SINGAPORE: Other laboratories are not using the same COVID-19 test kit and analytical instrument combination as a lab that had 33 “false positive” cases, the Ministry of Health (MOH) said.
Thirty-three previously confirmed COVID-19 cases, including a radiographer who worked at the Singapore Expo community care facility, had turned out to be negative cases upon retesting by the National Public Health Laboratory.
This was due to an “apparatus calibration issue” for one of the test kits used between May 5 and May 9, MOH said on Wednesday (May 13) in response to CNA’s queries.
“MOH has since reviewed the test results of the affected batches, and there were no false-negative results discovered from the review,” the health ministry added.
READ: COVID-19: 33 cases found to be 'false positives', including healthcare worker at Singapore Expo community care facility
None of the 12 other laboratories that are conducting COVID-19 tests are using the same test kit and analytical instrument combination, MOH told CNA.
“The laboratory has switched to another test kit that has been proven to work on the analytical instrument,” the health ministry said.
The 33 cases had been isolated after they were "assumed have COVID-19", and will be “further tested as necessary”, MOH added.
A large majority of COVID-19 tests in Singapore are conducted by the National Public Health Laboratory and public acute hospitals, supported by various private laboratories, the ministry noted.
“MOH regularly audits the test results of these laboratories. Laboratory test results are also checked against the patients’ clinical signs and symptoms,” it said.
The health ministry also reported on Sunday that two people from the public healthcare sector who worked at the Singapore Expo community care facility - Cases 18669 and 19360 - had "equivocal" results.
Their results were also sent to the National Public Health Laboratory for retesting, and they came back negative.
MOH told CNA that equivocal results “occur from time to time”.
“Laboratories also have a workflow for verifying equivocal results, including repeat testing with another comparable test kit, if available, and requesting for a new sample to be collected,” the ministry explained.
“If the issue cannot be resolved at their end, the samples are sent to the National Public Health Laboratory for confirmation.”
As a precautionary measure, public health measures, such as contact tracing, may be introduced for cases with equivocal results while pending verification, MOH said. These patients will also be isolated.
TESTING CAPACITY LOWERED
Singapore had to lower its COVID-19 testing capacity due to the issue at the laboratory that resulted in 33 false positive cases, MOH’s director of medical services Kenneth Mak said on Tuesday.
Authorities are giving the lab time to properly recalibrate and revalidate its test kits as well as work through its "quality assurance processes", Assoc Prof Mak added.
“We lowered our testing capacity accordingly to give them some space to work through these processes. We anticipate that this should complete, very quickly, and we should be able subsequently to return back to our current full test capacity. This may take place over the next few days,” he said.
Singapore was conducting between 7,500 and 7,600 COVID-19 tests a day before the issue at the laboratory was detected.
"The results that came out from that particular set of tests done were not interpreted correctly," he added.
“There were also some steps that had not been completed followed through. If those steps had been completely followed through, we might have perhaps picked some of these results a little bit earlier.
"We're working with the laboratory to complete this quality assurance process."
To avoid having incorrect results in future, MOH has put together advisories and guidance for all the laboratories involved in testing.
These advisories describe standard processes that they have to conduct to ensure that tests are performed correctly and that accurate tests are produced, said Assoc Prof Mak.