Risk for Tuberculosis Disease Among Contacts with Prior Positive Tuberculin Skin Test: A retrospective Cohort Study, New York City.

Background: Patients with prior positive tuberculin skin test (TST) results may benefit from prophylaxis after repeat exposure to infectious tuberculosis (TB).
Objective: To evaluate factors associated with active TB disease among persons with prior positive TST results named as contacts of persons with infectious TB.
Design: Population-based retrospective cohort study.
Participants: A total of 2,933 contacts with prior positive TST results recently exposed to infectious TB identified in New York City's TB registry during the period from January 1, 1997 through December 31, 2003.
Main Measurements: Contacts developing active TB disease ≤ 4 years after exposure were identified and compared with those who did not, using Poisson regression analysis. Genotyping was performed on selected Mycobacterium tuberculosis-positive isolates.
Key Results: Among contacts with prior positive TST results, 39 (1.3 %) developed active TB disease ≤ 4 years after exposure (≤ 2 years: 34). Risk factors for contacts that were independently associated with TB were age < 5 years (adjusted prevalence ratio [aPR] = 19.48; 95 % confidence interval [CI] = 7.15-53.09), household exposure (aPR = 2.60;CI = 1.30-5.21), exposure to infectious patients (i.e., cavities on chest radiograph, acid-fast bacilli on sputum smear; aPR = 1.9 3; CI = 1.01-3.71), and exposure to a U.S.-born index patient (aPR = 4.04; CI = 1.95-8.38). Receipt of more than 1 month of treatment for latent TB infection following the current contact investigation was found to be protective (aPR = 0.27; CI =  .08-0.93). Genotype results were concordant with the index patients among 14 of 15 contacts who developed active TB disease and had genotyping results available.
Conclusions: Concordant genotype results and a high proportion of contacts developing active TB disease within 2 years of exposure indicate that those with prior positive TST results likely developed active TB disease from recent rather than remote infection. Healthcare providers should consider prophylaxis for contacts with prior TB infection, especially young children and close contacts of TB patients (e.g., those with household exposure).