Abstract
BackgroundWe describe the identification of, and risk factors for, the single most prevalent Mycobacterium tuberculosis strain in the West Midlands region of the UK.Methodology/Principal FindingsProspective 15-locus MIRU-VNTR genotyping of all M. tuberculosis isolates in the West Midlands between 2004 and 2008 was undertaken. Two retrospective epidemiological investigations were also undertaken using univariable and multivariable logistic regression analysis. The first study of all TB patients in the West Midlands between 2004 and 2008 identified a single prevalent strain in each of the study years (total 155/3,056 (5%) isolates). This prevalent MIRU-VNTR profile (32333 2432515314 434443183) remained clustered after typing with an additional 9-loci MIRU-VNTR and spoligotyping. The majority of these patients (122/155, 79%) resided in three major cities located within a 40 km radius. From the apparent geographical restriction, we have named this the “Mercian” strain. A multivariate analysis of all TB patients in the West Midlands identified that infection with a Mercian strain was significantly associated with being UK-born (OR = 9.03, 95%CI = 4.56–17.87, p<0.01), Black Caribbean (OR = 5.68, 95%CI = 2.96–10.91, p<0.01) resident in Wolverhampton (OR = 9.29, 95%CI = 5.69–15.19, p<0.01) and negatively associated with age >65 years old (OR = 0.25, 95%CI = 0.09–0.67, p<0.01). A second more detailed investigation analyzed a cohort of 82 patients resident in Wolverhampton between 2003 and 2006. A significant association with being born in the UK remained after a multivariate analysis (OR = 9.68, 95%CI = 2.00–46.78, p<0.01) and excess alcohol intake and cannabis use (OR = 6.26, 95%CI = 1.45–27.02, p = .01) were observed as social risk factors for infection.Conclusions/SignificanceThe continued consistent presence of the Mercian strain suggests ongoing community transmission. Whilst significant associations have been found, there may be other common risk factors yet to be identified. Future investigations should focus on targeting the relevant risk groups and elucidating the biological factors that mediate continued transmission of this strain.
Highlights
DNA fingerprinting of Mycobacterium tuberculosis has a key role in TB control and cluster investigation as the molecular data obtained can be used to direct and focus public health control efforts [1,2]
M. tuberculosis strains Between 2004 and 2008, 4,830 isolates were typed from 31 referring laboratories in the West and East Midlands
We describe here the identification of the most prevalent M. tuberculosis strain in the West Midlands, which we have termed the Mercian strain
Summary
DNA fingerprinting of Mycobacterium tuberculosis has a key role in TB control and cluster investigation as the molecular data obtained can be used to direct and focus public health control efforts [1,2]. DNA fingerprinting enhanced the investigation of a large outbreak in North London where many of the epidemiological links would not have been established by routine contact tracing or traditional epidemiological investigations alone [3]. 1,012 clinical cases (18.7 per 100,000) in the West Midlands region of the UK with a 43% increase in case numbers in the region since 2000. Birmingham is the largest city in the West Midlands with a rate of 42.4 cases per 100,000 in 2008. There is large variation in the incidence of TB across the West Midlands, with rates highest in one urban area of Birmingham (.80 cases per 100,000) and lowest in rural Worcestershire (,4 cases per 100,000 in 2008) [9]. We describe the identification of, and risk factors for, the single most prevalent Mycobacterium tuberculosis strain in the West Midlands region of the UK
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