Tuberculosis transmission rates in South Africa and more specifically Cape Town have not changed at all over the past 100 years, even though people are living longer and being cured because of treatment. Many are cured, only to be infected again.
Addressing the 1st Southern African HIV Clinicians Society conference today, University of Cape Town Professor Robin Wood presented fascinating data on TB in Cape Town and New York over the past 100 years.
While both cities had similar TB epidemics in 1910, Wood was able to show how the US city managed to over time control the transmission rates and ultimately the mortality rates (27 people died in 2010), while in Cape Town the opposite happened and 3 000 people died in 2010.
“With the arrival of HIV, survival rates dropped like a stone,” Wood said in reference to South Africa. In New York long-term survival has continued.
Wood showed that “something horrible” started happening in Cape Town in the 80s and 90s. Among HIV positive patients, one-third of TB cases were found to be retreatment TB cases, meaning they had been cured, but infected again.
The pattern of high transmission was also corroborated by the fact that there were high levels of TB disease among children. In Cape Town, the majority of the population is infected before adulthood, again showing that transmission rates have not changed. Incidence rates among children are considered a measure of whether a TB control programme is functioning effectively.
Wood said that although the development of drugs in the forties has changed the mortality incidence, TB cases are now living only to get TB a second time.
“There is a failure to control transmission,” he said, adding that there was no evidence from the New York data that treatment alone had changed matters.
Posing the question as to what was driving the TB epidemic, Wood shared a novel study they were conducting which involved strapping a small device to individuals, measuring where they were most exposed to rebreathed air and in turn to airborne diseases such as TB.
Some of the data showed that children were most at risk in their homes and crèches with evidence of “quite a bit of risk” when using public transport.
Among the 18 to 24 year olds the risk was less in the household, but very high when using public transport and also in some work situations.
Wood said a large part of the problem was that the world was stuck on discussing the “ineffective” such as Directly Observed Treatment Strategies for TB versus the “unobtainable” which involved social development.