Tuberculosis (TB) presents itself in two forms, latent TB and active TB.
Dr Jim Teo, a respiratory and ICU physician at Nobel Chest and Internal Medicine Centre at Mount Alvernia Hospital and Gleneagles Medical Centre, said that one-third of the world's population have latent TB.
"This is when the TB germs are in the lungs, but...the symptoms don't show," he said.
A person with latent TB has a 10 per cent chance of it developing into the active form.
This is when the symptoms - which include chronic coughing, blood in the phlegm, fever, tiredness and night sweats - will start to show.
Active TB can be detected by a chest X-ray or a phlegm test.
Dr Teo said: "Most people get their active TB diagnosed too late, which is not good as they may already have infected other people.
"Early diagnosis is very important because active tuberculosis is very contagious."
Treatment for active TB consists of four different drugs for six to nine months. In more serious cases, the patient has to be hospitalised.
Dr Teo advised anyone who has been coughing for more than four weeks, or has blood in their phlegm, to consult their doctor immediately.
Latent TB which is typically what people are infected with, is much harder to diagnose because there are no symptoms.
It is diagnosed either through a skin test - called a Mantoux test - or a blood test.
Dr Teo advised anyone who has been in contact with a TB patient in the past to have themselves checked for latent TB immediately.
This article was first published on July 29, 2011, in The New Paper.