Background: Nigeria has the fourth highest tuberculosis (TB) burden worldwide. In this
study, mycobacterial agents from clinically symptomatic TB patients, regardless of HIV
co-infection were isolated and characterized, and resistance to isoniazid and rifampicin
determined.
Methods: Suspected TB cases were recruited from two TB clinics into a cross-sectional
study. All patients were screened for HIV, and their sputum samples were screened for
Mycobacteria using an algorithm that included smear microscopy, liquid broth and solid
media culture, TB-antigen detection assay, and molecular probe assays, to determine the
type of Mycobacterium and pattern of resistance to isoniazid and rifampicin.
Results: Of 1,603 patients screened, 466 (29%) had liquid broth culture-positive
pulmonary Mycobacterial infection. Of these, 444 (95%) had mycobacterial infections
and 22 (5%) were false-positive non-mycobacterial strains. Of the 444 cases, 375 (80%)
were infected with Mycobacterial tuberculosis (MTB) complex (354 M. tuberculosis, 1
M. bovis and 20 M. africanum) and 69 (15%) were Non-tuberculous mycobacteria
(NTM). HIV co-infection was detected in 101 (27%) of the MTB complex and 26 (38%)
of the NTM cases respectively.
Twenty-three (6.1%) of the MTB complex cases had organisms resistant to
isoniazid (3.5%), rifampicin (1.3%) or both, i.e. multi-drug resistant TB (MDR-TB,
1.3%), by molecular analysis, and of those, 8 (35%) had a prior history of TB treatment.
Currently available molecular assays are incapable of detecting drug-resistant NTM
strains. After controlling for prior treatment, cases with any resistance (i.e. at least to one
drug) were more likely to be co-infected with HIV compared to cases without any
resistance (OR=3.6, 95%CI=1.5-8.8; p=0.0039). Compared to M. tuberculosis, the NTM
cases were more likely to be HIV co-infected more likely to present with clinical
symptoms during the intense Harmattan dust storms from December to February
(OR=2.5, 95%CI=1.4-4.5; p=0.0034, and OR=2.2, 95%CI=1.2-3.8; p<0.0067 and
respectively), and less likely to be detected by the routine sputum smear test (OR=0.05,
95%CI=0.02-0.13; p<.0001).
Conclusions: The high frequency of smear-negative NTM cases with HIV co-infection
identified during the period of Harmattan dust storm presents a novel public health
challenge. Introduction of molecular detection assays to identify smear-negative NTM
and MDR-TB is a high priority