Special Edition

Battling the Spread of Covid-19

Key Points:

On March 18, 2020, our special edition article discussing the spread of COVID-19 emphasized reducing social gatherings and increasing ventilation as means for reducing the “Reproduction” number of the disease. The Reproduction number, Ro, is a ratio of infections caused by a single infected person placed in a crowd of people susceptible to a disease. At that time, Italy’s infections had skyrocketed to 35,000, shocking the world. The United States had less than 9200 reported infections. As of April 9, only 3 weeks later, Italy turned the corner on COVID-19 with slightly less than 150,000 infections while infections in the United States soar past 500,000. Both Italy and US have had to shut down their economies and are now encouraging or requiring residents to remain isolated and distanced. Figure 1 shows the total infections in 9 countries as of April 8, 2020.

Figure 1: Total COVID-19 infections in 9 countries as of April 8, 2020

South Korea, which had 8400 infections as of March 18, quickly began an aggressive program of testing, tracking and quarantine/isolation. As of April 9, South Korea reports 10,400 for an increase of 24% of infections over 3 weeks in comparison to Italy’s 425% infection increase and the US 5000% increase.

We are in the middle of the battle against COVID-19 in the US, and many regions of the world are just beginning to enter the battle. The actions we should have taken in the US and elsewhere, and the actions we need to double down on in order to extinguish COVID-19 are important to discuss and are the subject of this article. An “infection parameter” (IP) is defined that provides a descriptive estimate of a country, state, or community’s infection spread rate. A projection of the United States possible infection paths over the next few weeks is presented based on the US ability to reduce the infection parameter.

Build Equinox’s primary mission is our health and well-being. From our very beginning to redefine healthy homes in 2008, we have investigated disease transmission and sought better ways to design our homes, schools and businesses to improve the indoor environment. Unfortunately, as discussed in our initial special article on COVID-19, our homes, public buildings and transportation systems often increase the spread of contagions rather than contain and mitigate. For now, it is important to understand how to combat COVID-19. When we get past the spread of COVID-19, we need to redouble our efforts to protect our homes, schools, transportation systems, and public buildings from future occurrences of diseases.

Disease Transmission Progression Paths

South Korea took one path while Italy, the US and many other countries chose another path during the early stages of COVID-19 infections. The path South Korea has taken has kept infections low and has allowed businesses to continue operating. Italy, the US and other countries followed another path, resulting in shutdown of their economies except for essential services such as health care, food, and basic transportation.

South Korea’s path is only available for a brief period of time when infection numbers are low. During that time, aggressive tracking, testing and isolation of infected persons and persons who have been in contact with infected persons. Testing, tracking and isolation (TTI) must be relentlessly followed and must begin at the earliest sign of any infections. South Korea and other regions that were quick to respond with TTI must continue vigilance until the infections in the rest of the world are under control.

The TTI path can only be followed in the early phase of infection spread. Within a few short days, exponential growth of an infection into a wholly susceptible populace overwhelms a country’s ability to test, track and isolate. Once a region’s ability to conduct TTI is lost, the remaining choice is total isolation (“social distancing”) of everyone and shutdown of schools and businesses. Ideally, if every individual in a population group is perfectly isolated for a period that exceeds the duration of the disease’s incubation and illness, transmission of the disease ends and the disease dies out. For COVID-19, incubation is 4 to 5 days, followed by an average of 14 days of illness resulting in approximately 3 weeks of “perfect” isolation and shutdown.

The insidious nature of COVID-19 is its ability to infect a significant fraction of a populace without making them feel noticeably sick (ie, “asymptomatic” behavior). Asymptomatic persons grow the virus and then shed the virus through respiratory functions (breathing, coughing, sneezing, talking), infecting others. Asymptomatic people are difficult to track because they may not have fever, cough or other related symptoms. On the other side of the spectrum, COVID-19 is deadly for our elderly and infirm, as well as for a significant fraction of healthy, young people.

Perfect isolation cannot be attained in reality as essential functions such as our frontline medical professionals who interface with infected persons, and those in industries such as food, delivery, and essential equipment manufacturing. These interactions, coupled with persons who do not seriously follow isolation and distancing guidelines result in imperfect disease containment. As Italy, Spain, Germany and France enacted strict, enforced isolation measures, the disease infection rate has slowed. As of April 9, the spread of COVID-19 is decelerating in most European countries that lost control of the disease. Some countries, such as the Czech Republic, Denmark, Finland and Norway, were quick to act were able to enact TTI.

The United States lost control in New York by not enacting TTI early, while the state of Washington (where the earliest US infections were detected) struggled but successfully contained the spread rate of COVID-19. On March 16, New York reported 967 infections while Washington reported 904. As of April 8, New York reported 150,000 infections while Washington reported 9300. Washington’s rapid response allowed implementation of TTI procedures. Washington’s response is a demonstration that households, cities, counties, states and regions can enact local protocols to protect themselves regardless of the ineffectiveness and confusion of a nation’s government.

Once the TTI path option is lost, there are two branches on the path of total isolation and economic shutdown. One path is the undesirable spread throughout the populace until sufficient people have become infected that the immune and recovered fraction of people provide a “herd” immunity to the remaining fraction of susceptible people. For COVID-19, as discussed in our first special report, unrestrained growth of the disease would result in 40-70% infection of a population group, or approximately 160 million people in the US. A poorly defined and still to be determined fatality rate of 1 to 3% would be a horrifying 1.6 million to 5 million deaths along this path.

The second branch to total isolation and economic shutdown is a slowing of the infection rate, as currently observed in China, Italy, Spain, France and Germany, to a level that can be handled by medical staff and facilities, followed by continued strict enactment of total population isolation and economic shutdown until remaining infections are at a level where TTI can be substituted. Once TTI can be put in place, total isolation can be ended and economic activity can resume.

The US is on a path that might lead to sufficient disease spread deceleration that implementation of TTI is possible at some point, however, the path is a very narrow one, and one can fall off it easily and quickly land on the path toward renewed, unrestrained spread of the disease. One infected soul is an ember that can relight the COVID-19 blaze. The infection can come from anywhere in the world as we have observed. We are all in this together.

Infection Parameter - Turning the Corner

An “Infection Parameter” (IP) describes the effectiveness of a population group to restrict the spread rate of a disease. We define the IP based on a 14 day infection period that is the average length of a COVID-19 contagious period. Our IP parameter is related to the Reproduction number (Ro), however, IP is more descriptive of how many infections have occurred over one person’s entire infection period. For example, if one infected person infects one person per day for 14 days, the IP is 14. Another description of the IP is that it is ratio of infections of today to the number 14 days ago.

Figures 2 through 5 show the progression of the daily IP for 8 countries over the past month. We use international data from the Worldometers.info website for determining the IP levels for countries. Reliable infection data is still sparse, however, as of mid-March, data reports from many countries has reached a systematic level of regularity. Although the accuracy for many countries may not be great for many reasons (poor testing, poor recording, stressed medical systems, political clouding, etc), the countries represented in Figures 2 through 5 have been leading worldwide infections and demonstrate the range of pandemic response from South Korea’s rapid, controlled TTI to Italy’s loss and regain of control, and the US continued out-of-control procession.

Figure 2: Infection Parameters (IP) for 8 countries during the week of March 24 to 30, 2020.
Figure 3: Infection Parameter (IP) for 8 countries for the week of March 26 to April 1, 2020.
Figure 4 Infection Parameter (IP) for 8 countries from March 30 to April 5, 2020.
Figure 5: Infection Parameter (IP) for 8 countries as of April 2 to 8, 2020.

An IP of 2 is a level that keeps new COVID-19 infections at a level that does not tend to overly stress medical systems beyond their capacity and allows TTI to be enacted. That is, maintaining an IP of 2 should allow a conversion from total isolation of the entire populace and restarting of economic activities. Figure 2 shows the progress Italy has made, along with the path of IP reduction in Spain. Figures 3 through 5 show varying levels of progress made in other countries, with Iran and Germany making good progress to reach sustained IP levels of 2 or less. France has had some difficulty reducing IP to a sustained level of 2 while the US and the UK have lagged other countries but now seem to be making progress toward lower IP levels.

An IP of 1 is a level similar to Ro of 1, indicating that COVID-19 is no longer spreading. The closer a country can approach 1, the lower the infection spread. The impact reduced levels of IP are readily apparent in Figure 6, in which predictions are made for the US and South Korea with differing levels of IP as of March 6. Because today’s infections are pre-ordained by the past 2 to 3 week period of infection incubation and illness, the initial week of infection predictions for the US and South Korea are based on an IP of 7 and 2, respectively. South Korea is kept at an IP of 2 for the month of April, and the past week of data plotted on the predicted infection path are in good agreement.

Figure 6: Logarithmic plot of total infections with predicted infection paths for the US and South Korea plotted based on the Infection Parameter (IP).

Four possible infection paths are shown for the US in Figure 6. Three of the predicted paths for the US assume constant IP levels of 7, 2, and 1.5. The four path is a gradual improvement of the US IP from 7 (initial week) to 5 to 4 to 3 to 2 over successive 3 day periods, and a final period of 7 days to reach an IP of 1.5. The IP path of 7 represents the dire prediction of the US government made at the beginning of April in which infections were estimated to reach more than 10 million with estimated fatalities of more than 100,000.

If the US had communicated a sense of urgency and enacted effective steps immediately as of April 1 with IP levels of 1.5 to 2, infections could have been limited to 1 million or less with associated fatalities of 10,000. Gradual decreasing IP trends in the US during the first week indicate a drop of IP of 1 unit every 3 days. The orange line on Figure 6 projects continued decrease of IP from its current level of 4 to 5 to a level less than 2. If the US can keep improving isolation, distancing, and wearing masks, potential infections by the end of April can be kept below 1.5 million with fatalities below 20 to 30,000, a horrific number that we have not experienced in the US for many generations.

IP Trends in New York, Washington, Georgia and Illinois

Within the US, New York has been devastated by COVID-19. New Jersey, Michigan, Illinois and several other states are fighting to avoid the accelerated spread of disease. A clear and urgent national message in the US has yet to appear. Inconsistent messages to use face masks (to protect others around you), isolate, eliminate travel, and not gather has retarded the reduction of IP in relation to Italy other countries that experienced similar early infection growth rates.

A consistent national message and coordinated national response makes local responses more difficult, but fortunately, local responses are effective and should be pursued rather than waiting for leadership at higher levels. Figure 7 shows total infection case data for South Korea in comparison to infection cases reported for New York, Washington, Georgia and Illinois. New York, as the current epicenter of infections in the US is struggling to reduce the continued growth of COVID-19. As high as the infections numbers are for New York, without effective isolation New York’s infections can reach much more than 10 times the current level.

Figure 7: Total infections for South Korea and four States since February 2020.

Washington, the earliest site of recognized COVID-19 infections has been more effective than New York at restraining the growth rate of infections. Figure 7 shows Washington’s infections leveling in a manner similar to South Korea, but containment is difficult with porous borders and lack of widespread testing and tracking.

Georgia and Illinois have been following similar paths with high infection growth rates. Both states are showing signs of containment of COVID-19 spread. Figure 8 shows similar IP levels among the four states. Illinois and Georgia had much higher IP levels in the previous week, while New York has been gradually decreasing IP over the past two weeks. Washington’s ability to keep IP below 4 to 5 since early March allowed it to avoid New York’s explosive infection growth rate.

Figure 8: Infection Parameters (IP) for 4 States for the week of April 2 through 8, 2020.


Can our communities, countries and the world turn the corner and contain the unfettered spread of COVID-19? Normal will not happen for several weeks, and even though we are seeing signs of improvement in many regions of the world, we are in the middle of the battle and our focus needs to be on restricting the spread of COVID-19. Once we reach a level where we can switch to a path of TTI (testing, tracking, isolation) of infected cases, then we can determine how to return to more open, but cautious living. In the meantime, wear the mask to protect others, and thank our medical staffs and essential business employees working on the frontlines.

Figure 9 Wear the mask!


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