The University of Tennessee, Knoxville.
Effects of Knox County
Stay-at-Home Measures on COVID-19

A Policy Brief by the Howard H. Baker Jr. Center for Public Policy

in Partnership with the Coronavirus-19 Outbreak Response Experts (CORE-19)

April 13, 2020
Tennessee State Capitol and Flag
Using publicly available data from emerging research on COVID-19, this brief was written and reviewed by the Coronavirus-19 Outbreak Response Experts (CORE-19) at the University of Tennessee, Knoxville. It It provides insight on changes in number of COVID-19 cases in Knox County before and after implementing non-enforceable Stay-at-Home orders. 

How do Stay-at-Home measures affect Knox County?

Some debates have questioned the need to shut-down entire cities for what appears to be a low number of people contracting COVID-19, being hospitalized, and in some instances dying. Others contend that more is needed, including having enforceable orders instead of non-enforceable orders or guidelines. 

Prior to Knox County Stay-at-Home orders on March 23, the doubling rate of cases in the county was 3.43 days, which means there was a 29% rate increase in cases per day
If measures would not have been applied and the rate would have continued constant, there would have been 69,097 cases in Knoxville by April 30. From these 69,097 confirmed cases, an estimated 13,819 people would have required hospitalization. In fact, without measures the cases could have increased even more rapidly.
Knox County has approximately 1,505 staffed hospital beds and 173 ICU rooms, which is a much lower number than hospitalizations needed if measures were not taken.
From the time measures were implemented, the daily increase rate dropped from 29% to 16% after implementation.
From the time measures were implemented on March 23 until April 11, the doubling overall rate of cases in Knox County decreased to 5.57 days, which is equivalent to a daily increase rate of 16%. It is important to note that this was the expected and intended outcome of the order. The intention of the measures was to slow the rate of increase.
Just three weeks after implementation, that is what has continued to occur. The daily increase rate has decreased by 13% (from 29 to 16%) . At the current average daily growth rate, the expected number of cases by the end of the month, April 30th, is 2,680, from which 536 may need hospitalization.
More drastic measures which can reduce the doubling rate of cases to 8 days (13% daily rate increase) would lead to 1,584 cases by the end of the month, with an estimated 317 cases needing hospitalization. Furthermore, maintaining a rate of increase as observed from confirmed cases during the last seven days could lead to having 387 cases by the end of the month, with 77 needing hospitalization. This would likely be possible if social distancing is maintained in a similar fashion to the last few weeks.
Visualization of these projections are shown in Figure (1) and Figure (2) including projections of cases and hospitalizations, and dates in which orders were implemented in Knox County and TN statewide are highlighted in the figure.
The total number of confirmed cases in Knox County and a projection at the current rate of increase are included in Figure (3). Table (1) also shows a table of all confirmed cases in the county.

What is the rate of daily increase and

how is it calculated? 

The rate of daily increase indicates the variation at which the number of cases changed from the previous day. 
For example:
  • on March 29 there were 38 confirmed cases, and on March 30 there were 52 cases in Knox County. 
  • This means that on March 30 there were 14 new cases with respect to the previous day. (Calculated as 52-38=14).
  • Also, this means that there was a 37% rate of daily increase in cases from March 29 to March 30. 
Figure (1) below  shows the projected number of cases with previous doubling rate (3.43 days), current overall rate (6.39 days), current rate including number of cases from the last week only (22.43 days). The “without measures” rate is calculated from confirmed cases between March 17 and March 22 (day prior to Knox County’s first Stay-at-Home order). The "current rate" accounts for all reported cases from March 12 until April 11.
The rate corresponding to last seven days is assumed for an optimistic improvement scenario in which the doubling rate of cases continues to double as it has during the last seven days (calculated between April 5 and April 11) or from observed effects from stricter implemented measures.
Knox County Health Department, City of Knoxville, and TN statewide Stay-at-Home orders issues on March 23, April 1, and April 2, respectively, are highlighted.

The rate of increase calculated from confirmed cases confirmed during the last seven days is 4.46% (doubling case time of 22.43 days). The rate of increase prior to applying measures of Stay-at-Home on March 23 was 29.17% (doubling case time of 3.43 days). Given that effects from measures applied are observed between 5 and 14 days after implementation, it is likely we are currently observing effects from the Tennessee statewide order. More clear effects will be evaluated on April 17th.
Figure (1) Projections of Cases in Knox County based on Measures
Figure of Projected Cases in Knox County
Table of confirmed COVID-19 Cases in Knox County
Table 1: Confirmed COVID-19 cases in Knox County from March 12th until April 11th.

What is the doubling rate of cases, how can it be improved, and why does it matter?

The doubling rate of cases indicates how long it will take for the number of cases to double.
The current doubling rate of 5.57 days indicates that it will take approximately 5 to 6 days to have twice the number of cases the county has currently.
However, these projections are highly dependent on opportunities of contagion amongst the population. If successful measures are implemented and the contagion is reduced, the doubling rate will take longer. In other words, more days will pass before the number of cases double in number. 
This matters because when it takes longer to reach higher number of cases, medical facilities can treat patients over a period of time instead of having to treat them all at once. 
In other words, if the cases grow very rapidly, the number of people needing hospitalization at once will be much higher than if the same number of people would need treatment spread out over time. This is the same as "flattening the curve" that has often been discussed in the news and by other sources. 
Figure (2) below provides a projection of total hospitalizations with previous doubling rate (3.43 days), current overall rate (6.39 days), current rate including number of cases from the last week only (22.43 days).
The “without measures” rate is calculated from confirmed cases between March 17 and March 22 (day prior to Knox County’s first Stay-at-Home order). The current overall rate accounts for all reported cases from March 12 until April 11.
The rate corresponding to the last seven days is assumed for an optimistic improvement scenario in which the doubling rate of cases continues to double as it has during the last seven days (calculated between April 5 and April 11) or from effects from stricter implemented measures.
Total number of hospital staffed beds in Knox County is indicated in a dashed red line – indicating 1,505 beds.
Figure (2) Projection of Total Hospitalizations needed for Knox County
Projection of hospitalizations for Knox county
Although these projections at the current rate seem to not predict extremely large numbers when only projecting through the end of April, even projecting one week further to May 7 at the same rates, reveals that:
At the previous rate of increase of 29% (without applying measures) there would have been almost 6,000 deaths by May 7.
The scenario at the current overall rate of 16% indicates there would be approximately 100 deaths by May 7. At a more optimistic scenario as proposed with a 4.5% rate of increase there would be less than 10 deaths by May 7. This optimistic scenario would require that the doubling rate remains as observed during the last 7 days or better.  
Results are shown in Table (2) below. The table displays the projected number of cases, hospitalizations, and deaths calculated with the previous doubling rate (3.43 days), current rate (5.57 days), and a stricter rate (8 days).
Table (2) Projected Number of Cases, Hospitalizations, and Deaths,  
Table of cases, hospitalizations, and deaths by different rates
It is important to compare this mathematical projection with the known Knox County population
and possible measures.
The discussion in this brief indicates that the Stay-at-Home orders have decreased the average daily growth rate of cases from 29% to 18% in two weeks, and to 16% a week after that.
Stricter distancing measures will likely have a stronger effect and reduce the rate of increase even more. As observed from the confirmed cases during the last seven days, in which the rate increase is 4.46%, the measures have strong effects on the confirmed number of cases.
The Knox County Health Department issued a Stay-at-Home order on March 23, the City of Knoxville on April 1, and the TN statewide order was implemented on April 2. Since the incubation period of the virus is within 2 to 14 days, if the distancing measures are successful, we should see changes in the doubling rate by April 17. A visual of this information is included in Figure (4) below.
The projections in this brief are obtained by evaluating the effects of daily increase rates calculated from number of confirmed cases. Epidemiological considerations are not included in this evaluation.
Much like the weather, the closer the projection in time is to today, the more likely it is to be accurate. Weather forecast for tomorrow can be quite accurate, but they are not as accurate for two weeks ahead. In other words, the further out in time, the less accurate the projections.
Projected Cases
Figure (3) above shows the projected cases with current overall doubling rate of 6.4 days (blue) and current doubling rate determined utilizing data from the last 7 days only (orange). Inset shows currently confirmed cases (green).

Figure (4) below shows projected cases at current overall doubling rate of 6.39 days (blue) and rate from last seven days (orange). Dates of implementation of Knox County Health Department, City of Knoxville, and TN statewide Stay-at-Home orders are highlighted.
Knox cases and policy changes
20% of cases need hospitalization, and 14% of those
need ICU treatment.
As previously indicated, Knox County has approximately 1,505 hospital beds with necessary staff, and 173 ICU needs. At the current doubling rate of 5.57 days, there will be 6,254 cases in Knox County by April 30 (Figure 3).
It is estimated that 20% of cases need hospitalization and 14% of those hospitalized need ICU treatment, which implies 1,251 patients will be hospitalized, and 88 will need ICU treatment.
Figure 5, Figure 6, and Figure 7 show a projection of total cases, hospitalized patients, and patients in ICU assuming doubling rates of 5.57 days (current), and various scenarios of improvement between now and April 30, with doubling rates of 6, 7 , 8, 9, and 10 days.
It is important to highlight that the reference of approximately 1,505 hospital beds with the appropriate medical staff to manage it is the total of estimated beds in the county as reported by the American Hospital Directory and it indicates the overall total. It does not indicate the number of currently available beds.
Many of the beds may currently be in use, and new patients with COVID-19 will likely need hospital beds for several days to weeks (i.e. not all the 1,505 beds will be available every day).
It is critical to keep accurate and up-to-date information regarding availability of hospital and ICU beds throughout the county to make efficient use of resources.
Knox county case projection
Figure (5) above shows the projection of total cases assuming doubling rates of 6.39 (current overall rate), 8 days, 10 days, 15 days, and 22 days (approximately the rate from cases observed in the last seven days).
Knox county hospitalization projection
Figure 6 above shows the projection of total hospitalizations assuming doubling rates of 6.39 (current overall), 8 days, 10 days, 15 days, and 22 days (approximately the rate from cases observed in the last seven days). Total number of hospital beds in Knox County is indicated in a dashed red line – indicating 1,505 beds.
Knox county ICU case projection
Figure (7) above shows the projection of total hospitalized patients needing ICU treatment assuming doubling rates of 6.39 (current overall), 8 days, 10 days, 15 days, and 22 days (approximately the rate from cases observed in the last seven days). Total number of ICU hospital beds in Knox County is indicated in a dashed red line – indicating 173 beds.
Send your additional Stay-at-Home related questions to Dr. Deborah Penchoff or contact the CORE-19 research team. 
dpenchof@utk.edu  | core19@utk.edu | 865-321-1299

Coronavirus-19 Outbreak Response Experts (CORE-19) 

Dr. Marcy Souza

Dr. Deborah Penchoff, PhD

Penchoff is a High Performance Computing Scientist at the Institute for Nuclear Security (INS) at the Howard H. Baker Jr. Center for Public Policy. She also directs and manages the INS Scientific Fellows Program. Her area of expertise is data science, data analytics, and computer science. In recent years her focus has been on applications to needs in nuclear- and radio-chemistry.
Dr. Katie Cahill

Dr. Katie A. Cahill, PhD

Cahill is the Associate Director of the Howard H. Baker Jr. Center for Public Policy. She also is the Director of the Center's Leadership & Governance program and holds a courtesy faculty position in the Department of Political Science. Her area of expertise is public health policy. She leads the Healthy Appalachia project. 
Dr. Kathleen Brown

Dr. Kathleen C. Brown, PhD, MPH

Brown is an Associate Professor of Practice in the Department of Public Health and the Program Director for the Master's in Public Health (MPH) degree. Her research focuses on the health and well-being of individuals and communities. She has experience in local public health in epidemiology, risk reduction and health promotion.
Dr. Kristina Kintziger

Dr. Kristina W. Kintziger, PhD, MPH

Kintziger is an Assistant Professor in the Department of Public Health and the co-Director of the Doctoral Program. She has worked in academia and public health practice, and comes to Tennessee from the Florida Department of Health, where she worked as an epidemiologist and biostatistician. She is an environmental and infectious disease epidemiologist.
Dr. Matthew Murray

Dr. Matthew N. Murray, PhD

Murray is the Director of the Howard H. Baker Jr. Center for Public Policy. He also is the Associate Director of the Boyd Center for Business and Economic Research and is a professor in the Department of Economics in the Haslam College of Business. He has led the team producing Tennessee's annual economic report to the governor since 1995. 
Dr. Agricola Odoi

Dr. Agricola Odoi, BVM, MSc, PhD

Odoi is a professor of epidemiology at the University of Tennessee College of Veterinary Medicine. He teaches quantitative and geographical epidemiology and his research interests are in population health and impact of place on health and access to health services. He was a public health epidemiologist before joining academia.
Dr. Marcy Souza

Dr. Marcy J. Souza, DVM, MPH

Souza is an associate professor and Director of Veterinary Public Health in the UT College of Veterinary Medicine.  Her teaching and research focuses on zoonotic diseases and food safety issues. 

Disclaimer: the information in this policy brief was produced by researchers, not medical or public health professionals, and is based on their best assessment of the existing knowledge and data available on the topic. It does not constitute medical advice and is subject to change as additional information becomes available. The information contained in this brief is for informational purposes only. No material in this brief is intended to be a substitute for professional medical advice, diagnosis or treatment, and the University of Tennessee makes no warranties, expressed or implied, regarding errors or omissions and assumes no legal liability or responsibility whatsoever for loss or damage resulting from the use of information provided.

 

Howard H. Baker Jr Center for Public Policy
1640 Cumberland Avenue
Knoxville, TN 37996
Phone: 865-974-0931
Email: bakercenter@utk.edu
Online: bakercenter.utk.edu
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