Isoniazid Prevention Reduced TB Disease Risk in Household Contacts

A longitudinal cohort study published in Clinical Infectious Diseases found that isoniazid preventive therapy (IPT) was not associated with reduced tuberculin skin test (TST) conversion among household contacts younger than 5 years. IPT initiation was associated with a lower risk of progression to tuberculosis (TB) disease among household contacts of all ages.

Investigators enrolled adults with microbiologically confirmed pulmonary TB and their household contacts in Lima, Peru. Contacts underwent TST at baseline and 6 months and clinical evaluation for TB disease. For children younger than 5 years, new infection was defined as a ≥6-mm increase in TST induration between assessments. Disease progression in contacts of all ages included diagnoses made 15 days to 12 months after enrollment.

The TST-conversion analysis included 666 children younger than 5 years, of whom 361 (54.2%) initiated IPT. At 6 months, 103 children (15.5%) had converted. IPT initiation was not associated with conversion after adjustment (adjusted odds ratio [OR], 1.01; P=.97).

Cavitary disease in index participants was associated with increased conversion risk. Among 14,032 household contacts of all ages, IPT initiation was associated with reduced progression to TB disease (adjusted hazard ratio [HR], 0.45; 95% CI, 0.32-0.64). The association was more pronounced among children younger than 5 years (adjusted HR, 0.19; 95% CI, 0.10-0.36).

The investigators concluded that IPT was not associated with reduced TST conversion among children younger than 5 years but was strongly associated with reduced progression to TB disease across household contacts of all ages. The study separately evaluated acquisition of infection as measured by TST conversion and progression to diagnosed TB disease.

Source: Zazueta OE, Becerra MC, Galea JT, et al. The impact of isoniazid preventive therapy on tuberculosis infection and disease progression. Clin Infect Dis. Published online August 17, 2026. doi:10.1093/cid/ciag483