The Ministry of Health (MOH) will offer voluntary Tuberculosis (TB) screening to residents and former residents of Block 174D Hougang Avenue 1. This is a precautionary measure following the detection of a cluster of four individuals diagnosed with TB[1] residing in four different units at the block. Screening will be conducted free of charge, at the Tuberculosis Control Unit (TBCU) located at Moulmein Road from 26 October onwards.
2. Officers from the TBCU and the National Centre for Infectious Diseases (NCID) will be conducting house visits to all units at Block 174D Hougang Avenue 1 between 25 and 27 October, to engage affected residents and encourage them to go for the screening. Residents will be able to make appointments for TB screening at TBCU during the house visits. Residents who are not at home at the time of the visit can call the TBCU to make an appointment for screening. Former residents who had lived in the block from February 2020, and wish to be screened, may call the TBCU hotline at 6248 4430.
Identification of TB cluster
3. MOH was notified on 10 October 2020 of four TB cases involving residents of the same HDB block at 174D Hougang Avenue 1, who were diagnosed between January 2018 to June 2020. All four individuals live in different units of Block 174D. The cases had immediately started on treatment following diagnosis. Amongst them, two have completed treatment, while the remaining two are currently undergoing treatment and are no longer infectious. As individuals diagnosed with TB will rapidly become non-infectious once treatment starts, the cases are not an ongoing public health risk.
4. In line with MOH’s TB prevention strategy, the Singapore TB Elimination Programme (STEP) had initiated contact investigations upon notification of the four cases. Close contacts of the cases had already been identified and contacted by STEP for screening. Investigations for each of four cases at the time of their diagnosis did not identify each other as close contacts.
5. The cluster was subsequently determined due to the results of the genetic sequencing performed in October 2020 as part of retrospective testing of TB cases to determine possible linkages. This revealed that all four cases have similar genetic make-up. Investigations into the cases did not reveal any common links, other than that they live in the same block. They did not know or interact with one another, or congregate at the same common areas, and had also not identified each other as close contacts. The TB cluster therefore does not fit the usual pattern of TB spread.
6. TB is typically spread through close and prolonged contact with an infectious individual, and not by contact with items or surfaces touched by a person with TB. Therefore, persons who are contacted and screened following the detection of a TB individual typically comprise family members, close workplace colleagues and acquaintances from common social activities with close and regular interaction. This approach is recommended by the World Health Organization (WHO) and is practised in Singapore.
Precautionary TB Screening beyond close contacts
7. The expanded TB screening offered by MOH is a precautionary measure to assure and protect residents living in the same block. The exercise could help detect any undiagnosed TB cases. While screening is not compulsory, MOH strongly encourages residents to be screened. Those with positive screening results will be offered appropriate advice and follow-up. Those with active TB will be treated immediately while those with latent non-infectious TB will be monitored and treated if necessary.
8. The risk of transmission to persons who are not close contacts of a TB case is very low. Screening is thus not necessary for individuals who had occasionally visited the block or vicinity.
Health Advisory
9. TB is endemic in Singapore and latent TB infection is not uncommon in our population, as TB had been prevalent in Singapore until the 1970s and older Singaporeans could have been exposed to TB and acquired latent TB infection when they were younger. Persons with latent TB do not experience symptoms of TB and are not infectious.
10. TB is curable and the spread of TB is preventable. Early detection and prompt treatment of cases remain important in helping those infected and rendering them non-infectious. For individuals diagnosed with active TB, adherence to treatment is important.
[1] TB can be cured with anti-TB drugs. Treatment of active TB, which is sensitive to first-line anti TB drugs, usually involves a combination of different drugs, taken for six to nine months.