"It's complex" is a phrase that crops up frequently when asking health specialists to explain why South Africa is struggling to control tuberculosis.
Poverty, the prevalence of HIV/Aids, the legacy of apartheid, and individual health-seeking behaviour are among the factors that Professor Nulda Beyers, director of the Desmond Tutu TB Centre at Stellenbosch University, cites when discussing the TB epidemic in South Africa.
In contrast to a decrease in TB levels in other countries in the region, and despite South Africa's status as a middle-income developing country and substantial spending on health, TB levels in South Africa continue to rise.
"When something is out of control it's exactly that - one can't get away from it. Here in the Western Cape one in every three minibus taxis has a person with infectious TB in that taxi. Once it has reached those proportions it's very difficult to unravel what was the reason the figures got so very high," says Beyers.
"I think the question is, why doesn't everyone in South Africa have TB?" Beyers asks and then answers her own question, explaining how a healthy immune system manages to overcome TB.
"Even if people are infected, 90 percent will never get TB because we have a good immune system. But that is where HIV comes in. If the immune system goes down, then TB can flare up."
Public health officials often describe TB as HIV's "twin". HIV has been rampant in South Africa for the past two decades, exacerbated by prevarication in the late 1990s and early 2000s when former president Thabo Mbeki questioned the link between HIV and Aids, and his health minister denied the efficacy of antiretroviral medication.
After these tragic delays in combating the HIV/Aids pandemic, South Africa now provides antiretroviral therapy to some 1.7 million citizens - one of the world's largest public health Aids treatment programmes.
Besides the effect of HIV, poor nutrition, or other factors in weakening the immune system, poverty is a key factor in explaining the prevalence of TB. A classic public health study of Victorian England shows how TB levels declined throughout the 19th century in direct correspondence with improved living conditions and a reduction in poverty.
While Beyers is at pains to point out that wealthy, middle class people also contract TB, particularly given its widespread prevalence in South Africa, she says there are many reasons why poor people are more vulnerable to the airborne disease.