Study reveals men's higher TB rates driven by exposure, not biology

Tuberculosis kills and disables millions each year, and for decades public health researchers have noticed something consistent in the numbers: men get sick from it far more often than women do. Globally, men account for roughly two-thirds of all TB diagnoses. But why? A new study from researchers at University College London set out to answer a deceptively simple question: Are men catching TB more often because they encounter the bacteria more frequently in their daily lives, or because their bodies are somehow more vulnerable to the disease once infected?

The answer, it turns out, is the first one. In research published in eClinicalMedicine, the team analyzed data from more than 22,000 people enrolled in 11 prospective cohort studies spread across 14 countries—spanning Europe, Africa, Asia, and South America. What they found was striking in its clarity: men were significantly more likely than women to already carry a TB infection when the studies began, suggesting a lifetime of greater exposure to the bacteria. But when researchers accounted for this difference in prior exposure, men and women showed essentially equal rates of progressing from infection to active disease. The disparity, in other words, was not biological. It was epidemiological.

Tuberculosis is caused by bacteria that typically lodge in the lungs, though the infection can spread to other organs. The disease announces itself through a persistent cough, fever, night sweats, weight loss, and exhaustion. It spreads through the air—coughs, sneezes, speech, song—and takes hold most readily in people who spend extended time in close quarters with someone who is actively ill, particularly in spaces that are crowded or poorly ventilated. The fact that men encounter the bacteria more often than women raises an obvious follow-up question: Why?

Dr. Yohhei Hamada, one of the study's lead authors from UCL's Institute for Global Health, framed the implications carefully. The findings, he said, suggest that efforts to close the sex gap in TB burden might be more effective if they focus on reducing men's exposure to infection rather than solely on preventing progression from latent infection to active disease. In other words, the intervention point should be upstream—in the environments and circumstances where men are more likely to encounter TB in the first place.

That raises a set of questions the current research could not answer. What occupational exposures drive the difference? How do social environments, lifestyle choices, and access to healthcare factor in? The researchers are now calling for future work to investigate these mechanisms—the specific pathways through which men end up with higher TB exposure. Understanding whether the gap stems from workplace conditions, housing density, patterns of substance use, healthcare-seeking behavior, or some combination of these factors could reshape how public health programs approach TB prevention.

The study does carry limitations worth noting. Some participant groups were small, and critical information on smoking, alcohol use, and socioeconomic status was not uniformly available. The populations studied were mostly high-risk groups, and people who had received TB preventive treatment were excluded, which means the findings may not generalize perfectly to lower-risk populations or to people already engaged with TB prevention programs. Still, the core finding—that exposure, not susceptibility, explains the sex disparity—holds across the data.

For TB control programs worldwide, the implication is straightforward: if you want to narrow the gap between men and women, you need to understand and address the specific circumstances that put men at higher risk of encountering the bacteria. That is a different problem than treating the disease once it develops, and it will require looking closely at the social, occupational, and environmental factors that shape TB transmission in the first place.