Risk of developing tuberculosis from a school contact: retrospective cohort study, United Kingdom, 2009

To quantify the risk of developing tuberculosis (TB) following school contact with a student with smear positive respiratory TB in a population with a high background rate of tuberculosis, a retrospective cohort study was conducted. This study included all students and staff (n=1,065) at an inner city secondary school in Birmingham, United Kingdom (UK). Being in the same school year as the index case resulted in a significantly higher risk of being diagnosed with active TB (odds ratio (OR) 6.11) and either active or latent TB (OR 10.52) compared to the risk for pupils in other school years. Neither lower level classroom exposure in tutoring groups nor being a staff member resulted in significantly increased risk of infection. The number of cases detected in the school was significantly higher than compared with the TB notification rate for the respective age groups in the population in the area. This study is consistent with the small body of evidence that already exists suggesting that greater levels of classroom contact with a student with smear positive active TB significantly increases the risk of contracting active and latent TB. It also suggests that staff may be at a lower risk of active TB than students. It does not appear that being in an area with high TB incidence substantially alters the epidemiology of the outbreak or risk of transmission between students in comparison to other populations.