HIV infection is the greatest known risk factor for the progression of latent M. tuberculosis infection to active TB. In many African countries, 30-60% of all new TB cases occur in people with HIV, and TB is the leading cause of death globally for HIV-infected people. HIV infection is associated with a much higher risk of reactivation of latent TB, and a more rapid progression of disease. Whereas in HIV-negative people a positive TB skin test carries a 5-10% lifetime risk of reactivation, in HIV-positive people reactivation occurs at a rate of 5-7% per year.
As tests of immune reactivity against M. tuberculosis , the TST and IGRAs are often positive among persons with TB disease. Therefore, all persons with a positive TST or IGRA should be evaluated for the possibility of active TB disease. Most, but not all, HIV-infected persons with TB disease have symptoms (cough, fever, sweats, weight loss, lymphadenopathy); absence of any of these symptoms has a 97% negative predictive value for culture-positive TB, though this varies depending on pre-test probability. 45 The addition of a chest radiograph improved sensitivity of this screening algorithm, but decreased specificity. Obtaining a sputum culture is the gold standard for diagnosing pulmonary TB disease, but this is not cost-effective in screening asymptomatic HIV-infected persons, particularly in the United States where the prevalence of TB is very low. Therefore, symptom screening (asking for cough of any duration) coupled with chest radiography is recommended to exclude TB disease in a patient with a positive screening test.