16 May 2020 Blog Post: An Update on COVID-19 in Riverside County

Last week, you may remember, Riverside County officials voted unanimously to rescind all of the county’s stay-at-home orders as well as face mask requirements.

On May 9th, 2020: Riverside County reported 4,817 COVID-19 cases (199 per 100,000 population) and 204 deaths (8.4 per 100,000 population).

As of today, Riverside County reported 5,618 COVID-19 cases (227 per 100,000 population) and 242 deaths (9.8 per 100,000 population).

I began to aggregate the data from Riverside County as, no doubt, coronavirus cases and deaths will begin to increase in the coming weeks. This was not an easy task as the County Public Health Department does not publish these data it in a downloadable file so I needed to tabulate it by hand. Undeterred, I have been able to demonstrate the protective effect of state-wide shelter-in-place orders. When looking at graphs of both incident cases (Figure 1) and deaths (Figure 2), each show a clear graphical uptrend until mid to late April, when these level off (mortality) or noticeably decrease (cases).

[Statistical note here – to smooth the observations, rates are reported as weekly aggregates of the prior 7 days, expressed in a moving average. This is to account for known human variation in reporting – for instance, case reports drop precipitously on Saturday and Sunday with spikes on Monday. In Medicine we call this the parking lot effect. Your quality of care at a hospital relates directly to the number of cars in the parking lot – a scary topic for another time.]

We expect a lag time between any public health intervention (e.g. closing borders, case quarantine, social distancing) and case burden. This is because coronavirus has an incubation period between infection and the development of disease. There is a further delay until these symptoms come to the attention of a healthcare professional. Add to that the additional waiting for confirmatory test results. Studies from China have suggested that it can be up to a month before the effectiveness of a COVID-19 intervention can be visible. For mortality rates, this could be even longer.

Given that California shelter-in-place orders went into effect on 3/23/2020, the data from Riverside County about a month later show a drop in new cases from 6.12 per 100,000 population on 4/21/2020 to 4.97 on 4/29/2020. Incident case rates have continued to decrease. Mortality rates have remained flat at 0.25 for the last three weeks – while they haven’t increased, they have not declined either.

It is a shame that Riverside County could not even wait until death rates began to drop before deciding to rescind the public health measures that were keeping them safe. Hopefully the individual residents of the County are smarter and more cautious than their political and public health leadership. Time (and graphs) will tell.

𝗦𝗶𝗴𝗻 𝗨𝗽 𝗳𝗼𝗿 𝗢𝘂𝗿 𝗡𝗲𝘄𝘀𝗹𝗲𝘁𝘁𝗲𝗿

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