Meredith E. Slopen

Performance of Nucleic Acid Amplification Tests for Diagnosis of Tuberculosis in a Large Urban Setting

BACKGROUND A diagnosis of tuberculosis (TB) relies on acid-fast bacilli (AFB) smear and culture results. Two rapid tests that use nucleic acid amplification (NAA) have been approved by the US Food and Drug Administration for the diagnosis of TB based on detection of Mycobacterium tuberculosis from specimens obtained from the respiratory tract. We evaluated the performance of NAA testing under field conditions in a large urban setting with moderate TB prevalence. METHODS The medical records of patients with suspected TB during 2000-2004 were reviewed. Analysis was restricted to the performance of NAA on specimens collected within 7 days after the initiation of treatment for TB. The assays sensitivity, specificity, and positive and negative predictive values (PPV and NPV, respectively) were evaluated. RESULTS The proportion of patients with confirmed or suspected TB whose respiratory tract specimens were tested by use of NAA increased from 429 (12.9%) of 3334 patients in 2000 to 527 (15.6%) of 3386 patients in 2004; NAA testing among patients whose respiratory tract specimens tested positive for AFB increased from 415 (43.6%) of 952 patients in 2000 to 487 (55.5%) of 877 patients in 2004 (P < .001 for both trends). Of the 16,511 patients being evaluated for pulmonary TB, 4642 (28.1%) had specimens that tested positive for AFB on smear. Of those 4642 patients, 2241 (48.3%) had NAA performed on their specimens. Of those 2241 patients, 1279 (57.1%) had positive test results. Of those 1279 patients, 1262 (98.7%) were confirmed to have TB. For 1861 (40.1%) of the 4642 patients whose specimens tested positive for AFB on smear, the NAA test had a sensitivity of 96.0%, a specificity of 95.3%, a PPV of 98.0%, and an NPV of 90.9%. For 158 patients whose specimens tested negative for AFB on smear, the NAA test had a sensitivity of 79.3%, a specificity of 80.3%, a PPV of 83.1%, and an NPV of 76.0%, respectively. For the 215 specimens that tested positive for AFB by smear, we found a sensitivity, specificity, PPV, and NPV of 97.5%, 93.6%, 95.1%, and 96.8%, respectively. A high-grade smear was associated with a better test performance. CONCLUSION NAA testing was helpful for determining whether patients whose specimens tested positive for AFB on smear had TB or not. This conclusion supports the use of this test for early diagnosis of pulmonary and extrapulmonary TB.

Missed opportunities for tuberculosis prevention in New York City, 2003.

BACKGROUND Proper management and prevention can radically decrease the incidence of tuberculosis (TB). To further decrease TB cases in New York City, every opportunity for prevention must be utilized. This study sought to identify patients whose disease could have been prevented and describe missed opportunities for TB prevention. METHODS Patients diagnosed with TB from April to July, 2003 were identified using the New York City TB registry. Surveillance data, medical records, and patient interviews were used to determine whether patients missed a prevention opportunity or potential for screening. Preventable TB was defined as inappropriate screening of contacts and immigrants, inappropriate treatment of persons with prior TB diagnoses, or those who tested positive for latent TB infection (LTBI) as contacts, immigration, or in community settings. Potentially preventable TB was defined as occurring when those eligible for LTBI screening in community settings were not screened more than 1 year before TB diagnosis. Patients classified as having preventable or potentially preventable TB were grouped as patients with missed opportunities. We calculated the odds of missing a prevention opportunity using logistic regression. RESULTS Among the 218 study patients, 22% had preventable TB and 35% had potentially preventable TB. The most common missed opportunity among patients with preventable TB was the failure to initiate LTBI treatment. Birth outside of the United States was not associated with missing a prevention opportunity (odds ratio [OR] = 1.31, confidence interval [CI] = 0.71-2.39); however, extended travel outside of the United States increased the odds (OR = 2.51, CI = 1.19-5.69), particularly among non-US-born patients (OR = 3.01, CI = 1.21-8.59). Missed screening opportunities related to pregnancy, employment, or school attendance were encountered by over half of the study patients. CONCLUSIONS The majority of New York City TB patients in our cohort experienced at least 1 missed opportunity for prevention. Further study is warranted to determine whether LTBI treatment eligibility should be extended to those who travel for extended periods, particularly among the non-US-born patients.