Delayed tuberculosis diagnosis and tuberculosis transmission

SETTING: Tuberculosis (TB) patients and their close contacts reported to the Maryland Department of Health and Mental Hygiene from 1 June 2000 to 30 November 2001. OBJECTIVES: A recent prospective study found that 49% of pulmonary TB patients had total treatment delays ≥90 days. This cohort was analyzed to determine the association between total treatment delay and TB transmission. DESIGN: TB patient data were collected as part of a prospective cohort study; contact data were collected from local health departments. RESULTS: Close contacts of 54 US-born patients (n = 310) and those of 70 foreign-born cases (n = 393) received tuberculin skin tests (TSTs). Among contacts of US-born patients with a total treatment delay of ≥90 days, 40% had positive TSTs vs. 24% contacts of patients with shorter delays (aOR 2.34; P = 0.03). Other patient factors associated with TST positivity among contacts of US-born cases were black race (aOR 3.03; P = 0.05), sputum smear positive for AFB (aOR 3.29; P = 0.01) and chest radiograph with cavitation (aOR 3.11; P = 0.01). No associations were observed between foreign-born patients and risk of TST positivity among their contacts. CONCLUSION: Among US-born patients, delay in TB diagnosis is associated with greater transmission of infection to contacts and could be used independently of other index patient factors to identify contacts at greatest risk of TB infection.