County officials encouraged Nevada County residents to do their part in reducing local COVID-19 transmission in a press release Wednesday, following the state’s determination the day before that Nevada County met the red — or substantial — risk tier criteria for the first time since November.

“The past year has been challenging and frustrating, but the science is very simple and settled — each one of us must remain vigilant, avoid gatherings, wear our masks, limit indoor activities with others, practice social distancing, and take all precautions to avoid spreading the virus,” read the release.

In order to shift to the red tier guidelines — from the most restrictive, current purple tier designation — Nevada County will have to stay within the tier’s positivity rate and daily case metrics for two consecutive weeks.

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Nevada County will learn Tuesday whether it met criteria for the red tier. If it did, the county will enter that tier March 30.

Nevada County Director of Public Health Jill Blake echoed this sentiment Wednesday in a Q&A.

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“We are hopeful that we will move to the red tier, because we hope that our cases will be low enough for us to do so, but that will take the effort of everyone to get there,” said Blake.

Blake also explained the state’s method for calculating the figures used in determining counties’ tiers within the Blueprint for a Safer Economy system.

Daily case counts as shown on the county’s Coronavirus Dashboard, said Blake, reflect the dates that cases are confirmed to the county through laboratory results.

“When (the state is) looking at the data and determining our average case count over a certain period of time, they are not using the date that we heard about it,” said Blake. “They are using what they refer to as an episode date.”

The “episode date,” Blake explained, refers to the earliest date the case can be tracked back to — potentially the onset of symptoms, or the date of testing — “to have the best sense of when disease transmission is occurring.”

“So, you can’t take our numbers and do simple math, and come up with a daily average that will match the state’s, because the state is doing something that is more sophisticated, it takes more time, and it really gives you a much clearer picture of when disease transmission is happening in our community,” said Blake.

Victoria Penate is a staff writer for The Union. She can be reached at vpenate@theunion.com.