Suspecting Active Disease

Because the incidence of active disease is low in the United States (3.2/100,000 in 2012), diagnosis may be delayed as it is not considered in the differential diagnosis. Because it can present in many forms (classic TB pneumonia, pleural effusion, disseminated (miliary) tuberculosis, scrofula (lymphadenitis), renal, intestinal, CNS, and other extrapulmonary sites), it is important to consider in patients with a history of TB or latent infection, with risk factors for having been infected, and with risk factors that increase the risk of progression if infected

Although most people with active tuberculosis will have a positive TST or IGRA, a negative test result does not rule out active disease. The reason a person may progress to active disease may be due to decreased immunity. Decreased immunity may diminish the response to PPD or to TB antigen in an IGRA and additionally allow a latent infection to reactivate. TST and IGRA are key to screening asymptomatic patients for latent TB infection, but are not necessary for diagnosing active disease.

In settings where screening for active pulmonary disease is a priority (medical facilities, correctional facilities, and homeless shelters), symptom and risk factor review should be done on arrival, and suspected cases isolated and evaluated as soon as possible.

If contagious pulmonary tuberculosis is suspected,


・ Infection control should be initiated

・ Chest radiography should be obtained,

・ Sputum should be collected for AFB smear and culture, and

・ The health department TB program should be notified immediately

The Whatcom County Health Department will review and assure appropriate isolation measures are taken, can assess contacts, and can access advanced diagnostic testing through the state and CDC public health laboratories, if indicated. The nucleic acid amplification test (NAAT) done at the WA State Public Health Lab, is more sensitive than AFB smears, detects Mtb and M. avium, controls for interfering substances, and is run twice weekly, providing confirmation of diagnosis often weeks before culture results are available.