SETTING: Cross-contamination is not uncommon in mycobacteriology laboratories of high-income countries, as documented by bacterial genotyping. The extent of this problem in low-income countries is largely unknown, where this method is impractical. OBJECTIVE: To estimate the rate of cross-contamination in a high-volume tuberculosis (TB) laboratory in South Africa. DESIGN: Simulated sputum specimens labelled with false names were sent from a TB clinic, interspersed with patient samples, and processed for culture and microscopy. Results were interpreted in the context of the observed proportion of samples with positive microscopy and culture results. RESULTS: With microscopy, 6/190 (3.2%) simulated specimens were positive (estimated specificity = 96.8%). Considering the 881 positive microscopy results in 6093 clinical samples, we extrapolate that 19.3% (95%CI 7.0-42.8) of positive smears were false-positives. On culture, 2/190 (1.1%) of the simulated specimens were positive for Mycobacterium tuberculosis (estimated specificity = 98.9%). Considering the 1862 positive cultures from 6093 clinical samples, we estimate that 2.4% (95%CI 0.3-8.8) of positive cultures were false-positives. CONCLUSION: Simulated specimens offer a simple means of estimating the proportion of false-positive results, providing information on all sources of potential error from the clinic, through the laboratory and to reporting of results.
SETTING: Cross-contamination is not uncommon in mycobacteriology laboratories of high-income countries, as documented by bacterial genotyping. The extent of this problem in low-income countries is largely unknown, where this method is impractical. OBJECTIVE: To estimate the rate of cross-contamination in a high-volume tuberculosis (TB) laboratory in South Africa. DESIGN: Simulated sputum specimens labelled with false names were sent from a TB clinic, interspersed with patient samples, and processed for culture and microscopy. Results were interpreted in the context of the observed proportion of samples with positive microscopy and culture results. RESULTS: With microscopy, 6/190 (3.2%) simulated specimens were positive (estimated specificity = 96.8%). Considering the 881 positive microscopy results in 6093 clinical samples, we extrapolate that 19.3% (95%CI 7.0-42.8) of positive smears were false-positives. On culture, 2/190 (1.1%) of the simulated specimens were positive for Mycobacterium tuberculosis (estimated specificity = 98.9%). Considering the 1862 positive cultures from 6093 clinical samples, we estimate that 2.4% (95%CI 0.3-8.8) of positive cultures were false-positives. CONCLUSION: Simulated specimens offer a simple means of estimating the proportion of false-positive results, providing information on all sources of potential error from the clinic, through the laboratory and to reporting of results.
Authors: Ian Toma; Marc O Siegel; John Keiser; Anna Yakovleva; Alvin Kim; Lionel Davenport; Joseph Devaney; Eric P Hoffman; Rami Alsubail; Keith A Crandall; Eduardo Castro-Nallar; Marcos Pérez-Losada; Sarah K Hilton; Lakhmir S Chawla; Timothy A McCaffrey; Gary L Simon Journal: J Clin Microbiol Date: 2014-08-20 Impact factor: 5.948
Authors: Eric Miller; Christopher Cantrell; Melodie Beard; Andrew Derylak; N Esther Babady; Tracy McMillen; Edwin Miranda; Barbara Body; Yi-Wei Tang; Ravikiran Vasireddy; Sruthi Vasireddy; Terry Smith; Elena Iakhiaeva; Richard J Wallace; Barbara A Brown-Elliott; Erik Moreno; Heather Totty; Parampal Deol Journal: J Clin Microbiol Date: 2018-07-26 Impact factor: 5.948
Authors: Anne-Marie Demers; Suzanne Verver; Andrew Boulle; Robin Warren; Paul van Helden; Marcel A Behr; David Coetzee Journal: BMC Infect Dis Date: 2012-09-14 Impact factor: 3.090
Authors: Richard A Oberhelman; Giselle Soto-Castellares; Robert H Gilman; Maria E Castillo; Lenka Kolevic; Trinidad Delpino; Mayuko Saito; Eduardo Salazar-Lindo; Eduardo Negron; Sonia Montenegro; V Alberto Laguna-Torres; Paola Maurtua-Neumann; Sumona Datta; Carlton A Evans Journal: PLoS One Date: 2015-04-30 Impact factor: 3.240