Is tuberculosis more contagious than Covid-19?

The Ministry of Health (MOH) announced on June 24 that about 170 people at 2 Jalan Bukit Merah tested positive for tuberculosis (TB). The tests were offered to residents and workers at the block after seven people there were diagnosed with the disease between February 2021 and March this year.

The Straits Times answers some of your questions about the disease.

Q: What is TB and how does it spread?

A: TB is an infectious disease caused by a bacteria called Mycobacterium tuberculosis. The air-borne disease spreads when an infected person coughs, sneezes or breathes, and a person nearby inhales the expelled infected droplets in the air.

Transmission of TB often requires close and prolonged contact with an infected individual. TB does not spread via contact with items or surfaces touched by an infected person - unlike Covid-19.

People living in the same household and close workplace colleagues are at a higher risk of being exposed to TB and getting infected.

Q: What are the types of TB?

A: There are two types - latent and active.

For some people, the body's immune system naturally kills the TB bacteria when it enters the body and they are unaffected.

In others, the immune system might be unable to kill the bacteria but is able to prevent it from spreading in the body. This is known as latent TB, where the bacteria is suppressed but "asleep" in the body.

Those with latent TB are not ill, will not have any symptoms and are not infectious to others.

However, latent TB can later become active TB when immunity wanes - with the United States Centres for Disease Control and Prevention (CDC) estimating that, without treatment, 5-10 per cent of infected people will develop active TB at some point in their lives.

Active TB is when the body fails to kill or contain the bacteria, making the person ill. An individual with active TB will have symptoms and can potentially spread the disease to others.

About half of the people who develop active TB will do so within the first two to three years of being infected.

Q: What are some of the symptoms of active TB?

A: Symptoms include a persistent cough that lasts three weeks or longer - which might include coughing up phlegm or blood, low-grade fever, night sweats, fatigue, weight loss and chest pain.

Q: Does TB affect only the lungs?

A: While it primarily affects the lungs - what is known as pulmonary TB - it can also affect other parts of the body like the central nervous system, bones, joints and the abdomen. This is referred to as extra-pulmonary TB.

Q: What is the TB screening process?

A: Those with close and prolonged contact with an infectious person - usually family members and close workplace colleagues - may be called in to undergo blood tests and possibly a chest X-ray.

Q: What is the incidence rate for TB?

A: According to a 2021 World Health Organisation report, about a quarter of the global population has been infected by Mycobacterium tuberculosis, although only a relatively small proportion will develop active TB during their lifetime.

According to MOH, TB infections are not uncommon in Singapore, with the prevalence among those aged 70 to 79 being as high as 29 per cent.

There were 1,306 new cases of active TB among Singapore residents in 2021.

In 2020, the number was 1,360.

The probability of developing active TB is higher among people with underlying medical conditions like diabetes, as well as those with weakened immune systems due to age, among other factors.

Q: How serious is active TB?

A: Active TB is potentially fatal without treatment, with an estimated 1.5 million people dying from it globally in 2020.

However, with treatment, it is highly curable and death is rare.

Q: What is the treatment for TB?

A: Treatment usually involves taking a combination of antibiotics for six to nine months. MOH states on its website that more than 95 per cent of people with active TB are cured if they take all the medications as prescribed until completion.

It is crucial to complete the course of antibiotics as prescribed, even if symptoms improve, failing which there is a higher chance of a relapse and a greater possibility of TB becoming resistant to first-line anti-TB drugs.

Drug-resistant TB is more difficult to treat, as less-effective drugs will then need to be used, likely prolonging the course of treatment and considerably decreasing the chances of being cured.

Multi-drug resistant TB has fatality rates as high 30-40 per cent.

Those with latent TB infections might also be started on a course of preventive treatment to prevent the development of active TB disease in the future.

Q: What should those with active TB do to prevent the disease from spreading?

A: Those with active TB become non-infectious after two weeks of treatment. While infectious, they should stay at home to prevent infecting others. In the presence of other members of the household, they should wear a face mask and cover their mouth with a tissue when they cough or sneeze.

Those who display symptoms like a prolonged cough should seek medical attention early.

Q: Is there a vaccine against TB?

A: The Bacillus Calmette-Guerin vaccine is primarily used against TB.

In Singapore, it is part of the National Childhood Immunisation Schedule and given to all children at birth.

While it protects against other forms of TB like TB meningitis, which affects the brain lining, it offers limited protection against pulmonary TB.