Assessment of sputum smear-positive but culture-negative results among newly diagnosed pulmonary tuberculosis patients in Tanzania

Abstract

Diagnosis of pulmonary tuberculosis (TB) in technology-limited countries is widely achieved by smear microscopy, which has limited sensitivity and specificity. The frequency and clinical implication of smear-positive but culture-negative among presumptive TB patients remains unclear. A cross-sectional substudy was conducted which aimed to identify the proportion of nontuberculous mycobacteria (NTM) infections among 94 “smear-positive culture-negative” patients diagnosed between January 2013 and June 2016 in selected health facilities in Tanzania. Out of 94 sputa, 25 (26.60%) were GeneXpert® mycobacteria TB positive and 11/94 (11.70%) repeat-culture positive; 5 were Capilia TB-Neo positive and confirmed by GenoType MTBC to be Mycobacterium tuberculosis/Mycobacterium canettii. The remaining 6 Capilia TB-Neo negative samples were genotyped by GenoType® CM/AS, identifying 3 (3.19%) NTM, 2 Gram positive bacteria, and 1 isolate testing negative, together, making a total of 6/94 (6.38%) confirmed false smear-positives. Twenty-eight (29.79%) were confirmed TB cases, while 60 (63.83%) remained unconfirmed cases. Out of 6 (6.38%) patients who were HIV positive, 2 patients were possibly coinfected with mycobacteria. The isolation of NTM and other bacteria among smear-positive culture-negative samples and the presence of over two third of unconfirmed TB cases emphasize the need of both advanced differential TB diagnostic techniques and good clinical laboratory practices to avoid unnecessary administration of anti-TB drugs.

Assessment of GeneXpert GxAlert platform for multi-drug resistant tuberculosis diagnosis and patients’ linkage to care in Tanzania

“…Effective TB control interventions require early identification of TB infected persons and tailored therapies. As a result of limited performance of smear microscopy [ 1 , 2 ] and a slow generation time of mycobacteria on culture media [ 3 ], the WHO endorsed the use of GeneXpert MTB/RIF for rapid detection of TB and rifampicin resistance [ 4 ]. As rapid diagnostic tools become available, the main challenge remains on how responsive the health system is to ensure effective linkage of diagnosed patients to requisite healthcare.…”

Diagnosis of Osteoarticular Tuberculosis: Perceptions, Protocols, Practices, and Priorities in the Endemic and Non-Endemic Areas of the World—A WAIOT View

“…It is best to inform the microbiologist about the suspicion so that appropriate tests are carried out. Another important feature in NTM infections that helps in early diagnosis is a positive smear for acid-fast bacilli and negative GeneXpert [ 75 , 76 , 77 , 78 , 79 , 80 ]. The incidence of these infections is sizeable.…”

Genome sequence of Mycobacterium yongonense RT 955-2015 isolate from a patient misdiagnosed with multidrug-resistant tuberculosis: First clinical detection in Tanzania

“…This can be attributed to the use of suboptimal diagnostic tests, particularly in developing countries like Tanzania. The detection of acid-fast bacilli by smear examination of NTM can result in the misdiagnosis of TB cases (Hoza et al, 2016a,b;Mfinanga et al, 2014;Kilale et al, 2016;Mnyambwa et al, 2017a), which normally do not respond to anti-TB drugs, thereby leading to classification as MDR-TB (Lu et al, 2016;Shahraki et al, 2015). Most of the MAC members are naturally resistant to anti-TB drugs (Shahraki et al, 2015;Mpagama et al, 2013), which leads to the unnecessary administration of toxic second-line anti-TB treatments, thereby increasing the risk of the evolution of drug resistance.…”

“…The authors also revealed that members of M. yongonense Type I genotype harbour a unique DNA mismatch repair gene MutS4 family, that potentially serves as a putative driving force for the suggested HGT between the M. parascrofulaceum and M. yongonense Type I genomes through homologous recombination events (Kim et al, 2017). The occurrence of NTM in Tanzania has been reported frequently (Hoza et al, 2016a,b;Mfinanga et al, 2014;Kilale et al, 2016;Mnyambwa et al, 2017a), but characterization of the isolates has relied on suboptimal typing methods that have potentially hindered accurate species identification.…”