1346. Ruling out TB in New York City: Are Two NAATs (Nucleic Acid Amplification Testing) Enough?

Abstract Background Prompt diagnosis of pulmonary Mycobacterium tuberculosis (TB) infection can prevent nosocomial exposure. However, sputum smears are insensitive, and turnaround time for cultures can take weeks. Rapid diagnostics, such as nucleic acid amplification testing (NAAT), on respiratory specimens of patients suspected to have TB can improve diagnostic accuracy. Current practice at our institution is to obtain ≥ 3 NAATs in high-risk patients prior to discontinuing airborne isolation, but some studies have suggested that 2 negative NAATs may be sufficient. We conducted a retrospective study of patients at our institution diagnosed with TB. Methods The study was conducted at an academic adult hospital, an academic pediatric hospital, and a community hospital in New York City. Line lists of positive cultures for TB and positive NAATs from 2014 to mid-2018 were obtained from microbiology. Chart review was performed. Patient demographics, comorbidities, and radiographic findings were collected. Concordance between culture results and NAATs was evaluated. Incidence of inpatient TB exposure was noted. Results 82 cases of TB were found in the study period (see Figure 1). 45 cases were new inpatient diagnoses of pulmonary TB. The most common presenting symptoms were cough (69%), weight loss (49%), and fever (42%, see Table 1). 38/45 (84%) of patients were originally from a country other than the United States. 43/45 (96%) of patients had abnormal lung imaging. Cavitary disease was seen in 29%; other upper lobe disease was seen in 42%. Among smear-negative pulmonary TB cases, NAAT was positive in 11/16 (69%) of patients. Within this subgroup, the sensitivity of one NAAT was 41% when compared with culture. In smear-negative, NAAT-positive patients, NAATs were fully concordant with cultures in 4/11 patients (36%, see Table 2). The median number of positive NAATs was 1; the median number of positive cultures was 2. Five patients with pulmonary TB had negative NAATs altogether (median = 3); 2/5 resulted in TB exposure investigations after airborne precautions were discontinued following NAAT results. Overall, 13/45 (28%) of new diagnoses resulted in an exposure investigation. Conclusion Obtaining ≥ 3 NAATs in patients suspected of pulmonary TB improved diagnostic accuracy compared with obtaining 2 or fewer. Disclosures All authors: No reported disclosures.