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Understanding the epidemiology and clinical course of tuberculosis is hampered by the absence of a perfect test for latent tuberculosis infection. The tuberculin skin test (TST) is widely used but suffers poor specificity in those receiving the bacille Calmette-Guérin vaccine and poor sensitivity in individuals with human immunodeficiency virus (HIV) infections. TST responses for a target population in Harare, Zimbabwe (HIV prevalence, 21%), recruited in 2005-2006, were interpreted by using a separate calibration population in Harare, for which interferon-gamma release assays (enzyme-linked immunosorbent spot (ELISpot)) results were also known. Statistical fitting of the responses in the calibration population allowed computation of the probability that an individual in the target population with a given TST and HIV result would have tested ELISpot positive. From this, estimates of the prevalence of tuberculosis infection, and optimal TST cutpoints to minimize misdiagnosis, were computed for different assumptions about ELISpot performance. Different assumptions about the sensitivity and specificity of ELISpot gave a 40%-57% prevalence of tuberculosis infection in the target population (including HIV-infected individuals) and optimal TST cutpoints typically in the 10 mm-20 mm range. However, the optimal cutpoint for HIV-infected individuals was consistently 0 mm. This calibration method may provide a valuable tool for interpreting TST results in other populations.

Background: Cough lasting for > or = 3 weeks (i.e., chronic cough) indicates that a patient has suspected tuberculosis (TB). At the primary health care level, the spectrum of disease that causes chronic cough has not been previously investigated in a setting with a high prevalence of human immunodeficiency virus (HIV) infection., Methods: A total of 544 adults with chronic cough were recruited systematically from 2 primary health care clinics, and they were evaluated using preset first- and second-line investigations and diagnostic case definitions., Results: The overall prevalence of HIV infection among the study cohort was 83%. TB was the most common diagnosis, with 207 HIV-positive patients (46%) and 27 HIV-negative patients (30%) having confirmed or probable TB. Of these, 145 HIV-positive patients with TB (70%) and 20 HIV-negative patients with TB (74%) had smear-positive cases of TB. Only 17 HIV-positive and 2 HIV-negative patients had smear-negative but culture-positive cases of TB. Lower respiratory tract infections (n = 178; HIV prevalence, 79%) and pneumonia (n = 87; HIV prevalence, 89%) were the next most common diagnoses. Asthma (n = 26; HIV prevalence, 46%), posttuberculous disease and other fibrotic lung disease (n = 34; HIV prevalence, 88%), and cardiac disease (n = 15; HIV prevalence, 93%) were more common than were Pneumocystis jiroveci pneumonia and cryptococcosis (n = 8 and n = 5, respectively; HIV prevalence, 100%), and we found no cases of nocardiosis or histoplasmosis., Conclusions: TB was diagnosed for 43% of patients who presented with chronic cough to primary health care clinics in Harare, with 71% having smear-positive disease. The findings of TB culture added relatively little to the findings of fluorescent microscopy of concentrated sputum specimens. The prevalence of HIV infection was high across a range of diagnoses, suggesting that an HIV test should be recommended in the initial investigation of chronic cough.