Nationwide COVID spike has reached Fresno, central San Joaquin Valley. Cases double in week

The number of new COVID-19 cases reported in Fresno County last week was almost double what it was a week earlier, rising to its highest point in weeks.

The most recent update from the Fresno County Department of Public Health on Friday reflected 1,900 cases for the week, with no reports on Saturday, Sunday or Monday. That’s up from 989 in the week ending Dec. 25 – a 92% increase.

Last week also generated the largest number of new cases in the county since before Thanksgiving.

A similar trend occurred across the six counties of the central San Joaquin Valley. Throughout Fresno, Kings, Madera, Mariposa, Merced and Tulare counties, at least 3,651 cases were reported by local health departments, up from 2,027 cases a week earlier and by far the largest number of weekly cases since mid-November.

The increase in cases reflects an increase in the rate at which the virus is spreading in Fresno County and the Valley in recent weeks.

It also comes as local and state health officials continue to warn about the fast-spreading omicron variant of the coronavirus. Plus, the persistent and highly contagious delta variant for months has been the dominant strain of the virus both locally and nationwide.

Within a matter of weeks, the U.S. Centers for Disease Control estimates the proportion of new COVID-19 cases nationwide from the omicron variant climbed from less than 1% in the first week of December to nearly 60% by the week ending Dec. 25.

Still, the rate at which the virus is spreading among the population in Fresno County and neighboring counties is slower than it is statewide, as well as in more populous areas such as Contra Costa, Orange, Los Angeles and San Mateo counties.

Transmission rates climbing

Fully one-third of all new cases reported in Fresno County in the month of December came in the final week of the month — an increase that almost doubled the rate of new cases from a daily average of 13.8 per 100,000 residents on Dec. 1 to 26.3 on Dec. 31, and propelling the total number of people infected since March 2020 to almost 150,000.

Of those cases, 2,379 Fresno County residents have died from COVID-19, including 125 last month.

The rise in daily case rates aligns with an increase in what epidemiologists call the R-effective, or effective reproduction number – an estimate of the average number of people to whom a single infected individual can transmit the virus.

If the R-effective number is higher than 1.0, the number of infected people will increase, according to the state Department of Public Health. If it’s less than 1.0, the number of infected people will decline.

As recently as Dec. 16, the R-effective number for Fresno County was estimated at 0.99. Since that date, however, it has risen to as high as 1.29 last Friday – the highest it’s been since late July.

Statewide, the R-effective number was estimated at 1.78, suggesting that the spread of COVID-19 is “likely increasing rapidly,” according to the California Department of Public Health.

In some counties, however, the R-effective number is above 2.0 — meaning each infected person is expected to spread the virus to at least two other people. The highest rate as of Sunday was in Contra Costa County, at 2.29; followed by Orange County at 2.07, Los Angeles County at 2.03, and San Mateo County at 2.02.