Magnitude of Mycobacterium tuberculosis transmission among household and non-household contacts of TB patients

• Published in: The international journal of tuberculosis and lung disease Vol. 23; no. 4; pp. 433 - 440
• Main Authors: Kato-Maeda, M., Choi, J. C., Jarlsberg, L. G., Grinsdale, J. A., Higashi, J., Kawamura, L. M., Osmond, D. H., Hopewell, P. C.
• Format: Journal Article
• Language: English
• Published: France International Union Against Tuberculosis and Lung Disease 01.04.2019; International Union against Tuberculosis and Lung Disease (IUATLD)
• Subjects: Adult; Age Factors; Aged; Bacilli; Cohort Studies; Contact Investigation; Contact Tracing; Female; Health risks; Households; Humans; Infections; Male; Middle Aged; Mycobacterium tuberculosis; Mycobacterium tuberculosis - isolation & purification; Patients; Risk analysis; Risk Factors; San Francisco - epidemiology; Sputum; Sputum - microbiology; Tuberculosis; Tuberculosis, Pulmonary - diagnosis; Tuberculosis, Pulmonary - epidemiology; Tuberculosis, Pulmonary - transmission; San Francisco
• ISSN: 1027-3719; 1815-7920
• DOI: 10.5588/ijtld.18.0273

SETTING: The household and non-household contacts of patients with tuberculosis (TB) face varying degrees of risk of infection by Mycobacterium tuberculosis.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.