The retrospective MIRU-VNTR typing Mycobacterium tuberculosis strains cultured from patients living in the Cardiff area between 2000 and 2010
Cardiff Metropolitan University
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Tuberculosis is a major infectious disease worldwide and is the leading cause of death by a single infectious agent that can be controlled and treated. The World Health Organization aims to reduce the number of TB cases and half the number of TB deaths and prevalence by 2015. Tuberculosis is caused by Mycobacterium tuberculosis which belongs to the M. tuberculosis complex that also includes Mycobacterium bovis, Mycobacterium africanum and Mycobacterium microti. The bacterium is non- motile and non-encapsulated with a size of 2-4pm long and divides approximately every 16 to 2O hours. Mycobacteria require specialized media such as Lowenstein Jensen Media for its isolation. The study was carried out to retrospectively type all Cardiff TB isolates from 2000 to March 2010 so that an epidemiological profile of TB in Cardiff could be created and used to compare typing results of recent TB strains to determine if there was a historical connection between strains; and also aid in future outbreaks or cluster investigations. A total of 350 isolates from the Cardiff area were typed from 2000 to 2010 and these represented patients who have attended and were diagnosed with TB in a Cardiff hospital. TB isolates were typed using both the MIRU-VNTR and ETR- VNTR typing methods and results analysed by fluorescence based sequencer to determine predominance of TB type. The study found that a majority of TB cases in Cardiff were located in the South of the city such as Grangetown (2O.7%), Butetown (l2.6yo), Roath (12.3%), Cathays (7.4%) and Splott (5.3%). These five areas comprised 58.3% of the total number of Cardiff TB isolates and the areas with the lowest number of positive TB cases were mainly found in the Northern area of the city and included Caerau, Lisvane and Trowbridge that comprised of l.2% of TB cases. TB incidence rates were high in Butetown, Grangetown and Roath with both Butetown and Grangetown classified as high risk areas exceeding an incidence of 40 cases per 100,000 population whereas low TB incidence rates were found in areas such Canton, Cyncoed, Ely and Heath. When positive TB cases were compared to age and gender, cases were mainly isolated in the male population with an overall age group of between l5 years and 44 years old. TB strain distribution in Cardiff varied as over 50% of positive cases were caused by individual isolates and there were more than 128 strains with three or more isolates. 18.9yo of cases were caused by strains with greater than five or more isolates. The Cardiff Study discovered 22 common strains and these were identified as those with three or more isolates (strains 2, 11, 35, 70,74,76,80, 86, 94, 98, 99, 111, l15, 117, 126,132, 134, 150, 151, 154, 177 and 182). The dominant common strain in study was strain l15 followed by strain 98. Both strains were linked to known documented outbreaks in Cardiff. All positive TB cases were tested against first- line TB drugs, these include Ethambutol, Isoniazid, Pyrazinamide and Rifampicin. Thirty of these strains were resistant to one or more TB drugs (8.6%) and the remaining strains were fully sensitive to all TB drugs (9l.4%). 5.7% of strains were resistant to Isoniazid only, l.2% was only resistant to Rifampicin, O.6% of strains were resistant to Pyrazinamide only and no strains were resistant to only Ethambutol. 67.9% of resistant strains were common in males than females (32.1%) and the age range was 16-89 years old with a mean of 34 years. This study has revealed a number of factors played an important part in the number of TB cases in Cardiff. The study found that age, gender, ethnicity, social deprivation and geographical location can contribute to TB infection and disease. Age and gender in all TB cases isolated were predictably, as positive TB cases were generally seen in the male population and age group was again predictably as most cases of TB were observed in the 15 to 44 years olds. Individuals from ethnic background contributed to the high number of TB cases reported in Cardiff. By retrospectively typing the Cardiff TB isolates for the last decade, an epidemiological profile of TB in Cardiff was generated and found that TB cases are likely to occur in central areas within the city where there is large, concentrated population comprising a diverse ethic background. TB typing is a useful tool for determining the significance of particular strains and whether it is likely that a case is linked to pre-existing or previous cases or whether it has been contracted elsewhere.
MSc Biomedical Sciences
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