Sexual Inequality in Tuberculosis

Tuberculosis (TB) claims over 1.7 million lives throughout the world each year according to the most recent World Health Organization (WHO) report [1]. Men seem to be more affected than women, with a male/female ratio of 1.960.6 for the worldwide case notification rate (Box 1; Figure 1) [1]. In some countries this ratio may reach values as high as 3 (4.7 in Armenia for instance), but ratios below 1 are extremely rare and mostly correspond to very small populations of patients [1]. This excess of male pulmonary TB cases is seen in all regions of the world, and in almost all countries (Figure 2A), at least in non–HIV-infected patients. It is also seen in adults of all ages, but does not seem to apply to children and young adolescents (Figure 2B). As case notification is a complicated process, beginning with the recognition of initial symptoms and followed by clinical diagnosis and reporting, this indicator necessarily combines various factors, including, for example, differences in both susceptibility and exposure, help-seeking behavior, and access to health care services. Several reviews have discussed the possibility of undernotification of women due to greater difficulties in gaining access to clinics and in obtaining a timely diagnosis and treatment, particularly in developing countries [2]. Other confounding factors, such as smoking, alcohol and drug use, exposure to indoor dusts and air pollution, as well as the poor quality of sputum samples collected from women in some regions, may influence the sex bias observed in patients with TB [3–8]. The case notification rate therefore may not reveal the many facets of inequality between male and female patients with TB. However, the poorer access of female patients to health care does not account for the higher incidence of detection on the basis of positive smears in a number of situations, including low-income countries [9]. A recent multicentre case-control study conducted in three West African countries concluded that male sex is indeed a risk factor for TB, independent of other factors examined; in this case multivariate analysis of environmental and host-related factors found a male/female ratio of 2.03 among patients with TB (versus 1.12 in the contact population, p = 0.02) [5]. Unlike studies based on case notification, large, systematic prevalence surveys can provide us with information about genuine biological differences in susceptibility to TB between men and women, if indeed there are any. A prime example is provided by a large prevalence survey conducted in Bangladesh, in which more than 260,000 individuals (51% males) were visited in a house-to-house survey designed to detect cases of suspected TB, for possible subsequent confirmation by smear observation [10]. An excess of cases in males, with a sex ratio of 3:1 (48 males and 16 females with confirmed TB), was observed, even if confounding factors, such as income, awareness, and stigma were taken into account [11].