Performance of conventional PCR for detection of <i>Mycobacterium tuberculosis</i> in mouthwashes

Abstract

BACKGROUND
Lack of rapid, sensitive, and affordable diagnostics has greatly hampered tuberculosis control efforts in countries with high prevalence of human immunodeficiency virus (HIV) infection and anti-tuberculosis drug resistance. Although sputum smear microscopy remains the principal tool for diagnosing active Pulmonary tuberculosis, its sensitivity is quite low. The impact of sputum culture and drug susceptibility testing is limited by the long duration and complexity of the laboratory processes. Additional diagnostic challenges posed by extra-pulmonary tuberculosis, pediatric tuberculosis, and latent tuberculosis infection. M. tuberculosis PCR amplification in mouthwashes was compared with existing methods for diagnosis of tuberculosis.
MATERIALS AND METHODS
This study was carried out at Mbagathi Hospital, Nairobi, between January 2016 and December 2018. During the study period, all adult patients of either sex referred to the Mbagathi Hospital TB laboratory with clinical features suggestive of tuberculosis were recruited into the study. Mouthwashes were collected through rinsing with normal saline. Mouthwash results were compared with that of reference standard culture, Ziehl–Neelsen (ZN) smear microscopy the GeneXpert.
RESULTS
Of the 300 patients that fitted the study inclusion criteria, acceptable specimen samples were obtained from 210 patients whereby 165 patients whose cultures were read as either positive or negative had their results analyzed.70 (42.4%) patients were both culture and ZN smear-positive whereas 87(52.7%) were both culture and ZN smear negative.7(4.2%) patients were culture negative but ZN positive whereas 1(0.6%) was culture-positive but ZN smear negative.69(41.8%) patients were positive for both culture and PCR whereas 80(48.4%) were negative for both cultures and PCR.14 (8.4%) patients were, however, negative for culture but PCR positive.2(2.4%) of the patients were culture-positive but PCR negative.66 (40.7%) of the patients tested positive for both culture and GeneXpert whereas 87(53.7%) were both culture and GeneXpert negative. 2(1.2%) of the patients were culture negative but positive for GeneXpert and lastly,7 (4.3%) of the patients were culture-positive but GeneXpert negative. 45(27%) of the patients had their cultures contaminated. The test performances were as follows:100%,94%,92% and 94% for culture,90.1%,99%,90% and 91% for ZN smear, 83%,97%,81% and 83% for PCR and 97.1%,92%,88% and 90.1% for the GeneXpert respectively.
CONCLUSIONS
PCR test accurately and rapidly detected M. tuberculosis - specific DNA sequences of small numbers of mycobacteria in mouthwashes and was easily manipulable. Further refinements of the test may improve the diagnosis of tuberculosis in resource-constrained countries.