Hotspot criteria for counties and changing transmission factors

As the number of COVID-19 cases continues to rise around the United States, cities have been implementing social distancing and safety guidelines to help counteract the spread of the SARS-CoV-2 virus. Despite the efforts by local, state and federal government agencies, cases have continued to rise across the country and hotspot cities have developed.

According to the Center for Disease and Control and Prevention (CDC), as of Sept. 13, there were a total of 6,503,030 reported positive cases in the U.S. and there have been 193,705 deaths attributed to the virus. 

Currently, no North Dakota counties meet the criteria to be considered a hotspot. Although eight counties are at a moderate-risk level, the majority of counties in North Dakota are low-risk level or less. Currently, Gov. Doug Burgum has not implemented any safety measures beyond the federal guidelines.

According to the North Dakota Department of Health’s website as of Sept. 13, Cass County has reported the most positive cases (4,214), with 452 active positives and 77 total deaths. Burleigh County has reported 2,643 total cases with 513 active positives and 25 total deaths. Grand Forks County has reported 1,902 total cases with 262 active positives and 12 total deaths.

The counties with the highest COVID-19 rates per 100,000 residents are Benson County (3,849), Sioux County (3,052), and Stark County (3,597). The rates for Burleigh County, Grand Forks County and Cass County are 2,818; 2,733 and 2,366 respectively (Center for Disease Control and Prevention, 2020). 

Multiple federal agencies have collaborated to set standardized criteria for declaring a county a hotspot. There are four main criteria that need to be met for a county to be considered a hotspot:

 First, there must be over 100 new cases in the past seven days. Second, there must be an increase in cases from the previous week. Third, there must be either a decrease of less than 60% or an increase of cases during the three-day incidence period compared to the three days prior. Finally, the ratio of seven-day incidence to 30-day incidence must exceed 0.31. 

“During March 8-July 15, 2020, 818 (26%) of 3,142 U.S. counties were identified as COVID-19 hotspots; these counties included 80% of the U.S. population,” the CDC’s website states. “The daily number of counties meeting hotspot criteria peaked in early April, decreased and stabilized during mid-April-early-June, then increased again during late June-early July.”

The contributing factors to the spread of the disease have changed to varying degrees. Cases attributed to local outbreaks such as long-term care facilities, correctional facilities, food processing facilities and other workplaces have decreased from 56% during May 11-31 to 24% during June 1-July 13.

At the same time, cases connected to community transmission increased from 18% to 41% and cases from indiscernible factors have increased from 8% to 24% (Center for Disease Control and Prevention, 2020).