According to the World Health Organization, of the roughly 10 million people who fall ill with TB annually, over 80% survive, in most cases due to a six-month treatment course. Unfortunately, as with long COVID, being cured is not always the last hurdle and many people go on to struggle with post-TB lung disease.
Professor Keertan Dheda, a general physician, pulmonologist, and critical care specialist who heads up the Division of Pulmonology at Groote Schuur Hospital and the University of Cape Town, explains that post-TB lung disease refers to any chronic lung or respiratory abnormality (residual structural damage or scarring) after the successful completion of TB treatment.
"Unfortunately, TB is an infection where, despite successfully treating the lung infection, one can still be left with considerable residual lung damage, which may cause long-term symptoms and lung disability. We refer to this as post-TB lung disease," he says.
It may be asymptomatic, Dheda says, or may be associated with ongoing symptoms such as chronic shortness of breath (may be apparent only on strenuous effort), chronic cough, recurrent chest infections, chronic sputum production, and in some cases recurrent coughing up of blood. "A key point is that these symptoms often overlap with TB and therefore a common problem is inappropriate treatment for presumed recurrent TB (in those who have previously had TB). It is therefore important that doctors and the public be aware of this condition and that in those who have had previous TB, that new chest or lung symptoms may not necessarily mean that the person has TB again," says Dheda.
How big is the problem?
"Most people may have some sort of scarring or damage to the lungs but will have no symptoms," Dheda says. "About 5% of people may have significant chronic symptoms with associated reduction in their lung capacity. Then there's a group in the middle who may have infrequent symptoms or only display symptoms upon more strenuous effort. Although the proportion (5 to 10%) with significant damage and symptoms may seem like a small number, given the overall TB problem in the country, this translates into hundreds of thousands of sufferers over the long term."
The WHO estimates that 304 000 people fell ill with TB in South Africa in 2021 and that around 56 000 died of the disease that year. Our admittedly simplistic back-of-the-envelope calculations suggest that probably in the region of 20 000 people develop significant post-TB damage and symptoms that year. Since TB rates in previous years were substantially higher than in 2021 and people can live for years with post-TB lung disease, the estimate of hundreds of thousands with significant damage and symptoms seems about right. Many more will be living with less severe damage and symptoms.
Dr Alison Castle, infectious disease specialist and physician collaborator at the Africa Health Research Institute, says the burden of post-lung TB is enormous. "Millions of TB survivors are potentially suffering from post-TB sequelae like chronic lung disease, decreased exercise capacity, and hampered quality of life," she says. (Sequelae refers to a condition that follows a disease.)
Part of the difficulty in figuring out how prevalent post-TB lung disease really is, is that as with long COVID, symptoms and the severity of symptoms vary widely and are not always routinely tested for.
Millions of TB survivors are potentially suffering from post-TB sequelae like chronic lung disease, decreased exercise capacity, and hampered quality of life. - Dr Alison Castle
Castle says that severity depends on many aspects, including how severe and destructive the pulmonary TB disease course was and if other exposures co-exist, like smoking or environmental pollution. "Approaches to measuring severity include physiologic tests to measure lung functionality (six-minute walk test, spirometry), structural impairment using imaging, and health-related quality of life. Furthermore, recording symptoms, exacerbations, and hospitalisations are key features to measure severity of the disease," she says.
Types of post-TB lung disease and their treatment
Professor Martie van der Walt, director of the Tuberculosis Platform at the South African Medical Research Council, says patients may not be aware that their lungs may be damaged to the extent that they will have permanent damage. "Post-TB lung disease is most often typified by non-reversible airflow obstruction, and if shortness of breath persists during TB treatment or thereafter, medical care should be sought. Risk factors are smoking, non-adherence to TB treatment or non-completion of treatment, having had previous episodes of TB, delay in seeking treatment, and drug-resistant TB," says van der Walt. Lung impairment can become evident during TB treatment but is most often diagnosed after treatment, van der Walt tells Spotlight.
Dheda says post-TB lung disease may linger lifelong and, in most cases, the structural lung damage is not correctable. However, there are a number of treatment options that will depend on the manifestation in terms of the type of post-TB lung disease.
"Those with damage to the larger airways (also called bronchiectasis) may have recurrent chest infections, which may need to be treated with antibiotics. Because of compromised immunity, certain types of vaccinations against pneumonia and influenza, for example, will also be recommended," he says.
Another type of post-TB lung disease affects the small airways and results in a condition similar to asthma or Chronic Obstructive Pulmonary Disease (COPD) (disease typically associated with smoking cigarettes). This is usually treated with bronchodilators (medicines that tend to open up the small airways).
Scarring of lung tissue and residual cavities (holes or cysts in the lungs) can also cause lasting problems. "These may sometimes be infected by a fungus called aspergillus. This type of damage may be associated with chronic shortness of breath but also recurrent chest infections and coughing up of blood," says Dheda. In some cases, he says, surgical resection of the involved lung may be required in tandem with anti-fungal treatment.
In other cases, the lung lining may be thickened and scarred, or the pulmonary blood vessels may be affected resulting in 'high blood pressure' in the lung. "Ultimately, in specific cases, lung transplantation may be the only option [for] badly scarred lungs in younger patients with chronic symptoms. However, there is poor capacity and access to such options," he says, mentioning that the University of Cape Town and Groote Schuur Hospital is the only state-funded lung transplant service in Southern Africa.
Castle says except for smoking cessation, there is no evidence to demonstrate whether current therapies actually halt the progression of lung destruction or restore lung function. "Therefore, management focuses primarily on alleviating symptoms. This includes medications directed towards airflow obstruction or restrictive ventilatory defects such as bronchodilators, glucocorticoids, mucolytic, and anti-fibrotic agents. Many of these agents are already used in persons living with chronic lung disease from COPD or with asthma," she says, adding that surgery, lung ventilation techniques, pulmonary rehabilitation, patient education for self-management, and lung health awareness are other non-pharmacologic management strategies.
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She says there are some promising host-directed therapies to dampen the immune response during acute TB infection with the goal of preventing post-TB lung disease. However, these treatments are very much still in the experimental phase.
Smoke and environmental factors
Smoking is a complete no-go, Dheda says. "In fact, smoking increases susceptibility to TB and worsens post-TB lung disease."
He says that indoor and outdoor air pollution also worsens the symptoms and the course of the disease. "This is a common issue in South Africa, especially with the increase in electricity prices and power outages where resource-poor households cook using wood, or other biomass fuels, in poorly ventilated settings, resulting in chronic smoke exposure and inhalation," says Dheda.
"The severity of post-TB lung disease, in part," Castle says, "also depends on one's exposures in addition to having TB previously. For example, persons with TB may also have symptoms from smoking, drug use, occupational exposure, and biomass fuels, which can complicate identifying the exact symptoms of post-TB lung disease."
Under-researched
Ultimately, Dheda says the bottom line is that very little is known about post-TB lung disease compared to other lung diseases. "This is not only surprising but shocking given the extent of the problem," he says.
For example, he says it is not clear how to optimally treat each of the types of post-TB lung disease mentioned above and considerably more research is required to understand how to better manage these conditions. "There are several respiratory physicians in the country that have now focussed on research projects to look at this problem," he says.
