Since I trashed the utility of the two most cited national Covid metrics (cases and deaths) yesterday, I think it is only right that we talk today about some metrics that actually provide, or will provide, critical information on the disease and its population impact. Wide application of testing, both diagnostic and antibody, is necessary for this country to make rational decisions on our economy and society. We have not come close to achieving the level of testing that will be required, although we are expanding our test capacity and are headed in the right direction. Just please bear in mind that testing in a vacuum provides no guidelines for decision makers. The scientific basis for directing our way out of this nightmare also includes the careful analysis and correct interpretation of all of the metrics, some of which we are about to discuss.

Covid Hospitalizations – At this point in time, this is my favorite metric. Knowing the level of hospitalizations from Covid in a given metro or geographical area provides us with important information about the disease on a number of levels. First, by knowing the hospitalizations and the daily trend in hospitalizations, we immediately know whether the disease is at, or approaching, our hospital bed and ICU capacity. Since any wave of these infections may overwhelm our health care system, close attention to this metric is critical to our response. In addition, tracking Covid hospitalizations provides public health officials with another indicator of the overall incidence of the disease in the community. A steady increase or decrease in Covid hospitalizations clearly mirrors community levels of the disease, with about a 5-7 day lag. Similarly, a steady rate of Covid hospitalizations means the the disease is remaining static in your community. I also realize that the accuracy of Covid hospitalizations as a statistic is reliant on the accuracy of the diagnostic tests. Even with that limitation, I believe this is the metric that should be most relied on currently to assess the impact of Covid on a population.

Diagnostic Test Positivity Rate – Many states are using this metric as one of the criteria for decisions on opening segments of the economy. Where I live, the number of tests performed and the overall positivity of those tests are reported daily by the media. The concept behind all of this attention is that if the proportion of the diagnostic tests that are positive falls (say from 8% to 7%) that means that the level of Covid in the population is falling and we can continue to open our society. I am not faulting the logic behind that concept, the only problem is that you can’t make those comparisons until you have your testing up to the level that represents the entire state/county/city population. Up until recently, the only people who were tested were symptomatic patients about to be admitted to the hospital. Now, in my county, there are tents set up at the white people’s mall for free testing. Guess who is going? Of course, the test positivity rate is going to drop when the denominator is flooded with people who have had almost no chance of exposure over the last 7 weeks. The positivity rate of diagnostic tests will be a good Covid metric over the coming months, just don’t pay it too much attention right now.

Antibody Testing – What a frightful mess this is! A Covid antibody test should tell a person whether they have been exposed to the virus at levels that would cause the body to develop antibodies to this specific virus. Basically, about 2 months ago, out of fear of being accused by this White House of slowing Covid response, FDA abdicated its responsibility of assessing the accuracy of tests for Covid virus antibodies. The result is that the US market has been flooded with poor quality antibody tests. Over 150 different brands of tests in about 60 days. Many of which are as useful in determining whether an individual has been exposed to this virus as a ouija board. The final outcome of all of this confusion is that, for most of these tests, a positive test does not mean that you have had the virus and, with equal certainty, a negative test does not mean you have not had the disease. There, isn’t that helpful. This problem becomes even more important because most Americans believe that a positive antibody test affords immunity to the person – they are invulnerable and noncontagious. Neither of those beliefs may be true even with accurate antibody testing. The good news is that the FDA has waded back into the fray and will begin assessing these testing methods and taking the least sensitive and specific ones off the market. When that happens, the level of positive antibody tests in a population will provide the only data on the historical prevalence of Covid for that community and that is important information on the scope of the infection.

One additional caveat for all of the Covid metrics: these data are reported by myriad sources – health departments, private labs, hospitals. Because of temporary data collection or reporting issues, recent daily reports may not completely reflect the actual results for that particular day. The best way to accurately assess these reports is to view recent trends to determine the direction the virus may be taking in your community.

We learn more about this virus and this disease every day, although some of what we learn causes initial confusion and great concern. Gone are the days when we thought Covid was simply a contagious respiratory disease that held children harmless. Nothing seems that simple anymore. On the positive side, as we learn more, our arsenal of weapons to combat the virus will increase. Personally, I don’t expect to be vaccinated for Covid by this time next year. I’d love to be proved wrong, but I think we are many more months away from that stage of Covid response than elected officials are claiming. If I am right, the metrics that we talked about in yesterday’s essay and in today’s will be critical in determining our country’s way out of this public health morass. So, get familiar with them.