Transmission of Mycobacterium tuberculosis From Patients Who Are Nucleic Acid Amplification Test Negative

• Published in: Clinical infectious diseases Vol. 67; no. 11; pp. 1653 - 1659
• Main Authors: Xie, Yingda L, Cronin, Wendy A, Proschan, Michael, Oatis, Richard, Cohn, Silvia, Curry, Scott R, Golub, Jonathan E, Barry, Clifton E, Dorman, Susan E
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 13-11-2018
• Subjects: Adult; and Commentaries; Cluster Analysis; Editor's Choice; Female; Genotype; Humans; Male; Maryland; Medical Records; Middle Aged; Mycobacterium tuberculosis - genetics; Mycobacterium tuberculosis - isolation & purification; Nucleic Acid Amplification Techniques; Retrospective Studies; Sputum - microbiology; Stem Cells; Tuberculosis, Pulmonary - diagnosis; Tuberculosis, Pulmonary - transmission; Young Adult; Maryland; diagnosis; transmission; nucleic acid amplification test; infectiousness; tuberculosis
• ISSN: 1058-4838; 1537-6591
• DOI: 10.1093/cid/ciy365

We assessed the transmission risk of pulmonary tuberculosis patients whose sputum nucleic acid amplification tests (NAAT) were negative. We estimated that, at minimum, sputum NAAT-negative tuberculosis patients had approximately a 5% risk of transmitting tuberculosis.
Abstract
Background
Among adults with signs and symptoms of pulmonary tuberculosis (TB), recognition of transmissible TB has implications for airborne infection isolation and public health activities. Sputum smear-negative TB patients account for around one-fifth of tuberculosis transmission. The tuberculosis transmission risk of TB patients with negative results on nucleic acid amplification test (NAAT) of respiratory specimens has not been established. We sought to estimate the tuberculosis transmission risk of NAAT-negative TB patients.
Methods
We retrospectively reviewed Maryland TB program data collected from 2004 to 2009, during which time NAAT using the Mycobacterium Tuberculosis Direct Test (MTD) was performed routinely. Patients with sputum Mycobacterium tuberculosis (M.tb) isolates having matching genotypes were assigned to clusters. Transmission sequence was approximated by collection order of individuals' first culture-positive specimens. Minimum transmission risks of NAAT (MTD)-negative TB patients and of smear-negative TB patients were estimated based on individuals' positions within clusters.
Results
Among 809 patients with culture-confirmed TB, M.tb genotypes were available for 782 (96.7%). For NAA-negative TB patients, the minimum transmission risk estimate was 5.1% (95% CI 0-11.4). For smear-negative TB patients, the minimum transmission risk estimate was 11.2% (95% CI 7.2-15.3).
Conclusions
Minimum transmission risk of NAAT-negative TB patients was lower than that of smear-negative TB patients. However, transmission risk of NAA-negative TB patients appears to not be negligible.