Surge, What Surge?

The growing consensus I have heard from patients is that we are having a COVID-19 surge in Los Angeles and, given such, they are wondering what additional precautions need to be taken. I was somewhat surprised to hear that we were experiencing an increase in cases in the County, as this has not been seen in our practice case numbers. Whereas November 2022 we say 29 cases, case rates here at Santa Monica Primary Care have been a slow drumbeat since March. 6 cases in March, 7 in April, 4 in May, 5 in June, 6 in June and only 2 thus far in the first 10 days of August.

But turning to headlines, I can see why a surge is of concern.  Yesterday the Los Angeles Times headline blared “COVID-19 is heating up all around’ this summer. Should we be wearing masks again?” (link:  According to Dr. Peter Chin-Hong, a UC San Francisco infectious diseases expert, said transmission is increasing and “we haven’t seen the crest yet” of the wave.

Now I understand that my small slice of the medical universe is not necessarily generalizable, but generally with a communicative patient population I’m aware when case burdens increase – whether it be flu, RSV, or COVID.  

Reading further into the Los Angeles Time’s coverage, state Epidemiologist Dr. Erica Pan noted that California’s test positivity rates have gone up in the last two to three weeks, “and I’m sure many of you are anecdotally both hearing about friends and family and colleagues … about some more circulating COVID,” Pan said. “Thankfully, our hospitalizations are looking very reassuring so far.”

Those who have followed my blog posts in the past will remember that test positivity rates are an inaccurate and problematic metric as it depends on the denominator of who is being tested. Few go to public health labs or obtain reportable PCR tests any more; rather most COVID cases are identified through home testing which are not reportable to public health agencies.

When diving into Los Angeles County Data, Dr. Pan is indeed correct that test positivity rates have increased, but not just over the past 2 to 3 weeks but rather over the past 2 to 3 months. Test positivity rates were as low as 2.9% in early May and have climbed to 7.9% in the last week in July (Figure 1 below).

Left unmentioned by the Los Angeles Times and Dr. Pan is the sharp decrease in testing itself (the denominator of test positivity). Only 45 Daily tests per 100,000 population are currently being reported to the County (Figure 2 below). For reference, at the height of the January 2022 surge there were 2,744 reportable tests being performed daily per 100,000 population. As numbers become smaller, the accuracy of a reported metric becomes less accurate.

To account for this statistical noise, we turn to prevalence rate which is the estimated number of active (not necessarily infectious) cases per 100 individuals. Currently, the County’s prevalence rate stands at 0.22 or, expressed differently, 22 cases per 10000 individuals. While this is an uptick compared to the rate seen in early May (9 cases per 10000 individuals), it is far lower than the late February rate of 60 cases per 10000 individuals (Figure 3 below).

It is important to note that mid to late summer surges have been a feature of COVID-19 in years past, most notably in 2022 when prevalence rates indeed surged to an estimated 9.7% of the population having the infection.  Placing this summer in perspective – the green line in Figure 4 below suggests that we are having an unexpected lull in cases, certainly when compared to prior years.

This is not to suggest that cases will not increase moving forward. In 2021 (red line), cases increased significantly through late July and peaked mid-August. However, at this point in time, there does not seem to be evidence of increased community transmission nor a particularly significant population burden of disease, particularly when compared to prior years.