Diversity of Mycobacterium tuberculosis strains in Nairobi, Kenya

Abstract

Setting: Tuberculosis (TB) patients attending 16 public health facilities in Nairobi, Kenya.

Objective: To determine the Mycobacterium tuberculosis (M.tuberculosis) strain families circulating in Nairobi, Kenya.

Methods: Sputum specimens from consecutive new and previously treated smear positive pulmonary TB patients were collected between February and August 2010 and cultured on Lowenstein9Jensen media. Spoligotyping was done on DNA extracted from the first isolate of each patient. The international spoligotype data base (SpolDB4) was used to group isolates into strain families.

Results: Fourty seven different strain families were identified from 536 isolates. The principal groups were; CAS1_KILI 96/536 (17%), T1 69/536 (12%), Beijing 65/536 (12%), LAM9 46/536 (9% ), LAM3 & S/Conversant 37/536 (7% ), LAM11_ZWE 26/536 (5%), CAS1_DELHI 24/536 (4%) and T2 24/536 (4%). Others identified and are found in the SpolDB4 were 113/536 (21%). A possible new M.tuberculosis strain family was identified with 21/536 (4%) isolates which was designated as Nairobi subtype. Others identified not previously included in the SpolDB4 accounted for 15/536 (3%).

Conclusion: We found a diverse array of M.tuberculosis strain families which could be indicative of a cosmopolitant polulation with frequent migration that may suggest that the dorminant strain families may have been present in the population for an extended period of time or on going transmision of closely related strains families. The emergence of the Beijing strains poses a serious threat to TB control due to its high virulence and frequent association with multidrug resistance. We therefore call for strenghthening efforts on early case finding through enhanced public health education campains and provision of accessible diagnostic services with enhanced treatment compliance.