Recurrent tuberculosis in the pre-elimination era.

Recurrent tuberculosis (TB), defined as TB that recurs after a patient has been considered cured, constitutes a challenge to TB control. In low TB burden countries, the underlying causes and consequences of recurrent TB are poorly understood. We conducted a literature review to summarise the evidence of recurrent TB in low-burden settings and to address current gaps in knowledge. We included peer-reviewed publications on studies conducted in countries with an estimated TB incidence of <100 cases per 100 000 population. The Newcastle-Ottawa scale was used to assess study quality. The review yielded 44 manuscripts, 39 of which were reports of observational studies and 5 of clinical trials. The median percentage of TB patients experiencing an episode of recurrent TB after treatment completion was 3.4% (interquartile range [IQR] 1.6-6.0, range 0.4-16.7) in studies with a median follow-up of 7.8 years (IQR 5-12, range 2-33). The median percentage of recurrences attributable to endogenous reactivation (rather than exogenous reinfection) was 81% (IQR 73.1-85.5, range 49-100). Commonly identified risk factors for recurrence in low-burden settings included infection by the human immunodeficiency virus, low socio-economic status, foreign birth and infection with drug-resistant TB. Current understanding of recurrence in low-burden settings is limited, in part due to substantial methodological differences between studies. Further research is required to delineate the mechanisms of TB recurrence, its health and clinical impact, as well as the implications for TB elimination efforts in low-burden countries.