An observational study on the incidence of tuberculosis among a cohort of HIV infected adults in a setting with low prevalence of tuberculosis.

Background: Tuberculosis (TB) remains a main cause of morbidity and mortality among individuals infected with HIV. We investigated the incidence of TB among a cohort of HIV infected patients attending a setting with low TB burden where screening for latent TB infection is not routinely carried out.

Methods: an observational cohort study on HIV-infected adults attending the HIV clinic at Queen Elizabeth Hospital Birmingham, UK between 1 January 2011 and 30 September 2015. Patients with culture-proven TB after HIV diagnosis, or those treated for clinical diagnosis of the infection, were classified as having "active TB".

Results: 1824 patients were included in the study (5347 patient years of follow up), of whom 21 patients developed TB (16 microbiology confirmed). Of the 666 new HIV diagnoses, six patients developed TB within one month, giving a TB prevalence at the time of HIV diagnosis of 0.9%. The total TB incidence for the remaining 1818 patients was 2.81 cases per 1000 patient years (95% CI: 1.63-4.53). TB incidence was significantly more common among patients with CD4 ≤ 200 cells/mm³ compared to those with CD4 > 500 cells/mm³ (28.2 vs. 1.22 per 1000 patient years, p < 0.001), and in patients with VL ≥ 40 copies/mL compared to <40 copies/mL (8.30 vs. 1.42, p < 0.001).

Conclusion: In settings with low TB prevalence, early start of combined antiretroviral therapy and intensified TB case finding protocols may significantly reduce the incidence of TB.