Is scaling up active case finding the missing piece in our TB response?

By Sean MacDonell 

South Africa has one of the highest burdens of tuberculosis (TB) in the world. The World Health Organization (WHO) estimates that 322 000 people in South Africa had active TB disease in 2017, meaning they were presenting symptoms and could spread the TB bacteria. Approximately 60% of these people were also living with HIV. TB is the leading reported cause of death among people living with HIV and in South Africa overall (although models indicate that HIV still causes slightly more deaths). 

Increased access to antiretroviral treatment (ART) has meant that fewer people with HIV have developed TB and died of TB. But what else can be done to reduce TB rates besides improving access to ART for people living with HIV?

Although TB rates are slowly decreasing globally, there appears to be consensus in the TB research community that more must be done in order to reduce TB rates more quickly. One area where more can be done is active case finding (ACF).

What is active case finding?

People with TB are often diagnosed through passive case finding (PCF) when they present to clinics (primary health care centers) with TB symptoms. ACF is generally considered to be any other method of reaching people with TB outside of the primary health care system. According to the WHO, ACF is “the systematic identification of people with suspected active TB, using tests, examinations or other procedures that can be applied rapidly.” 

Because ACF is often defined as anything that is not PCF, different definitions have been employed by different people in different studies. This creates difficulties when trying to compare ACF interventions, as people may be describing distinct interventions while calling both ACF. 

Regardless, the purpose of ACF is widely agreed upon: to find people with undiagnosed active TB and to link them with treatment in order to help them get healthy and to reduce the period of infectiousness. Once people with TB start taking treatment, they become non-infectious very quickly. By the time someone goes to a clinic for help, that person may have transmitted TB to as many as ten or fifteen other people–ACF can help prevent these onward transmissions by getting people onto treatment more quickly.

In this way it is thought that greater ACF efforts particularly among high-risk groups will greatly reduce the number of people with active TB. High-risk groups for TB are people living with HIV, children, the elderly, mine workers, inmates, military personnel, and healthcare workers – in addition to people in the same household as someone with active TB or other close contacts of someone with TB.

Currently, ACF has not been widely undertaken in South Africa due to the stress it would put on the already overburdened health care system. “It comes down to perceived resources and disease burden being attended to in primary health clinics,” explains Erika Mohr-Holland, a Khayelitsha-based epidemiologist for Doctors Without Borders whose focus is on drug-resistant tuberculosis (DR-TB). “If health care workers are attending to a lot of sick people it becomes a lesser priority to see those who are perceived as well.” Therefore, there has been little focus on ACF and prevention. “It’s all on treatment,” says Mohr-Holland.

Contact tracing

One form of ACF is contact tracing. It is defined by the WHO as “the identification and follow-up of persons who may have come into contact with a person with active TB.” The WHO assumes each person has at least three close contacts. Contact tracing is probably the most widely implemented form of ACF in South Africa. 

Contact tracing was one of the ACF interventions in the ZAMSTAR study, a cluster randomised control trial carried out in areas with high burdens of TB/HIV in South Africa and Zambia. Contact tracing was performed through frequent household visits and screenings for contacts of patients with active TB. This resulted in a relative reduction in TB prevalence (the percent of the population who has TB) of approximately 22% compared to matched communities where these interventions were not implemented. 

 Mobile clinics

The use of mobile clinics for TB screening is another form of ACF.  Mobile clinics are clinics operated out of specialized vehicles and  are typically located in areas that do not have immediate access to primary health clinics. Mobile clinics can be especially useful as they can reduce barriers to access, such as the cost and time of travelling to a clinic. They can also tailor the services they offer to the communities that they are in. 

Both mobile clinics and house-to-house visits were used to conduct TB screenings in the DetecTB study, a cluster randomised control trial in Zimbabwe. Both interventions used sputum smear-microscopy. However, the mobile clinic intervention detected more TB cases than house-to-house visits. This led to a relative reduction in TB prevalence of 40% in the mobile clinic community compared to before the intervention.

Mobile clinics may more readily provide access to chest radiography, or x-ray, (CXR) as a screening tool. CXR is cheaper than other screening methods, is shown to provide accurate results in high TB/HIV burden areas, and may detect TB prior to someone developing symptoms. 

What needs to be done

Cost is one of the main barriers to implementing ACF interventions in resource limited countries. However, mathematical models can help us predict the costs and benefits of different ACF interventions. One recent model found an aggressive scaling-up of ACF could reduce the incidence of TB in South Africa by 55% and reduce mortality by 72% by 2025 (compared to 2015 numbers). Another found that scaling-up of ACF could reduce total patient costs by 28 billion rand between 2016 and 2035. The further development of reliable mathematical models, particularly with a focus on the South African context,  should be prioritised. 

It is not always clear which intervention, or combination of interventions, may be best for a certain district, province, or segment of the population. Therefore, in addition to more modelling work, there is a need for more cluster randomised control trials to determine the effectiveness of these different interventions. Large studies such as ZAMSTAR, DetecTB, and Kharitode are giving important indications of what works and what does not, but we still need more evidence. 

However, waiting until more trials are conducted and the evidence is even clearer is not an option given South Africa’s high TB incidence. We simply cannot afford to wait. Current evidence leaves little doubt that TB prevention through some form of ACF, probably both increased contact tracing and mobile CXR clinics, must be scaled up in order to accelerate the fight against TB. Whether or not the resources will be found to do this properly will be a good measure of the South African government’s commitment to fighting TB.

  • MacDonell is a Spotlight intern and a student at Carleton College in the United States.

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