Two more people are feared to have contracted tuberculosis in an Ang Mo Kio block where six drug-resistant cases have already been identified.
The Ministry of Health (MOH) said yesterday that the two suspected active cases, which are potentially infectious, are currently "being followed up for treatment, monitoring, and contact tracing".
The ministry will also carry out DNA tests to see if they are related to the cluster of six cases, although "this may take some time".
In what it described as a "highly unusual occurrence", six people in Block 203, Ang Mo Kio Avenue 3, were diagnosed with the same strain of multi-drug-resistant TB over a four-year period.
The four households involved said they did not know each other and had not interacted. The disease typically requires "close and prolonged contact" to spread.
The discovery triggered a four- day precautionary screening exercise at the foot of the block to pick up undiagnosed cases. This ended on June 19, though a second round of house visits to encourage more people to get tested was held last Saturday. During the visits, MOH officers offered to collect blood samples to make testing more convenient for residents.
A total of 223 residents and former residents were tested in the first round. An estimated 350 people live in the block.
In addition to the two new suspected cases, another 45 people were found to potentially have a latent form of the disease. This means that they have no symptoms and cannot spread TB.
Tests also picked up three people who previously had TB, but had already completed treatment. These were not related to the drug-resistant cluster, MOH said. The ministry is following up with nine people who completed only part of the screening, which involves both an X-ray and a blood test.
MOH added yesterday that those who may have latent TB have been advised to monitor themselves for symptoms. Tan Tock Seng Hospital's TB Control Unit will check up on them every six months for the next two years.
"Treatment may be offered on a case-by-case basis after assessment by the TB Control Unit," it said, adding that four people in this group have started treatment.
Latent TB is not uncommon among Singaporeans. It affects only 2 per cent of people aged 18 to 29, but nearly 30 per cent of those aged between 70 and 79.
MOH said the baseline prevalence of TB in the affected block is expected to be up to 23 per cent, after considering factors such as its demographic profile. "The rate of latent TB among those who were screened on-site... is about 22 per cent, within the upper end of the expected baseline prevalence range."
Screening results from another 12 people who got their tests done at Sata CommHealth clinics, as well as those who were screened last Saturday, are still pending.
MORE IN TOP OF THE NEWS