By Wilson Walker

SAN FRANCISCO (KPIX) — Bay Area hospitals’ intensive-care capacity — the key metric now being monitored by the state — hovered around 22 percent on Saturday. It had tumbled from 29% Wednesday to about 21% on Friday.

Two regions — the San Joaquin Valley and Southern California — have already passed below the 14 percent threshold, triggering stay-at-home orders. Five Bay Area counties took a preemptive move in that direction on Friday.

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Although the ICU metric is barely four days old, it’s becoming clearer how that number will behave and what a trend might look like.

“You know, it’s just the way it is, there’s going to be some wobble in the numbers, says UCSF epidemiologist George Rutherford. “What you want to see is the overall trend and follow that.”

From automobile accidents to people requiring major or emergency surgery, any number of things can drive the ebb and flow of ICU numbers on any given day. Coronavirus is just part of the demand on a system that has limits.

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“ICU space is not infinite,” Rutherford said. “If we were to absolutely stop transmission this morning — just stop it — we have three weeks of people in the pipeline headed toward ICUs.”

What we see in our hospitals today largely reflects transmission from two to three weeks ago. That means any holiday-driven surge would still be coming.

“We know that a lot of COVID transmission occurred over the Thanksgiving weekend,” said Santa Clara County health officer Dr. Sara Cody. “And while we can’t see that yet reflected in our numbers, we do have some really warning metrics that are telling us that that transmission did occur.”

Take the current surge plus whatever further surge is coming and match that against the effort to short-circuit those trends with a preemptive lockdown. It is a contest that will take time to play out.

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“It’s going to be a while until we can … clearly see trends,” Dr. Rutherford said. “We’ve had a lot of advice around Thanksgiving, we’ve had some acceleration post-Thanksgiving and we’re now entering a new phase of lockdown in five counties. There’s a lot of push-pull stuff going on and to see how it equilibrates is going to take a few days.”