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- More than half of people in South Africa who are already sick with TB may not realise it because they do not have any of the symptoms often linked with the disease, such as coughing and weight loss.
- Researchers do not yet know to what extent people with asymptomatic TB spread the disease.
- South Africa's health system has switched gears to catch more cases of asymptomatic TB.
Our idea of what a TB patient normally looks like probably needs an update, says Emily Wong, an infectious diseases researcher at the Africa Health Research Institute in Durban.
Until recently, scientists have said you would know you have active TB if you were losing weight, coughing all the time, or experiencing fever or night sweats.
Active TB is the term health workers use to describe an infection that can no longer be contained by your immune system because the bacteria is replicating in your body too fast.
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This classic picture is changing.
More than half of people who have TB might not know they were ill (in other words, they were asymptomatic), according to the first study to determine how widespread the disease really is in South Africa.
This evidence, that there are so many asymptomatic cases in South Africa, led to a change in the way government health facilities will manage the disease from this year onwards.
The country's latest TB action plan (which runs from 2023 to 2028) has, for example, switched gear to find more such symptomless TB cases by beefing up methods for diagnosing cases, such as digital chest X-rays, at state facilities.
Digital chest X-rays are better at picking up traces of TB disease than the GeneXpert test, which analyses people's sputum, found 2020 research published in the International Journal of Tuberculosis and Lung Disease.
Although the machines are pricey, a study across 64 prisons in South Africa found the cost might be worth it in high-risk cases because screening with digital chest X-rays can catch symptomless cases, which would have gone unnoticed otherwise.
About a third (32%) of the R25 billion South Africa has budgeted to test, treat and prevent TB from now until 2028 will be spent on finding people with TB, the country's strategy document for dealing with HIV, TB and sexually transmitted infections estimates.
The health department said it would publish treatment guidelines for asymptomatic TB.
But many questions about asymptomatic TB remain unanswered.
In March, we interviewed Wong for an episode of The Bhekisisa Podcast to find out what we do know about this category of TB, and what we do not.
Here is a summary of what she said:
What are the characteristics of the average TB patient?
It was hard to say anymore, Wong said, because in the last couple of years, researchers realised the conventional image of a person with TB was inaccurate.
The public health and research community used to say someone who has active TB feels really ill. This person is often coughing a lot, losing weight or experiencing fevers or night sweats.
But new research from South Africa is showing more than half (58%) of people in a large national survey in whose sputum samples the TB germ was found, did not experience any of the symptoms health workers are typically taught to look for when diagnosing TB.
They may even say they feel well and have been continuing with their daily lives as usual, completely unaware their bodies are fighting a TB infection.
This category of TB is called subclinical, or asymptomatic TB.
What is the difference between latent, subclinical, and full-blown TB?
Latent TB is when someone has been infected by the germ that causes TB (Mycobacterium tuberculosis), but it is hiding somewhere in the body in a quiet state and not spreading because the person's immune system is containing the infection.
The health department does not test people in South Africa for latent TB. But studies have shown between 34 and 88% of participants in surveys conducted in townships in Cape Town and Johannesburg were infected with the germ but did not develop illness.
Subclinical (asymptomatic) TB is different.
Researchers think, at this stage the TB bacteria are replicating and the immune system is putting up a fight to beat the bug.
This battle causes some damage, but it is not severe enough yet to make the person lose weight or cough all the time or cause enough discomfort to result in their going to a clinic to get help.
So, you may be in an early state of TB disease but not be aware of it.
When someone has full-blown TB disease (active TB), the fight between their body's immune system and the bug is ramped up to the point where they feel ill and have the symptoms health workers typically look for when they suspect a TB infection.
Will someone with subclinical TB eventually develop symptoms of full-blown TB?
Researchers are interested in this question, but there is no clear answer to it yet.
It is likely some people who have subclinical TB will develop full-blown TB, especially if they do not find out about it while they are still in the early stage of the disease.
But it is hard to know for sure in how many cases this will happen, because people are unlikely to get themselves tested for TB if they are not feeling ill.
What further complicates the answer is when a doctor does find out a patient has asymptomatic TB, they will prescribe treatment straight away.
It would be unethical for doctors to delay treating somebody for TB disease so they could see whether that person will eventually experience symptoms.
That also means, for the most part, researchers do not find out what would have happened if there were no treatment.
Do people with asymptomatic TB also spread the bacteria to others?
This is another question to which researchers do not yet have the complete answer.
Scientists think if someone has the TB organism in their sputum, it is probable that they could transmit that organism to someone else.
Researchers have always thought TB germs spread mostly through coughs. But with asymptomatic TB, people are not coughing.
However, there is new evidence from a study in Cape Town, published in the American Journal of Respiratory Critical Care Medicine in 2022, which shows TB germs in respiratory droplets released from simple, deep breathing can be just as infectious as those in coughs.
This new information would imply people with asymptomatic TB could indeed be passing the bug on to others.
How does South Africa's health system handle asymptomatic TB?
Until recently, people were not tested for asymptomatic TB in South Africa. But new guidelines, published by the national health department in February, now recommend people who may have a high risk of getting TB (such as people with HIV, health workers and children, or who live in a household with somebody on TB treatment), should get chest X-rays and have their sputum tested during their regular clinic visits.
This project has already started around the country, so it is possible people could be diagnosed with asymptomatic TB through these efforts.
When people test positive for TB (whether they have symptoms or not), South Africa’s guidelines recommend they take a six-month course of antibiotics to clear up the infection.
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Wong said researchers want to find out whether people with asymptomatic TB might have a milder form of TB.
If that is the case, then perhaps they could take a shorter course of TB treatment to clear the infection. That way, they will not have to deal with the side effects (which can include nausea or skin rashes) for so long, and can get back to their daily lives quicker.
No studies have been conducted to test this idea yet.
What should people do if they are worried about getting infected with TB?
South Africa's guidelines say anyone who has been exposed to the bug can get a course of TB preventive treatment that will stop them from falling ill as long as they test negative for active TB first.
That includes people who have been in contact with somebody on TB treatment in the last year, whether that person lives with them, or is a teacher, colleague, family member or friend.
How does TB preventive medicine work?
In South Africa, the preventive treatment against TB available in most public sector clinics (and given to people with HIV) is called isoniazid. This antibiotic is taken as a pill daily for a year.
In people who are infected with both HIV and TB, as in South Africa, the medicine stops people from developing full-blown TB disease in about 60% of cases.
There are also shorter treatment options, such as getting a weekly dose of two antibiotics, isoniazid and rifapentine, for three months. This treatment is commonly called 3HP, but it is not widely available at state clinics yet.
How do people react to research findings about asymptomatic TB?
"A while back, I presented some of my research to colleagues here [at the Africa Health Research Institute]. The data showed that 10% of people with asymptomatic TB had a drug-resistant version of the bug which means one of the most effective medicines such as isoniazid no longer works].
"Among them were some people who had an early version of extensively drug-resistant TB [XDR-TB], but also had no symptoms.
"XDR-TB can’t be treated with any of the antibiotics normally used to treat TB [namely isoniazid and rifampin], nor any of the next-best type of drugs called fluoroquinolones, or another class of antibiotics, such as bedaquiline or linezolid.
"People started looking around the room, visibly worried, as if they were wondering whether people around them might have asymptomatic TB."
Wong said she thought it was researchers and the department's responsibility to figure out how asymptomatic TB really worked - and get the TB epidemic under control.
That meant, she added, setting up a sensible plan to screen, test and treat people for TB, and to give those who have a high risk of getting infected but test negative preventive therapy.
What should we do to prevent the stigma around TB spreading?
Wong compared it to how people thought about HIV infection long ago.
Before antiretroviral drugs were available to treat HIV, people automatically thought simply being infected with the virus was the same as having severe Aids - and imminently dying.
But then, as people got tested earlier, they could get treatment long before they got ill.
More effective treatment also became available, as did preventive drugs, which meant people could carry on with their lives as normal and stay healthy for long.
"All of this has helped us to change our idea of what HIV is, and helped us to fight the stigma around it," said Wong.
"If we end up changing our image of TB from someone who's very sick to an earlier image of what it means to have TB [but without any symptoms], we could decrease stigma. But this is a process. It doesn't happen overnight."
This story was produced by the Bhekisisa Centre for Health Journalism. Sign up for the newsletter.
