COVID-19 Cases in California have Surged

COVID-19 case count has been increasing significantly in California in June (see figure below), but compared to some of the other hot states like Florida, Texas, and Arizona, its growth has roughly matched the growth in testing capacity and its positivity rate (percent of test results returning positive) has stayed below 7% unlike FL, TX, and AZ whose positivity rates are more than double this.  While hospitalizations have also increased in CA it has not approached full capacity as they have in TX.  Most importantly its death count has declined through May, and even with the recent outbreaks in June it has remained steady rather than surge along with cases.

Death counts usually lag confirmed case counts by 1-2 weeks but we remain optimistic that CA death counts will only increase modestly this summer.  The reasons are fivefold:

1.      Expanded testing has turned up milder and asymptomatic cases which while still contagious do not usually result in deaths.

2.      Expanded testing has skewed toward younger adults who have case fatality rates much lower than older adults (see figure below) and will lower the Case Fatality Rate (CFR = deaths/cases) for the state as a whole from 6% this spring to below 2% this summer.

3.      Earlier diagnosis and treatment could reduce hospital stay times and fatalities as drugs such as Remdesivir and Dexamethasone could be used to slow progression and allow the body’s natural defenses to help patients recover.  The availability of plasma from previously infected patients could also help. (From a forecasting perspective - slowing the progression would also increase the lag time and delay the upturn in death counts.) 

4.      Better treatment techniques such as proning (laying the patient on his stomach) delay or eliminate the need for ventilators which are difficult to wean patients off. 

5.      Government is responsive to changes in data and willing to do such things as mandate mask usage  and delay reopening when infections accelerate. 

Given all this, our forecast for CA is that death counts will edge up modestly in July to around 70 per day from its June average of 61 per day due to the June surge in cases.  CFR will stabilize below 2%, the ratio of the right axis for death counts to the left axis for case counts in the uppermost figure.  The CFR dependence on age will continue to show the steep exponential behavior (seen in many other countries around the globe such as Spain and South Korea) demonstrated in the lower figure with older people (>80yrs old) having a thousand times greater chance of dying from COVID-19 (27%) than younger people (<17yrs old).  Gender and existence of comorbidities will also affect CFR.  COVID-19 remains a difficult beast to tame so continued vigilance on the part of individuals, businesses, and governments is required to prevent new outbreaks.