BACKGROUND: Data on the impact of incomplete contact investigation on TB incidence among healthcare professionals (HCPs) after TB exposure are limited.METHODS: This was a prospective cohort study with 2-year follow-up among Thai HCPs exposed to TB to determine TB incidences and factors associated with TB development.RESULTS: Of the 398 HCPs with TB exposure, 367 (92%) participated in the study; 342 HCPs were included in the final analysis; 311 participated in contact investigations; 303 underwent chest X-ray; 252 completed baseline TB and latent TB infection screening using tuberculin skin test (TST); 210 had negative baseline TST; and 45 completed follow-up tests at 3 months. Altogether, 20 HCPs developed TB (2.92/100 person-years). TB incidences in HCPs not participating in or not completing the investigation at any step were higher than in those who completed the evaluation (11.29 and 2.90, respectively, vs. 0/100 person-years; P < 0.05). No participation in contact investigation and no baseline chest X-ray were independent factors associated with TB development (adjusted odds ratio [aOR] 6.7; P < 0.001 and aOR 8.9; P = 0.01, respectively).CONCLUSION: Study findings indicate increased risks of TB development among HCPs not undergoing or not completing contact investigations and underscore the need for interventions to improve contact investigation participation and completeness.