Performance of conventional PCR for detection of Mycobacterium tuberculosis in mouthwashes

BACKGROUNDLack 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 METHODSThis 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.RESULTSOf 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.CONCLUSIONSPCR 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

Ep25-335-23 It’s not TB but what could it be? Abnormalities on chest X-rays from the 2016 Kenya National Tuberculosis Prevalence Survey

Background: The prevalence of diseases other than tuberculosis(TB) detected on chest-Xray(CXR) during TB screening in Kenya is unknown. Our study aimed to characterise and quantify non-TB abnormalities on CXR and to compare radiologist interpretation with Computer-Aided Detection for Tuberculosis (CAD4TB). We hypothesized that non-TB abnormalities requiring further clinical input are prevalent and may be missed using CAD4TB. Design/Methods: We undertook a cross-sectional study from May 2019-February 2020, analyzing CXRs from the 2016 Kenya National TB Prevalence Survey, sam- pling films classified either as “abnormal, suggestive of TB” or “abnormal other”. We developed a reporting tool which comprised four anatomical categories and a list of common diagnoses. Readers were blinded, films double reported and discordant results resolved by a third reader. We used CAD4TB 6.0. and R v3.6.2. for analysis. Results: Of 1123 films sampled, 600(53.4%) were ab- normal (Figure-1). Prevalence of abnormalities in major categories: 26.3% (95% CI 23.7%-28.9%) heart and/ or great vessels, 26.1% (95% CI23.5%-28.8%) lung parenchyma, 7.6% (95% CI 6.1%-9.3%) pleura and 3% (95% CI 2.1%-4.2%) mediastinum. Prevalence of active-TB 4% (95% CI 2%-4%), severe post TB lung changes (bronchiectasis/destroyed lung) 2% (95% CI 0-2%). Non-TB related diagnoses: cardiomegaly 23.1% (95% CI 20.6%-25.6%), suspected cardiac failure 1.9% (95% CI1.2-2.8%), non-specific airspace opacification/ interstitial disease 6% (95% CI 4%-8%), suspected emphysema 2% (95% CI 2%-4%) and mediastinal masses 0.8% (95% CI 0.4%-1.5%). Median CAD4TB scores: Severe post TB lung changes 76 (IQR 71-81), active-TB 66 (IQR 55-72), suspected emphysema 57 (IQR 54-59), non-specific airspace opacification/interstitial disease 56(IQR 50-61), mediastinal mass 52 (IQR 47-59) and cardiomegaly 50(IQR 46-56). Conclusions: Abnormalities unrelated to TB were prev- alent, most notably cardiomegaly. These non-TB ab- normalities will go undetected using CAD stratification based on threshold scores alone. Further refinement of CAD algorithms to include non-TB diagnoses could attenuate this risk. Incorporation of blood pressure monitoring and spirometry should be considered in TB screening activities