Tuberculosis prevalence and incidence rates from repeated population-based screening in a district in Ethiopia: a prospective cohort study

ABSTRACT Objective In Ethiopia, a third of the estimated tuberculosis cases are not detected or reported. Incidence estimates are inaccurate and are rarely measured directly. Any tuberculosis program will miss some tuberculosis cases and assessing the ‘‘real’’ incidence under program conditions is useful to understand the situation. This study aimed to measure the prevalence and incidence of pulmonary tuberculosis based on three rounds of household visits in the adult population of Dale in Ethiopia. Design A prospective population-based cohort study. Setting Every household in Dale district was visited three times at 4-month interval over 12 months. Participants Individuals aged 15 and more years were followed. Outcome measures Microscopy smear-positive PTB (PTB s+), bacteriologically confirmed PTB (PTB b+) by microscopy, GeneXpert, or culture, and clinically diagnosed PTB (PTB c+). Results Among 136,181 individuals, 2052 had presumptive TB in round1, including 93 with PTB s+, 98 with PTB b+, and 24 with PTB c+; adding those with PTB who were already on treatment, the total number of PTB was 201, and the prevalence was 147 (95%CI: 127–168)/100,000 population. Out of all detected PTB patients by screening, PTB s+ was 65%, PTB b+ was 67%, and PTB c+ was 44%. During 96,388 person-years follow-up after round1 to round3 end, 1909 had presumptive TB, 320 had PTB, and the total incidence of PTB was 332 (95%CI: 297–370)/100,000 person-years, while the incidence of PTB s+, PTB b+, and PTB c+ was 230 (95%CI: 201–262), 263 (95%CI: 232–297), and 68 (95%CI: 53–86)/100,000 person-years, respectively. Conclusion The prevalence of PTB s+ was similar to the national survey and local studies, but only a third of prevalent PTB cases had been notified. The incidence rate was highest in those aged 25–34 years, indicating ongoing transmission. Finding missing people with TB through repeated screening can reduce transmission. Strengths and limitations of this study This study included a large sample and worked closely with the national tuberculosis program and the community structures that contributed to its sustainability. We report not only tuberculosis prevalence but also incidence based on three rounds of household visits, which is often not reported elsewhere. The study screened a very high proportion of households in the district, giving an accurate measure of the burden of tuberculosis, where the probability of missing people with TB is small. Tuberculosis cases notified were chosen the year before the study because we could not separate the patients identified by the screening from those who attended the health services themselves. We did not perform GeneXpert and culture for all smear-positive tuberculosis cases, so there was a difference between microscopy smear-positive and bacteriologically confirmed tuberculosis cases, which was very small.