When the state announced Oct. 6 that Humboldt County was going to be upgraded in California's tiered COVID-19 risk assessment, it was cause for celebration in many circles.

After all, the news means shopping centers can re-open common areas and restaurants can increase dine-in capacity to 50 percent, while movie theaters and gyms could similarly begin serving more people. The county's new "yellow" (Tier 4) status in the state's color-coded system also means museums and the local zoo can lift capacity limits entirely, while churches can begin filling up to 50 percent of their pews. Perhaps the biggest change is the new tier allows bars and breweries that don't serve meals to resume indoor operations, also at 50 percent capacity.

But health officials have been quick to caution that Humboldt County's margin for error is razor thin and even a small spike in local cases could thrust the county back into the state's more restrictive orange tier (Tier 3) or beyond.

"That can change with one large outbreak," Health Officer Teresa Frankovich said at a media availability the day after Humboldt's status change. "We really need everybody to stay on board with what they've been doing because it's working."

Frankovich is not wrong, as Humboldt County's COVID-19 case numbers have fallen sharply in recent weeks. While the county confirmed 85 new cases through the first two weeks of September, it had confirmed 22 over the first 13 days of October as the Journal went to press. But a careful combing of the numbers at play in the state formula also shows that Humboldt County's position is precarious and its change in status was only made possible by a new state "equity metric."

The state's four-tier risk structure dictating what can reopen where and when relies almost exclusively on two metrics: testing positivity rate and the average number of new cases confirmed daily per 100,000 residents. Both metrics are tracked over the course of a week to determine what category a county falls in. Yellow requires a county to see fewer than one new case daily per 100,000 residents with a test positivity rate of less than 2 percent. For orange, counties need to have an average of fewer than four daily cases per 100,000 residents and a test positivity rate below 5 percent. Red (Tier 2) requires counties to have fewer than seven daily new cases per 100,000 in population and a positivity rate of less than 8 percent. Counties seeing more than seven new cases daily per 100,000 residents or a positivity rate of 8 percent land in the purple tier (Tier 1), the state's most restrictive. Together, the two metrics are aimed at determining how overall caseloads are growing in a county and the degree to which the disease is being identified, as higher testing positivity rates are an indication that the virus may be moving undetected through a community.

Generally, a county can only be upgraded to a less restrictive tier if both its measures fall within that tier's thresholds for three consecutive weeks. But if a county's measures fall within those of a more restrictive tier for two consecutive weeks, its status is downgraded and additional restrictions put in place.

Since the state unveiled the new system in September, Humboldt County has spent much of its time in the upper reaches of the orange tier, mostly due to the rate at which it was confirming new cases. Frankovich has said the state gives some leeway to counties on the cusp, and it appears Humboldt County has benefited from that at times, as it had averages of 4.34 and 4.02 daily confirmed cases per 100,000 residents for consecutive seven-day periods in early September, but was never vaulted into the red tier, likely because the county's testing positivity rate — around 1.5 percent — has remained well below the state average. But the county was also simply nowhere close to falling into the yellow tier. That is, until the state released its equity metric just as local caseloads began trending sharply downward.

Designed to address the higher rates of disease and critical outcomes in minority communities, the state's equity metric attempts to tie a county's movement through the risk tiers to the spread of disease in its most at-risk populations.

To do that, the state is looking at the Health Place Index, which ranks census tracts under 14 health measures, giving them a score between 1 and 100 to measure their local health conditions, with 100 being more healthy and 1 less. The state's equity metric is complex and shifts based on what risk tier a county falls into, but basically requires that a county's "at risk" census tracts — those with an index score lower than 25 — don't lag measurably behind its overall numbers when looking at testing positivity rates.

In Humboldt County, the only two areas that fall into that at-risk category are Hoopa and the southeastern area of the county around Blocksburg. Testing has been made widely available in both areas, with a massive effort to test all Hoopa residents following a large outbreak there in early August and the county holding numerous testing days in Southern Humboldt using its OptumServe facility, which county officials have successfully mobilized despite its original intent to be a stationary site.

Because the test positivity rate was below 2 percent in those areas (likely because of proactive testing efforts), the state allowed Humboldt to move into the less restrictive yellow tier even though its daily average of confirmed new cases was two per 100,000 residents — double the state's threshold.

While that makes the county's newfound status seem precarious, there are some reasons for optimism. The state's tiered system operates on a two-week delay, meaning the tiers announced Oct. 6 were based on data from the week ending Sept. 26, which offers us a peek into the future.

Humboldt County's daily case averages dropped in the two seven-day periods following Sept. 26 — to 1.8 cases per 100,000 residents for the week ending Oct. 3 and 1.16 for the week ending Oct. 10. Through one lens, that makes Humboldt's status seem fairly secure for the coming weeks, as it would need to exceed the thresholds for two consecutive weeks before falling into a more restrictive category. But through another lens, that's all contingent on the exemption allowed by the equity metric, meaning a spike in testing positivity rates in either Hoopa or Southern Humboldt could change the county's status in a hurry.

Local health officials have taken a cautious tone when discussing the county's new yellow status, probably in large part because they realize that with a county of approximately 135,000 residents and a disease that can spread exponentially, things can change in a hurry and the actions of even a single household or business can have reverberating impacts.

After all, Frankovich has said Humboldt County's status would not have been lowered to yellow had it had a daily average of more than 2 new cases per 100,000 residents, which is exactly what it was averaging the week ending Sept. 26. If that's accurate, just one additional case confirmed that week would have caused Humboldt's bars to remain closed. For context, last month the county traced 30 cases over the span of a couple weeks back to a single social gathering in Southern Humboldt.

During her recent media availability, Frankovich conceded this puts some business owners in a difficult position, having to make staffing and hiring decisions without knowing at what capacity they'll be able to operate just a couple of weeks down the road, if they're still allowed to operate at all.

"I'm certainly aware of concerns about investing in inventory and infrastructure and additional staffing and all those pieces that may go along with adding, for instance, indoor operations to an outdoor operation, and I do think that business owners need to really put some thought into ... with our margin [for error] so small," she said. "If we were sitting well below two on our case rate, I'd feel more confident but ... it does not take much to push us above that number."