Risk factors associated with in-hospital mortality among patients with active TB disease: 25-year experience in the US

Background: A negative tuberculin skin test (TST) is associated with poor clinical outcome among persons with TB disease. However, the relationship between a negative TST and in-hospital mortality among patients with active TB disease has not been studied. We hypothesized that a negative TST, indicating weak cellular immune response to tuberculin, would be associated with in-hospital mortality.

Methods:This retrospective cohort study analyzed 961 patients with active TB disease hospitalized at University of Texas Health Science Center at Tyler between January 1, 1985 and December 31, 2010. We included a 25% simple random sample of patients with uncomplicated TB and 100% of three groups with complicated TB disease (drug resistant TB, HIV-coinfection, and serum drug-level monitoring). We defined negative TST as <10 mm induration. We examined the association between sociodemographic and clinical factors, TST, and hospital mortality. The crude association was evaluated using the Rao-Scott chi-square test accounting for stratified, unequal probability sample design.

Results: 635 individuals were included in the final analysis representing a total of 1806 patients of whom 19.2% had negative TST results and 2.9% died in-hospital. Notable characteristics included foreign-birth (47.9%), malnutrition (22.7%), homelessness (18.0%), positive HIV status (2.5 %), positive AFB smear (48.7%), prior history of TB (16.7%), and MDR TB (1.7%). Negative TST results, age, and malnutrition showed significant association with in-hospital mortality (all p values<0.005). The risk of dying in hospital was 2.2-fold (95% CI: 1.1-4.2) higher in patients with a negative TST than patients with a positive TST.

Conclusion: Negative TST results, as well as increasing age and malnutrition were significantly associated with in-hospital mortality, possibly reflecting weakened cellular immune reaction to Mycobacterium tuberculosis antigens. TST results may identify patients at higher risk of death.