Background: Although large clinical trials reported in 1960s suggested that preventive therapy in subjects with tuberculosis (TB) infection reduces the risk of developing TB by 70-90%, the therapy in our TB clinic seems to be more effectiveness.

Objective: We retrospectively evaluated the efficacy of the present contacts investigation, especially of preventive therapy for further improvement of TB control for children.

Methods: We examined 273 asymptomatic infants and children younger than five years who had household contacts with active TB patients and visited our clinic for contact investigation. After the diagnosis at the first visit to our TB clinic, they were treated and/or observed for at least two years to assess whether contact investigations and following treatment are appropriate. Since infants less than a year are underdeveloped in cell-mediated immunity and their tuberculous lymphadenopathy can be overlooked on standard chest radiographs, chest CT scans were added.

Results: At their first visit, 60 (22%) out of 273 subjects were diagnosed as TB, and 37 (14%) were suspected as TB. We treated them by combinations of anti-TB medicines including isoniazid and rifampin for six to 12 months, and they did not relapse during the observation period. Twenty-six subjects (9%) were diagnosed uninfected. However, a three-year-old girl developed bilateral hilar lymphadenopathy two months later when the reexamination was done. A hundred and fifty subjects (55%) were diagnosed to have TB infection. They received preventive therapy with isoniazid (10 mg/kg/day) for six months. Among them, a four-month-old boy developed TB disease soon after starting to take isoniazid and was treated by the combination of anti-TB medicines. Other 149 subjects completed the therapy, and none of them developed disease during the observation period. There was no increase in serum GOT and/or GPT to > 100 IU/L within one month after starting to take isoniazid.

Conclusion: The present contacts investigations and treatments in our TB clinic are useful ways to find out and control TB diseases and infections, and it might be suggested to start the six-months preventive therapy after active TB has been ruled out in all infants and children who had close contacts with active TB patients for preventing TB disease and latent TB infection in the future even their clinical and laboratory examinations do not suggest infection.