Q What is the difference between latent and active tuberculosis infections?

A People with active TB infections often have a persistent cough that can last three weeks or more, as well as symptoms such as a low- grade fever or chest pain. When they cough, they can spread the disease to other people.

However, those with latent TB infections have no symptoms and do not feel sick. They cannot infect others with TB. In fact, nine in 10 people with healthy immune systems may be infected by TB bacteria but never know it, as they will never develop the active disease.

Q What are the chances of latent TB infections becoming active?

A Among those with latent TB infections, nine in 10 will not develop an active disease.

Of the remainder, about half will develop an active disease within two years. The other half will develop it at some other point in their lives, after the two-year mark.

Q Why is multi-drug-resistant TB such a concern?

A As the name implies, drug-resistant TB does not respond to the first line of drugs most commonly used to fight the bacteria.

These resistant strains often arise when people do not complete their treatment, allowing the remaining TB germs to grow and mutate.

Those with normal strains of active TB can be cured with six to nine months of treatment, but treatment for those with the drug-resistant varieties lasts 20 to 24 months.

Q Is TB a major problem here?

A The incidence of TB among Singaporeans and permanent residents last year was 38.4 per 100,000 - the second lowest in Asia after Japan.

There were 1,498 new cases reported among residents last year, less than 1 per cent of which were multi-drug-resistant.

The World Health Organisation classifies Singapore as a country with a "moderate" TB burden.