Incidence or Prevalence?

What does "recovered" mean? We have seen literally 56+ million people test positive for COVID-19, according to Johns Hopkins (on 11.19.20). Pew Research says that 14% of adults in the U.S. have either tested positive or "are ‘pretty sure’ they have had it." That is a fairly significant number. The fact is that this virus is extremely widespread.
But, the impact is so varied for different people. We have all heard about the "risk factors" in the news, as also published by the Center for Disease Control. But, that may not explain all of the variety in different people's reactions and symptoms. And, the reactions can be quite different. According to the Mayo Clinic
"COVID-19 symptoms can sometimes persist for months. The virus can damage the lungs, heart and brain, which increases the risk of long-term health problems."
Fortunately, there are also those who "recover completely within a few weeks." Anecdotally, I know people who have tested positive and claim to have never experienced symptoms. What determines which of these any one of us might anticipate?
And, what does "recovered" mean? According to, there have been about 56 million cases of COVID-19 worldwide (as of 11.19.20). There have also been about 39 million "recoveries" worldwide. That means currently about 17 million cases worldwide have not recovered. The same site says that almost 1.4 million have died of COVID. Thus, presumably about 15.6 million are currently afflicted with the disease, that is "symptomatic" and capable of spreading it. That is .2% of the 7.9 billion people on the planet.  
But, then the statistics become curious. The "recovery" rate for various nations is detailed.
                            Courtesy Statista. 
Striving to put those figures into context, what percentage of cases are "recovered" versus "active?" According to this data, it varies notably from country to country. 
And, we are bombarded with the diagnosis volume in our country, state, or county. The numbers are parroted daily by the news media. In recent days, the focus has been on the "increasing numbers." or the "second wave," or a "spike" in diagnosis rate. But, when I see these numbers, I am reminded of Albert Einstein: "Not everything that can be counted counts and not everything that counts can be counted." So, perhaps there is merit in discussing how things are being counted?
The Center for Disease Control (CDC) recognized this early on in the COVID-19/SARS-CoV-2 pandemic. The importance is "having a case definition helps to make sure cases are counted the same way everywhere." Therefore, it cast a definition, and "in the United States, a confirmed case of COVID-19 is defined as a person who tests positive for the virus that causes COVID-19." Thus, when we discuss that 56+ million, those are each a "positive" test (perhaps if you test positive twice you are counted twice?). 
Explaining further, the CDC explains that "case" count and differentiates it also. It explains that "incidence" is the "number of new cases reported over a specific period of time." Thus, since the beginning of this pandemic, the "incidence" is that 56+ million. However, we are also steered to a separate term, the "Prevalence," which is the "number of cases at one specific point in time."
So, consider if we were counting incidence and prevalence of theme park visitors instead. According to the Orange County Register, 57,000 is the average daily attendance at Disney Magic Kingdom. So, if we are discussing "incidence" then we look to the point of beginning (October 1, 1971) and we might say there are over a billion park visitors (1,023,150,000 = 17,950 days at 57,000 each). No wonder the lines are so long! But that is misleading. People have come, visited, and gone. They are not all there in line today. The "prevalence" today is perhaps 57,000. The prevalence last week might have been 399,000 (7 * 57,000). But no one is going to say "a billion people is a lot so I won't visit." 
So, it is perhaps the "prevalence" upon which we should focus our anxiety and even fear? Harvard Medical School suggests that:
"Most people with coronavirus who have symptoms will no longer be contagious by 10 days after symptoms resolve. People who test positive for the virus but never develop symptoms over the following 10 days after testing are probably no longer contagious, but again there are documented exceptions. So some experts are still recommending 14 days of isolation." 
Knowing that symptoms may take some time to appear (according to Florida, it could take up to 14 days), this creates a window of about 28 days during which someone might pass the SARS-CoV-2 virus to you, leading to contracting COVID-19, however the period might be shorter. 
Returning to "prevalence," then, it is likely that most of those 56+ million positive test-result individuals do not pose a threat to you or me. Instead, it is likely that the threat we face is only those "who test(ed) positive" in the last 28 days (up to 14 days after exposure for symptoms to appear, and thus get tested, followed by 14 days at the outside for contagiousness to abate). The time period could of course be shorter in the event that testing is done on surveillance (you learn of potential exposure and test before symptoms). 
The relevant "incidence" period as of November 22, 2020 is not 266 days (March 1, 2020 first diagnosis in Florida), but 28 days. The risk we face is not the 56+ million "cases" (positive diagnoses), it is the cases positive in the last 28 days (counted from when this post was written 11.19.20). According to OurWorldinData, 41.4 million of those total diagnoses had occurred as of October 22, 2020. Thus, the real concern, the "prevalence" for infection is 15 million (56m - 41.1 m) worldwide as of now. That is still a sizeable volume of people to avoid contact with, but it is far smaller than the 56 million touted by the news. 
Even better, most of those 15 million people do not live your town, shop at your supermarket, or attend worship with you. The bad news is, of course, that you don't have to be exposed to dozens of "cases" to become ill; one exposure will do. What, then is the Florida picture using this 28-day construct of relevant prevalence?
According to the Florida Department of Health, there have been 905,248 cases ("incidence") since March 1, 2020. The news recently has included headlines of Florida's "approaching one million" cases, suggesting that milestone has some relevance. Perhaps it does in terms of measuring our long-term experience through 2020. But, while that makes for a catchy headline, the relevant fact is that between October 22, 2020 and November 18, 2020, that prevalence for Florida is far less, only 150,442. Of the 21,477,737 Floridians, that is .7%. That is higher than the risk worldwide, but remains less than one percent. 
Breaking that analysis even further, what is really relevant is how many infected "cases" there are where you are (your grocery store, your house of worship, your workplace). There is relevance in how often you leave home, and what sorts of destinations that entails. I know a gentleman that has not been in a restaurant since March. I have been in dozens. I know people who are using "touchless" grocery pickup. I have spoken to people who compulsively wear masks (one does even in their own personal vehicle). You can take precautions as you see fit. You can literally reduce the number of people you meet while not wearing a mask to 0, if you choose.
The point is that overall prevalence is likely a better guide for us than incidence since March 2020. While there is merit in keeping track of the overall infection rate for many analyses, the risk to each of us comes down more to the prevalence and frankly our behavior. If we avoid crowds, wash hands, socially distance, wear masks, etc., it improves our odds should we happen upon someone that is positive and within that contagious period. Thus, while it we may feel powerless, it is suggested that we each have significant power to avoid this infection while we wait for the vaccination that is right around the corner, "coming soon to a pharmacy near you."
Of note, between October 22, 2020 and November 18, 2020, that prevalence for Florida was only 150,442. Of the 21,477,737 Floridians, that is .7%. On November 19, 2020 Florida reported 8,228 cases, so that is added to the running 28 day total in this model of prevalence, but the total cases for October 22, 2020 (3,692) would be similarly removed. The real change of concern is the difference, which is 4,536 (8,228 - 3,692). The total for the 28 days October 23, 2020 through November 19, 2020 is 154,978, still .7%. 
The fact remains that most of those people have appropriately quarantined and avoided you. Most of you have appropriately washed hands often, worn a mask when in enclosed spaces, practiced social distancing, and avoided crowds. While the headlines focus on incidence, our better focus is prevalence. There are not a billion visitors in Disney World today, and there are not 931,827 people in Florida with COVID-19 today. The prevalence is relevant to our risk of encountering the SARS-CoV-2, and that incidence number may really only be of interest to scientists who study such things. 
  • Read Also

    About The Author

    • Judge David Langham

      David Langham is the Deputy Chief Judge of Compensation Claims for the Florida Office of Judges of Compensation Claims at the Division of Administrative Hearings. He has been involved in workers’ compensation for over 25 years as an attorney, an adjudicator, and administrator. He has delivered hundreds of professional lectures, published numerous articles on workers’ compensation in a variety of publications, and is a frequent blogger on Florida Workers’ Compensation Adjudication. David is a founding director of the National Association of Workers’ Compensation Judiciary and the Professional Mediation Institute, and is involved in the Southern Association of Workers’ Compensation Administrators (SAWCA) and the International Association of Industrial Accident Boards and Commissions (IAIABC). He is a vocal advocate of leveraging technology and modernizing the dispute resolution processes of workers’ compensation.

    Read More

    Request a Demo

    To request a free demo of one of our products, please fill in this form. Our sales team will get back to you shortly.