The COVID-19 transmission risk has increased from “moderate” to “high” in the four communities involved in the Contact Tracing Collaborative, which consists of Greenfield, Deerfield, Montague and Sunderland.

The collaborative is reporting seven active cluster infections (of three or more people at one site) and case incidence has increased by 67% over last week’s figures. Both data points contributed to public health officials’ recommendation to raise the alert status to red, marking a high transmission risk in the community for the first time in months.

Additionally, copies of the virus per liter of wastewater also increased over last week’s statistics, as did the positivity rate. Average daily hospitalizations, however, decreased from 2.25 to 1.

“One thing we’re noticing that is really strange … is there’s a lot of people that have never had COVID before and they’re getting it for the first time now,” said Public Health Nurse Megan Tudryn.

Tudryn emphasized the importance of masking to limit spread. She added that people need to remember to stay home for five days after a positive test and to mask for an additional five days afterward.

“I started wearing a mask again when I went to the grocery store,” she said. “I think if you don’t want to get sick and be out of work … you may want to consider wearing a mask because the spread is definitely high.”

In combination with wastewater testing, the four municipalities factor in hospitalization numbers, positivity rates and case numbers to determine COVID-19 risk levels.

The following three zones, defined by the Contact Tracing Collaborative, are used to gauge risk levels of COVID-19 transmission in the four communities. For the risk level in the area to change, at least two measures need to apply.

Red zone: High COVID-19 risk

Masking recommended.

■Cluster infections (of three or more people at one site): five or more.

■Percent positive tests out of total tests performed: greater than 10%.

■Hospitalizations: five or more.

■Increase in case trend.

■Increase in wastewater trend.

Yellow zone: Moderate COVID-19 risk

Masking encouraged.

■One to four cluster infections.

■Stable positive testing.

■Fewer than five hospitalizations.

■Stable case incidence.

■Stable wastewater.

Green zone: Low to minimal COVID-19 risk

Masking optional.

■No cluster infections.

■Decrease in positive tests.

■Decrease in hospitalizations.

■Decrease in case incidence.

■Decreased virus copies in wastewater.