Microscopic observation drug susceptibility assay, a rapid, reliable diagnostic test for multidrug-resistant tuberculosis suitable for use in resource-poor settings.
There is an urgent need for new tools to improve our ability to diagnose tuberculosis (TB) and multidrug-resistant TB (MDR-TB) in resource-poor settings. In a retrospective analysis undertaken in a region with a high incidence of TB, we evaluated the performance of the microscopic observation drug susceptibility assay (MODS), a novel assay developed in Perú which uses an inverted light microscope and culture in Middlebrook 7H9 broth to detect mycobacterial growth. MODS detected 94.0% of 1,908 positive sputum cultures, whereas Lowenstein-Jensen (LJ) culture detected only 86.9% (P < 0.001). The median time to culture positivity was 8 days (compared to 16 days for the same 208 samples by LJ culture; P < 0.001, Wilcoxon signed rank test). The results obtained by direct susceptibility testing using MODS demonstrated excellent concordance for isoniazid and rifampin and the detection of multidrug resistance with those obtained by indirect colorimetric methods: the microplate Alamar Blue assay (MABA) and the tetrazolium microplate assay (TEMA) (agreement, 95, 98, and 94%; kappa values, 0.8, 0.7, and 0.7, respectively). The concordance of the susceptibility testing results for ethambutol and streptomycin was poor. MODS is a novel assay which can detect the organisms responsible for TB and MDR-TB directly from sputum inexpensively, rapidly, and effectively. A comprehensive prospective evaluation of MODS is under way in Perú, and independent validation in nonresearch laboratories should be undertaken at the earliest opportunity.
Laboratorio de Investigación de Enfermedades Infecciosas, Universidad Peruana Cayetano Heredia, San Martín de Porras, Lima, Perú. dajmoore@imperial.ac.uk
David A J
DA
Moore
Daniel
D
Mendoza
Robert H
RH
Gilman
Carlton A W
CA
Evans
María-Graciela
MG
Hollm Delgado
Jose
J
Guerra
Luz
L
Caviedes
Daniel
D
Vargas
Eduardo
E
Ticona
Jaime
J
Ortiz
Giselle
G
Soto
Jose
J
Serpa
D000995:Antitubercular Agents / Q000494:pharmacology*; D003470:Culture Media; D006801:Humans; D008826:Microbial Sensitivity Tests; D008853:Microscopy / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000254:growth & development* / Q000302:isolation & purification; D011203:Poverty; D015203:Reproducibility of Results; D013183:Sputum / Q000382:microbiology; D013997:Time Factors; D014376:Tuberculosis / Q000175:diagnosis / Q000382:microbiology; D018088:Tuberculosis, Multidrug-Resistant / Q000175:diagnosis* / Q000382:microbiology
D000995:Antitubercular Agents; D003470:Culture Media