Coronavirus Contextualized, 17th edition: Exploring, through data, COVID-19 in Nevada and beyond
Welcome to the 17th installment of “Coronavirus Contextualized,” a recurring feature in which we explore some of the numbers swirling around in the time of coronavirus.
Through these stories, we hope to parse the numbers, including confirmed cases of COVID-19, people tested, number of hospitalizations and deaths, and provide some context to them. You can view the prior editions of “Coronavirus Contextualized” here on our coronavirus page.
These stories serve as a written roundup of the COVID-19 trends we kept our eyes on this week, with all graphs and charts living permanently on our COVID-19 data page, where they are updated multiple times a day with the latest numbers.
We’re continuing to take suggestions for what kind of data, graphs and trends you would like to see analyzed in future versions of this story or included in a future update of our data page. Reach out to [email protected] with any feedback.
Below, we take a look at some of the latest COVID-19 trends in Nevada, as cases appear to be decreasing but deaths remain high.
A comparison of test positivity rates
More than one in 10 people who have been tested for COVID-19 in Nevada since the beginning of the pandemic in March has been positive for the virus.
Specifically, that figure was 10.7 percent as of Thursday, slightly down for the first time after 28 days of increases. However, the decrease was likely the result of the state reporting a relatively typical number of new positive cases, 729, and the highest number ever of new people tested, 10,359. Dividing those two numbers gives a daily test positivity rate of 7 percent, the first single-digit daily test positivity rate since early July.
However, it’s important to note that the new positive cases and the new people tested reported by the state on any given day don’t reflect people who were tested that day, or even the previous day. Rather, they reflect the most recent lab reports the state has received — meaning they could include results of tests taken one day ago or even 10 days ago, depending on how long the lab took to process the sample and send it to the state.
That’s why it’s often better to look at this data with a seven-day average that will smooth out the data, evening the impact of one day with a small number of new cases and a large number of new people tested, or vice versa. As of Thursday, the seven-day average daily test positivity rate was 24.9 percent.
The state of Nevada, on its COVID-19 dashboard, used to calculate the daily and cumulative test positivity rates the same way — by taking the total number of people who tested positive and dividing them by the total number of people who have been tested. However, it changed its methodology this week, now calculating test positivity by taking the total number of positive tests and dividing them by the total number of tests.
It is also now reporting that data on a five-day lag, with the goal of actually reporting the data based on the sample collection date. Put more simply, that means that the daily test positivity rate the state reported on Thursday, 16.5 percent, actually refers to data from five days ago; however, it also actually reflects samples that were collected that day — not just whatever results happened to roll in that day.
State officials, on a press call this week, gave two reasons for the change in how they are calculating the test positivity rate. For starters, the state was having issues with a vendor that was causing backlogs with the state receiving lab results and creating anomalies in the data. For instance, the daily test positivity rate was 45.2 percent on Monday, 39.5 percent on Wednesday and 7 percent on Thursday. State officials said Friday that the problem has now been fixed.
The change will allow the state to offer a more complete picture of the test positivity rate from five days ago, with the caveat that the data is also less up to date because of the five-day lag. That also means that it would remove anomalies caused by more results just happening to roll into the state’s system on one day versus another.
The second reason is that state officials want to ensure that they’re capturing people who get tested multiple times for whatever reason. State data show that 79 percent of people who have gotten tested for COVID-19 have only gotten tested once; 16 percent have gotten tested twice; and 5 percent have gotten tested more than twice.
Of those who have gotten tested more than once, 14 percent tested positive on their first time and 86 percent tested negative. Of those who first tested positive, 54 tested positive on their second test and 46 percent tested negative; of those who first tested negative, 5 percent tested positive and 95 percent tested negative on their second result
Looking at individual tests does offer a more up-to-the-moment picture of how many people are actively testing positive or negative for the novel coronavirus.
However, in other ways it can make the data more murky: If someone is required to get tested every week for work, they may have eight negative tests from the last eight weeks, thus perhaps deflating the test positivity rate in the overall dataset. Conversely, if someone contracts the novel coronavirus and continues to test positive twice or three times after their initial test, their multiple positives could inflate the test positivity rate.
Both ways of calculating test positivity may be helpful to look at for different reasons. The people method gives a sense of how many new, individual human beings have contracted COVID-19 in the community out of all the human beings who have gotten tested. The tests method offers a broader picture of what individual test results themselves are saying, a picture that would include repeat positive and negative results.
Cases and deaths
The data show that while a still-large number of new COVID-19 cases are being reported publicly each day, the number of new cases being identified is actually decreasing. As of Thursday, the seven-day average of new cases reported each day was 952, down from a high point of 1,176 on July 20. The numbers have fluctuated day to day but have been generally trending downwards.
In the last seven days, 6,667 new cases have been reported, or about 12.4 percent of the total number of COVID-19 cases reported since the beginning of the pandemic.
However, deaths hit a new high point this week, with the seven-day average of new deaths reported each day hitting 15.7 on Wednesday. The state has reported 95 deaths in the last seven days, or a little more than 10 percent of the 902 COVID-19 deaths in Nevada reported since the beginning of the pandemic.
It is important to note, however, that state officials have said that deaths lag new cases by about five weeks, meaning that even if cases are trending in a better direction, it will take some time for the number of new deaths reported to decrease as well.
COVID-related hospitalizations appear to have reached a plateau in Nevada, with cases fluctuating between 1,100 and 1,200 for the last 16 days. However, it is a high plateau, with hospitalizations climbing to a record of 1,165 on July 31. The previous high during the beginning of the pandemic was 711 hospitalizations on April 8.
As of Wednesday, the most recent day for which hospital data is available, 1,117 people were in the hospital with confirmed or suspected COVID-19.
The number of people in the ICU with COVID-19 hit a new high on Saturday, at 339, with ventilators peaking at 214 on Tuesday. As of Wednesday, those numbers were down at 307 and 208, respectively.
As of Tuesday, the last day for which the Nevada Hospital Association has published its detailed report, 77 percent of licensed hospital beds and 67 percent of licensed ICU beds were occupied.
Age and coronavirus
People in their twenties continue to make up the largest share of COVID-19 cases in Nevada, at 21.8 percent. They’re followed closely by those in their thirties, who make up 19.8 percent. Those in their forties make up 17.4 percent and those in their fifties make up 14.6 percent.
Those aged 60 and up continue to make up a smaller and smaller share of the total number of COVID-19 cases in Nevada. Those 70 and up made up 10.3 percent of COVID-19 cases in late June, compared to only 6.5 percent as of Thursday. By comparison, those aged 10 to 19 made up only 6.3 percent of cases in late June and are now responsible for 8.1 percent of cases, nearly overtaking those in their sixties, who make up 8.5 percent of cases.
Those under 10 continue to represent the smallest share of COVID-19 cases, at 3.3 percent as of Thursday.
County by county
Clark County continues to have, by far, the highest rate of coronavirus cases per 100,000 residents, at 2,038 as of Thursday. Washoe County comes in at third with 1,193 cases per 100,000, with Elko County at 993, Lander County at 922, Nye County at 804, Carson City at 590 and Humboldt County at 588.
All other Nevada counties have fewer than 500 cases per 100,000 residents.
Gov. Steve Sisolak announced this week a set of new criteria the state will use to determine whether counties are at elevated risk for the spread of COVID-19. Those criteria include:
- The average number of tests per day per 100,000, calculated over a 14-day period. If this number is less than 150, a county could be considered at risk.
- The case rate per 100,000, calculated by taking the number of cases diagnosed and reported over a 30-day period. If this number is greater than 200, a county could be considered at risk.
- The case rate per 100,000 and the test positivity rate, calculated over a 14-day period with a seven-day lag. If the case rate is greater than 50 and the test positivity rate is greater than 7.0 percent, a county could be considered at risk.
Counties that meet no criteria will be considered “low risk,” those that meet one will be “growing risk,” those that meet two will be “moderate risk” and those that meet three will be “high risk.” Those considered anywhere from growing to high risk could be subject to additional restrictions to mitigate the spread of COVID-19.