Burden of new and recurrent tuberculosis in a major South African city stratified by age and HIV-status

Abstract

Aim: To describe the burden of tuberculosis (TB) in Cape Town by calculating TB incidence rates stratified by age and HIV-status, assessing the contribution of retreatment disease and estimating the cumulative lifetime TB risk in HIV-negative individuals.

Methods: Details of TB cases were abstracted from the 2009 electronic TB register. Population denominators were estimated from census data and actuarial estimates of HIV prevalence, allowing calculation of age-specific and HIV-stratified TB notification rates.

Results: The 2009 mid-year population was 3,443,010 (3,241,508 HIV-negative and 201,502 HIV-positive individuals). There were 29,478 newly notified TB cases of which 56% were laboratory confirmed. HIV status was recorded for 87% of cases and of those with known HIV-status 49% were HIV-negative and 51% were positive. Discrete peaks in the incidence of non-HIV-associated TB occurred at three ages: 511/100,000 at 0-4 years of age, 553/100,000 at 20-24 years and 628/100,000 at 45-49 years with 1.5%, 19% and 45% being due to retreatment TB, respectively. Only 15.5% of recurrent cases had a history of TB treatment failure or default. The cumulative lifetime risks in the HIV-negative population of all new TB episodes and new smear-positive TB episodes were 24% and 12%, respectively; the lifetime risk of retreatment disease was 9%. The HIV-positive notification rate was 6,567/100,000 (HIV-associated TB rate ratio = 17). Although retreatment cases comprised 30% of the HIV-associated TB burden, 88% of these patients had no history of prior treatment failure or default.

Conclusions: The annual burden of TB in this city is huge. TB in the HIV-negative population contributed almost half of the overall disease burden and cumulative lifetime risks were similar to those reported in the pre-chemotherapy era. Retreatment TB contributed significantly to both HIV-associated and non-HIV-associated TB but infrequently followed prior inadequate treatment. This likely reflects ongoing TB transmission to both HIV-negative and positive individuals.

Figure 1. Population age and gender pyramid of Cape Town at mid-year 2009.

Data based on South African census data .

Figure 2. The numbers of tuberculosis notifications in 2009, which were recorded as HIV-infected, HIV-uninfected and of unknown HIV-status, stratified by 5-year age group.

Figure 3. The numbers of tuberculosis notifications of new and recurrent disease in patients with known HIV-negative status, stratified by 5-year age group.

Figure 4. Notification rates for all, new and recurrent tuberculosis cases for HIV-negative residents aged 15 years to 49 years in Cape Town.

HIV-uninfected population denominators derived from the product of Cape Town age population pyramid , and 1-HIV-prevalence .

Figure 5. The estimated cumulative risk for new (initial) and retreatment episodes of tuberculosis between birth and 75 years of age for Cape Town residents remaining HIV-uninfected.

Figure 6. The numbers of tuberculosis notifications of new and recurrent disease in patients with known HIV-infection, stratified by 5-year age group.

Figure 7. Notification rates for all, new and recurrent tuberculosis cases for HIV-positive residents aged 20 years to 54 years in Cape Town.

HIV-infected denominators derived from the product of Cape Town age population pyramid , and HIV-prevalence .