Ketchikan’s locally-reported pandemic alert level ticked up a tier on Wednesday. The change is from “low” to “moderate” — the second-lowest of four levels. The increase in risk follows public health officials announcing they’ve been unable to determine the origin of at least four of the past week’s COVID-19 cases. That’s an indication that the virus is moving through town — or in clinical parlance, “community spread.”

That’s concerning for public health authorities, as it means there are carriers spreading the illness and likely unaware they’re doing it.

The change in risk level doesn’t add any restrictions to Ketchikan’s daily life. But officials ask residents to ensure they’re paying special attention to pandemic precautions like hand-washing, social distancing and wearing a mask in public

Three additional community spread cases before Monday could lead officials to raise the risk level to “high.” That would prompt schools to shut down some classroom sessions and move part of the school day online. If one or fewer cases of undetermined origin develop by next Wednesday the level could return to the lowest risk. There are other factors involved.

Local authorities announced three new cases of COVID-19 on Thursday. One of those is travel-related, officials say, and the source of the remaining two cases is under investigation.

State health officials, on the other hand, use a three-tier system, and southern Southeast Alaska’s state alert level remains low. That region, which includes Ketchikan, Metlakatla, Prince of Wales Island and Hyder, is the only low-risk area in the state, according to data from the Department of Health and Social Services.

COVID-19 is spreading rapidly in much of the state. The Kenai Peninsula and Mat-Su Boroughs are seeing the fastest spread, state health officials said Wednesday. Case numbers remain high in Anchorage and Fairbanks, as well.