Lack of symptoms, patients’ reticence hinder TB detection

SINGAPORE — Tuberculosis (TB) is difficult to detect and trace as it has a long incubation period and symptoms are not always apparent, while patients are sometimes unwilling to reveal who they have been in contact with, said doctors TODAY spoke to.

Dr Leong Hoe Nam, an infectious diseases specialist at Mount Elizabeth Novena Specialist Centre, noted that the long incubation period means that the disease can be contracted and remain dormant in the body until immunity levels fall.

That person could have contracted it during his travels and not realise it, he added.

Likewise, a person with active TB might not display typical “cough-sick symptoms” such as fever, or a loss of appetite and weight. “Because of that, (they) do not realise (they) are infected with tuberculosis”, said Dr Leong.

On Wednesday, the Ministry of Health revealed that a cluster of six multi-drug-resistant TB patients had emerged in one public housing block in Ang Mo Kio, with the first case dating back to 2012. How it spread to three patients who had no prolonged contact with the first three patients has yet to be determined.

Dr Ong Kian Chung, a respiratory specialist at Mount Elizabeth Hospital, said that latent TB will not display any symptoms, making it harder to detect. These cases can only be diagnosed through blood or skin tests.

Even some active TB cases do not show symptoms such as coughing, as a patient’s immune system might keep the TB under control.

A person exposed to the TB bacteria from an infectious patient may develop latent TB infection. For the vast majority of people, this means the bacteria will remain inactive in their body. One in 10 will develop active TB, and among this group, half will develop it within the first two years of acquiring the infection.

In the process of tracing the spread of the disease, some patients may only recall people they have met recently, while others may not be comfortable with sharing private information, said Dr Leong.

Calling TB an “evasive bacteria”, Dr Leong said he was not surprised to learn about the Ang Mo Kio cluster, although it was uncommon for the authorities to conduct genetic fingerprinting of the particular TB strain as the routine practice is to conduct contact screening.

Dr Ong added that the cluster in Ang Mo Kio was particularly unusual because there are very few cases of such drug-resistant strains in Singapore.