Is early tuberculosis death associated with increased tuberculosis transmission?

Anu Parhar,Rabia Ahmed,Mary Lou Egedahl,Courtney Heffernan,Zhiwei Gao,Richard Long

doi:10.1371/journal.pone.0117036

Anu Parhar, Rabia Ahmed + Show 4 more

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https://doi.org/10.1371/journal.pone.0117036

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Abstract

IntroductionTuberculosis (TB) is now a relatively uncommon disease in high income countries. As such, its diagnosis may be missed or delayed resulting in death before or shortly after the introduction of treatment. Whether early TB death is associated with increased TB transmission is unknown. To determine the transmission risk attributable to early TB death we undertook a case-control study.MethodsAll adults who were: (1) diagnosed with culture-positive pulmonary TB in the Province of Alberta, Canada between 1996 and 2012, and (2) died a TB-related death before or within the first 60 days of treatment, were identified. For each of these “cases” two sets of “controls” were randomly selected from among culture-positive pulmonary TB cases that survived beyond 60 days of treatment. “Controls” were matched by age, sex, population group, +/- smear status. Secondary cases of “cases” and “controls” were identified using conventional and molecular epidemiologic tools and compared. In addition, new infections were identified and compared in contacts of “cases” that died before treatment and contacts of their smear-matched “controls”. Conditional logistic regression was used to find associations in both univariate and multivariate analysis.Results“Cases” were as, but not more, likely than “controls” to transmit. This was so whether transmission was measured in terms of the number of “cases” and smear-unmatched or -matched “controls” that had a secondary case, the number of secondary cases that they had or the number of new infections found in contacts of “cases” that died before treatment and their smear-matched “controls”.ConclusionIn a low TB incidence/low HIV prevalence country, pulmonary TB patients that die a TB-related death before or in the initial phase of treatment and pulmonary TB patients that survive beyond the initial phase of treatment are equally likely to transmit.

Highlights

Tuberculosis (TB) is a relatively uncommon disease in high income countries
In a low TB incidence/low HIV prevalence country, pulmonary TB patients that die a TBrelated death before or in the initial phase of treatment and pulmonary TB patients that survive beyond the initial phase of treatment are likely to transmit
In that study, which used both conventional and molecular epidemiologic methods, only 3 cases could be linked by molecular epidemiologic methods alone to one or more secondary cases

Summary

Introduction

Its diagnosis may be missed or delayed resulting in death before or shortly after the introduction of treatment. The diagnosis of TB can be missed or significantly delayed increasing the likelihood of morbidity and mortality in incident cases. In addition to poor individual outcomes early TB death results in poor public health outcomes as measured by an increased number of secondary cases or other transmission events, is unknown. Persons with a missed or delayed diagnosis may be expected to have more advanced disease and be more infectious at presentation; on the other hand, those who die before or shortly after treatment is initiated may be expected to be older, co-morbid and possibly socially isolated, limiting the number of opportunities for transmission [5, 10].

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