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CMAAO Coronavirus Facts and Myth Buster 116: Prediction Formulas |
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CMAAO Coronavirus Facts and Myth Buster 116: Prediction Formulas
Dr KK Aggarwal,  04 June 2020
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(With inputs from Dr Monica Vasudev)

936: Round Table Expert Zoom Meeting on “Formulas in relation to COVID-19 pandemic for better understanding of data”

30th May, 2020; 11am-12pm

Participants: Dr KK Aggarwal; Dr Alex Thomas; Dr AK Agarwal; Dr DR Rai; Dr Suneela Garg; Dr Girdhar Gyani; Dr Ashok Gupta; Dr Jayakrishnan Alapet; Mr Bejon Misra; Dr K Kalra; Mrs Upasana Arora; Dr Major Prachi Garg; Ms Ira Gupta; Dr Sanchita Sharma

  • It has been seen that 1% of symptomatic cases die.
  • Expected number of symptomatic cases: Number of deaths x 100 will give the expected number of symptomatic cases in society on that day. For instance, if the number of deaths is 400. So, by this definition, the approximate number of cases should be 40,000.
  • Corrected death rate: Currently, the death rate is calculated as number of deaths today vs. number of cases today. Instead, it should be number of deaths today vs. number of cases 14 days back. The corrected death rate is 5.76%.
  • Doubling time: The doubling time in India is 14 days, Russia 20 days, Brazil 13 days, whereas the doubling time is longer in other countries (USA 36 days, UK 37 days, Spain 40 days, Italy 57 days, France 52, Germany 55 days). If social distancing is not maintained, numbers in India are going to be very high. India will be in top 6 in one week.
  • China conducted 6.5 million tests for coronavirus, where 6 new cases were detected two weeks ago; 200 cases were found, mostly people who showed no symptoms. The ratio of undocumented cases for each documented case in Wuhan is 1:33, i.e., there were 33 asymptomatic cases for every one new infection. This is a reliable study as the total population was tested and not a sample population.
  • In a study from New York City, this ratio is 1:10, i.e., there were 10 asymptomatic patients, for every positive patient. New York conducted an antibody testing study, while Wuhan did antigen test. The reliability of antibody test is unknown. There are smaller studies from Iceland (1:2), Germany (1:5), California (1:5).
  • According to CDC, the mortality is less than 0.3% as we are missing asymptomatic cases.
  • As RTPCR is 67% specific, add 30% in government figures of number of cases; more the number, less will be the mortality.
  • People who are brought in dead are declared as COVID-negative; COVID is not reported as the primary cause of death; therefore, these cases may not be counted.
  • To get the actual number of deaths, multiply the government figures by 2.
  • Deaths per million population: US 316, Spain 580, World 47.1, India 4. While this number for India may seem very good, we must not compare country to country. We must compare epicenter to epicenter. Mortality in China is very high, if only Wuhan is taken, but if you add rest of China, the mortality becomes very low.
  • Herd immunity threshold (HIT): It is calculated as R0-1 divided by R0 (R0 or R naught is reproduction number).

o   If R0 is 3, then 66% of population would need to get infected to develop herd immunity

o   If R0 is 2, then 50% of population would need to get infected to develop herd immunity.

o   If R0 is 1.5, then 33% of population would need to get infected to develop herd immunity.

o   If R0 is 1.4, then 28.5% of population would need to get infected to develop herd immunity.

o   If R0 is 3.5, then 71.5% of population would need to get infected to develop herd immunity.

In New York, infection stopped when 23% of the population had the infection. Their R value was 1.3. The HIT was 23%.

So, the day we cross 20% of cases, we will see regression of infection with no new cases in the community. First to do this will be Delhi or Maharashtra, next will be Tamil Nadu and West Bengal.

Scenarios

  • If no measures are taken (such as lockdown, social distancing, or any other), the disease continues to spread; R0 is 2.66.
  • In moderate lockdown, transmission is reduced (R0) to 2 during the lockdown, transmission resumes at R0 of 2.4 after the lockdown; a surge in post-lockdown period is expected.
  • Hard lockdown: R0 is reduced to 1.5 during lockdown, then transmission resumes at R0 of 2.4.
  • Hard lockdown + continue social distancing/isolating symptomatic cases: R0 is reduced to 1.5 during lockdown, then we can continue at R0 of 2 through social distancing and isolation.
  • Families rather than individuals are now being affected. During lockdown, the message that went out was to stay at home and wear a mask when going out. This message needs to be changed. People who go out and come back to their house should continue to wear a mask; else one person will infect the entire family. Social distancing at home is as important as social distancing in office or outside at other places.
  • Every death should be audited to find out if these deaths could have been prevented.
  • The virus has different presentations in different patients.

o   It is a viral disorder and is self-limiting in 90% patients. Antivirals should be given within 48 hours.

o   The virus behaves like HIV in some patients; if lymphopenia or reduced CD4 cell count, give anti-HIV drugs.

o   It produces hyperimmune inflammation, so if there are signs of hyperinflammation such as high ESR, CRP and ferritin, anti-inflammatory drugs such as HCQ, indomethacin become important.

o   It behaves like bacteria, so azithromycin can be given; azithromycin may cause cardiotoxicity, so doxycycline may be given, which also covers atypical bacteria.

o   It produces thrombo-inflammation; fibrinogen and D-dimer levels are raised; such patients have moderate/severe illness. Give anticoagulant – heparin, nafamostat.

o   It produces silent hypoxia; oxygen supplementation with high flow nasal cannula, BiPAP (if required) and ventilator (only 1%).

o   Cytokine storm and ARDS: this is terminal illness and managed as per protocol for ARDS.

  • The fear and stigma around a dead body (Covid) needs to be removed. Once a body is cleaned as per protocol and wrapped, it is not infected. There is no risk of spread of infection and so no need for PPE for cremations.
  • The minimum space requirement for working in office, according to WHO, is 100 sq ft per person. In India, the standard is 75 sq ft per person for living.
  • A patient who came to the clinic in the morning and tests positive in the evening, answer the following question:

o   Was the patient wearing a mask? If yes, then ask,

o   Was the doctor wearing a mask? If yes, then ask,

o   Was the surface decontaminated in the morning? If yes, then ask,

o   What was the contact time? If less than 30 min: Monitor; If more than 30min: Quarantine

  • Best protection guidelines for doctors as well as patients should be displayed in each clinic.

Dr KK Aggarwal

President CMAAO

 

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