Abstract

Recurrence of TB in an individual can occur due to relapse of the same strain or reinfection by a different strain. The contribution of reinfection and relapse to TB incidence, and the factors associated with each are unknown. We aimed to quantify and describe cases attributable to relapse or reinfection, and identify associated risk factors in order to reduce recurrence. We categorised recurrent TB cases from notifications in London (2002–2015) as relapse or reinfection using molecular (MIRU VNTR strain type) and epidemiological information (hierarchical approach using time since notification, site of disease and method of case finding). Factors associated with each outcome were determined using logistic regression in Stata Version 13.1 (2009–2015 only). Of 43,465 TB cases, 1.4% (618) were classified as relapse and 3.8% (1,637) as reinfection. The proportion with relapse decreased from 2002 (2.3%) to 2015 (1.3%), while the proportion of reinfection remained around 4%. Relapse was more common among recent migrants (<1 year, odds ratio (OR) = 1.99, p = 0.005), those with a social risk factor (OR = 1.51, p = 0.033) and those with central nervous system, spinal, miliary or disseminated TB (OR = 1.75, p = 0.001). Reinfection was more common among long term migrants (>11 years, OR = 1.67, p = <0.001), those with a social risk factor (OR = 1.96, p = <0.001) and within specific areas in London. Patients with social risk factors were at increased risk of both relapse and reinfection. Characterising those with relapsed disease highlights patients at risk and factors associated with reinfection suggest groups where transmission is occurring. This will inform TB control programs to target appropriate treatment and interventions in order to reduce the risk of recurrence.

Highlights

  • Recurrence of TB in an individual can occur due to a regrowth of the same strain of Mycobacterium tuberculosis that caused the previous TB episode, known as relapse, or reinfection by a different strain [1]

  • For patients with a previous history of tuberculosis treated in London, those who did not complete their previous course of treatment were excluded as their illness may otherwise be an extension of their original episode

  • If strain typing was available for both episodes: cases were defined as relapse if the strain types were indistinguishable or 1 MIRU VNTR unit difference and reinfection if strain types were different

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Summary

Objectives

We aimed to quantify and describe cases attributable to relapse or reinfection, and identify associated risk factors in order to reduce recurrence. The main objectives of this study were to determine the number and proportion of TB cases attributable to relapse or reinfection based on surveillance data from 2002 to 2015 and to identify and describe characteristics associated with either relapse or reinfection

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