Staying at home has proven to be a very effective tool to stop the spread of COVID 19. Millions of lives have been spared by this intervention, but at huge economic cost. With only a small fraction of the world’s population thus far infected, pressure is building to get economic engines running again. Unfortunately, most communities are not prepared to suppress the next phase of viral transmission which could be physically and emotionally much more traumatic.
Every country has chosen a strategy to deal with COVID 19 based on perceived risks, costs, and availability of materials for screening. The consequence of these strategies to fight the virus is now reflected on the scoreboards that track the disease. A dramatic example of how those choices make a difference is demonstrated by comparing the experiences of South Korea and the US in the first few months of the pandemic.
On Feb 15th, South Korea reported a total of 28 cases of COVID 19, while the US reported 15. At that time, South Korea began a vigorous contact tracing program and quickly ramped up to 10,000 tests per day. The US did not reach that level of testing until the end of March, and has made little effort at contact tracing. By April 1 the consequence of this delay became painfully apparent. While South Korea was hitting a plateau just below 10,000 cases, US infections soared to 216,000. In the two month stretch from Feb 15 to April 15, South Korea managed to reduce its new cases to 25-30 per day, while the US leads the world with 27-32,000 per day.
South Korea has performed 53 tests for each positive case (53:1) allowing them to evaluate virtually everyone with a potential exposure, even if asymptomatic. The US, on the other hand, has tested only 5 people for each positive case (5:1). At this rate, people with mild or even moderate symptoms are often told to “assume that you have it and stay home”. More importantly, asymptomatic individuals who have been exposed to someone with infection are not sought after or tested. Limited testing capacity in the US has prevented the largest group of infected individuals from being identified, those with minimal or no symptoms. The US counts over one million cases now, but many would estimate that the real number of infections is closer to ten times that number. This is likely to be confirmed by antibody testing which is underway.
Identification and isolation are the tools at our disposal. Many countries, including the US, have ordered people to stay at home, but only some countries have committed themselves to aggressive identification of infections. From the data presented on the Worldometer COVID tracker, the relationship between each nation’s commitment to screening and the resulting prevalence of infection can be observed. Using the ratio of tests performed to the number of confirmed cases, countries can be grouped by the intensity of their testing program.
The table below shows the average of 6 countries from each testing range. . Only South Africa had a ratio that fell in the 30-40 range (37:1). The US and South Korea are shown separately but their test ratios are 5:1 and 53:1 as stated previously. Countries included in this analysis: <10: US, Italy, Spain, France, UK, Belgium; 10-15: Chile, Pakistan, Singapore, Dominican Republic, Austria, Germany; 15-20: Israel, Canada, Finland, Egypt, Saudi Arabia, Colombia; 20-30: Norway, Greece, Malaysia, India, Poland, Czechia; 30-40: South Africa.
|Total number tested /
number of cases
Number of new cases per day* /
|11 – 15||38.0|
|16 – 20||20.6|
|21 – 30||6.6|
|31 – 40||2.4|
*number of new cases per day represents an average of the 7 days from 4/15 to 4/22/20. These are new diagnoses, not necessarily early stage infections.
These data show that more screening results in lower disease activity three months into the pandemic. Many of the countries reviewed have a low total infection burden and are not in the same predicament as the US. However, South Korea is more densely populated than the US, and, for a short time, had the fastest growing outbreak in the world outside of China, yet they managed to shut the infection down with an aggressive program. The fact that the number of new infections correlates with the extent of testing suggests that such data can be used as a guide to determine appropriate screening targets.
For instance, if the US increased its testing program to 25 tests for each positive result, the number of new cases per day could eventually drop from our current level of 28,000 to approximately 2200. A five-fold increase in nasal swab tests along with a serious effort at contact tracing would be required. Such a drop in new infections would obviously take months to observe since the first few months of increased screening will turn up many more people that have thus far been uncounted.
It is important to recognize that the number of active infections, not the total number of infections, are what determine the ability of the virus to spread. Since the virus appears to be shed at its highest levels during the early stages of infection, and that these early stages are most often asymptomatic or only mildly symptomatic, it is essential that we improve our ability to identify newly infected individuals. This will only happen with aggressive contact tracing to identify those that have been recently exposed, but should also include screening of high risk populations such as healthcare workers, supermarket employees, transit workers, and communities where living conditions are not conducive to social distancing. The majority of tests, therefore, should be done on people that feel well, the opposite of what we have been doing in the United States.
Screening programs in the US also vary widely from one state to another and should have influence on how and when stay at home orders can be relaxed. States with a very low disease burden that are prepared to continue aggressive testing and contact tracing may have an opportunity to relax their stay at home policies. Hawaii (41:1) and Alaska (31:1) are in the best position to do so, but the 9 states testing 15:1 to 30:1 may also be able to open parts of their economies.
|Total number tested/# of cases||States|
|< 10||NY, NJ, MA, PA, MI, IL, GA, CT, CA, MD, CO, AL, RI, DE, IN, IA, LA, OH, SC, SD, TX, VA, DC|
|10 – 15||FL, NC, MO, AZ, WI, MS, NE, KS, KY, OK, ID, NH, NV, TN, AR,WA|
|16 – 20||ME, VT, WY|
|21 — 30||UT, NM, OR, WV, ND, MT|
All other states need to augment their programs, in particular, the states with the lowest screening ratios and the heaviest disease burden: NY (2.5:1), NJ (2:1), Michigan (3:1), and Connecticut (3:1). Georgia (5:1) is leading the charge on reopening parts of their economy but will likely discover that they are not prepared to handle the virus just yet. Putting the economy back on the shelf may prove to be harder the second time around.
The time to begin a higher level of screening is now, while our country is mostly still at home. Once people with sub-clinical infections resume normal activities, the case numbers will steadily rise. We lost an opportunity to suppress this infection because of a delay in testing in the early stages of the pandemic, we should not lose another opportunity after making such a costly investment in suppressing COVID 19 by staying at home.
Being prepared to reopen the economy requires more than just testing. It is essential that we have an abundant supply of the things that protect us, from PPE to hand sanitizers. Currently we do not. Social distancing and the use of masks in the presence of others should be standard procedure. It would help if our leaders would adhere to these rules.
We would also be better prepared if we had a clearer understanding on how to fend off the virus. How often does the nasal swab (RT PCR), that we rely on so heavily, give false negative results, since such errors could really fan the flames of a pandemic. In addition, we need data that elucidates when infected individuals shed contagious viral particles, and especially when this shedding stops. Currently we use RNA detection (RT PCR) which is not the same as contagious viral particles. Patients are positive well into the 4th and 5th weeks of infection by PCR, but limited data suggests that contagious viral particles disappear long before that. Meanwhile, we are letting people out of isolation 3 days after their fever and most other symptoms resolve. It would be comforting to know that contagious particles are no longer present at that time.
Creating the infrastructure to ramp up testing and contact tracing will be rate limiting for many states. In the meantime, we can rely on staying home as the one extremely effective tool at our disposal. It has given us some control over this virus and has already made our communities safer, but we should not give it up until we have confidence in our ability to monitor and isolate almost every case of COVID 19. For most parts of the country, another 1-2 months of concerted effort will be life saving and may allow many parts of the economy to open up while we wait eagerly for a vaccine.