, 2.36; 95% CI, 1.31-4.27). Cases were less likely to have extrapulmonary disease (AOR, 0.47; 95% CI, 0.24-0.95).

Conclusions

TB exposure resulting from inadequate isolation is frequent in health care settings. Extrapulmonary involvement resulted in earlier airborne isolation. Being a transplant recipient, having chest radiograph findings typical for TB, and sputum positivity acid-fast bacilli upon staining were associated with increased risk of inadequate isolation.

Molecular Epidemiology: A Tool for Understanding Control of Tuberculosis Transmission

One of the primary goals of tuberculosis control programs is to interrupt the transmission of Mycobacterium tuberculosis. The development of several genotyping tools has allowed tracking of strains of M. tuberculosis as they spread through communities. Studies that have combined the use of genotyping with conventional epidemiologic investigation have increased the understanding of the transmission and pathogenesis of tuberculosis. This article reviews some of the lessons learned using these new epidemiologic tools.

Drug-susceptible Mycobacterium tuberculosis Beijing genotype does not develop mutation-conferred resistance to rifampin at an elevated rate

The Mycobacterium tuberculosis Beijing genotype has drawn attention because it is often strongly associated with multidrug-resistant tuberculosis (MDR-TB). A possible reason is that the Beijing strains may have an enhanced capacity to develop drug resistance. In this study, we used the Luria-Delbrück fluctuation test to investigate whether strains of Beijing and non-Beijing genotypes exhibit differences in the acquisition of drug resistance. The M. tuberculosis reference strain H37Rv and 12 fully drug-susceptible clinical isolates, 6 of which were of the Beijing genotype, were examined. To determine the distribution of rifampin-resistant mutants, 25 independent cultures were made for each strain. The average mutation frequencies for the non-Beijing (H37Rv included) and Beijing genotypes were estimated to be 4.4 x 10(-8) and 3.6 x 10(-8), respectively. The corresponding average mutation rates for the non-Beijing and Beijing strains were 1.3 x 10(-8) and 1.1x 10(-8) mutations per cell division, respectively. The results suggest that the association of the Beijing genotype with MDR-TB is not due to an altered ability to develop resistance.

Global dissemination of the Mycobacterium tuberculosis W-Beijing family strains

A large, genetically related group of Mycobacterium tuberculosis strains, variously called W or Beijing, is distinguished by specific molecular markers and referred to as the W-Beijing family strains. Molecular epidemiological studies suggest that these strains are highly prevalent throughout Asia and the countries of the former Soviet Union and they have also been reported in several other geographical regions, including North America. Although the spread of W-Beijing family strains in diverse populations is well documented, the underlying host-pathogen factors accounting for their continued dissemination and burden of disease have yet to be determined.

Lessons from recent nosocomial epidemics

This review describes important examples of recent nosocomial infection epidemics. Current trends suggest that emerging problems in nosocomial infections include increased nosocomial epidemics in out-of-hospital settings, contamination of medical devices and products, and antimicrobial resistance. Increased attention should be focused on outbreak investigations in these areas.