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Guide to the Application of Genotyping to Tuberculosis Prevention
and Control
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Tuberculosis Genotyping Case Studies: How TB Programs
Have Used Genotyping
Algorithm to Detect False-Positive Cultures
Genotyping can help identify instances of incorrect TB diagnoses
that are based on false-positive cultures. Incorrect diagnoses can
result from laboratory cross-contamination of cultures, mislabeling
of patient specimens, collection errors, and reporting errors. Such
errors occur in an estimated 1%–3% of all reported cases of TB,
and as many as 300 persons per year in the United States may be
started erroneously on anti-tuberculosis treatment. Universal genotyping
permits TB programs to establish simple algorithms to flag suspected
errors.
The California Department of Health Services, in collaboration
with San Francisco General Hospital, Santa Clara Valley Medical
Center, and Solano County Public Health Laboratory, evaluated this
type of algorithm to find methods to decrease the occurrence of
laboratory cross-contamination (Jasmer 2002).
During the study period from January 1998 through June 1999, cultures
for 296 patients were positive for M. tuberculosis, and cultures
for ten patients met one or more of the criteria for possible false-positive
cultures. A review by a panel of experts determined that TB was
misdiagnosed for six patients (representing 2% of all patients with
cultures positive for M. tuberculosis) because of laboratory
cross-contamination. In four of the six cases, contamination probably
occurred when reagents were dispensed from a common flask. This
practice was discontinued on the basis of the findings of this study.
(See Chapter 6, Applying Genotyping Results to Tuberculosis
Control Practices, for more information on investigating false-positive
cultures.)
Last Reviewed: 05/18/2008 Content Source: Division of Tuberculosis Elimination
National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
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