Making sense of Montana’s COVID-19 data

As Montana passes into the dog days of a socially distanced summer, it’s been 20 weeks since the state’s first confirmed cases of COVID-19, announced March 13, signaled the global pandemic’s arrival in Big Sky Country.

A bewildering array of developments have been packed into that span: school closures, a stay-at-home directive, an economic reopening, a mask mandate — not to mention federal relief bills, anti-health order protests, anti-racism protests and a primary election conducted for the first time entirely by mail.

As Montanans try to make sense of the pandemic and its wide-ranging implications, many have turned to data in search of answers. Case count figures published each morning on the state’s official COVID-19 dashboard have become as familiar as social distancing and face masks.

Taken together with data compiled by the COVID Tracking Project, those figures provide a wide-angle look at the pandemic’s progression in Montana, from the initial round of cases to this summer’s new wave. Here’s the story they tell:

THE TOP-LINE METRIC: CASE COUNTS

Daily case counts show an early wave of cases that slackened following Gov. Steve Bullock’s March 28 stay-at-home directive, and then a renewed upswing in confirmed infections after the state shifted into its second-phase reopening in early June.

By early July, the number of daily cases routinely clocked in above the state’s initial peak. March 27, the day before the governor’s stay-at-home order went into effect, state health officials reported 37 new COVID-19 cases. The last time Montana’s daily case count was that low was July 6.

In total, the state had reported a cumulative 3,814 COVID-19 cases among Montana residents as of July 30. Because the official state case counts follow national data guidelines designed to avoid duplication between different states, these figures exclude most out-of-state residents who’ve tested positive while visiting Montana. Supplemental information on the Montana Department of Public Health and Human Services website indicates the state had recorded 187 cases of COVID-19 in visitors as of July 30, about 5% of the official total.

Additionally, because the official case counts represent only coronavirus cases that have been confirmed by lab testing, there’s some question as to how comprehensively they reflect the state’s true COVID-19 situation. To evaluate how much faith to put in those top-line numbers, it’s worth looking at two other metrics: the number of COVID-19 tests conducted on Montanans and the percentage of tests returning positive results, a metric known as the positivity rate.

Efforts to test Montanans for COVID-19 have ramped up substantially over the course of the pandemic. As Bullock began to roll back the state’s initial distancing orders April 29, he said he hoped to bring the state up to 60,000 tests a month, or 15,000 tests a week. While acknowledging that health efforts continued to work around testing supply shortages, Bullock also said the state would supplement targeted testing of symptomatic people with surveillance testing providing broad-based monitoring for the virus.

In the weeks since, the state has focused surveillance testing efforts on tribal communities and elder care facilities where residents are at particularly high risk for the virus, and also offered drive-through testing events in several communities. As testing supplies have become less scarce, the state has also relaxed its guidance specifying who qualifies for testing. For example, contact tracing investigations now typically involve testing everyone who has come into close contact with a confirmed COVID-19 case, whereas earlier efforts tested only close contacts showing symptoms.

Backlogs in recent weeks have delayed some test results and forced the cancellation of some surveillance testing. In aggregate, though, Montana has seen increasingly thorough monitoring for the coronavirus. The state reported results for 2,138 tests the week of April 26, according to the COVID Tracking Project data. The week of June 21 it reported 11,717. Last week it reported 19,136 results.

Increased testing, the governor has acknowledged, does lead to higher case counts as a broader search for the virus finds COVID-19 cases that would have otherwise gone undocumented. “Additional testing — we will identify more cases, people who might not have gotten tested [before],” Bullock said at a June 4 press conference.

So does that mean Montanans can write off the summer surge in coronavirus case counts as simply a matter of more comprehensive disease monitoring? In a word: No. The key to telling the difference between a real virus uptick and a testing artifact is tracking the positivity rate, which a coronavirus data guide published by Johns Hopkins University points to as a way to assess the relationship between testing and official case counts.

In essence, the logic behind the positivity rate measure is this: If a large percentage of coronavirus tests are coming back positive, that’s a sign that public health workers are testing only the people most likely to be infected — and an indication that testing may not be reaching enough people to give a reliable sense for how widespread the virus is among Montanans. Lower positivity rates, in contrast, are a sign that testing programs are testing enough people to provide reliable information on the outbreak.

Citing a World Health Organization recommendation, Johns Hopkins specifies a 5% positivity rate as a target benchmark for state-level testing programs.

Early in the pandemic, when only a handful of COVID-19 tests were being conducted in Montana each day, the state’s positivity rate fluctuated around the 5% benchmark. The aggregate positivity rate for tests conducted the week of March 29, for example, came in at 4.5%

When Montana’s case numbers ebbed in late April and early May, the positivity rate fell as the state ramped up testing. From late April to mid-June, Montana’s weekly positivity rate for COVID-19 tests never exceeded 2%. Put another way: even as Montana’s testing program cast a wider net, relatively few new cases were found.

But by mid-June, weeks into Montana’s testing ramp-up, the number of new COVID-19 cases identified each day began to swing upward. The positivity rate also rose, poking above 5% on a daily basis several times in July and averaging 4.3% the week of July 19.

That higher positivity rate means the number of cases identified in Montana has grown faster than the testing net has been widened. That, in turn, is evidence that Montana’s summer rise is more than a mere testing artifact — and that the virus truly has become more widespread in the state’s communities in recent weeks.

OTHER WAYS TO MEASURE A PANDEMIC

The official coronavirus data also provides two other metrics that help track how the pandemic is progressing independent of the case count figures: the number of Montanans hospitalized with COVID-19, and the number of deaths attributed to the virus. While Montana has seen relatively few COVID-19 deaths, both measures align with the official case counts.

Hospitalization counts are in effect a proxy for the number of acute COVID-19 cases, as well as a measure of how much stress the pandemic is putting on Montana’s health care system. While data for the number of Montanans hospitalized with the disease isn’t available before April 9, hospitalization counts echo the case counts in showing a May lull and a June-into-July resurgence.

Among the primary public health concerns throughout the pandemic has been the potential for the disease to snowball to the point where it overwhelms the ability of Montana hospitals to treat severely ill patients. While Yellowstone County, with Montana’s largest current COVID-19 outbreak, reports that demands on its local health care system are “beginning to outpace capacity,” state-level counts indicate Montana as a whole does have adequate hospital bed capacity for the time being.

As of July 28, the state had 1,026 hospital beds, including 202 intensive care unit beds, according to the state health department. Of Montana’s 52 hospitalized COVID-19 patients on that date, spokesman Job Ebelt said, eight were in intensive care, and three of the ICU patients were on ventilators.

While the 55 cumulative COVID-19 deaths Montana recorded through July 30 border on too small a data set to provide insight into the pandemic’s overall trend, they also cluster around the early spring and mid-summer case count peaks. 

A total of 16 COVID-19 deaths were reported by the state in March and April, with a 25-day stretch from April 30 to May 25 during which no COVID-19 deaths were reported. The virus’ summer case count surge has also begun to pull the state’s death count higher, with 32 deaths reported so far in July.

A significant number of Montana’s deaths are tied to outbreaks in elder care facilities. A March-April outbreak at the Marias Heritage Center in Shelby, for example, resulted in at least 29 cases and six deaths. More recently, a COVID outbreak this month has infected nearly every resident at the Canyon Creek Memory Care facility in Billings. According to the Billings Gazette, that outbreak was responsible for 15 deaths as of July 29.

It remains to be seen how much further death counts and other COVID-19 metrics might climb. In the meantime, public health officials continue to urge Montanans to keep their distance in public settings and wear face masks to minimize the spread of the disease. 

These numbers, they maintain, are statistics that the public’s actions can shift.

About the data used here:

Case counts and other state-level figures cited in this piece are sourced to the COVID Tracking Project, which has compiled the information reported via daily updates on Montana’s official coronavirus dashboard. These numbers may vary slightly from figures reported by other sources and, as discussed above, exclude nonresident COVID-19 patients who were diagnosed while visiting Montana.

News outlets looking to republish this piece under MTFP’s story sharing terms can find print- and web-optimized versions of these graphics for republication here. The code used to produce these graphics is also publicly available here.

Further reading:

• How to Understand COVID-19 Numbers, Caroline Chen and Ash Ngu / ProPublica
• Which U.S. States Meet WHO Recommended Testing Criteria, Johns Hopkins University Coronavirus Resource Center
• Montana overview, COVID Tracking Project