Ventilating the study of a stubborn epidemic
AS A schoolboy in Birmingham, Robin Wood was once given the task of opening and closing the high windows in his classroom using a long pole. Good ventilation was considered key to sound health and a sharp mind.
Wood is now a leading scientist at the University of Cape Town, puzzling over why the city has such a raging tuberculosis (TB) epidemic. He spends much of his time hunting for clues on how the disease is spread, and how it has been in the past.
Unlike European cities that exported TB to SA along with their colonial-era immigrants in the 19th century, Cape Town has never managed to get the disease under control. There were almost 30,000 newly notified cases of TB in 2009 among the city’s 3.4-million inhabitants, according to a study published in the scientific journal PLOS ONE. The incidence of TB in Cape Town was 479 per 100,000 of the population in 2014, according to the Western Cape health department.
By contrast, the incidence in New York was just 7.7 cases per 100,000 in 2015.
“Cape Town alone has more TB each year than the US, Canada, UK and Germany put together. The question is why,” says Wood, co-director of the Desmond Tutu HIV Centre and a researcher at UCT’s Institute of Infectious Disease and Molecular Medicine.
Wood and his colleagues have turned to records collected by health authorities over more than a century in three cities hard hit by TB in the early 1900’s — New York, London and Cape Town.
They plotted TB notification rates between 1910 and 2012 and noticed something startling. Even before the advent of the first antibiotic treatment in the late 1940’s, the rate was plummeting in New York and London and continued to fall steadily over the course of the century.
Yet in Cape Town it remained stubbornly high and today remains at levels last seen in industrialising Europe in the 19th century. The TB notification rate hovered at about 450 cases per 100,000 between 1910 and 1945, fell briefly after the introduction of antibiotic therapy to a low of 250 cases per 100,000 in 1970, but rose again to 450 per 100,000 in 1995 and soared with the HIV/AIDS epidemic to 850 per 100,000 in 2010.
Many healthy people get infected with TB but never develop the disease, but the HIV weakens the immune system and makes people more susceptible to it. Yet even among HIV-negative people, the TB notification rate in Cape Town between 2009 and 2012 was breathtakingly high: 445 per 100,000 population. (It was 6,338 per 100,000 among those who were HIV-positive). A similar pattern was observed for TB mortality rates.
The period between 1950 and 1960 in Cape Town offers a clue as to why the disease remains rife, says Wood, as this was the only time when a significant fall in TB mortality was recorded. During this era the city embarked on a process known as “active case finding” in which it screened masses of people for TB rather than waiting for sick people to care. TB mortality declined by 60%.
“It’s a bit of circumstantial evidence suggesting that maybe we need to think again,” says Wood.
The scale of Cape Town’s TB problem means there are large numbers of infected people spreading the disease for months before they are diagnosed and start treatment. Breaking the back of the epidemic will require breaking this transmission cycle, says Wood.
“In places like the Cape Flats and the townships, people get infected multiple times,” he says.
People living in these communities inhabit a veritable soup of TB, because they are exposed to hundreds of different strains of the disease.
SA’s TB control policies are aligned with the World Health Organisation’s and focus on diagnosing and treating patients who seek medical attention, rather than actively looking for cases. Wood says this policy is based on evidence from the West’s experience with TB and suggests the programme needs to be adapted to different circumstances.
“If you are in a Pollsmoor Prison cell for 23 hours a day, with no ventilation and overcrowding at 300%, the TB control programme cannot be the same as outside or you won’t touch the epidemic. We can’t treat our way out of it,” Wood says.
Wood has also been studying the risk of TB transmission among high school children from Masiphumelele township, by kitting them out with carbon dioxide monitors and tracking their movements.
Carbon dioxide is a proxy measure for shared air, and enabled the researchers to estimate where the students were at highest risk of catching TB. They found the pupils spent 60% of their time in rooms where the carbon dioxide level was above a safe threshold, the worst of which were poorly ventilated classrooms.
This kind of work has made him a keen advocate for well ventilated classrooms, as better air flow would reduce pupils’ risk of catching TB. Like prisoners, they are compelled to spend much of their time in a confined and crowded space.
The least the education system can do is make sure their schools don’t make them sick, he says.