456 test positive for Covid-19 on first day of new rapid antigen tests
Officially, the city added 2,877 new cases on Thursday, according to the government’s daily health bulletin, that showed that there had been 65 new fatalities.Updated: Jun 19, 2020, 03:45 IST
Four hundred and fifty-six people were found infected with the coronavirus disease (Covid-19) in the national capital in a new testing programme involving quick-result kits across containment zones, where 7,040 samples were collected on Thursday.
The tests were carried out through new “antigen” test devices that can be used on-site, and Thursday’s rapid sampling numbers are close to the 8,700-odd RT-PCR tests carried out by labs across the city on Wednesday, underscoring how such kits can ultimately speed up the test-trace-isolate process that health experts across the world see as crucial to containing the pandemic.
Officially, the city added 2,877 new cases on Thursday, according to the government’s daily health bulletin, that showed that there had been 65 new fatalities. The new infections came from 8,729 RT-PCR tests, resulting in a confirmation rate of 3.3%. The results from the antigen test results were not included in the bulletin.
Rapid antigen testing was done at 193 centres in Delhi on Thursday. A total of 7,040 people were tested of whom 456 tested positive for the infection. At the beginning, those people are being tested whose houses are in the containment zones,” tweeted acting health minister Manish Sisodia on Thursday.
The new programme is part of the Union and state government’s effort to ramp up the number of tests in Delhi by six times by the end of this week.
The city administration has asked district teams to test those who live in the 242 containment zones in Delhi and are willing to be tested. The new test, developed by a South Korean company and manufactured in Manesar, is highly specific (99.3% to 100%) -- meaning a positive result on the test is a “true positive” and does not need any confirmatory test.
The sensitivity is between 50.6% to 84% depending on the viral load, meaning those who test negative might still have the infection and are advised to go for a test through the more reliable RT-PCR method if they show symptoms of the disease.
The tests began on a day the government announced that lab tests will be capped at Rs 2,400, a day after it was suggested by a committee formed by the Union government.
“Two important decisions have been taken in connection with Covid-19 testing in Delhi: The rate for testing has been reduced to Rs 2,400 and from today, rapid antigen testing has begun by which results will be available in 15 minutes,” said chief minister Arvind Kejriwal in a tweet, adding that he hoped the decisions will address problems faced by the people.
Apart from being quicker than lab-based RT-PCR tests, antigen tests are cheaper – one kit costs Rs 450 – and differ in technology as they look for specific protein associated with the Sars-Cov-2 virus, the pathogen that causes Covid-19. The lab tests look for the exact nucleic signatures of the virus.
A third mechanism that can give quick results is the antibody test that checks for the presence of disease-fighting antibodies in a person’s blood, but these have proven to be unreliable and scientists are not sure when and for how long the antibodies can be detected.
When antibody tests were rolled out on April 21, only 62 people were tested in one district on the first day. The test was discontinued from the following day after several states reported wide variation in results from the China-sourced kits.
“This is certainly a good way of ramping up testing – these tests are cheaper and faster. And at the community level, the test will enable us to identify more cases of Covid-19, they can then be asked to remain in isolation at home preventing further spread of the infection,” said Dr Jugal Kishore, head of the department of community medicine at Safdarjung hospital.
“The test is not very sensitive, meaning it can give false negative reports. If it’s a false positive, all we would be doing is keeping more people in isolation. Since there is a chance of false negatives with this test, it will have to be reconfirmed. Having said that, the sensitivity of the RT-PCR test is also about 67% and not very different from this test,” he added.
On Thursday, people in containment zones began reaching the testing facilities – set up mostly in neighbourhood government schools, dispensaries and mohalla clinics – where they were seated at 1m distance before they were administered the test.
At the Sarvodaya Kanya Vidyalaya in Naraina in west Delhi, around 50 people gathered after community volunteers reached out and persuaded people living in a nearby containment area to come to get diagnosed.
Four people in a full-body suit in an air-conditioned room called people one by one. One paramedic collected naso-pharyngeal swabs, before a second one took it and inserted into a tube. This process is meant to inactivate the virus, and dissolve it in a solution that was then put on the main test strip that would give the final result.
A third person numbered the antigen kits with a permanent marker and wrote down the name of the tested person along with the kit number on another sheet. The fourth entered this data to an online portal.
“There were teething troubles on Thursday, with a lot of the time being wasted on setting up the centres. It will be streamlined in a couple of days,” said a district-level health official, asking not to be named.
“The antigen testing is very beneficial for district teams as we get a result immediately and ask people to remain in quarantine if they have the infection. This prevents further spread. It also ensures that people who do need to be admitted to hospitals, reach there in a timely manner,” this person added.
Apart from the containment zones, the antigen tests are likely to be rolled out in Delhi’s hospitals within a couple of days. In a hospital setting, the ICMR recommends the test be used for those who develop influenza-like symptoms, are immune-compromised because of an existing condition, or are undergoing procedures such as chemotherapy and dialysis.
“We have already ordered the tests and should get it within a couple of days. Once that happens, we will start testing patients who fit the ICMR criteria with the antigen kits. Those who test negative will be tested using RT-PCR. In the absence of the antigen test, we would have had to test all the people using RT-PCR, which is time and resource-intensive,” said Dr DK Sharma, medical superintendent of AIIMS.