Why is TB more common in men than in women?

Sex or gender

  • Gender: biological and behavioral differences determining “the state of being male or female”)
  • Sex: biological differences in males and females

In most countries, tuberculosis (TB) notification is twice as high in men as in women. Although there is clear evidence that socioeconomic and cultural factors leading to barriers in accessing health care may cause undernotification in women, particularly in developing countries, biological mechanisms may actually account for a significant part of this difference between male and female susceptibility to TB. The role of biological gender has been determined in a number of infectious and noninfectious diseases. However, there is an absence of information on the role of biological gender in TB. Thus, investigations should be conducted to clearly understand the role of sexual hormones, sex-related genetic background and genetic regulations, and metabolism, among other factors, in susceptibility differences between men and women. This research may help not only to fully understand the obviously biased gender distribution among TB cases, but also to better adapt future intervention strategies at the community level. In this review, we expand on the various issues relating to TB notification and gender bias.

Large prevalence surveys have suggested that the sex bias observed in pulmonary TB cases may result partly from genuine biological differences in male and female susceptibility to M. tuberculosis infection or the development of TB disease. This finding would not be particularly surprising, as many studies in humans and experimentally infected animals have established clear links between sex-specific factors, including steroid hormones and genetic variants, and the differential susceptibility of males and females to a number of other infectious and noninfectious diseases. In particular, gender bias among pulmonary microbial diseases is not restricted to TB, and important sex differences in the incidence and severity of a number of respiratory tract bacterial infections have been reported in the literature. As a selected example, it has been shown that men have a four-times higher risk of developing nosocomial Legionella pneumophila infection than women. Only 5% to 10% of individuals exposed to M. tuberculosis develop TB, and up to 70% of those who do develop the disease are male. In other words, the human population as a whole is remarkably resistant to M. tuberculosis, but women seem to be even more resistant to the bacillus than men. So, why do only a minority of individuals, other than patients with HIV/AIDS, fail to control infection? Why are women less likely to develop TB than men? Why are some women more resistant to TB than other women exposed to a similar extent? Field research consortia including not only microbiologists, immunologists, and human geneticists, but also epidemiologists and sociologists, should be established to unravel the many faces of sexual inequality in TB, and to decipher the delicate mechanisms involved in natural and sex-associated resistance to TB. Such work would facilitate the design of future intervention strategies for combating the disease and the development of useful tools for evaluating prognosis and protection in future clinical trials.

Sexual Inequality in Tuberculosis. PLoS Med 6(12): e1000199. doi:10.1371/journal.pmed.1000199

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6 Responses to Why is TB more common in men than in women?

  1. Chris Upton says:

    Lots of complicated explanations…
    My question would be “what has to happen for infection to occur after exposure?”
    Does the bug have to be sucked deep into the lungs?
    If so, do men, on average, perform more extreme physical activity (incl. manual labor) that could explain this?

    • Wilma says:

      After exposure to TB, infection normally only occurs in individuals who are immune compromised (people on immune-suppressing medication or HIV-infected, for example). Healthy individuals are normally able to ward off the infection (although the bacteria may become dormant and develop into disease when the individual becomes immune compromised).

  2. AJ Cann says:

    I still have doubts about reporting bias in some countries, but overall it’s clear that there is something we need to get to the bottom of here.

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