Evaluation of a two-step approach for large-scale, prospective genotyping of Mycobacterium tuberculosis isolates in the United States.

Genotyping of Mycobacterium tuberculosis isolates is useful in tuberculosis control for confirming suspected transmission links, identifying unsuspected transmission, and detecting or confirming possible false-positive cultures. The value is greatly increased by reducing the turnaround time from positive culture to genotyping result and by increasing the proportion of cases for which results are available. Although IS6110 fingerprinting provides the highest discrimination, amplification-based methods allow rapid, high-throughput processing and yield digital results that can be readily analyzed and thus are better suited for large-scale genotyping. M. tuberculosis isolates (n = 259) representing 99% of culture-positive cases of tuberculosis diagnosed in Wisconsin in the years 2000 to 2003 were genotyped by using spoligotyping, mycobacterial interspersed repetitive unit (MIRU) typing, and IS6110 fingerprinting. Spoligotyping clustered 64.1% of the isolates, MIRU typing clustered 46.7% of the isolates, and IS6110 fingerprinting clustered 29.7% of the isolates. The combination of spoligotyping and MIRU typing yielded 184 unique isolates and 26 clusters containing 75 isolates (29.0%). The addition of IS6110 fingerprinting reduced the number of clustered isolates to 30 (11.6%) if an exact pattern match was required or to 44 (17.0%) if the definition of a matching IS6110 fingerprint was expanded to include patterns that differed by the addition of a single band. Regardless of the genotyping method chosen, the addition of a second or third method decreased clustering. Our results indicate that using spoligotyping and MIRU typing together provides adequate discrimination in most cases. IS6110 fingerprinting can then be used as a secondary typing method to type the clustered isolates when additional discrimination is needed.

Unsuspected recent transmission of tuberculosis among high-risk groups: implications of universal tuberculosis genotyping in its detection.

BACKGROUND: The initiation of universal genotyping revealed 3 clusters of 19 patients with tuberculosis (TB) in Wisconsin, with no apparent epidemiologic links among most of them. An epidemiologic investigation was conducted to determine whether genotype clustering resulted from recent transmission. METHODS: We conducted additional interviews with patients and reviewed medical records. Places frequented by the patients while they were infectious were visited to identify contacts. RESULTS: Our investigation revealed several previously unrecognized possible sites of TB transmission: a single-room occupancy hotel, 2 homeless shelters, 1 bar, and 2 crack houses. Seven patients with previously diagnosed TB were added to the clusters. Of 26 patients, we identified epidemiologic links for all but 1. Common risk factors among patients included alcohol abuse, crack cocaine use, homelessness, and unemployment. Additionally, 98 contacts missed during routine contact investigation were identified. CONCLUSIONS: Transmission of TB, particularly among high-risk groups, may go undetected for years. Our investigation demonstrated the value of universal genotyping in revealing unsuspected recent TB transmission and previously unrecognized sites of transmission, which can be targeted for specific TB interventions.

Laboratory role in tuberculosis control.

The term "tuberculosis" (TB) refers to infection with the bacterium Mycobacterium tuberculosis that has progressed to active disease. This disease is a public health threat because it is caused by a microorganism that is potentially fatal for humans, and transmission is commonly through the inhalation of airborne droplets expelled by infectious persons with active disease. The World Health Organization (WHO) estimates that there are more than 8 million new cases of TB each year, 2 million deaths from the disease each year, and that one-third of the world population is infected with M. tuberculosis and at risk for active disease. In 2003, the 100-year anniversary of the founding of the Wisconsin State Laboratory of Hygiene (WSLH), TB is recognized as a disease that is preventable and now almost always treatable. An early and accurate diagnosis of TB is perhaps the most significant intervention step in TB control. Early diagnosis permits expedited treatment and limitation of spread. An effective TB laboratory program plays an essential role in the early and accurate diagnosis and appropriate treatment of TB. This article examines that role.