SINGAPORE - The threat of latent tuberculosis (TB), where people unknowingly carry an inactive form of the disease in their bodies, remains in Singapore and is a reason why new TB cases crop up among the older generation here.

Of the 1,536 new cases reported among Singapore residents in 2017, two in three were 50 years old and above, said the Health Ministry today (March 23) in an update on the TB situation here. Most of the new cases were males, and includes some children as well.

To nip the problem in the bud, hospitals such as National University Hospital (NUH) have been stepping up efforts to treat more patients before they become infectious.

TB is is an air-borne disease that usually affects the lungs, and can also affect other body parts like the brain, lymph nodes, kidneys and bones. It can be eliminated by taking medication for six to nine months.

While most people exposed to the TB bacteria do not become infected, those who do will develop latent TB which is not infectious. But as they grow older, or when their immunity weakens, the dormant bacteria becomes active, and they become infectious and suffer symptoms, which include a persistent cough, fever and chest pain.

Up to 30 per cent of older residents in Singapore have latent TB. This is because TB had been prevalent in Singapore until the 1970s, said MOH.

Even so, instances of TB infection continue to be in the public eye today. In 2016, it was reported that several people living in a block of flats in Ang Mo Kio had been diagnosed with a resistant form of TB, prompting MOH to offer free screening for the block's residents. In the same year, at least one pre-school student was diagnosed with latent TB, after a trainee teacher at the Bridges Montessori preschool in Punggol tested positive for the disease.

At NUH, efforts have been made in recent years to identify pockets of patients who have weakened immune systems to undergo a routine latent TB screening.

They include those undergoing bone marrow and liver transplants, as well as those about to take drugs for different types of arthritis such as rheumatoid arthritis.

The screening, which began more than five years ago, was extended to patients with the human immunodeficiency virus (HIV) in August last year (2017), after a study by the hospital found that TB could have been prevented in up to 40 per cent of cases by sending these people for screening.

"Preventive therapy given for latent TB would significantly decrease the progression to active TB, which can be fatal and cause strokes and significant morbidity," said Dr Catherine Ong, a consultant at NUH's division of infectious diseases.

"In addition, only one medicine, compared to four, is taken without the need for directly observed therapy (for latent TB). This translates to lower costs, and less chance of drug adverse events."

Around one-fifth of the 300 HIV patients at the hospital have been screened, when previously none had, said Dr Ong. Singaporean patients pay a subsidised $100 for the blood tests to check for latent TB. The tests normally cost $255 without subsidies.

HIV patient Mark Tan, 37, (not his real name) feels "really thankful" that his latent TB was flagged and treated after a routine screening in December last year.

"I was surprised that I have latent TB as I thought it was extinct. All I knew was TB is contagious and causes death," said Mr Tan, who is undergoing a nine-month treatment.

Although the 1,536 new cases in 2017 was slightly lower than the 1,617 cases reported in the previous year, the emergence of multi-drug resistant TB remains "a serious public health challenge", said MOH. This is where the disease becomes resistant to the two most powerful anti-TB drugs, and arises because of interrupted treatment or the incorrect use of antimicrobial drugs.

Last year, there were six such cases, including two Singapore-born residents. The ministry noted that "support and encouragement" from others is vital in ensuring TB patients complete their treatment.

Such support is being provided at Tan Tock Seng Hospital's (TTSH) TB Control Unit, where volunteers have been bringing cheer to seriously ill TB patients for the last two years. Every week, three to five volunteers play musical instruments, tell stories, exercise, garden or play board games with 10-odd patients for more than an hour.

These warded patients are of lower socio-economic status and have very little family and social support during their six- to nine-month stay, said Dr Cynthia Chee, director of the TB Control Unit. "Having people come to visit them will go a long way in their treatment journey."