Gender
Tuberculosis fatality in women (adjusted for age and extent of disease), as compared with men, may be higher without chemotherapy35 while, after the introduction of chemotherapy, it is lower36. Forms of tuberculosis with higher fatality rates (disseminated disease, meningitis and advance pulmonary disease) comprise a lower proportion of all cases in women as compared with men35.
When rates of tuberculosis disease are very high, young women aged 20 to 30 years are the group most likely to suffer from tuberculosis disease83. Even when tuberculosis disease is substantially lower and the highest rates are observed in elderly men, young women are more likely to develop disease after becoming infected90 and young women are often more frequent among cases aged under 25 years. Contagious cases are less frequent among older women as compared with men (figure 3). While women are equally likely to be referred for diagnostic examination (figure 4), the yield of cases among suspects is greater for men (figure 5)91.
Tuberculous infection is more frequent in young girls (figure 6), while among older persons, men are often more likely to have significant tuberculin reactions92. Differences in prevalence between the genders are not clearly understood. The excess in older men may be due to a greater likelihood of continuing exposure among men after childhood.
Ethnicity
In a study of children who were contacts of cases of active tuberculosis, prior to the advent of chemotherapy, a comparison was made between Canadian Aboriginal children and children of European origin93: death in the Aboriginals was 9.1 times more common than among Europeans; subsequent development of active disease was 4.9 times more frequent.
Tuberculosis disease rates vary widely in different ethnic groups, even where case-finding characteristics are similar94. These differences can largely be explained by a striking difference in the probability of infection in youth95. The site of tuberculosis also varies according to ethnic group96: lymph node tuberculosis is strikingly more frequent in persons born in Asia; genitourinary tuberculosis is more frequent in persons born in Europe.
Marital status
Tuberculosis disease is more common among those who never married as compared with those who have ever been married97. This was borne out in an evaluation of 2,573 cases of tuberculosis notified in Canada from 1970 to 197298 (table 3). In all age groups, notification rates were highest in the group who never married, with intermediate rates, in most groups, for those divorced or widowed. This gradient was much greater for men than for women. Stratification of the population by socioeconomic level caused this gradient to disappear89 suggesting that marital status was confounded by socioeconomic level (never married and divorced/widowed persons were more likely to live in areas of poverty).
Tuberculosis disease has always been known to be associated with poverty10. A number of possible poverty-related factors could contribute to tuberculosis. Nevertheless, few studies have identified which of these factors is most important. In a study in the city of Vancouver, unemployment emerged as the most powerful factor and was independent of socioeconomic level99. Although tuberculous infection is more common in those who live in districts with the lowest socioeconomic level the rate of development of tuberculosis in those already infected was so high (figure7) as to be explainable only by recent infection with rapid subsequent development of disease, an observation confirmed by recent studies of DNA fingerprinting in large cities of the United States41 43.
Body habitus
A strong relationship has been demonstrated between mortality from a variety of conditions, including tuberculosis, and the size and shape of the body100. The association with tuberculosis deaths is strongest in men, with tall and thin persons being at greater risk of dying from tuberculosis. Studies of the health effects of exposure to ambient particles have shown similar relationships101, suggesting that the pattern of deposition of ambient particles may be the explanation for this relationship.
Other personal factors
Tuberculosis disease is significantly more frequent when individuals suffer from other conditions. These include: HIV infection102; diseases that require treatment with immune suppressive therapy103; gastrectomy104, diabetes mellitus105 and silicosis106. These have been nicely summarized in a review by Rieder and colleagues17.
2. Place
Location of residence
Tuberculosis mortality, case rates and prevalence of infection vary widely with the location of residence. Current estimates indicate that a high proportion of all cases and deaths of tubereulosis occur in low income countries. These differences are almost entirely explained by the density of contagious cases in the community but are augmented by the increased probability of transition from being infected to being contagious where a high proportion of the population has compromised immunity due to HIV infection.
Tuberculosis has a different course in rural as compared with urban areas89 107. Within the urban area, however, the striking relation between location of residence in the urban area and the level of tuberculosis10 is largely explained by socioeconomic level. Some studies108 109 showed a much higher prevalence of significant tuberculin reactions in those living in the poorer areas, suggesting selective migration to these areas of individuals who were infected; other studies110 111 did not confirm this finding.
