Much of the increase of COVID-19 cases in Missouri last week was driven by cases in a few specific geographical areas, once again highlighting the importance of identifying case clusters and opening questions of when and how public health authorities respond to outbreaks.
Missouri Gov. Mike Parson said Thursday that 60 percent of the new cases of the disease in the state last week were driven by cases in Southwest Missouri, St. Louis and Kansas City.
Parson was reassured by decreasing case growth rates elsewhere in the state and in Southwest Missouri, as well as the stabilization of the number of hospitalizations in the state — down approximately 50 percent from a peak of more than 1,200 in early April to roughly 600 in June.
Cases were already increasing in Southwest Missouri before statewide public health restrictions were fully lifted June 16, and the Missouri Department of Health and Senior Services announced June 23 it was attempting to "box in" the outbreak in Barry, Jasper, McDonald and Newton counties.
The "box-in" containment strategy involves rapid deployment of widespread testing in a certain area, followed by isolation of infected people then tracing and isolation of everyone those people may have been in contact with.
That strategy was initially focused on congregate living facilities such as nursing homes, jails, prisons, mental health facilities and dormitories. DHSS Director Dr. Randall Williams said last month a case in long-term care facilities is an easy trigger for identifying a potential hotspot of infections.
If one resident or one staff member of a long-term care facility is infected, Williams said, the facility is obligated by rule to report it to DHSS within 24 hours.
For outbreaks in food-processing plants, at events or in prisons, "we get feedback from the local health departments, and most of the time they alert us, and they say 'We're seeing an increased number of cases down there that we think are a result of this either geographical entity, or living entity, or some nexus where we think those cases are from,'" Williams said.
The outbreak in Southwest Missouri involves a Tyson Foods plant in McDonald County, though there were other case clusters in the region.
"It's clinical judgment for anything other than long-term care facilities," Williams said of when a box-in strategy is triggered. He added that if testing indicates an outbreak, "subjectively, we're more likely to go in than not."
When someone does get infected with the coronavirus, it's so far become less likely in Missouri they will infect more people — though that's dependent on the public's efforts to maintain social distancing, wear face masks and practice good hand hygiene, as well as health authorities' efforts.
Williams said last week the infectivity rate, or "R naught," of COVID-19 has decreased statewide from an April 7 peak of 2.8 to somewhere between 1.1-1.2 — meaning every person infected with COVID-19 likely infects one other person, whereas before they were likely to infect more than two people.
An infectivity rate of less than 1 means people are getting infected but not passing it on to someone else — how the pandemic would eventually subside.
As of June 30, Southeast Missouri had the highest rate — 1.34 — with a margin of error of 0.07, according to DHSS data; the rate could be as low as 1.27 or as high as 1.41.
Northwest Missouri had the lowest rate — 0.59 — with a 0.1 margin of error.
Central Missouri had an R naught of 1.08, with a 0.11 margin of error.
Southwest Missouri had an R naught of 1.10, with a 0.09 margin of error.
All of the models included with the information projected there will most likely be an increase in hospitalizations this month in every region of Missouri except the northwest — though how much of a possible increase varies widely within and between the other regions.
For now, as of Thursday, McDonald County continued to have the highest rate of cases per 100,000 people, at 2,469.88 cases per 100,000 people.
Of the four Southwest Missouri counties health authorities responded to with a box-in strategy last month, only Barry remained in the top 10 counties with the biggest seven-day percent increases in cases, as of Thursday.
Phelps County was in the lead at the time, with 22 cases a week before having become 44 cases by Thursday, a 100 percent increase.
Shannon and Taney counties had 56 percent increases over the past week — from seven cases to 11 in Shannon County, and from 43 up to 67 cases in Taney County.
Maries and Texas counties rounded out the top five, with 50 percent increases, both with four cases that had increased to six over the week.
Barry County's cases had increased 42 percent, from 43 to 61 cases.