title: Risk of tuberculosis among contacts of isoniazid-resistant and isoniazid-susceptible cases.
abstract: OBJECTIVE
  To compare the risk to household contacts of isoniazid (INH) susceptible and INH-resistant cases of tuberculosis (TB) in a rural community in South India.
  
  
  METHODS
  In all, 5562 contacts of INH-susceptible and 779 contacts of INH-resistant patients and 246,845 persons with no TB case in the home were followed for 15 years, with surveys every 2.5 years comprising radiographic and sputum examination, selective follow-up of high-risk individuals and passive surveillance. If a new case developed, the household members were assigned to the 'INH-susceptible' (n = 7088) or 'INH-resistant' series (n = 526), whichever appropriate. Logistic regression and Cox's proportional hazards model were employed.
  
  
  RESULTS
  The baseline prevalence of tuberculous infection was respectively 70% and 56% in contacts of INH-resistant and INH-susceptible patients (P < 0.001), compared to 46% in non-contacts. The incidence of culture-positive TB was respectively 295 and 311 per 100,000, compared to 162/100,000 in non-contacts. The adjusted hazard ratios were 2.4 and 2.0 for contacts of INH-resistant and INH-susceptible patients.
  
  
  CONCLUSIONS
  The baseline prevalence of tuberculous infection was substantially higher in contacts of INH-resistant than INH-susceptible patients, but the incidence of tuberculous disease over a 15-year follow-up was similar in the two series, and twice as high as in non-contacts.
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000995:Antitubercular Agents / Q000494:pharmacology* / Q000627:therapeutic use; D002675:Child, Preschool; D016358:Contact Tracing; D004311:Double-Blind Method; D004352:Drug Resistance, Microbial; D005260:Female; D006801:Humans; D007194:India / Q000453:epidemiology; D007223:Infant; D007231:Infant, Newborn; D007538:Isoniazid / Q000494:pharmacology* / Q000627:therapeutic use; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000302:isolation & purification; D012307:Risk Factors; D012424:Rural Population; D017678:Sex Distribution; D013183:Sputum / Q000382:microbiology; D014376:Tuberculosis / Q000175:diagnosis / Q000188:drug therapy* / Q000453:epidemiology / Q000635:transmission*; D032581:Tuberculosis Vaccines / Q000008:administration & dosage; D055815:Young Adult
chemical_list: D000995:Antitubercular Agents; D032581:Tuberculosis Vaccines; D007538:Isoniazid