Photo Courtesy of Abbott

What you need to know about COVID-19 Testing and Infection Numbers

You have been paying attention to the COVID-19 situation. You watch the numbers on the TV, you look at the graphs on Facebook and Twitter, and you hope that the country is able to increase those testing numbers. You are looking for hope that the curve is flattening and for the light at the end of the tunnel that represents a return to normalcy.

You also do not know who to believe in a time of so much misinformation.

You hope that the infection count and infection rate-ticker and the numbers are the best way to make your own decisions, but let's get a few things straight about the numbers before you make life and death decisions.

Behind the infection count and rates of new infections is a whole other story that is important to understand. The way that healthcare professionals and epidemiologists think about testing and infection rate is sometimes counter-intuitive to what the news-media highlights during their daily COVID-19 updates. It may seem like a TRUE fact, but sometimes those trying to interpret the numbers miss the whole truth.

Let’s take a closer look at the world of testing and the world of epidemiology when it comes to understanding the spread and scope of disease.

When it comes to infectious diseases, like COVID-19, it is important to understand three main concepts:

Concept #1: We can only test who we can access

Concept #2: Often we count those who test positive and official reporting is challenging

Concept #3: Biomedical tests are not 100% accurate

To better understand how these concepts relate to the numbers you see on the news and on charts that circulate the internet, let's look at epidemiology broadly.

Epidemiologists study disease and its spread. The field has broadened since it first emerged as a way to study infectious diseases, like cholera, that used to plague human society. While this seems like a thing of the past, there is always a risk of new infectious diseases, like COVID-19, emerging.

One of the primary goals of epidemiologists is to understand how many patients actually have a disease (known as prevalence) and the rate by which new individuals acquire the disease (known as incidence).

Said differently, the goal is to understand the number, or population, of patients that have the disease. Let’s use COVID-19 as our example.

For the sake of this example, let’s assume that the circle labeled “population” below is the TRUE number of people that have COVID-19. Then, let’s say that that the circle labeled “sample” is the group of patients that are actually tested for COVID-19. The population is TRULY infected with COVID-19 and individuals in the sample are the ones out of that population that have been tested.

As you can see, not all of the patients in the population of COVID-19 infected individuals have been tested. This brings me to Concept #1.

Concept #1: We can only test those to which we have access

If you take anything away from this article this is probably the most important one. We can only test patients who we can physically access to administer a test.

In our diagram above, the group of patients we test in the sample circle does not cover all the patients that TRULY have COVID-19 in the population.

Let's look at this a little closer. If you started to develop a cough, shortness of breath, and a fever, you would likely suspect that you have COVID-19. Thus, you would likely contact your physician, and, with any luck, you would have a test within a few days and a test result shortly after that. This is a good thing and you end up in the sample circle.

Or, another example, let’s say that you start to get very sick. You have difficulty breathing, you have a fever, and you feel like you have a truck on your chest. You may choose to seek emergency care and end up in the hospital. At the hospital, recognizing the symptoms of COVID-19, they would administer the test to you. Thus, once again, you end up in the sample circle.

Or, let's say that we, as a country, want to start really working hard to stop this virus. We might set up drive-through testing sites all throughout the country. You, wanting to be safe, decide to pack up your family and drive to the testing site where you can all get tested. Thus, all of you end up in the sample circle.

These are the three primary ways in which we test individuals. But, we cannot get to everyone.

What if an individual does not go through one of those scenarios? What if they have mild symptoms and choose NOT to call their doctor, do NOT require hospitalization, and do NOT go to a testing site for the sake of being tested? What if the individual has the disease but does not show symptoms and therefore would not seek testing or medical attention? The individuals in these scenarios could still have COVID-19 and be infectious, but would likely not get tested.

Or, what about this example: what if there is a part of the country where testing is unavailable?

If we start to do a whole bunch of testing in North Carolina, but North Dakota does not have very many testing sites, then we will get a whole bunch of new positive cases in North Carolina, but very few in North Dakota.

We get results where we look for them.

Unfortunately, the disease could be spreading in North Dakota, but we would have no idea if we were not testing there. The message reported on the news would say something like “North Dakota is safe from COVID-19.” However, that may not be actually TRUE because the testing capacity is too low to catch the growth in the disease.

Thus, in both of these situations, we do not have access to individuals for testing, but the disease could still be spreading.

The numbers in the media are often counts of positively tested patients received from official reporting. But, as we saw in the previous scenarios, it is very possible that the disease is infecting more people than we are able to test — and therefore report.

As in the diagram above, the numbers reported to the media and through official channels may only count the group of people in the sample circle. But, the TRUE number of infections is still the population circle.

Concept #2: Often we only report positive tests and reporting is challenging

Once a positive test is received, there are procedures followed by local health departments, hospitals, and physicians. These positive tests are reported through official channels. These “official” counts of the disease are often the same ones that are shown on the news and on the charts that circulate on social media.

However, these channels suffer from two main issues. One, due to Concept #1 they are often under-reported and because of the manual nature of reporting there is often a delay.

As with most things, there are human beings involved in the counts and there are many places from which the counts are received. Thus, the hundreds of health departments and thousands of healthcare facilities often have quite the task they must perform on-top of caring for patients and managing the emergency.

Reports and counts from the “boots on the ground” are added to the national counts and tracked by national-level public health agencies like the CDC.

But, as testing takes time and there are numerous communication channels; there are often delays that inhibit real-time evaluation of the situation in the population of infected patients. This delay and the issues with testing can result in under-estimated infection numbers that are publically reported.

Imagine being a nurse with 10x COVID-19 positive patients on your shift. Your primary responsibility is providing life support to these patients. When it comes to reporting, you report positive cases to the unit you work on, then that unit reports the numbers to the hospital, then the hospital reports them to the local health department, which reports the numbers to the state health department, and then finally reports reach the CDC or other national resources.

Have you ever played the game of telephone while managing an overflowing hospital with patients that need respiratory support? This process can sometimes cause delays in reported case numbers.

Thus, if a whole bunch of new cases is one day behind from a county in Illinois, then they will not be counted in that week’s tally. This is an oversimplification, but the actual reporting of data can be a factor that impacts the tracking of the disease and the availability of real-time data.

This system is not perfect, but it usually works pretty well for diseases that are relatively under control. But, understanding the delay effect and the under-estimations that result can be important when making decisions.

The bottom line is that the numbers that we see on the news can be under-estimations and can be delayed. Thus, making decisions on today’s numbers alone can be problematic.

But, all of this that we have discussed to this point are at the mercy of something far more difficult to control. Enter, Concept #3.

Concept #3: Biomedical tests for any condition are less than 100% accurate

Now, here is the real kicker that causes challenges when it comes to testing for diseases.

In any disease, the use of a laboratory test to understand whether a patient has a disease, or not, has some margin of error. These errors are often defined as a false positive or a false negative. The goal of any test is to ensure the highest degree of correct answers. We want to know for sure that a patient truly has the disease of interest. If a test cannot give us a reasonably high rate of correct answers then it is not used as a test — but even a good test has some margin of error.

Let’s use the chart below to better understand what this means for our COVID-19 testing situation. In this figure, the top of the chart is the TRUE status of the patient. “Disease or Condition”= COVID-19 infected and “NO Disease or Condition” = NOT infected. These are the TRUE answers to the question, “does this patient have COVID-19?”

The left side of the chart is titled “test,” which, for us, represents the results of the COVID-19 test that is administered to a patient. On this side of the chart, you can see the situation where the result of the physical test is shown. “Test Positive” = Test Readout shows COVID-19 Infection and “Test Negative” = Test Readout shows NO COVID-19 Infection.

As you can see, there are two scenarios where a false answer is found (B & C). This means that the TRUE status of the patient does not match the answer provided by the test. In any testing situation, you will find a certain percentage of individuals tested will end up in this situation.

If a test produced a false negative for a patient, it means that the patient TRULY has COVID-19, but the test said no. Conversely, if the test produces a false positive, it means that the patient TRULY does NOT have COVID-19, but the test said yes.

In an infectious disease situation, we are happier to see a false positive because it will result in a patient being more careful and likely will have more protective measures taken to prevent the spread of the disease.

False negatives, on the other hand, are dangerous. If a patient is incorrectly told they do NOT have COVID-19, they may unknowingly infect other people because they may touch people, hug their friends, and go into public without knowing they are infectious. Hey, they think they don’t have COVID-19, so they are celebrating. But, at the same time, they are infecting others.

During COVID-19, we know that we are experiencing some number of false negatives — it is likely a high number due to the volume of tests we are administering. Thus, there are likely asymptomatic people walking around spreading disease thinking they are doing no harm.

This concept is always at play. The goal of any test is to get as many correct answers to the question, “does this person have COVID-19?” Unfortunately, tests for any disease have a margin of error.

These three concepts have a tremendous effect on our ability to understand the TRUE situation with the COVID-19 pandemic. The numbers that are reported on the official news or on social media charts are NEVER the exact TRUE number of patients that have COVID-19. There is a margin of error — and one that often results in an under-estimation of the infection rate.

Thus, when we look to make projections or to act on the information provided in these charts it is important to understand that they do not represent the exact TRUE number of patients with the COVID-19 infection. There is often a delay or an under-estimation of the actual TRUE trends in the disease spread.

This creates problems for real-time reactions to the situation on the ground. Making quick decisions based on today’s data may result in bad decisions being made.

But, these numbers do give us some idea about the trends when viewed over time. Unfortunately, the publication of these numbers also causes problems related to misinformation.

These concepts open up the data to interpretation by individuals who are inexperienced in how the healthcare system and epidemiologists handle disease tracking — we never rely on a single data point to make decisions.

You may see your friends on social media making claims about data without the proper disclaimers. You may see politicians indicating that things are improving in one area and not another. But, interpretation of the data as fact and without the complete understanding, can be dangerous.

To truly understand the state of the COVID-19 situation is to admit that we often know less than we think we do.

This situation affects all aspects of our lives. It is tremendously impactful for the globe. People are experiencing hardships, they are suffering, and they are dying.

Because of the impact, many individuals will attempt to use this time for political and economic gain at the expense of others — and they will use data to do it.

But, reputable epidemiologists and most healthcare professionals have dedicated their lives to studying disease in order to protect people from suffering and death.

They are the ones that act with an abundance of caution and that use their expertise to add additional value to the officially-reported data — there is more to be said than the numbers. Politicians have the power and ability to heed the warnings or to act in another manner in conflict with the recommendations of public health officials.

Many of the steps taken to prevent the spread and impact of this disease are uncomfortable and scary. But, political issues aside, there is only one way to stop the spread of this disease — isolation. Without a vaccine, we are powerless to prevent infection if one human contacts an infected individual.

Here are some things that we do know for a fact and can use to make decisions even if the most recent data does not provide enough information:

  1. Respiratory viruses are extremely infectious. They spread from person-to-person and surfaces-to-person. The only way to stop them without a vaccine is to keep people away from each other through social and physical distancing.
  2. There are hotspots. Your area may be fortunate to have fewer cases of TRUE infection. But, there are many areas that are hit hard. If an area opens up, it can also quickly become a new hotspot if the disease is still moving through the population.
  3. Urban areas and highly populated areas (like New York) have higher rates of infection because people are closer together. Also, these areas have higher concentrations of individuals of low-income that are at higher risk of infection.
  4. Individuals with existing chronic illnesses like diabetes, heart disease, asthma, obesity, and autoimmune diseases are at higher risk of death or serious disease.
  5. The death rate climbs when hospitals are overwhelmed and ventilators are unavailable to support patients that need them.
  6. Your efforts to limit contact with other people protect you, your family, and the rest of your community. This whole outbreak started with a single first case.
  7. People that make a living working at physical locations in foodservice, grocery stores, and transportation are at higher risk because they contact more people.

You will see many claims made in the coming weeks and months. I hope that this article will allow you to think a bit more clearly about the statements made by politicians, leaders, and your friends on social media.

And, I hope this leads you to have faith in the depth of knowledge brought to the table by healthcare professionals and those trained in these situations.

It is never just the graphs or the counts, but it is often the deeper meaning behind them that allows us to beat diseases like COVID-19.



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Robert L. Longyear III

Robert L. Longyear III

Co-Founder @ Avenue Health | VP Digital Health and Innovation @ Wanderly | Author of “Innovating for Wellness” | Healthcare Management and Policy @ GeorgetownU