Unveiling the prevalence of undetected tuberculosis across Africa

Unveiling the prevalence of undetected tuberculosis across Africa
Undetected tuberculosis is growing across Africa.

Kampala, Uganda | By Michael Wandati | Scientists have highlighted a concerning trend in Africa, where four out of five individuals are harboring undetected tuberculosis (TB), posing a significant challenge to control efforts.

They emphasized that over 80% of TB patients do not display the typical symptom of a persistent cough, complicating detection and facilitating the spread of this deadly infection.

“This raises the possibility that those who have tested negative may be unknowingly transmitting the infection.”

TB is predominantly transmitted by coughing, but probably also through simply breathing.

“Cough has for long been perceived as the primary mechanism by which tuberculosis is transmitted, although recent bioaerosol studies suggest that cough is not needed for expelling bacilli,” say the scientists.

The findings, published on March 12 in the Lancet Infectious Diseases, by researchers led by Amsterdam UMC and the Amsterdam Institute for Global Health and Development, revealed data from over 600,000 individuals in Africa and Asia. The study indicated that 82.8% of tuberculosis cases lacked a persistent cough, with 62.5% having no cough symptoms at all.

Moreover, the research conducted between 2007 and 2020 demonstrated that a quarter of those without a cough exhibited high levels of bacteria in their sputum, suggesting a high likelihood of being highly infectious.

Despite this, many tuberculosis control programs primarily rely on the presence of a persistent cough as the key symptom for initiating diagnostic procedures, particularly for HIV-negative patients seeking care at health facilities.

High-incidence settings

In regions with high TB incidence rates, the team observed that 21% of identified TB patients lacked a persistent cough, and 18% showed no cough symptoms at all, yet had a positive sputum smear. Smear-positive TB is significantly more contagious, being 4–5 times more likely to spread compared to smear-negative TB.

These findings provide a potential explanation for the persistent challenge in reducing the TB burden in Africa and Asia, despite extensive efforts aimed at diagnosis and treatment.

“We already knew there was a giant gap between the 10.6 million who get ill with TB and the 7.5 million cases that were registered by health authorities in 2022,” says Frank Cobelens, Professor of Global Health at Amsterdam UMC and Senior Fellow at the AIGHD.

“A persistent cough is often the entry point for a diagnosis, but if 80 percent of those with TB don’t have one, it means that a diagnosis will happen later, possibly after the infection has already been transmitted to many others,” he added.

In regions with high TB incidence rates, this phenomenon could significantly contribute to disease transmission and the overall TB burden.

The study examined data from national monitoring schemes in 12 countries and revealed that, in addition to the absence of a cough, over a quarter of TB cases displayed no symptoms whatsoever. Notably, these characteristics were more prevalent among women than men.

“When we take all of these factors into account, it becomes clear that we need to really rethink large aspects of how we identify people with TB. It’s clear that current practice, especially in the most resource-poor settings will miss large numbers of patients with TB. We should instead focus on X-ray screening and the development of new inexpensive and easy-to-use tests,” says Cobelens.

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In recent decades, significant progress has been achieved in the diagnosis and treatment of TB. However, despite these advancements, out of an estimated 10.6 million individuals worldwide who developed TB in 2022, only 7.5 million cases were officially reported, leaving a gap of 3.1 million undiagnosed cases.

A portion of this diagnostic gap may stem from cases where individuals with TB pathology do not exhibit symptoms typically associated with tuberculosis. Consequently, this oversight could contribute significantly to delayed or missed diagnoses, thereby impeding the effectiveness of tuberculosis control efforts on a global scale.

In Africa, TB stands as the second leading cause of death from a single infectious agent, surpassing even the toll of HIV and AIDS. In 2022, approximately 2.5 million people on the continent contracted TB, equating to one new case every 13 seconds and representing a quarter of all new TB cases worldwide.

Africa accounted for over 33% of all TB-related deaths in 2022, with an estimated 424,000 deaths out of the global total of 1.267 million.