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Magnitude of Mycobacterium tuberculosis transmission among household and non-household contacts of TB patients
OBJECTIVE: To quantify new infection and to determine the risk factors associated with new infection among named contacts in San Francisco, CA, USA.
DESIGN: We performed a cohort study in patients with culture-positive pulmonary TB. We analyzed patient, contact, environmental and bacterial characteristics.
RESULTS: Of the 2422 contacts named by 256 patients, 149 (6.2%) had new infection due to recent transmission from 79 (30.9%) patients. Of the 149 new infections, 87 (58.4%) occurred among household contacts and 62 (41.6%) among non-household contacts. Numerous acid-fast bacilli in sputum (odds ratio [OR] 2.64, 95%CI 1.32–5.25) and contacts being named by more than one patient (OR 2.90, 95%CI 1.23–6.85) were associated with new infection among household contacts. Being older than 50 years (OR 1.93, 95%CI 1.09–3.41) and an Asian/Pacific Islander (OR 3.09, 95%CI 1.50–6.37) were associated with new infection among non-household contacts.
CONCLUSIONS: Fewer than one third of patients caused new infection to his/her contacts. A substantial proportion of transmission resulting in new infection occurred outside of the household. The risk factors for infection among household and non-household contacts are different and should be considered when prioritizing control interventions.
Keywords: contact investigation; risk factors
Document Type: Research Article
Affiliations: 1: Curry International Tuberculosis Center, Division of Pulmonary and Critical Care Medicine, University of California San Francisco, Zuckerberg San Francisco General Hospital and Trauma Center, San Francisco, California, USA 2: Curry International Tuberculosis Center, Division of Pulmonary and Critical Care Medicine, University of California San Francisco, Zuckerberg San Francisco General Hospital and Trauma Center, San Francisco, California, USA, Division of Pulmonary Medicine, Department of Internal Medicine, Chung-Ang University School of Medicine, Seoul, South Korea 3: Office of Equity and Quality Improvement, Population Health Division 4: Tuberculosis Control, San Francisco Department of Public Health, San Francisco, California 5: Qiagen, Medical and Scientific Affairs, Redwood City, California 6: Department of Epidemiology and Biostatistics, University of California, San Francisco, San Francisco, California, USA
Publication date: 01 April 2019
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