Infrequent MODS TB culture cross-contamination in a high-burden resource-poor setting.
One obstacle to wider use of rapid liquid culture-based tuberculosis diagnostics such as the microscopic observation drug susceptibility (MODS) assay is concern about cross-contamination. We investigated the rate of laboratory cross-contamination in MODS, automated MBBacT, and Lowenstein-Jensen (LJ) cultures performed in parallel, through triangulation of microbiologic (reculturing stored samples), molecular (spoligotype/RFLP), and clinical epidemiologic data. At least 1 culture was positive for Mycobacterium tuberculosis for 362 (11%) of 3416 samples; 53 were regarded as potential cross-contamination suspects. Cross-contamination accounted for 17 false-positive cultures from 14 samples representing 0.41% (14/3416) and 0.17% (17/10248) of samples and cultures, respectively. Positive predictive values for MODS, MBBacT (bioMérieux, Durham, NC), and LJ were 99.1%, 98.7%, and 99.7%, and specificity was 99.9% for all 3. Low rates of cross-contamination are achievable in mycobacterial laboratories in resource-poor settings even when a large proportion of samples are infectious and highly sensitive liquid culture-based diagnostics such as MODS are used.
Moore
David A J
DA
Department of Infectious Diseases and Immunity, Imperial College London Wellcome Centre for Clinical Tropical Medicine, W12 0NN London, UK. davidajmoore@msn.com
Caviedes
Luz
L
Gilman
Robert H
RH
Coronel
Jorge
J
Arenas
Fanny
F
LaChira
Doris
D
Salazar
Cayo
C
Carlos Saravia
Juan
J
Oberhelman
Richard A
RA
Hollm-Delgado
Maria-Graciela
MG
Escombe
A Roderick
AR
Evans
Carlton A W
CA
Friedland
Jon S
JS