Early and Efficient Detection of Mycobacterium tuberculosis in Sputum by Microscopic Observation of Broth Cultures

Abstract

Early, efficient and inexpensive methods for the detection of pulmonary tuberculosis are urgently needed for effective patient management as well as to interrupt transmission. These methods to detect M. tuberculosis in a timely and affordable way are not yet widely available in resource-limited settings. In a developing-country setting, we prospectively evaluated two methods for culturing and detecting M. tuberculosis in sputum. Sputum samples were cultured in liquid assay (micro broth culture) in microplate wells and growth was detected by microscopic observation, or in Löwenstein–Jensen (LJ) solid media where growth was detected by visual inspection for colonies. Sputum samples were collected from 321 tuberculosis (TB) suspects attending Bugando Medical Centre, in Mwanza, Tanzania, and were cultured in parallel. Pulmonary tuberculosis cases were diagnosed using the American Thoracic Society diagnostic standards. There were a total of 200 (62.3%) pulmonary tuberculosis cases. Liquid assay with microscopic detection detected a significantly higher proportion of cases than LJ solid culture: 89.0% (95% confidence interval [CI], 84.7% to 93.3%) versus 77.0% (95% CI, 71.2% to 82.8%) (p = 0.0007). The median turn around time to diagnose tuberculosis was significantly shorter for micro broth culture than for the LJ solid culture, 9 days (interquartile range [IQR] 7–13), versus 21 days (IQR 14–28) (p<0.0001). The cost for micro broth culture (labor inclusive) in our study was US $4.56 per sample, versus US $11.35 per sample for the LJ solid culture. The liquid assay (micro broth culture) is an early, feasible, and inexpensive method for detection of pulmonary tuberculosis in resource limited settings.

Cost-effectiveness in the diagnosis of tuberculosis: choices in developing countries

“…The first method is early, feasible, and inexpensive for detection of pulmonary tuberculosis. The cost was 4.56 US dollars per sample versus 11.35 US dollars for LJ solid media [59]. A limit of micro-broth culture is that an inverted light microscope to visualize the characteristic cording growth of MTB is required, which is not a standard piece of lab equipment, and few labs have this tool.…”

“…When coupled with drug sensitivity testing, this assay has been called microscopic observation of drug sensitivity (MODS). MODS is a non-commercial TB liquid-culture method that is recommended by the World Health Organization for detection and drug susceptibility testing of MTB [14]. It is based on the observation of the cord formation of MTB grown in a liquid medium.…”

The diagnostic utility of line probe assays for multidrug-resistant tuberculosis

“…The detection of TB DNA from dead bacteria can lead to a higher rate of false positive results when assayed against culture results, and this reduces the specificity. 12 In addition, the culture in itself is an imperfect gold standard, having a sensitivity of only 77% 16 for sputum samples, and thus when culture is taken as a reference standard, a new test under evaluation can appear false positive.…”

‘Cough‐triggered’ tuberculosis screening among adults with diabetes in Tanzania

“…Our primary case definition for tuberculosis is based on the American Thoracic Society definition [17,[20][21][22]. Patients must meet two of the three following criteria: (1) symptoms of tuberculosis (cough, fever, night sweats, etc.…”