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Staff photo by C.B. Schmelter / A worker takes a sample at the Alstom COVID-19 testing site on Tuesday, Sept. 22, 2020 in Chattanooga, Tenn.

Coronavirus cases are surging in Hamilton County and Southeast Tennessee, part of a nationwide spike in cases as temperatures drop and people experience coronavirus fatigue, which causes them to take risks that they would have avoided months earlier.

While cases have spiked locally, they have yet to reach the peak the area experienced over the summer when, in July, the county averaged 121 new cases a day, hospitalizations were well above 100 and, several weeks later, death totals climbed.

As of Monday, the county was averaging 107 new cases a day in the past week and there were 80 hospitalizations from the virus, according to the Hamilton County Health Department.

The coming colder months pose a serious risk of spreading the disease further as northern states such as Wisconsin and the Dakotas experience sharp increases in infections.

Dr. William Schaffner, a Vanderbilt University infectious diseases expert, warned Tennesseans should learn from the struggles northern states are facing.

"As it gets colder, we spend more time indoors closer to each other. And that's an environment where the virus loves to spread," he said. "We anticipate a sustained increase unless we really do something about it this winter. And we'll be fighting off influenza at the same time."

Local officials have warned against coronavirus fatigue, something they said is already driving spread around Chattanooga.

As the Times Free Press continues to cover the pandemic, here are the data points that reporters are monitoring as the region faces another COVID-19 surge.

POSITIVITY RATE

Schaffner said one of the best ways to measure how the virus is spreading in the community is to look at test positivity rates.

The higher the level of positivity, the higher the degree of spread there is in a community, Schaffner said. Areas should aim for a rate of less than 5%, a goal that indicates how many people are being infected with every new confirmed case, he said.

"If we can get it less than that it usually means that everybody who has the virus is spreading it to less than one other person," Schaffner said. "But if you're spreading it to at least one other person, that means the outbreak is staying steady. [And] if you give it to two people and each of them gives it to two people obviously, oops, we're going up."

On Monday, Hamilton County averaged a 12% positivity rate for its tests in the past week. That number is nearly double what it was at the beginning of October.

7-DAY AVERAGE

Reports of new cases can spike and drop significantly from one day to another. Rather than drawing quick conclusions from a single-day dramatic change in new cases, the seven-day moving average of new cases presents a clearer picture of whether cases are trending up, down or flattening.

For example, on Oct. 1, the county averaged 61 new cases a day in the previous week. By the end of the month, however, the county averaged 114 new cases a day in the previous seven days. The seven-day moving average line shows a clear trend upward that might be harder to spot if you looked at the new cases reported each day, which during that time span ranged from 53 to 134 a day.

HOSPITALIZATIONS

As the virus spreads and more people are infected, a percentage of them will have serious cases of the virus and need more medical care including hospitalization and, potentially, being placed in the intensive care unit.

Because of the way the virus affects the body — usually taking days to present symptoms and weeks to worsen to the point of needing medical care — increases in hospitalizations often lag several weeks behind spikes in cases and spread in the community.

Schaffner said monitoring hospitalization data provides a sense of how stressed the local health care infrastructure is.

"That's a very stable kind of metric on the serious side," he said. "It lags behind the proportion of tests that are positive because hospitalizations lag a little behind and behind them come deaths. But hospitalizations will give you a sense of how the health care system in your community is managing. And that can set off alarm bells."

On Monday, the health department reported 80 hospitalizations, with 27 of those being Hamilton County residents. Chattanooga's three hospitals treat patients from the surrounding area, which is why monitoring cases in the region is important.

PER CAPITA CASES

Local leaders and health experts have pointed out that what happens in the area surrounding Hamilton County affects residents within the county. The county is the only place in the surrounding Tennessee and Georgia region with a mask mandate, a public health provision that researchers at Vanderbilt said leads to fewer hospitalizations compared to places without a mask mandate.

Hamilton County hospitals treat patients from the surrounding area, which can increase pressure on health care infrastructure if there is already a significant local need for treatment. In order to compare what is happening with the virus in rural areas with fewer residents than Hamilton County, new cases are calculated per 10,000 residents.

The virus can also spread from rural areas into the urban center of Chattanooga. In September, cases surged in rural communities, while the numbers flattened in Hamilton County. The amount of commuting and travel between counties, involving many places without mask mandates, can further spread the virus.

DEATHS

As Schaffner said, increases in deaths often follow several weeks after increases in hospitalizations. The summer spike of new cases and hospitalizations led to records in July but the damage of the surge was not felt in Hamilton County until August, which became the deadliest month so far for the virus, killing 27 people then.

Regionally, places such as McMinn County and Franklin County reported spikes in deaths in October. McMinn County reported 13 new deaths in the month and Franklin County reported 15 new deaths. Hamilton County reported 14 deaths in October.

However, the recent surge in cases locally may not lead to the high death totals the area experienced in August. First, the virus is infecting younger people, who are not at as high a risk for serious complications, at higher rates than older groups. Second, doctors have a better understanding of how to treat the virus than they did in the early months of the pandemic, leading to better outcomes for those who are hospitalized.

Contact Wyatt Massey at wmassey@timesfreepress.com or 423-757-6249. Follow him on Twitter @news4mass.

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