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TB relapse occurs sooner after treatment than reinfection
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Researchers have identified trends distinguishing endogenous reactivation of tuberculosis and exogenous reinfection with tuberculosis in patients with recurrent infections.
In a retrospective, population-based cohort study, the researchers investigated smear-positive cases that were treated successfully from 1996 to 2008 in a suburb of Cape Town, South Africa. Of the 203 recurrent cases, 130 had paired DNA fingerprint data and were included in the analysis.
The fingerprint data indicated that 64 of the recurrent cases were relapses and 66 were reinfection. Within the first year, there were 44 recurrent cases, nine of which were reinfection. In the subsequent years, 57 of 86 recurrent cases were because of reinfection. After the first 2 years, 43 of 60 recurrent cases were due to reinfection.
The researchers found a strong association between relapse and earlier recurrence. The association remained after restricting the analysis to recurrent cases after cure: 66% were relapses during the first 2 years vs. 27% later than 2 years.
The peak relapse rate was 3.93% (95% CI, 2.35-5.96) per annum, 0.35 years after completing treatment, and then declined steadily. The peak reinfection rate was 1.58% (95% CI, 0.94-2.46) per annum, 1.2 years after completing treatment. When the researchers included smear-negative, culture-positive recurrent episodes, the associations between relapse, reinfection and time to recurrence did not change.
“Future research should serve to improve our understanding or programmatic and individual risk factors for relapse and reinfection tuberculosis,” the researchers wrote. “A more comprehensive model of strain persistence and repeated infections that takes into account mechanisms such as treatment adherence, mixed infections and acquisition of drug-resistance would be valuable.”
Disclosure: The researchers report no relevant financial disclosures.
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