Dip in Mumbai’s asymptomatic casesUpdated: Apr 29, 2020 00:39 IST
After the Brihanmumbai Municipal Corporation (BMC) revised its guidelines for testing suspected Covid-19 cases in Mumbai on April 15, with a circular that directed all assistant commissioners not to collect samples from any person not showing Covid-19 symptoms such as cough or fever, the percentage of asymptomatic cases among those who have tested positive has gone down to 35% to 40%, as per data available for April 22. Until mid-April, the number of asymptomatic cases among those who tested positive ranged upto 70% to 80% of the total cases.
Through this change in approach, the percentage positivity (number of positive patients emerging from the total number of tests done) of the city increased to 6.7% on April 23, as opposed to 4.5% on April 15, according to the BMC.
On April 15, the BMC issued a circular as per Indian Council of Medical Research’s guidelines, directing all assistant commissioners (or ward officers) and lab incharge not to collect samples from persons not showing any symptoms.
This circular mandates that testing will only be done for symptomatic persons (who have cough, fever), symptomatic high-risk contacts of Covid-19 positive patients, people over 60 years of age who are high-risk contacts of Covid-19 positive patients whether they are showing symptoms or not, healthcare workers, pregnant women if they are risk contacts of patients, and patients on dialysis and chemotherapy. The circular barred any persons not showing symptoms from getting tested. Meanwhile asymptomatic high-risk contacts of positive patients can get if they develop symptoms, or after careful observation between 5 and 14 days of contact.
The civic body’s rationale was to effectively utilize its testing capacity. Until then, the percentage positivity in the city stood at 4.5%.
As of April 22, between 35% and 40% of the patients are asymptomatic, and between 40% to 45% of the patients are symptomatic.
On the other hand, the BMC scaled up its testing per day. The present average of tests per day rests at 2,200. According to the BMC, number of tests conducted per day increases by 3% daily. On April 17, the BMC conducted its maximum number of single-day tests, at 4200, as of data available on April 22.
According to the BMC data, upto March 31, Mumbai conducted an average of 300 tests per day. In the first week of April, this figure increased to 1,000+ tests a day, in the second week of April it increased to 2,000+ a day, and in the third week of April it increased 3,000+ tests a day. On April 1, BMC conducted 1100 tests per day; on April 7 it increased to 1700 tests per day; on April 8 it increased to 2200 tests per day; on April 15 it increased to 2700 tests per day; on April 16 it increased to 3100 tests per day; and on April 22 it increased to 3,700 per day. Approximately 4500 tests are being done in the city per million population of Mumbai.
A senior civic officer said, “With focused testing on those who really need it, we are getting better results. We decided not to screen asymptomatic risk contacts of positive patients too soon, to avoid a false negative. Doing a test within the first five days can lead to a negative result, as the virus can take up to 7 days from the day of contraction to show up in a test. They are kept under observation and quarantine.”
Daksha Shah, BMC’s deputy executive health officer, said “We are rigourously testing. We are testing high-risk contacts of positive patients, even if they are asymptomatic. According to ICMR guidelines, they are being tested between five and 14 days from the day of contact, for more accurate results. Once you are a positive patient, regardless of whether you are asymptomatic or symptomatic, your high-risk contacts and with comorbidity are tested between five and 14 days.”
Sanjay Pattiwar, independent public health consultant, said, “We have to rationalise and use our test resources judicially, as they are depleting. Our priority, or any government’s priority in cases of shortage of supply during such a health emergency should be safeguarding patients, patients’ contacts, health workers, symptomatic, and then asymptomatic, in that order. Asymptomatic patients have lower threat of transmitting the diseases, as they are not showing symptoms such as cough, cold. They have lower scope of throwing the virus out of their bodies. Besides with recent awareness of wearing masks, and personal hygiene, 90% chance of transmission of asymptomatic persons transmitting it is reduced. People now are sensitised, and are careful not to touch their face, or eyes when they go out.”