This will be Bhutan’s biggest Serological surveillance looking for COVID-19 antibodies
The Health Minister Dechen Wangmo said that the Ministry of Health, starting from 30th July to 4th August is conducting more than 10,000 COVID-19 tests using Rapid Test Kits or Rapid Diagnostic Test (RDT).
Lyonpo said that this will be the largest Serological surveillance or survey for Bhutan to get a feel of the virus. The total numbers could go up to or around 15,000.
The test kit will be testing for antibodies but the difference with a Sero-survey is that it will not just look for active COVID-19 cases, but also look at detecting antibodies in ones who may have had COVID-19 and recovered without even knowing it.
The head of the Royal Center for Diseases Control (RCDC) Dr Sonam Wangchuk said that the Sero-survey will be focusing mainly on vulnerable communities in the southern border which basically means communities and families who live right along the border.
These will cover the border regions of the seven districts of Samtse, Chukha (Phuentsholing), Dagana,Sarpang, Zhemgang, Pemagatshel and Samdrupjongkhar.
He said that in addition to the above, tests will also be done in Thimphu and Paro given the high population in these two places and also the high level of movement in and out of these areas.
The focus in the Thimphu and Paro tests will be on the mobile community which are taxi and bus drivers to start with.
RSTA, as of now, has already identified around 500 taxi drivers who will be tested as part of the sero-survey.
Dr Sonam pointed out that a large portion of COVID-19 cases are asymptomatic and there are people who may cross the border and bring in the virus without even knowing it.
He pointed out that a challenge for the survey will be the fact that Bhutan does not have a local positivity rate which is the number of people testing positive out of every 100 being tested.
Dr Sonam said that as per the testing criteria frontline health workers would be tested though they undergo regular tests, then health workers in these places would be tested and then two people from every household in the vulnerable communities would be tested. People with co-morbidity conditions in these places would also be tested.
Others to be tested are frontline workers like Dessups, BAFRA, RBP, RBA, Immigration, Customs, Bank Money Changers, loaders and other volunteers.
On a specific date all people coming to the flu clinic and 10 percent all regular OPD attendants are to be tested.
Similarly again on a specific date 20 percent of a school population will be tested and 20 percent of people in industries will be tested (see image).
The doctor pointed out that the aim of the sero- surveillance will be to detect any silent community transmission especially of an asymptomatic nature. He said so far one would only know about cases if a COVID-19 positive person visited a health center but around 80 percent of COVID-19 cases are either mild or asymptomatic.
He said the monsoon season is the flu season and people may even mistake it with the common flu or any other normal tropical diseases.
He also pointed out that with the monsoon in spate and rivers swelling up people may not even visit the local health centers, and the same hostile conditions will also pose a challenge for those doing the surveillance.
The aim is to finish the test within one week and then announce the results later together.
He said that the survey would look at how many probable cases are detected. He said that 10,000 is just an initial estimate and the actual numbers of tests would exceed it.
Dr Karma said that one major factor behind the survey is the increasing number of cases across the border. He said that the tests this time are not only larger in number but it is also more aggressive in terms of going out among the communities to test.
The Rapid Test Kits or RDT will check for antibodies through blood and once they are found then the RT-PCR test will be done as a confirmatory test by taking mouth and nasal samples to check for any active confirmed infection.
Dr Sonam, however, also pointed out the RDT test limitations. He said the RDT test kit sensitivity is around 70 percent though the claims are of it being higher which means that it would detect antibodies in 70 out of 100 people.
International studies show that RDT may not be able to detect antibodies in an early stage of COVID-19 infection as adequate antibodies are not formed or it may not be able to pick it up after a period of recovery.
He said the specificity for these kits are 90 percent which means that accuracy of detecting the type of antibodies which in this case is for COVID-19.
This means it would be 90 percent right in identifying the type of antibodies with only 10 percent errors where cross-reactivity or confusion with antibodies for other types of Corona viruses and other viruses come into play.
Revisiting the first sero-surveillance and the Jomotsangkha case
Though large in number, this is not the first sero-surveillance as one had been done earlier in May 2020 along the southern belt where around 1,500 people were tested using RDT.
At the time, a shopkeeper from Jomotsangkha tested positive for COVID-19 virus antibodies and the whole area was put under a lockdown. The RDT test was repeated six times and each time he came out positive.
The Health Minister, in a press conference, on 8th May announced that the shopkeeper had tested positive for Immunoglobulin M (IgM) antibodies which develops specifically as a reaction by the body to fight COVID-19 and this meant he had been exposed at some time to the virus.
Since he had no travel history the minister at the time pointed out that the source of his infection may have been from the community.
The person tested negative on the RT-PCR test for COVID-19 which meant that he did not have an active infection and could not infect others.
At the time there were some from the government who said in a media outlet that the positive test for antibodies by the RDT was due to a possible cross reactivity with another corona virus or even the common flu. Questions were also raised on the accuracy of the RDT test kit itself.
What seems to have informed this sense of strong and loud denial at the time both in the government and sections of the media was the fact that others in the community did not test positive, he tested negative in the RT-PCR for an active COVID-19 infection, the person had not travelled out and neighboring Assam at the time had not officially reported many cases.
The person was kept in quarantine till 20th May for a period of 21 days and tested again on 21st May where he tested negative for the IgM and also the longer term IgG antibodies.
It now emerges that the RDT was not the only test done at the time to check for IgM antibodies. As multiple RDT tests showed him to be positive a sample was sent to RCDC Thimphu around two weeks later to do a more accurate ELISA test for the IgM antibodies to help rule out cross reactivity. A variation of this ELISA test is also used to detect HIV.
The RCDC had to procure this new ELISA test for COVID-19 antibodies which had a sensitivity of 90 to 95 percent and more importantly a specificity of 95 to 99 percent. This means it would be more accurate than the RDT.
Dr Sonam said that even this much more specific ELISA test showed that the shopkeeper did have COVID-19 specific antibodies which is IgM.
This information was not announced at the time by the government.
This test and finding now challenges the cross-reactivity theory put forth by some in the government in a media outlet.
The Doctor said that there are test kit limitations, but when it comes positive in the ELISA test then the Jomotsangkha case was put as a ‘probable case’ who could have been ‘potentially exposed’.
The doctor, said that at the time looking at it epidemiologically there were not many official cases saying, “although India was reporting very few cases we know that there were already a lot of cases spreading across the community.”
He said epidemiologically it was not that much of risk then but now the risk is higher due to the large number of cases in India.
The doctor said that while the shopkeeper did not have a travel history the question is if he had close contact with somebody either with somebody coming to him or if he picked it up at a gathering.
Situation across the border
India on 4th August saw 52,050 cases taking the total to 18,55,745 cases and 803 deaths taking the death toll to 38,938 deaths. Of this 586,298 are active cases with 12,30,509 recoveries.
West Bengal saw 2,716 new cases on the same day with a total of 78,232 cases and 53 deaths with a total of 1,731 deaths.
Assam saw 2,371 new cases with a total of 45,275 cases and four new deaths taking the death tally to 109.
Arunachal Pradesh has 1,758 cases and 3 deaths and Sikkim has 688 cases with one death.
All adjoining districts of the above states with Bhutan have active and growing COVID-19 cases.
However, a serological survey in Delhi recently showed that 23.48 percent of the people had been exposed to COVID-19 as they had developed antibodies. It also showed a large number of people had remained asymptomatic.
A sero-survey in Mumbai showed that 57 percent of slum residents and 16 percent of non-slum residents had developed COVID-19 antibodies.
The sero-survey in Delhi and Mumbai shows that the actual number of infected cases are far higher then what are being found in tests.