South Africa has the third highest incidence of Tuberculosis globally and the incidence is closely linked to the country’s high HIV epidemic. With almost six million people living with HIV, the country has the highest number of HIV-positive people in the world. And this group of people is more at risk of contracting TB than those who don’t have HIV. This can be easily illustrated if doctors were to perform, for example, a Tuberculin Skin Test on both HIV-positive and negative patients. This is whereby a clinician injects a substance called Tuberculin into your forearm to determine whether you have been exposed to TB.
Often, it is found that ‘for people who are HIV non-infected, if your skin tests positive, that means you’ve been exposed to TB and you’ve developed some form of latent to sub-clinical infection and in your lifetime you will have a 10% chance of that breaking down to active disease’, says Dr Francesca Conradie, president of the Southern African HIV Clinicians’ Society.
‘However, in the HIV-infected person they’d actually have a 10% chance per year of developing active disease, which, if you just do the math, we’re looking at about a 30 times increase in the HIV-infected person’, she says.
Explaining why people living with HIV have a greater risk of developing active TB, Dr Conradie says ‘that is because the host defences in the HIV-infected person are defective. What happens normally is that the person will breathe in TB, it will settle as latent or sub-clinical. You can get re-activation of a latent disease, which is higher in the HIV-infected person. Because of the amount of TB bacilli that we all live in, they are more prone to get disease as an adult’.
Many South Africans have TB, yet are unaware as they don’t have symptoms. This is called latent or asymptomatic TB and it can be typical in HIV-infected people. But it is difficult to identify such patients as there is a lack of tools to determine TB infection in asymptomatic people.
‘We do not currently have any interventions for those that are asymptomatic ‘ latent TB infection. We intervene where we treat the high-risk groups for latent TB infection. Therefore, we need tools that will assist us with excluding TB in these patients, especially in those that are HIV-positive. And, then again, where they develop active TB disease we need tools that will assist us in picking up TB quite early in those patients and that will assist us as well to achieve our broad targets of reducing mortality as a result of TB as well as improving the treatment outcomes’, says Dr Lindiwe Mvusi, Director of the DOTS (Directly Observed Treatment System) Co-ordination programme in the national Health Department.
Dr Mvusi says current diagnostic methods are ill-equipped to diagnose TB in HIV-positive people. She says while a new technique, the Gene X-pert was introduced in 2011, the disadvantage of new devices such as this is that they are not accessible to all health facilities.
‘We’ve been relying mainly on the smear microscopy and we’re aware that this was one of the reasons why we were not picking up people with TB early because of its limitations in terms of the sensitivity of the test in a high-burden HIV prevalence setting. There have been a number of diagnostic tools that have been approved by the WHO, but where they are located, it’s at reference laboratory level as well as the intermediate level, which would be the regional level and, in some instances, district level. But we do not have anything as yet at facility level where we can have a point of care test, which would ensure that we determine that the patient has TB whilst we have the patient in the facility and start them on treatment rather than relying on them coming back’, she says.
She says more work needs to be done to design better diagnostic methods. But in the meantime, what can be done to prevent more TB infections in people who have HIV?
‘Going forward, the intention is to intensify case finding, which means we’ll have to use whatever tools are available to ensure that this happens until we have full coverage of (the) Gene-Xpert or whatever other tests which will come up in the coming five years. Whilst doing that, also focus on TB prevention and one of the things is infection control ‘ Isoniazid Preventive Treatment for high-risk populations. We still need effective vaccines and we’ll also scale up the initiation of ART because that can also prevent TB’, says Dr Mvusi.