FARGO — Cass County is once again standing out among North Dakota’s urban centers as the location seeing the most rapid growth in new COVID-19 cases.

As of Thursday, April 8, Cass County had 529 active cases, three times the 173 cases in Burleigh County, which includes Bismarck, and almost 10 times greater than Ward County, which includes Minot.

Health experts say the more rapid increase in Cass County, the most populous in North Dakota, stems from multiple factors, but many involve the metro area’s dynamism and connectedness — attributes that help foster business activity, but also can be exploited by the coronavirus.

“The most likely explanation or the factor that contributes most is the increased density of population,” said Dr. Avish Nagpal, Sanford Health’s chief infectious disease physician.

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Greater density means more people living close to one another, more people gathering in crowded settings, more people traveling, more people attending events or socializing in bars and restaurants, he said.

But the Fargo-Moorhead metro area is likely a harbinger, and Nagpal expects North Dakota’s other urban centers will start to see more rapid spread once again also.

“I’m pretty sure Bismarck and Grand Forks will follow the same pattern over the next few weeks,” Nagpal said.

Lane Trisko, a senior analyst with Essentia Health who is part of the team that is modeling the pandemic, agrees that the increase in cases now in Fargo-Moorhead likely will spread out to other urban areas.

“I wouldn’t be surprised if we were to see that as well,” he said, referring to rising cases in other North Dakota cities.

Cass and Clay counties, home to Fargo-Moorhead, have experienced rapid spread over the past two weeks, with a high percentage of tests turning up positive. In Cass, the positivity rate over the past seven days has been more than 10% and in Clay, the positivity rate has been 7.5%, Trisko said of numbers tracked by Essentia.

But Trisko, Nagpal and others do not expect to see a rise in cases resembling the area's peak last fall. That’s because many people now have been vaccinated, especially the older and more vulnerable segments of the population.

In Cass County, 50.9% have received one vaccine dose and 35.8% are up to date on their COVID-19 vaccines. In Clay County, 35% have received at least one dose.

Also, many in the Fargo-Moorhead metro area already have been infected by the virus and recovered, Trisko said. In Cass, almost 13% have recovered and in Clay, almost 12%, he said.

“That’s not an insignificant number by any means,” he said. It also has reached the level of herd immunity, Trisko added, at which so many people have been vaccinated or recovered that the virus can’t spread.

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Besides being a business hub and a travel hub, Fargo-Moorhead is a major college town and also has a more active nightlife scene than other cities in the area, said Desi Fleming, director of Fargo Cass Public Health.

The increase in cases is largely driven by younger people who are less likely to have been vaccinated, she said.

“We’re a large population hub,” she said. “We have a lot of people and a lot of movement,” including schools that are back in session and sports games or tournaments.

Population density isn’t always a clear driver of cases, Trisko said, but he believes it’s a factor now in Fargo-Moorhead, especially now that “COVID-19 fatigue” has led to more lax behavior among some.

Variants of the virus that spread more easily also could be part of the reason for the more rapid spread in Fargo-Moorhead, Fleming and others said.

“We have seen an increase in the number of variants,” said Brenton Nesemeier, a state of North Dakota epidemiologist based in Fargo. Two variants from California that are circulating in North Dakota are 20% to 30% more transmissible, and a variant first detected in the United Kingdom also spreads more rapidly, Nesemeier said.

“Thankfully, our older population is vaccinated now,” he said. Although Nesemeier doesn’t expect a repeat of the peak in cases last fall. “There is always concern when we’re seeing increases.”

COVID-19 hospital admissions at Sanford Health in Fargo have risen, with 26 as of Thursday, including three in the intensive care unit, with one patient on a ventilator. Those numbers don’t put a strain on hospital staff or resources, Nagpal said.

“I don’t anticipate reaching a crisis level in the hospital that we had last fall,” he said, when Sanford had a peak of 116 patients with about 40 on ventilators at one time.

The average age of hospital patients has decreased to 53, reflecting that fewer elderly people are getting infected, he said. Those showing up in the hospital are either unvaccinated or only partially vaccinated, Nagpal said.

One patient who was fully vaccinated has COVID-19 — but it’s a mild case and not the reason the patient is in the hospital, he said. “Practically every patient who is hospitalized is a non-vaccinated patient,” Nagpal said.

Dr. Paul Carson, an infectious disease specialist who teaches public health at North Dakota State University, said the movements and patterns of the virus are "a bit mysterious" and will be studied for years. He agreed that multiple factors are at play, including the return to in-school learning and the public's fatigue in adhering to precautions.

"Why Cass now?" he said. "I simply don’t know. We see the hints already in other counties around the state that I suspect will not be far behind."

Medical experts stressed the importance of everyone getting vaccinated to control the spread of the virus and to prevent serious illnesses.

Population density of North Dakota’s four metro counties:

  • Cass: 94.5 people per square mile

  • Burleigh: 55.5

  • Grand Forks: 48.6

  • Ward: 34.3

Source: Statistical Atlas