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Tuberculosis is a communicable respiratory disease. A group of researchers led by Maeve Lalor conducted a cohort study to determine household transmission of tuberculosis in England by combining epidemiologic and molecular strain typing data.
Tuberculosis is a communicable respiratory disease prevalent in some third world countries. In first world countries where the prevalence of this disease is low, molecular strain typing can help identify cases and further reduce transmission of the disease.
In a recent article published in BMC Medicine, a group of researchers led by Maeve Lalor conducted a cohort study estimating the number of cases of tuberculosis in England due to recent household transmission. All tuberculosis cases notified to the Enhanced Tuberculosis Surveillance System in England from January 1, 2010 to December 31, 2012 were included in the study. A 24-loci MIRU-VNTR strain typing was used to determine if the infection was due to recent transmission. Cases were classified as having a household link if they were reported from the same address regardless of the strain typing results, or if 2 or more cases from the same household were reported. After combining data from strain typing and household links, cases were further classified as having a confirmed, probable, possible, or refuted household transmission event. Confirmed household transmission was defined as having 2 cases positive for strain typing and household link; probable transmission as 2 cases with positive household links but with indistinguishable strain typing; possible transmission as 2 cases with positive household link but with one or both not having a strain typing profile; and refuted as 2 cases with positive household link but with different strain typing profiles. Risk factors for being a household transmitter were also identified.
The results of the study show that 1849 out of 24,060 (7.7%) tuberculosis cases reported lived in a household with another case. 1242 cases out of 1849 identified did not have a strain typing profile. For those with strain typing data, 386 (64%) had confirmed, 66 (11%) probable, and 155 (25%) refuted household transmission. The following risk factors for being a household transmitter were identified: age <25 years old, UK-born with Black African, Indian, and Pakistani ethnicity, and being born in Romania or Somalia.
Overall, the results of this study demonstrate the use of strain typing to identify tuberculosis cases. Contact tracing is an important aspect of the management of communicable diseases like tuberculosis. Techniques aimed at improving contact tracing may help reduce the number of tuberculosis cases as well as reduce transmission rates.
Written By: Karla Sevilla