It is difficult to set tuberculosis (TB) control targets in Singapore, as a significant number of older people have latent TB infections, said Senior Parliamentary Secretary for Health Amrin Amin yesterday.

But he added that in the long term, Singapore's goal is to benchmark itself against high-income countries with TB rates of fewer than 20 cases per 100,000 people.

"Due to previous exposure, where TB rates were quite high in the 1950s and 1960s, there is now a fairly significant number of older Singaporeans with latent TB infections," Mr Amrin said.

"Waning immunity in older adults also contributes to reactivation of this latent TB later on in life, hence it is quite hard to set a firm target to achieve TB control."

There were between 37 and 41 cases of TB for every 100,000 people here in the past five years. Last year, nearly half of those who developed active TB were aged 60 and older.

Latent TB is estimated to affect between 2 per cent and 29 per cent of Singaporeans. Someone with a latent infection has no symptoms, does not feel sick and cannot spread TB to others. But one in 10 eventually develops an active form of TB.

Responding to a question on multi-drug resistant TB (MDR-TB), Mr Amrin said patients with MDR-TB are isolated for treatment until they become non-infectious, which takes about two months.

They have to undergo directly observed treatment, which involves taking medication in the presence of a nurse, for two years.

"We have also adopted new technologies such as rapid DNA tests for drug resistance, reducing time taken for identification of MDR-TB from two months to a few hours to facilitate early intervention," he said.