A Century of Tuberculosis Epidemiology in the Northern and Southern Hemisphere: The Differential Impact of Control Interventions

Abstract

Background: Cape Town has one of the highest TB burdens of any city in the world. In 1900 the City of Cape Town, New York City and London had high mortality of tuberculosis (TB). Throughout the 20th century contemporaneous public health measures including screening, diagnosis and treatment were implemented in all three settings. Mandatory notification of TB and vital status enabled comparison of disease burden trajectories.

Methods: TB mortality, notification and case fatality rates were calculated from 1912 to 2012 using annual TB notifications, TB death certifications and population estimates. Notification rates were stratified by age and in Cape Town by HIV status (from 2009 onwards).

Results: Pre-chemotherapy, TB mortality and notification rates declined steadily in New York and London but remained high in Cape Town. Following introduction of combination chemotherapy, mean annual case fatality dropped from 45-60% to below 10% in all three settings. Mortality and notification rates subsequently declined, although Cape Town notifications did not decline as far as those in New York or London and returned to pre-chemotherapy levels by 1980. The proportional contribution of childhood TB diminished in New York and London but remained high in Cape Town. The advent of the Cape Town HIV-epidemic in the 1990s was associated with a further two-fold increase in incidence. In 2012, notification rates among HIV-negatives remained at pre-chemotherapy levels.

Conclusions: TB control was achieved in New York and London but failed in Cape Town. The TB disease burden trajectories started diverging before the availability of combination chemotherapy in 1952 and further diverged following the HIV epidemic in 1990. Chemotherapy impacted case fatality but not transmission, evidenced by on-going high childhood TB rates. Currently endemic TB results from high on-going transmission, which has been exacerbated by the HIV epidemic. TB control will require reducing transmission, which is inexorably linked to prevailing socio-economic factors.

Fig 1. TB mortality and case fatality rates over time.

A. TB mortality rates over time. B. TB case fatality rates over time. Note. Rates from 1913 to 1965 are for London County Council (current Inner London) [17], thereafter for the Greater London Area (Inner and Outer London)[23, 24]. CT, Cape Town; NY, New York.

Fig 2. TB notification rates over time.

The current (2009–2012) HIV-negative rate in Cape Town was 445 per 100,000 population, the HIV-positive rate was 6338 per 100,000 population (not shown). Note. Rates from 1913 to 1965 are for London County Council (current Inner London) [17], thereafter for the Greater London Area (Inner and Outer London) [23, 24]. CT, Cape Town; NY, New York.

Fig 3. Age-stratified TB notification rates per decade over time.

Note. Y-axes are on a logarithmic scale (base 10). Age-stratified rates in Cape Town were not available prior to 1930. Cape Town rates for 2002 and 2010 include TB in HIV-infected persons.

Fig 4. TB notification rates among children aged 0–4 years per decade over time.

Note. Y-axes are on a logarithmic scale (base 10). Age-stratified rates in Cape Town were not available prior to 1930. Cape Town rates for 2002 and 2010 include TB in HIV-infected persons.