Case Update: April 13th

Originally posted April 13th, 2020, on Facebook


I have another good news/bad news post for you today. First the good news. Yesterday, 8pm on April 12th, the rate of new infections for the world, the US, California, and San Diego County, were all below 5%! Our efforts are paying off!

Some of you may wonder if this is a Sunday Effect, a lowering of new case numbers just because it’s a Sunday, and there may fewer people performing tests that day. While it’s certainly true that there have been fewer new cases on Sunday, I noticed that in past weeks, a Sunday drop has often been followed by a lower rate for the entire next week. Last week for example, the rate was below 10% on Sunday, a big drop, but remained low for the entire next week. If this trend holds, then we may have rates near 5% for the entire next week.

The bad news isn’t really new, but rather a new study of the Basic Reproductive Number (R0). This number is a measure of infectiousness and is an attempt to calculate the average number of people that an infected person will pass the virus to. For a typical flu, this number is 1.28. For the first SARS virus in 2002, it was around 3. As recently revealed in a pre-publication paper [Sanche et al. High Contagiousness and Rapid Spread of Severe Acute Respiratory Syndrome Coronavirus 2. July 2020, pre-print captured April 13th, 2020. Em. Inf. Dis. 6(7)], the actual R0 value is 5.7, twice as high as originally thought, and 4.5 times more infectious than the typical flu.

Early on, there was a lot of discussion on whether this virus was spread by droplet transmission (coughing and sneezing) or by aerosol transmission (singing, laughing, shouting, even just talking). The new paper, along with several stories in the news, suggests that SARS-2 is indeed spread at least to some degree by aerosol transmission.

So here’s the take away from this post. We are doing better, but we’ll have to be very careful how we “go back to normal”. The virus has the potential of springing back to life if we just go back to normal right away. If people are to go back to work anytime in the next few weeks, we will need to remain diligent, yes, possibly wearing masks at work, and do wider spread testing to find infected people. Stay tuned on this evolving situation!

Don’t fear, but be smart!

PS Pre-published journal articles have not yet received final approval and may change before publication!

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