Understanding the genetic diversity of Mycobacterium tuberculosis is needed for a better understanding of the epidemiology of TB and could have implications for the development of new diagnostics, drugs, and vaccines. M. tuberculosis isolates were characterized using spoligotyping and were compared with the SpoIDB4 database of the Pasteur Institute of Guadeloupe. A total of 53 different patterns were identified among 192 isolates examined. 169 of the isolates were classified into one of the 33 shared SITs, whereas the remaining 23 corresponded to 20 orphan patterns. 54% of the isolates were ascribed to the T family, a family which has not been well defined to date. Other prominent families were CAS, Haarlem, LAM, Beijing, and Unknown comprising 26%, 13%, 2.6%, 0.5%, and 2.1%, respectively. Among HIV-positive patients, 10 patterns were observed among 25 isolates. The T (38.5%), H (26.9%), and CAS (23.1%) families were the most common among HIV-positive individuals. The diversity of the M. tuberculosis strains found in this study is very high, and there was no difference in the distribution of families in HIV-positive and HIV-negative TB patients except the H family. Tuberculosis transmission in Addis Ababa is due to only the modern M. tuberculosis families (CAS, LAM, T, Beijing, Haarlem, and U). 1. Introduction Tuberculosis (TB) continues to be a major public health problem in Ethiopia. Currently Ethiopia is rated seventh among the 22 high-TB-burdened nations of the world, with a prevalence of 394 per 100,000 population in the year 2010 [1]. This situation has been worsened by the country’s HIV/AIDS epidemic and emerging Multidrug-Resistant (MDR) TB. HIV prevalence was 3.5% in 2009 and among TB patients 15% were coinfected with HIV and the rate of MDR is 1.6 in new cases and 12% in retreatment cases [2]. Despite the high-TB burden in the country, very limited information is available on the genetic diversity of M. tuberculosis strains and the impact of HIV disease on this diversity. Molecular typing techniques have been extensively used to speciate strains of M. tuberculosis involved in TB infections, studying molecular epidemiology of M. tuberculosis, providing insights into dissemination dynamics, evolutionary genetics, and detection of suspected outbreaks and person-to-person transmission [3]. Although recent studies are recommending the use of robust markers such as single nucleotide polymorphisms (SNP) or large sequence polymorphisms (LSP) for a better understanding of strain lineages [4], Insertion sequence (IS) 6110 restriction fragment length
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