As the number of Missourians testing positive for COVID-19 rises, so too can confusion about what case numbers mean and how they can be used to understand how COVID-19 is impacting the state.

As of Saturday, 12,385 people in Missouri had been tested through the Missouri State Public Health Laboratory, 21 mobile testing sites and nine commercial labs, according to DHSS Communications Director Lisa Cox. Of those, 838 people tested positive, including 49 in Boone County, and 10 people have died.

At the state lab, the rate of positive tests has hit 10%, which is higher than at commercial labs, according to state officials.

According to Cox, the state lab has tested 931 people, 92 of whom tested positive, resulting in a positivity rate of about 9.9%. But positivity rates drop when they account for testing done at commercial labs and change on a daily basis.

In the past week, for example, the positivity rate, which is calculated by dividing the number of positive cases by the number of total cases reported in a single day, increased from 4.37% on Monday to 7.14% on Wednesday. Cox said that positivity rates have not yet been calculated for Thursday and Friday.

Because the state and commercial labs are testing more people — around 2,000 a day as of this weekend — dramatic jumps in positive cases can occur even if the percent of positive tests doesn’t grow.

Cox also said that it is virtually impossible to figure out when people reflected in the state’s daily positives updates were actually tested, because labs operate on different timelines. The state lab, for example, is able to turn results in 24 hours from when the specimen arrives at the lab, whereas some private labs can take up to nine days to turn results. So, the new number of cases reported every day could include individuals tested yesterday and individuals tested last week.

DHSS Director Randall Williams said it is also important to recognize that people currently being tested in Missouri are those already suspected of potentially having COVID-19, whether it’s because they show symptoms or were in contact with someone known to be positive.

Why the difference?

One explanation for why positivity rates are higher in the state lab than in commercial labs is because their requirements to be tested are stricter.

According to state testing guidelines that were first issued Sunday by Williams, testing for people who are asymptomatic through either the state lab or commercial labs “is not recommended.” People who may be prioritized for testing, per those guidelines, are hospitalized patients with COVID-19 symptoms, symptomatic people with underlying conditions in 65-plus living facilities, or anyone who develops symptoms within 14 days of being in contact with someone who’s tested positive for COVID-19 or is awaiting COVID-19 results, including health care providers.

These guidelines have meant that there are limits on the number of people who can be tested for COVID-19 in Missouri. But concerns about test shortages, though not unique to Missouri, are not something Williams thinks the state will need to worry about long term, for a couple of reasons.

First, Williams said, is there is some evidence to suggest that COVID-19 transmission may slow in warmer weather. The specific paper Williams cited was first published March 17 by Qasim Bukhari and Yusuf Jameel at MIT. The paper’s key finding is that 90% of COVID-19 transmissions have been recorded within a temperature range between 37.4 degrees and 62.6 degrees.

Additionally, Williams said that Missouri tends to move out of flu season around April 15, meaning the number of people with coughs and fevers caused by the flu will go down and, thus, the number of people who appear to be symptomatic and may qualify for testing will go down.

State comparison

One thing the state is tracking, Williams said, is how Missouri compares to the rest of the United States and other countries fighting the spread of COVID-19.

One trend that has been identified in the U.S. and that Missouri mirrors is the clustering of cases in urban areas. This is different than what Williams said has happened in places like Italy, where cases appeared in rural areas and spread to urban ones. About half of Missouri’s cases, Williams noted, are in St. Louis city and St. Louis County.

This is one reason that the map on the DHSS site shows raw case numbers by county, as opposed to cases per 100,000 people. By mapping raw cases, clusters are more easily visible.

“We have enough positives now that we know that there is community transmission, and we know that community transmission can end up in our high-risk groups, like nursing homes,” Williams said Friday. That’s why, he said, “social distancing is really important.”

Williams said the state now has evidence of community transmission of COVID-19 in Kansas City, St. Louis, Springfield and Columbia.

Williams also said that the state owns 123 adult ventilators and 24 pediatric ventilators and is trying to get 220 more. Right now, Williams said, the current number of ventilators is sufficient. During a Saturday conference call between Williams and the Missouri State Medical Association, Williams said that the state makes ventilators available to hospitals that request them.

For more COVID-19 related news, see our section dedicated to COVID-19 updates.
  • Spring 2020 state government reporter. I am a senior studying data journalism. I can be reached by email at or on Twitter at @ashlyn_ohara.

  • Mark Horvit is the state government editor. Call me at 817-726-1621 with story ideas, tips or complaints.

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