HomeThe risk of progression from TBI to active TB is largely dependent on the immune competency of the host. Age and sex appear to directly affect the immunologic response and the risk of disease: morbidity is greater among young children (<5 years of age), especially infants; young adults, especially females; and older adults, especially males. In high-burden countries, the population-attributable fraction of undernutrition for TB is 27% according to the WHO.96,97 In Canada, inadequate diet has been associated with acquiring M. tuberculosis infection in an Inuit community.97 In a study from Peru, biosocial household factors contributed to the risk of TB among contacts.98 The seasonality of TB (with the highest incidence in spring and early summer) has been attributed to reduced sunlight and vitamin D deficiency during the winter months in some studies but not in others.99–101 Ethnic differences have been offered as factors determining host immune response, with some support.102 A growing body of evidence suggests that host genetic factors are important in determining susceptibility to TB as well.103–105 Most important from a clinical perspective are the many medical conditions that are well-known to affect host immunologic response and increase the risk of progression from TBI to active TB disease. These are reviewed in detail in Chapter 4: Diagnosis of Tuberculosis Infection.
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