Staff photo by C.B. Schmelter / At Baylor School, the entire campus has been tested multiple times through the school's on-site lab, which since August has yielded over 3,000 test results for students and employees with a positivity rate around 0.6%.

What is a coronavirus "cluster?" It depends on who's answering the question.

Some spokespeople for places on the list of local cluster spots released by the Hamilton County Health Department in response to a Times Free Press request said they weren't surprised to learn they were designated as such, while others questioned why their facility made the list.

"We had 17 of our staff, all tested positive, basically at the same time," said David McNabb, president and CEO of Adult and Teen Challenge Mid South, a residential care facility for people with substance use disorders. "It didn't surprise me that we're on somebody's map as being a hotspot."

Even with safety protocols in place, the virus managed to find its way into the facility, McNabb said.

"Probably the first positive test that we had, based here on campus, was probably right around the first of September," he said. "We don't know how it entered the campus, and we don't know exactly how it was transferred."

Teresa Dinger, administrative director of marketing and admissions at Siskin Hospital, said the facility has conducted nearly 3,000 tests since the start of the pandemic. So far, 10 of those have returned positive.

"Out of 3,000 tests, to have less than half a percent, that hardly felt like a cluster, right? So that was a little surprising, but also it's great in that we've had so few," Dinger said.

Melissa McPheeters, a health policy research professor at Vanderbilt University Medical Center, said that the term "COVID cluster" can be difficult to understand, because "cluster" means different things to different people, and the way that departments of health around the country define clusters is not consistent.

In general, she said public health workers use the word cluster to describe a location where disease incidence is occurring above what's expected in a specific geographical place during a defined period of time.

"It doesn't necessarily mean that there's an active and ongoing outbreak in that particular location. It just means that these are the set of locations where during this pandemic we have seen the most cases," McPheeters said. "You hear about clusters of cancer. That's when we're seeing more cases in this defined geographic location over a certain period of time than we would typically expect to see. And so that's the way the word is getting used in [Tennessee]."

McPheeters also cautioned against using the data to make comparisons with other facilities or places across the state or country, because different departments, businesses or school systems may report positive cases differently.

Lisa McCluskey, a spokeswoman for CHI Memorial, said the health department's numbers are higher than what the hospital has on record, but that could be because the health department tracks probable cases in addition to confirmed ones.

"I'm not quite sure how to explain it other than the number includes probable — or those awaiting test results — and positive. Every employee who is suspected of COVID and is reported to employee health is immediately tested. When I looked at our list, the vast majority were negative," she said in an email.

The Hamilton County Health Department uses the same definition for cluster as the Tennessee Department of Health: two or more confirmed or probable cases of COVID-19 that are linked by the same location of exposure — such as a hospital, nursing home or grocery store — or exposure event — such as a party or gathering — that is not a household exposure.

The health department's list was obtained by the Times Free Press through an open records request and reveals the county's largest recent coronavirus clusters, meaning facilities on the list have had 10 or more COVID-19 cases since the beginning of the pandemic, as well as at least one new case in the past 28 days. For businesses and hospitals, the list includes employees only. For schools and long-term care facilities, the numbers include staff in addition to students and residents.

McPheeters said that "there's nothing surprising" about Hamilton County's list given that the coronavirus is highly contagious.

"Places where you're going to have people congregating for extended periods of time, you're going to have an increased risk of there being more cases because there's just more opportunity for that virus to be transmitted," she said. "That's really different than places where people just go in and out because we know that longer periods of time in the presence of the virus increase risk of getting infected."

Hamilton County's list includes many of the area's biggest employers with large numbers of essential workers — those who continued to work throughout the shutdown and who don't have the option to work remotely — such as hospitals, food packaging and manufacturing facilities.

The University of Tennessee at Chattanooga topped the county's list with 405 cases among students and staff over the past six months.

McPheeters said that COVID-19 transmission among college students is a nationwide issue, so it makes sense to see a higher number of cases attributed to a university. More than 35 colleges have reported at least 1,000 cases over the course of the pandemic, and more than 230 colleges have reported more than 100 cases, according to the New York Times.

Dawn Ford, chief epidemiologist and an assistant provost at UTC, said in an email that most of the university's cases don't meet the U.S. Centers for Disease Control and Prevention's definition of a cluster, which is "an unusual aggregation of health events that are grouped together in time and space and are reported to a health agency."

"Based on this definition, the vast majority of UTC cases are not part of a cluster, because there was not a specific location on campus common to the cases," Ford said. "A laboratory-confirmed positive test of a UTC community member (employee, student, contractor) is a UTC case. These cases are self-reported and/or we receive the information from the health department.

"A UTC student who is taking all online classes and has not been to campus this year is counted as a UTC case, because they are part of the UTC community," she said.

There has been some transmission between students who live together in a house or apartment and among athletes, Ford said. UTC's highest number of cases per week occurred in August, and cases have been trending down ever since, she said.

Similarly, as K-12 students have returned to instruction nationwide in a variety of capacities, schools have worked to abate the spread of the virus.

As of Friday, Hamilton County Schools reported 10 active employee cases and 30 active student cases with a total of 559 close contacts but did not have any schools on the cluster list. School officials have said that the vast majority of students and staff catch COVID-19 during activities outside of the classroom, such as carpooling or at parties where people aren't using proper personal protective equipment.

Baylor School physician Dr. David Bruce said in addition to general protocols of physical distancing and wearing masks, the private school's proactive surveillance testing identified cases that may have otherwise gone unknown. Most of the school's 20 associated cases were found in asymptomatic students prior to returning to campus.

"They were not exposed on campus, nor did they expose anyone because we tested them beforehand," Bruce said.

Since classes resumed in August, Bruce said the entire campus has been tested multiple times through the school's on-site lab, which since August has yielded over 3,000 test results for students and employees with a positivity rate around 0.6%.

"We have exceptionally, 10-fold lower numbers on our campus [than] in the county," Bruce said. "And I say that's afforded because we are surveillance testing."

The Times Free Press has had the list since Monday, but waited to publish the entire list until all the facilities had a chance to comment.

The entities on the list who responded told the newspaper they're working hard to keep people safe. But even with robust protocols in place, people can catch the virus in the community and the risk of transmission remains as long as most of the population hasn't achieved immunity through recent infection or a vaccine.

"The skilled nursing industry across the country is seeing consistent increases in employees who test positive because they have to continue their routines outside of work, such as taking children to school and shopping for groceries," said Jennifer Solomon, Eastern Division Vice President, Life Care Centers of America.

Representatives from Boyd Buchanan School, Moccasin Bend Mental Health Institute, M&M Industries, Alexian Village Health and Rehabilitation, Integrity Elite AllStars, Chattanooga Rescue Mission and Encompass Health Rehabilitation Hospital either declined, were not reachable or had yet to comment at the time of publication.

Silverdale Detention Center, Volkswagen, Amazon Fulfillment Center, Koch Foods, Pilgrim's Pride, Standifer Place and McKee Food Corporation did not respond to requests for comments on Monday when the Times Free Press published the first portion of the list.

McPheeters said that it's important to note that the cluster list is used as a tool for the health department to spot patterns and trends.

"They're saying, 'Gosh, over the course of this pandemic, we are seeing the most cases in these particular kinds of venues, so we're going to step up our interventions in those areas,'" she said. "It's very much a working document — not necessarily intended to be used by people to make decisions about what they do as individuals."

Contact Elizabeth Fite at or follow her on Twitter @ecfite.