Antibody tests show few positive results
More than 1,000 people in Bermuda have taken a test to find out if they have antibodies to the novel coronavirus, with less than 3 per cent getting a positive result.
The Ministry of Health said yesterday the low figure was consistent with Bermuda having local transmission of Covid-19, with clusters of cases, as opposed to more serious community transmission.
A spokeswoman told The Royal Gazette: “As we do not have community transmission, we are expecting our numbers to be much less.
“The exact number expected is unknown, but in comparison to the United Kingdom — which is estimated at 17 per cent [for London] — the figures we are observing are consistent with ‘local transmission, clusters of cases’.”
She added: “The presence of antibodies tells us nothing about immunity. It is still unknown if having antibodies means one is protected from getting reinfected again. The figures speak to exposure, not immunity.”
Michael Ashton, Chief of Medicine at the Bermuda Hospitals Board and an infectious diseases specialist, told a press conference last week the implications of the antibody tests were still to be determined.
He said: “I think that most of these tests now, as long as they have gone through a vetting process and a validation process, can likely say whether a person has been exposed to the virus, but in terms of the immune response, that is unclear at this point.”
Dr Ashton added: “There is value in doing epidemiologic studies and what that will allow us to do is understand the prevalence of a disease on the island and help our physicians further interpret the PCR tests and any further tests based on prevalence that’s measured.”
As of last Thursday, 1,103 finger prick rapid antibody tests had been administered to the “General Bermuda population” according to the ministry.
The lateral flow immunoassay test kits show the presence in those tested of IgM and IgG antibodies, both common immune system antibodies that signal the body fighting off the coronavirus infection.
David Burt, the Premier, told Parliament on Friday the sensitivity of the test was 87.9 per cent for IgM and 97.2 per cent for IgG.
For a test with 87.9 per cent sensitivity, 12.1 per cent of negative results would be expected to be false.
Mr Burt said the specificity of the test, which indicates the likely number of false positives, was 100 per cent.
The Premier said the tests were supplied by Healgen Scientific LLC in the United States.
The antibody tests can be taken for free at the Government Drive-Through Testing Facility at Southside, along with the polymerase chain reaction tests, which look for active infections.
The Ministry of Health spokeswoman said: “To date, 2.9 per cent of the general population have tested positive for either antibody.”
She added in an e-mailed response: “So far, it has been gathered that some of these persons include: previous PCR positives, spouses of known positives who tested PCR negative, close contacts of known positives who tested PCR negative, suspected positives who were not tested due to the strict World Health Organisation guidelines and limited testing supplies at the start of our outbreak, and those in known international outbreaks [cruise ships].
“The status of the rest are still under investigation.”
The spokeswoman said in addition to the 1,103 people in the general population, antibody tests were also done on 81 people in quarantine, who flew into Bermuda from Britain. Results for that group were not provided.
Experts in the United States have questioned whether the coronavirus antibody tests on the market deliver accurate results.
The Ministry of Health said another antibody test available on the island was the enzyme-linked immunosorbent assay test used for detecting or quantifying antibodies.
Details of where that test was being administered and results so far were not provided.
Dr Ashton told the press conference that the King Edward VII Memorial Hospital was outsourcing antibody tests to the local Helix lab.
He said the hospital was also doing a specialised test for the convalescent plasma treatment, which may be used on severely ill Covid-19 patients in the future.
Mr Burt told the House of Assembly the antibody test at Southside was approved by the Australian Ministry of Health’s Therapeutic Goods Administration.
The ministry spokeswoman said Bermuda was using a comprehensive list from the WHO of international regulatory bodies.
“As this pandemic is global, we look to the global list,” she said.
Finger prick test: the story so far
The Government started offering an optional finger prick antibody test for Covid-19 at its Southside testing facility on May 9.
David Burt, the Premier, said the free test was being introduced, in addition to the PCR test that looks for active infection, to “determine the reach of this virus in our community”.
The Government said the individual antibody test results “will not be provided at this time”, but that “in due course, the physicians of individuals who have elected to take the antibody test will be informed whether or not they have Covid-19 antibodies present in their bodies”.
Members of the public who had the test done in the first few days contacted The Royal Gazette querying why they were not being given the results.
On May 16, Carika Weldon, the doctor who runs the government facility, tweeted that approval had been given to release the test results, with positives going to doctors and negatives to be e-mailed directly to those tested.
A Ministry of Health spokeswoman said last Tuesday that those who took the test should get their results within about 48 hours.
She added yesterday: “Everyone tested from May 9 onward has received their antibody results now.
“Initially results were not given in the first week as the way in which results were to be conveyed was still being finalised.
“Measures were taken to prevent misinterpretation of results. Once this was done, all results were released with a very clear statement on what the results may mean.
“Also note, only negative results are e-mailed. Positive results are seen by the GP on their portal on the system and they contact patients.”
• Tests at Southside can be booked at https://bdagovcovid.resqwest.com
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