Biggest Sero-survey of 16,450 tests show no Community Transmission in Bhutan yet

But two cases from outside the quarantine center in the last 48 hours now pose a challenge

The Ministry of Health from 30th July to 4th August conducted the largest Serological Survey of 16,450 Rapid Diagnostic Tests (RDT) focusing on the vulnerable populations along the southern borders and also the mobile population of taxi and truck drivers that moves to Thimphu and Paro, to look for any possible signs of community transmission.

The RDT Sero-survey tests not only look for active COVID-19 infections but also those who have antibodies that indicate that the person may have had COVID-19 and cured himself or herself without even knowing it.

Of all the 16,450 tests there was not even a single active COVID-19 case and only one woman in Phuentsholing town tested positive for Immunoglobin G (IgG) antibodies. IgG antibodies normally develops in the longer term after a person has fought off COVID-19 or SARS-CoV-2.

The woman, however, tested negative on the RT-PCR test twice with a gap of 24 hours which means she does not have an active infection and so cannot infect others.

All the first contacts of the person have been traced and have also all tested negative for both COVID-19 and any antibodies. The woman lives alone and does not have any travel history.

The head of the Royal Center for Diseases Control (RCDC) Dr Sonam Wangchuk said given the large number of tests this could also be a case of cross reactivity or the Kit confusing the antibodies of another virus for COVID-19.

He said epidemiological data like many others testing negative, first contacts testing negative, no travel history etc. are also pointers.

He said no Kit is perfect and given the large number of tests some anomaly can come up too.

In the Phuentsholing case two types of RDT test kits were used and both showed the lady had IgG.

However, the doctor said that to truly confirm if it is a case of cross reactivity or even a false positive a more accurate and reliable ELISA antibodies test would be run as soon as the sample reaches RCDC via an ambulance.

He said that normally Immunoglobin (IgM) antibodies develop first followed by IgG later but he said studies have shown them to develop together which may also be due to the inability to detect IgMs earlier.

The doctor in an earlier interview had said while RDT test kits have a sensitivity of 70 percent to pick up antibodies and 90 percent specificity to identify COVID-19 related antibodies, the ELISA test has a 90 percent sensitivity and 95 to 99 percent specificity.

Dr Sonam Wangchuk said that of the around 24,000 people living along the Indian border around 16,000 plus had been tested which is 55 percent of the population. He said this a huge sample size even for a Serological survey.

“We are absolutely convinced that there is no community transmission for now,” said Dr Sonam.

He said apart from the 16,450 tests there is already active mass surveillance going on across the country with suspected cases and their contacts being constantly tested.

The Health Minister Dechen Wangmo had earlier said that this is the largest Serological survey for Bhutan to get a feel of the virus. 

Of those tested 38.4% were from the urban community and 21.3% from rural community consisting of vulnerable border populations where two to three people were tested from every household.

 17.4% were frontline workers (RBP, RBA, Dessups, Immigration, Customs volunteers), 13.7% were from schools, 4.3% from factories and industries, 2.7 % of mobile population (truck, taxi and bus drivers) and 2% from hospitals (flu clinic and 10% of OPD patients on a specific date).

The test covered the 7 Dzongkhags in the south having a border with India plus taxis and public transport. Of the total population tested 5% were elderly and 3.5% had medical conditions.

The sero-survey comes in part due to the large number of cases across the border. Dr Sonam earlier said that given the either asymptomatic and or even mild symptoms in around 80 percent of COVID-19 cases people could have mistaken it for flu or other tropical diseases and would not have come to the hospital.

The survey was about going out among the community and testing the most vulnerable aggressively.

The sero-survey was conducted for mainly vulnerable populations living along the border in Samtse, Chukha, Dagana, Sarpang, Zhemgang, Pemagatshel and Samdrupjongkhar. It also included taxi and public transport drivers heading to Thimphu and Paro.

This is the second Sero-survey as one had been conducted along the south with only around 1,500 samples the result of which was announced in May 2020 with one shopkeeper having IgM antibodies.

Initially it was speculated to be a cross reactivity case but an ELISA test done two weeks later confirmed he had IgM.

So while the overwhelming data shows that Bhutan is free of active Community Transmission, the occasional blips, now matter how small, also show that people cannot take things for granted and must take precautions especially with India crossing two million cases and a growing number of cases right across the border.

A 27-year-old Gelephu woman testing positive outside the quarantine center and the resultant national lockdown , and the latest being a 25-year-old loader from Phuentsholing also testing positive outside the quarantine center will however shake the no-community transmission stand.

It will all depend now on what the final first contact tracing data now shows.

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