The Risk of Tuberculosis Reinfection Soon after Cure of a First Disease Episode Is Extremely High in a Hyperendemic Community

Abstract

Elevated rates of reinfection tuberculosis in various hyperendemic regions have been reported and, in particular, it has been shown that in a high-incidence setting near Cape Town, South Africa, the rate of reinfection tuberculosis (TB) disease after cure of a previous TB disease episode is about four times greater than the rate of first-time TB disease. It is not known whether this elevated rate is caused by a high reinfection rate due, for instance, to living circumstances, or a high rate of progress to disease specific to the patients, or both. In order to address that question we analysed an extensive data set from clinics attended by TB patients in the high-incidence setting near Cape Town, South Africa and found that, in fact, the (average) rate of reinfection (as opposed to the rate of reinfection disease) after cure of a previous TB disease episode is initially about 0.85 per annum. This rate diminishes rapidly over time and after about ten years this rate is similar to the rate of infection in the general population. Also, the rate of progress to disease after reinfection is initially high but declines in subsequent years down to the figure typical for the general population. These findings suggest that the first few months after cure of a TB disease episode form a critical period for controlling reinfection disease in a hyperendemic setting and that monitoring such cured patients could pre-empt a reinfection progressing to active disease.

Fig 1. For Series 1 through 3 the values of λ ₁ and λ ₂ are respectively (0.05; 0.025), (0.3; 0.025) and (0.025; 0.01).

Fig 2. A schematic showing the breakdown of the 3364 patients with a documented first TB disease episode.

Fig 3. The mean risk of reinfection disease manifesting a given number of years after cure of a prior cured disease episode is shown together with confidence intervals.

Trend lines are fitted and these are used to estimate the gradients of the risk graphs. The trendline for the mean risk of reinfection disease only is shown and its parameters are displayed.

Fig 4. The Kaplan Meyer survival plot from Table 1.

Fig 5. The confidence intervals for l₂ are not plotted since they are too small to be visible.