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Diagnostic Characteristics of Cough Aerosol Cultures of Mycobacterium Tuberculosis as Predictors of Transmission
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A1154 - Diagnostic Characteristics of Cough Aerosol Cultures of Mycobacterium Tuberculosis as Predictors of Transmission
Author Block: K. P. Fennelly1, C. Acuna-Villaorduna2, E. Jones-Lopez3; 1Pulmonary Medicine, NHLBI, Bethesda, MD, United States, 2Boston University, Wellesley Hills, MA, United States, 3Section of Infectious Disease, Boston University School of Medicine, Boston, MA, United States.
Rationale. A diagnostic test that could predict which tuberculosis (TB) patients are infectious and when they become non-infectious would be helpful for infection control practitioners and clinician. In a prospective cohort study (Jones-Lopez EC et al, AJRCCM 2013) , we reported that cough aerosol cultures of Mycobacterium tuberculosis (Mtb) predicted new infection among household contacts (HHCs) of persons with active pulmonary tuberculosis better than sputum smear or culture. Follow-up of this cohort revealed that incident TB disease was also associated with exposure to cough aerosol positive cases (Jones-Lopez EC et al, Clin Infect Dis 2016). We re-analyzed those published data to assess the value of cough aerosols cultures as a diagnostic test of infectiousness of TB patients. Methods. We created 2 x 2 tables and calculated the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of ‘high cough aerosols (10+ CFU) of Mtb’ from source cases of pulmonary TB as the diagnostic test. We used 2 different outcomes to define transmission: (1) tuberculin skin test (TST) conversion and (2) conversions of both TSTs and interferon gamma release assays (IGRA; QunatiFERON Gold In-Tube, Cellestis). Results. Using TST conversion as the outcome, the sensitivity of high cough aerosol cultures was 40%, specificity was 89%, PPV was 69%, and NPV was 71% (66%, 76%). Using both TST and IGRA conversions as the gold standard, sensitivity was 58%, specificity was 92%, PPV was 69% and NPV was 87% (80%, 92%). Conclusion. Using both TST and IGRA conversions as the more rigorous definition of new infection in HHCs, high cough aerosols had good specificity and NPV in this cohort. These data suggest that high cough aerosols cultures have potential use as a good ‘rule-out’ test of infectiousness in TB, as there is a high probability that a TB patient with a negative test will not transmit infection, i.e., is not infectious. Point of care tests are becoming available that have the potential to assay cough aerosols using molecular methods. If these prove to be good surrogates for cough aerosol cultures, they may help to prioritize resources or to facilitate decisions regarding discharge of TB patients into the community.
Author Block: K. P. Fennelly1, C. Acuna-Villaorduna2, E. Jones-Lopez3; 1Pulmonary Medicine, NHLBI, Bethesda, MD, United States, 2Boston University, Wellesley Hills, MA, United States, 3Section of Infectious Disease, Boston University School of Medicine, Boston, MA, United States.
Rationale. A diagnostic test that could predict which tuberculosis (TB) patients are infectious and when they become non-infectious would be helpful for infection control practitioners and clinician. In a prospective cohort study (Jones-Lopez EC et al, AJRCCM 2013) , we reported that cough aerosol cultures of Mycobacterium tuberculosis (Mtb) predicted new infection among household contacts (HHCs) of persons with active pulmonary tuberculosis better than sputum smear or culture. Follow-up of this cohort revealed that incident TB disease was also associated with exposure to cough aerosol positive cases (Jones-Lopez EC et al, Clin Infect Dis 2016). We re-analyzed those published data to assess the value of cough aerosols cultures as a diagnostic test of infectiousness of TB patients. Methods. We created 2 x 2 tables and calculated the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of ‘high cough aerosols (10+ CFU) of Mtb’ from source cases of pulmonary TB as the diagnostic test. We used 2 different outcomes to define transmission: (1) tuberculin skin test (TST) conversion and (2) conversions of both TSTs and interferon gamma release assays (IGRA; QunatiFERON Gold In-Tube, Cellestis). Results. Using TST conversion as the outcome, the sensitivity of high cough aerosol cultures was 40%, specificity was 89%, PPV was 69%, and NPV was 71% (66%, 76%). Using both TST and IGRA conversions as the gold standard, sensitivity was 58%, specificity was 92%, PPV was 69% and NPV was 87% (80%, 92%). Conclusion. Using both TST and IGRA conversions as the more rigorous definition of new infection in HHCs, high cough aerosols had good specificity and NPV in this cohort. These data suggest that high cough aerosols cultures have potential use as a good ‘rule-out’ test of infectiousness in TB, as there is a high probability that a TB patient with a negative test will not transmit infection, i.e., is not infectious. Point of care tests are becoming available that have the potential to assay cough aerosols using molecular methods. If these prove to be good surrogates for cough aerosol cultures, they may help to prioritize resources or to facilitate decisions regarding discharge of TB patients into the community.
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