In 2007, an extensive contact screening investigation into onward transmission of tuberculosis was instigated at a hospital in Northern Ireland following diagnosis of pulmonary multi-drug resistant TB in a healthcare worker. Interferon gamma release assays (IGRAs) were used to test 333 patients and 98 staff. We investigated for evidence of onward transmission and recent infection based on analysis of clinical, demographic and IGRA data. We also described within-patient variability of IGRA results. Among patients and staff, increasing age of patients was the only factor associated with IGRA positivity. Greatest within-subject variability of IU/mL in serially-tested patients/staff was seen in those with a positive IGRA test and this did not correlate with increased exposure to the index case. IGRA positivity being largely explained by increasing age in patients and previous TB contact in staff lends weight to the conclusion that IGRA positivity reflected previous infection rather than recent transmission.

Due to an increase in bovine tuberculosis in cattle in the United Kingdom, we investigated the characteristics of Mycobacterium bovis infection in humans and assessed whether extensive transmission of M. bovis between humans has occurred. A cross-sectional study linking demographic, clinical, and DNA fingerprinting (using 15-locus mycobacterial interspersed repetitive-unit-variable-number tandem-repeat [MIRU-VNTR] typing) data on cases reported between 2005 and 2008 was undertaken. A total of 129 cases of M. bovis infection in humans were reported over the period, with a decrease in annual incidence from 0.065 to 0.047 cases per 100,000 persons. Most patients were born pre-1960, before widespread pasteurization was introduced (73%), were of white ethnicity (83%), and were born in the United Kingdom (76%). A total of 102 patients (79%) had MIRU-VNTR typing data. A total of 31 of 69 complete MIRU-VNTR profiles formed eight distinct clusters. The overall clustering proportion determined using the n ؊ 1 method was 33%. The largest cluster, comprising 12 cases, was indistinguishable from a previously reported West Midlands outbreak strain cluster and included those cases. This cluster was heterogeneous, having characteristics supporting recent zoonotic and humanto-human transmission as well as reactivation of latent disease. Seven other, smaller clusters identified had demographics supporting recrudescence rather than recent infection. A total of 33 patients had incomplete MIRU-VNTR profiles, of which 11 may have yielded 2 to 6 further small clusters if typed to completion. The incidence of M. bovis in humans in the United Kingdom remains low, and the epidemiology is predominantly that of reactivated disease.