Older age was a strong, independent predictor of mortality. Given the aging of the American population, mortality from TB in the elderly is an enormous concern. Mortality may be higher in older adults because they may receive less vigorous care, or older persons may have more severe disease because of a decreased immunologic status and decreased baseline functional status. Older people with TB have been shown to have more extensive disease, based on chest radiograph findings at presentation. Importantly, age may have a modifying effect on TB illness itself, making the diagnosis of TB more difficult. Older TB patients have a higher prevalence of nonspecific symptoms, a lower prevalence of fever, and less frequently manifest a positive tuberculin skin test. This less classic presentation may contribute to the longer delay in presentation and initiation of treatment, and may lead to a higher risk of death.
Comorbid illness has substantial influence on patient outcomes.” Comorbidity indexes, utilizing ICD-9, clinical modification, codes from hospital discharge records, have been shown to predict the survival of patients with various health conditions. In our study, comorbidity, measured by the DCI, was similarly found to be a significant predictor of mortality. Specifically, diseases such as renal failure and liver disease may cause difficulties in TB treatment given the increased risk of toxicity of first line TB drug therapies.2 Although HIV status is included in the measure of DCI, we also examined it separately because of its previously demonstrated relevance to TB outcomes.’ A diagnosis of HIV in our study was not associated with higher mortality. Previous studies that have examined the relationship suggest that the severity of immunodeficiency, or CD4 count depletion, is an independent predictor of mortality in TB patients with HIV. Clinical laboratory data, such as CD4 count, were not available in this database, so we were unable to assess the severity of HIV disease in these patients, which may explain why it was not predictive of death.