Doctors may have found a key reason TB affects more men than women

Men are more likely than women to already be infected with tuberculosis, but no more likely to fall ill once that infection is there.

That is the key reason researchers now put forward for one of the oldest puzzles in the disease, in work published on 12 August 2026 in the journal eClinicalMedicine by an international team led by University College London's Institute for Global Health.

It does not settle the question, and the team said so plainly. But it moves the weight of evidence towards the moment of infection and away from what happens inside the body afterwards, and that has consequences for how countries go about finding and preventing cases.

Two stages, two possible explanations

Tuberculosis is unusual in that catching the bacteria and falling ill from it may be separated by years or decades, although illness can also follow much sooner. A person can breathe in the bacteria, carry it quietly, and never know.

Only a minority go on to develop active disease. When that disease is in the lungs, it can cause a long cough and weight loss, and it can spread through the air to others.

That gap between the two stages is why the sex difference has been so hard to explain. Men might develop more TB because they pick up the bacteria more readily, or because their bodies are more likely to let a quiet infection turn into disease, or because of some mix of both.

What the researchers did

The team pooled individual data from 11 studies that had followed people forward in time rather than taking a single snapshot.

Together the studies covered 22,424 participants in 14 countries across sub-Saharan Africa, Europe, Asia and South America, enrolled between 2005 and 2017.

Participants were followed for a median of 2.8 years, and 411 of them, or 1.8%, developed TB disease during that time. Two-thirds were adults.

This was not a survey of the general population.

Just over half the participants came from Europe and about a third from South Africa and Zambia, and the groups studied were mostly people already at higher risk of TB.

What made the analysis possible is that everyone was tested for infection when they joined, which let the researchers ask the two questions separately.

Where the gap opened

At enrolment, 38.1% of men already had a positive TB infection test compared with 35.0% of women.

Once age was accounted for, men had about 12% higher odds of being infected (odds ratio 1.12, 95% confidence interval 1.02 to 1.22) — a small gap, but a real one.

After that point the difference disappeared.

Among those already infected at the start, TB disease developed at 15.6 cases per 1,000 person-years in men and 16.3 in women, with no statistically significant difference between the two.

Among those who tested negative at the start, later TB risk showed no significant difference either.

In the researchers' own framing, the well-documented excess burden of TB among males appears more consistent with differences in infection risk than with a large sex difference in progression from infection to disease.

What it cannot say

The study measured infection, not exposure.

A positive test shows that someone has picked up the bacteria at some point; it does not show how often they encountered it, where, or when.

So the finding is consistent with men being exposed more often, but it is equally consistent with men being more likely to become infected when they are exposed.

The authors say directly that future work is needed to establish which.

Nor did the analysis capture the things that might explain either possibility.

Information on factors such as smoking, alcohol and economic circumstances was incomplete for some participants, and work, housing and social environments were not examined.

Differences in how men and women use health services could also play a part, though the study was not designed to measure that.

Biology is not ruled out. The authors note that sex-related differences in immune response cannot be excluded, and concluded that the higher burden among men is likely to reflect several mechanisms rather than a single pathway.

The design matters too.

Pooling prospective cohorts is a strong way to approach this question, but it remains observational. It shows a pattern across populations. It does not prove what produces that pattern.

Why it matters for TB programmes

Yohhei Hamada, a co-first author from UCL's Institute for Global Health, said in a university news release that reducing inequalities in TB exposure among men may have a greater impact on narrowing the sex gap than measures focused solely on progression from infection to disease.

The study itself did not test which approach would work best.

Earlier modelling pointed in a similar direction. Work by Dodd and colleagues, published in the American Journal of Epidemiology in 2016, estimated that 57.3% of new infections in South Africa's Western Cape and 65.7% in Zambia were attributable to contact with adult men.

Those were model estimates rather than observed transmissions.

The African picture

Tuberculosis killed an estimated 1.23 million people worldwide in 2024, out of 10.7 million who fell ill, according to WHO's Global Tuberculosis Report 2025.

Among adults aged 15 and over, an estimated 5.8 million men and 3.7 million women fell ill, alongside 1.2 million children under 15. Men made up 54% of all cases, and a larger share once children are set aside.

The WHO African Region accounted for about a quarter of all cases, with an estimated 2.62 million people falling ill in 2024.

WHO's Regional Director for Africa, Dr Mohamed Janabi, said in his World TB Day message in March 2026 that TB killed an estimated 378,000 people in the region in 2024.

Progress has been real.

Between 2015 and 2024, TB deaths in the African Region fell by 46% and the incidence rate by 28%, and WHO says South Africa has met the 2025 target for reducing TB incidence.

But an estimated 600,000 people with TB in the region are not diagnosed or treated each year, and WHO has warned that cuts to international donor funding in 2025 threaten prevention, diagnosis and treatment services.

That gap in diagnosis is what makes the study's question worth asking in Africa. If later research pins down the settings where men are picking up the infection, those are the places where a programme could close the gap rather than manage it.

What changes now

The study does not introduce a treatment and does not replace national or clinical guidance on testing, prevention or care.

What it gives programme planners is a narrower target: the sex gap appears to open at infection, not afterwards.

The obvious next study is the one this team could not run — measuring the work, housing and social contact patterns that might explain why men arrive at that point more often.

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