Sex TB: Key Insights on Disease Localization and Hormones

Tuberculosis strikes men roughly twice as often as women worldwide, but the numbers only scratch the surface of a deeper biological story. A large meta-analysis of prevalence surveys across low- and middle-income countries found a pooled male-to-female ratio of about 2 to 1 for bacteriologically confirmed TB, with the gap widening further when only smear-positive cases were counted.¹ Yet this isn’t just a question of who gets sick more often. Sex hormones, genetic factors tied to the X chromosome, and differences in immune wiring all shape where TB lodges in the body, how severe it becomes, and how well treatment works.

The Global Sex Gap in TB

Every nationally representative prevalence survey included in a recent systematic review found higher TB rates among men than women. The overall male-to-female ratio for bacteriologically confirmed TB was about 2.0, and for smear-positive TB it rose to roughly 2.4.¹ That gap is consistent across world regions, though its size varies. Some of the disparity reflects behavioral factors: in many settings, men smoke and drink more than women, both of which independently raise TB risk. A large prospective cohort study found that smoking roughly doubled the odds of active TB, with risk climbing in a dose-dependent way with more cigarettes and more years of the habit.² Men also tend to have more occupational exposure in high-burden countries, and in some cultures they interact in crowded settings more than women.

But behavior doesn’t explain the whole picture. Even after researchers adjust for smoking, alcohol use, and socioeconomic factors, a biological sex effect persists. The immune system itself responds differently depending on whether testosterone or estrogen is the dominant circulating hormone, and these differences play out in the lungs, the lymph nodes, and the reproductive organs.

How Testosterone Tips the Scales

The clearest experimental evidence for a hormonal link comes from mouse studies. In one widely cited experiment, intact male mice had significantly higher bacterial loads in their lungs and died faster from TB than either female mice or castrated males. When researchers removed the testes at day 60 after infection, bacterial counts dropped and the expression of protective immune signals like TNF-alpha, IL-12, and interferon-gamma rose sharply.³ In other words, removing the main source of testosterone reversed much of the male disadvantage.

The mechanism appears to involve testosterone’s dampening effect on the branch of immunity that fights intracellular bacteria. A recent review of sex hormones and TB concluded that testosterone consistently weakens Th1-type immune responses, the very arm of the immune system responsible for containing Mycobacterium tuberculosis inside immune cells, and instead nudges the system toward anti-inflammatory pathways that are less effective against TB.⁴ Human epidemiological and clinical data line up with these lab findings, showing that adult males are more susceptible to active TB than premenopausal women of the same age.

What Estrogen Does Differently

Estrogen’s role is almost a mirror image. In a cell-culture study using human bronchial epithelial cells infected with M. tuberculosis, estradiol treatment reduced the number of viable bacteria inside cells and decreased necrosis, a form of cell death that helps the bacterium spread.⁵ Interestingly, estradiol achieved this partly by inhibiting autophagy, the cell’s self-eating process, in the infected cells. The effect was replicated by an agonist specific to estrogen receptor alpha, suggesting a targeted hormonal pathway rather than a generic anti-inflammatory effect.

Estrogen may also offer some protection to the liver during TB treatment. A study of patients on standard anti-TB drugs found that men had significantly higher transaminase levels than women, pointing to greater susceptibility to drug-induced liver injury. The researchers attributed part of that difference to estrogen’s hepatoprotective effects and to sex-based variation in the expression of cytochrome P450 enzymes, which metabolize TB drugs.⁶ So the hormonal landscape doesn’t just affect who gets infected; it appears to shape how well the body tolerates the cure.

Progesterone and Contraceptive Use

Estrogen isn’t the only female hormone that matters. Medroxyprogesterone acetate (MPA), used in injectable contraceptives like Depo-Provera, showed both glucocorticoid and progestogenic properties in a study of immune cells from women. When cells from MPA users were stimulated with BCG (the tuberculosis vaccine strain), they produced significantly lower levels of several key cytokines, including IL-12p40, which is important for the Th1 response against TB. These women also had lower numbers of circulating monocytes, a frontline immune cell in TB defense.⁷

This finding has real implications for women in TB-endemic regions where injectable contraceptives are among the most widely available family-planning methods. Whether the immunosuppressive effect of MPA translates into a measurably higher TB risk at the population level is still an open question, but the laboratory signal is concerning enough to warrant attention in settings where both TB prevalence and MPA use are high.

Where TB Settles in the Body

One of the most striking sex differences in TB is where the disease shows up. Among patients who already have pulmonary TB, women are significantly more likely than men to also develop extrapulmonary disease, meaning TB that spreads to lymph nodes, the pleura, bones, the central nervous system, or the reproductive organs. A population-based study from Taiwan found that women with pulmonary TB had about 30% higher odds of concurrent extrapulmonary TB than men, and among patients 45 and older the difference was even more pronounced, with women roughly twice as likely to develop extrapulmonary involvement in a hospital-based analysis.⁸

A separate study that tracked TB patients across their lifespans found a similar pattern: after adjusting for age, women had about 48% higher odds of developing extrapulmonary TB. The sex difference was most prominent in the 40-to-69 age range, precisely the years surrounding menopause.⁹ Why extrapulmonary TB tilts female remains debated, but one theory is that the very immune profile that helps women contain lung disease more effectively may also promote bacterial dissemination through the bloodstream to distant sites.

On the other hand, when TB does stay in the lungs, men tend to get a more destructive form. Men showed higher rates of cavitary disease (about 23% versus 13% in women), bilateral lung involvement, and smear-positive sputum.⁹ Cavitary TB is particularly significant because the cavities are full of bacteria and make patients far more infectious to others. This contributes to the higher transmission rates seen from male TB patients in many settings.

Tuberculous Lymphadenitis and the Female Tilt

One specific form of extrapulmonary TB, cervical lymph node involvement (historically called scrofula), shows a female predominance. A descriptive study of tuberculous lymphadenitis patients found it most common in young women aged 21 to 30.¹⁰ This is consistent with the broader pattern of women being more susceptible to extrapulmonary TB but adds an age-specific detail: lymph-node TB peaks in women during their peak reproductive years, when estrogen levels are highest. Whether the hormone itself directs bacteria toward lymph nodes or whether immune trafficking patterns differ by sex is still being worked out.

Genital TB and Fertility

TB’s ability to colonize the reproductive organs is one of its most devastating and underappreciated consequences, and it affects men and women through different pathways.

Female Genital Tuberculosis

In women, genital TB most often targets the fallopian tubes and the uterine lining. A systematic review and meta-analysis estimated that genital TB is present in roughly 35% of women investigated for infertility in endemic regions, making it one of the leading causes of tubal-factor infertility where TB is common.¹¹ The disease causes extensive scarring and adhesion formation. In a recent case report, a 30-year-old woman undergoing infertility evaluation was found to have complete destruction of one ovary along with loss of normal tubal and uterine architecture, all from longstanding genital TB.¹²

The diagnostic challenge is considerable. Many women with genital TB have no pulmonary symptoms and no abnormal chest X-ray, so TB may not even enter the clinical picture until tissue is biopsied during a fertility workup. In endemic countries, clinicians increasingly recommend screening for genital TB as part of any infertility investigation, especially when tubal damage is found without an obvious cause like prior pelvic inflammatory disease.

Male Genital Tuberculosis

In men, TB most commonly reaches the reproductive tract via the bloodstream and seeds in the epididymis. From there it can spread to the testes and prostate. A review of the disease found that the epididymis is the most frequently affected organ, and the infection is characterized by extensive fibrosis that may persist even after successful antibiotic treatment.¹³ In a case series of 47 men with epididymal TB, painless scrotal swelling and scrotal pain were equally common presenting symptoms, each occurring in about 45% of cases.¹⁴ Sinus tracts draining through the skin formed in about 13% of patients, a sign of late diagnosis.

Male genital TB also causes infertility, often through obstruction at multiple points along the reproductive tract. Unlike simple vasectomy reversal, the obstruction from TB tends to be multi-site and accompanied by dense scar tissue, making surgical reconstruction difficult or impossible in many cases.¹³ The disease can also present in adolescents. A case report documented isolated epididymal TB in a 16-year-old boy whose only symptoms were three months of scrotal swelling and two months of coughing.¹⁵

The Age Puzzle

Sex differences in TB don’t appear all at once. In children under five, the infection rates between boys and girls are similar or even slightly favor girls. A study of household contacts in Brazil found that among children under five, girls actually had a higher proportion of TB infection than boys (about 63% versus 45% among exposed contacts). But the trajectories diverged as children aged: girls showed their steepest increase in infection between ages 5 and 14, while boys caught up later, with their sharpest increase between adolescence and age 39.¹⁶ By age 40 and beyond, both sexes had converged at similarly high levels of infection, but men had begun to far outpace women in rates of active disease.

This timeline strongly suggests a pubertal hormone effect. The male disadvantage in active TB emerges around the time testosterone levels rise in adolescence and remains most pronounced through the working-age years, while women’s relative protection is greatest during the reproductive years and diminishes after menopause. The U-shaped pattern in women’s TB severity, with the lowest rates of cavitary disease and smear positivity occurring in the 50-to-59 age group (perimenopausal years), points to a complex interplay between declining estrogen and changing immune function.⁹

Pregnancy Changes the Immune Equation

Pregnancy creates a temporary but dramatic shift in the immune system that has specific consequences for TB. A longitudinal study of HIV-negative Ethiopian women found that TB-specific interferon-gamma responses were actually higher during the third trimester than during earlier pregnancy or after delivery. This was unexpected, because the general immune suppressiveness of pregnancy would predict the opposite. Meanwhile, responses to a non-specific immune stimulant (mitogen) were lower in the third trimester, confirming that the overall immune system was indeed dialed down.¹⁷

The researchers interpreted this as evidence that latent TB becomes more immunologically active during late pregnancy, potentially because the bacteria begin replicating as general immune surveillance drops, which then triggers a compensatory TB-specific response. This dynamic may explain why the postpartum period is a particularly high-risk window for TB reactivation: once the pregnancy-related immune suppression lifts, the immune system’s encounter with newly multiplying bacteria can tip into full-blown active disease.

Treatment Outcomes Favor Women

The sex differences extend well past diagnosis. A large retrospective cohort study in Tanzania found that men had about 10% higher risk of dying during TB treatment and a 56% higher risk of treatment failure compared with women.¹⁸ A prospective study from India confirmed the pattern from a different angle: women had a 40% lower risk of unfavorable treatment outcomes, driven largely by a much lower recurrence rate after completing therapy.¹⁹

Part of this gap may trace back to the same hormonal mechanisms that shape susceptibility. If testosterone suppresses the immune pathways that clear bacteria, men may harbor more residual organisms at the end of treatment, raising the chance of relapse. Additionally, the higher rates of cavitary disease in men mean more bacteria at the start of treatment, which is itself a known predictor of treatment failure. And men’s greater susceptibility to drug-induced liver injury can lead to treatment interruptions or dose reductions that undermine cure rates.

Why Sputum Tests Miss More Women

The diagnostic tools used to confirm TB have their own sex biases. Sputum smear microscopy, the most widely available test in low-resource settings, depends on coughing up a good-quality sputum sample. Significantly more men than women produced a set of three adequate specimens in one study, and women’s positive smears were more likely to be low-grade, meaning they had fewer visible bacteria per field.²⁰ Another study confirmed higher proportions of low-grade positive smears among female patients, especially at the extremes of age.²¹

This matters because when diagnostic thresholds require a certain bacterial density to count as positive, women’s lower-grade smears can be classified as negative even when they have active disease. The revised WHO case definition, which includes “scanty” smears as positive, was found to substantially improve TB detection in women, narrowing the sex gap in case detection. Molecular tests like GeneXpert are less affected by sample quality, but they remain unavailable in many of the places where TB is most common.

BCG Vaccine Responses

Even the world’s oldest and most widely used TB vaccine works differently depending on sex. A multi-omics analysis of BCG vaccine recipients found that women exhibited significantly stronger short-term vaccine efficacy than men, as measured by interferon-gamma response.²² The difference was less pronounced over the longer term but still trended in the same direction. Given that BCG’s overall effectiveness against adult pulmonary TB is already highly variable, the fact that sex further modulates the response is relevant for next-generation vaccine development. Researchers are increasingly arguing that TB vaccine trials should be designed and powered to detect sex-specific efficacy, rather than reporting pooled results that may hide meaningful differences.

Leptin, Wasting, and the Immune Feedback Loop

TB is notorious for causing severe weight loss, and the metabolic hormone leptin may be one link between wasting and worsening immunity. In TB patients, plasma leptin levels drop, driven by loss of body fat. But a study of TB patients found that inflammation itself independently suppresses leptin production beyond what fat loss alone would explain. Since leptin supports cell-mediated immunity, the kind the body needs to fight TB, falling leptin levels may create a vicious cycle: the sicker and thinner a patient gets, the less leptin they produce, and the weaker their immune defense against the very infection causing the wasting.²³

This has a sex dimension because women generally have higher baseline leptin levels than men at any given body-fat percentage, owing to estrogen’s stimulatory effect on leptin production. If leptin provides a degree of immune protection, women may enter the disease with a larger metabolic buffer before hitting the danger zone of severe immune suppression. That buffer is speculative at the population level, but it fits neatly with the broader pattern of women mounting stronger immune responses to TB and tolerating the disease and its treatment with fewer catastrophic outcomes.