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COVID-19 statistics: Making sense of the numbers

The Department of Health reports new cases of COVID-19 in Bay County, bringing the total to 83....
The Department of Health reports new cases of COVID-19 in Bay County, bringing the total to 83. (MGN)(WJHG)
Published: May. 18, 2020 at 2:50 PM CDT
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Millions of Americans have been monitoring the spread of COVID-19 since it was first confirmed in the country earlier this year. However, it can be easy to get overwhelmed when trying to process the various statistics tracked by federal, state, and city governments across the country.

Dakota News Now spoke with Dr. David Basel, an infectious disease specialist with Avera Health, to help make sense of statistics, testing, and other common questions around COVID-19.

Which stats are most important?

Dr. Basel said there is one statistic he keeps a particularly close eye on.

"The number that I pay the most attention to is actually the raw hospitalization numbers in the state," Dr. Basel said.

South Dakota tracks this stat as "current hospitalizations." While people tend to look first at case numbers, Dr. Basel said hospitalizations are actually a more reliable representative of how things are trending.

The key behind the value of hospitalizations - consistency. It's not affected by the many variables that impact raw testing or total case numbers.

"I would say that the testing statistic you got to be most careful about are the ones around the positive cases," Dr. Basel said. "Whether that's the overall number of positive cases, or the number of positive cases per capita. Any of those test positive numbers can be really skewed by how much testing we're doing."

Dr. Basel said case numbers would be reliable if the number of tests performed remained the same. The problem is - they do not.

The number of tests done per day in South Dakota vary substantially day to day. They generally increase as the state obtains more testing supplies, but they can still rise or drop drastically. A couple weeks ago, the state was processing 200-300 tests per day. Last week, that number hovered in the 600s, but then on Friday, spiked to over 900. On Monday, the total number of tests done was down to 486.

In addition, mass test events can greatly skew case numbers. In early May, nearly 4,000 Smithfield Foods employees and their families were tested as the plant prepared to resume operations. In the days that followed, South Dakota saw some of its largest increases in cases in the days that followed. And on Monday, health officials are beginning a new

involving every nursing home and assisted living center in the state. This will further skew both testing and positive case numbers.

Hospitalizations numbers are more reliable in that they are not subject to changes in testing. State health officials can track that number precisely each day by communicating with the state's health care providers. While hospitalizations do not track the numerous cases currently active among South Dakotans, officials say they are reflective of the actual spread.

"Our number of hospitalizations does have an impact with the COVID-19 response as a good indicator for activity level of transmission within the community," State Epidemiologist Joshua Clayton said in a recent press briefing.

Dr. Basel said he keeps a particularly close eye on the doubling rate - how fast hospitalizations go from 10 to 20, 20 to 40, and so on. He said this was a very concerning statistic in South Dakota in early April, when it was doubling every three to four days.

"That's when we began working very closely with city, state, governments, saying 'Hey we really need to get serious about the social distancing here, or we're going to be overwhelmed,'" Dr. Basel said.

The doubling rate stabilized, and has flattened over the past few weeks. As of Monday, 77 South Dakotans are currently hospitalized due to COVID-19. The state did not track current hospitalizations until April 20, when 56 people were hospitalized. This means the current doubling rate is at least four weeks. In addition, the number has hovered in the 70s to 80s for the past two weeks, which official say is a positive sign.

While hospitalization numbers are more reliable - they're not perfect.

"It's a little bit of a lagging indicator," Dr. Basel Said. "It takes two to three weeks for thing to be brewing, cases to be brewing in the community, before people start getting sick enough to come to the hospital. So when the governor made the announcement we're going to start opening things up again, it will take several weeks before we'll see that translated into an increase in hospitalizations, if we're gonna see that."

In addition to monitoring the spread of the disease, hospitalization statistics also give officials an active gauge for the state's COVID-19 hospital capacity. The main push behind early social distancing efforts in South Dakota was to slow the spread of the disease to give health care providers time to make more beds available for COVID-19 patients. In the past two months, providers responded by adding thousands of extra beds. Sec. of Health Kim Malsam-Rysdon recently said South Dakota now has over 2,400 hospital beds available for COVID-19 patients.

Who gets tested?

Another common question when it comes to testing - who gets tested, and why. Officials have long focused on people displaying COVID-19 symptoms. Some have asked why don't we just try testing everyone, or at least everyone who has come in contact with somebody diagnosed with the disease.

It's matter of supply - and effectiveness.

Dr. Basel said false negatives - where a test says a patient does not have COVID-19, but they actually do - are much more common among asymptomatic patients.

"The test itself doesn't work as well in patients without symptoms, because the virus load isn't high enough, and so you're not going to detect it as well. That false negative rate, is probably under ten percent in somebody that's hospitalized. In somebody who doesn't have any symptoms and feels pretty well, that number may be 30 percent," Dr. Basel said, though he clarified that those exact testing percentages are still in question, as are many things about the disease since scientists are still in the early stages of studying it.

And while the state's testing supplies are increasing, they are not infinite. This means officials need to use the tests the state does have in areas where they will be the most effective.

There are tests that may be helpful for those without symptoms, called serology or antibody testing. They are supposed to tell if a patient has had the virus before. However, so far, there have been issues with these tests.

"There's a lot of potential for cross reactivity to common cold coronaviruses out there. So if we detect antibodies, 90 percent of the time it's going to be to the new COVID-19, but ten percent of the time, it might be to the common cold. So we gotta be really carefuly to how to interpret that test, we don't want to give people a false sense of security," Dr. Basel said, again clarifying that the accuracy percentages are not certain.

Dr. Basel said at this point, antibody testing is more useful to large statistical testing rather than individual cases. When the tests are performed in large numbers, they are accurate enough to give officials an idea of just how many people have had the disease. But he said he would hesitate to make any personal medical decisions on an individual level based on the test.

In fact, there is still not a scientific consensus on whether getting COVID-19 once makes you immune to getting it again.

"COVID is just too new," Dr. Basel said. "We don't know for sure. We think that if you've had it once, we think you're going to be protected once for a certain length of time. It hasn't been around long enough to prove that yet."

When will we get back to normal?

We asked Dr. Basel one other common question - when will things get back to normal?

Dr. Basel said a vaccine would be the major milestone, but that is still at least months away, likely longer. He said for some elements of society, we may just get used to a new normal.

"This is 9/11 moment," Dr. Basel said, referring to the aftermath of the terrorist attacks on Sept. 11, 2001. "I think society will change a certain amount, probably going to have bigger space between us in line and at the airport. We're gonna have more space than we had before because of this."