Tuberculosis (TB) continues to be a leading cause of
morbidity and mortality globally and HIV/TB co-infection remains a major
threat. TB infection in HIV patients has different clinical presentations and
manifestations, thereby being a diagnostic challenge as well. AFB sputum
microscopy remains the diagnostic test of choice for pulmonary TB in resource-limited
settings despite reports of eroded sensitivity in people living with HIV. To improve the chance of detecting AFB by
microscopy, national guidelines recommend collection of two sputum specimens instead
of one specimen, though providing dual specimens is often a practical challenge
for HIV infected individuals.
Hence a team of researchers from Chennai had evaluated
if concentrating single sputum specimen could improve the sensitivity of
detection of TB by sputum smear microscopy. Considering the increasing number
of reports of Mycobacteria other than tuberculosis (MOTT) as opportunistic
pathogens in immune-compromised hosts and most MOTT cases tend to be smear
negative and culture positive, they had also evaluated the performance characteristics
of concentration method to detect Mycobacterium
tuberculosis (MTB) and MOTT rather than AFB detection. The study involved
sputum specimens from 146 HIV infected patients and 403 HIV status unknown
patients presenting with clinical signs and symptoms for TB. Direct sputum
smear and smear from sputum concentrated by modified Petroff’s method were made
and stained by Ziehl-Neelsen method. AFB culture was performed by BACTEC TB 460
radiometric method as the reference method. Results of direct, concentrated
sputum smear microscopy were compared with AFB culture results in a blinded
evaluation. McNemar’s test and two-sample proportion tests were used and
statistical analyses were performed using GraphPad Prism ver5.0 and SPSS
ver12.0 softwares.
Concentration of single sputum specimen was found to significantly improve the sensitivity of AFB smear microscopy in HIV infected TB suspected cases and also in HIV status unknown TB suspected cases. When the performance characteristics of direct and concentrated single sputum smears in detecting MTB and MOTT were separately analyzed, the concentration method significantly improved the sensitivity to detect only MTB to two-fold among HIV infected subjects. The sensitivity of detecting only MOTT among the HIV infected TB suspected cases plunged to 9.1% and upon concentration of sputum specimen, the sensitivity of detecting only MOTT increased to 36.4%, though not statistically significant. Thus, this sputum concentration method could be helpful to increase the sensitivity of TB diagnosis, particularly for HIV patients in resource-constrained settings with limited access to culture based TB diagnostics.
Concentration of single sputum specimen was found to significantly improve the sensitivity of AFB smear microscopy in HIV infected TB suspected cases and also in HIV status unknown TB suspected cases. When the performance characteristics of direct and concentrated single sputum smears in detecting MTB and MOTT were separately analyzed, the concentration method significantly improved the sensitivity to detect only MTB to two-fold among HIV infected subjects. The sensitivity of detecting only MOTT among the HIV infected TB suspected cases plunged to 9.1% and upon concentration of sputum specimen, the sensitivity of detecting only MOTT increased to 36.4%, though not statistically significant. Thus, this sputum concentration method could be helpful to increase the sensitivity of TB diagnosis, particularly for HIV patients in resource-constrained settings with limited access to culture based TB diagnostics.
Reference: Could concentrating single sputum improve the performance of smear microscopy
in detecting TB among HIV patients? The Journal of infection.2012; doi:10.1016/j.jinf.2012.09.015.
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