Prevalence of non-tuberculous mycobacterial infections among tuberculosis suspects in Nigeria.

backgroundNigeria is ranked in the top five countries for tuberculosis deaths worldwide. This study investigated the mycobacterial agents associated with presumptive clinical pulmonary tuberculosis (TB) in Nigeria and evaluated the pattern and frequency of mycobacterial infections over twelve calendar months period.

methodsSputum samples from 1,603 consecutive new cases with presumptive diagnosis of TB were collected from August 2010 to July 2011. All sputum samples were incubated for detection of mycobacterial growth and those with positive acid fast bacilli (AFB) growth were tested to detect mycobacterium tuberculosis (MTB) complex and characterized to differentiate between MTB complex species. Cultures suggestive of Non-tuberculous mycobacterial infections (NTM) were sub-cultured and characterized.

resultsOf the 1,603 patients screened, 444 (28%) culture-positive cases of pulmonary tuberculosis were identified. Of these, 375 (85%) were due to strains of MTB complex (354 cases of M. tuberculosis, 20 M. africanum and one case of M. bovis) and 69 (15%) were due to infection with NTM. In contrast to the MTB complex cases, the NTM cases were more likely to have been diagnosed during the calendar months of the Harmattan dust season (OR = 2.34, 1.28-4.29; p = 0.01), and aged older than 35 years (OR = 2.77, 1.52-5.02, p = 0.0007), but less likely to have AFB identified on their sputum smear (OR = 0.06, 0.02-0.14, p<0.0001). Among those with NTM infection, cases 35 years or younger were more likely to have co-infection with HIV (3.76, 1.72-8.22; p = 0.0009) compared to those older than 35 years.

interpretationThe high proportion of younger patients with clinical pulmonary TB due to NTM and co-infection with HIV and the likely role of the seasonal dust exposure in the occurrence of the disease, present novel public health challenges for prevention and treatment.