Context matters for local, state COVID-19 data. Here’s why.

By Miranda Willson

Wednesday, April 22, 2020 | 2 a.m.

Last week, the Southern Nevada Health District released a map showing how many people tested positive for coronavirus in each Clark County ZIP code.

Tuesday’s version of that map shows the ZIP codes 89148, 89117, 89107, 89108, 89031, 89030 and 89110 as having the most people who have tested positive. As of Tuesday, 107 people in 89110 had tested positive for coronavirus, more than in any other Las Vegas Valley ZIP code.

But the number of cases per capita tells a very different story.

For every 10,000 residents, 89109 had the most COVID-19 cases with approximately 50 infected people as of Tuesday. The ZIP code includes most of the Las Vegas Strip and has just 6,464 residents, according to the Clark County Department of Comprehensive Planning.

After 89109, the following ZIP codes have the most coronavirus cases per 10,000 residents: 89144, 89169 and 89107 each have approximately 22 infected people; 89085 has 19; 89106 has 17; 89141 has 16; and 89030 and 89139 each have about 15 COVID-19-positive cases per 10,000 residents.

The ZIP code 89110, by comparison, has approximately 13 coronavirus cases per 10,000 residents.

The discrepancy among ZIP codes with the most infections per capita and with the most total infections underscores the importance of accurately interpreting COVID-19 data, said Brian Labus, an epidemiology expert at the UNLV School of Public Health.

“When the Health District put out that map of cases by ZIP code, lots of people freaked out because they didn’t know what it was,” Labus said.

With more state and local data being released on coronavirus infections, deaths and testing, Las Vegans should keep in mind several factors when trying to gauge just how badly coronavirus is hitting their state, county or neighborhood, Labus said.

At the local level, not only should people think about whether their neighborhood has more people, but also whether it skews younger or older, Labus said. While coronavirus has infected Clark County residents of all ages, it is more likely to be serious or fatal in older people. So far, only one individual in Clark County under age 25 has died of the disease, while 110 of the county’s 141 deaths were people over 65.

Inconsistent COVID-19 testing rates is another factor to remember, Health District officials say. The rate of testing across ZIP codes has not been publicly released, and the health district doesn’t know how testing is affecting case numbers in each ZIP code.

“If we see more cases in a certain area, it’s difficult to say if there are more cases in that area or if people who (are) living in that area are more likely to seek testing,” Health District spokesperson Jennifer Sizemore wrote in an email.

Testing issues also affect countywide and state data when comparing Clark County and Nevada to other metropolitan areas and states.

Nevada had tested 32,347 people for COVID-19 as of Monday evening. That’s more than some states with comparable populations of close to 3 million people, such as Arkansas, Iowa and Kansas, but less than other similarly sized states such as Utah and Mississippi, according to The Atlantic’s COVID Tracking Project. The project, which breaks down how many COVID-19 tests have been conducted in each state, reports that Utah had tested 68,311 people and Mississippi had tested 51,434 as of Monday.

Although some states are testing people for COVID-19 more extensively than others, most health experts agree that more tests must be done nationwide to accurately assess the disease’s prevalence. Southern Nevada faces the same problem.

“Because testing is limited by the number of tests available, the overall number of cases is an underestimate, but we don’t know by how much,” Sizemore wrote.

Nonetheless, adjusting Clark County and other communities’ coronavirus cases by population still provides a more useful comparison than raw case numbers.

While the county had 3,099 cases as of Monday, it’s per-capita case count is about 132.3 cases per 100,000 residents, according to a county-level case tracker developed by Big Local News of Stanford University. That’s comparable to the rate in Los Angeles County, considered a coronavirus hotspot in the United States last month, which now has 137.6 cases per 100,000 residents. It’s also close to Washoe County’s per-capita COVID-19 case number of 140.4 per 100,000 residents, even though Washoe County has approximately one-fifth the number of cases as Clark County.

Because it takes up to 14 days for infected people to begin to show symptoms and up to one week or more for test results to come back, the public should also recognize that data on coronavirus cases “is looking into the past,” Labus said.

“If we stopped all disease transmission today, we’d still have new people developing it and new reports of disease over the next month,” he said.