Public-health officials and politicians in Colorado often talk about the number of COVID-19 cases, hospitalizations and deaths in the state. But they speak much less frequently about another statistic that's absolutely key to understanding why the third wave of the virus is spreading so quickly, in part because of its weird, technical name and confusion over exactly what it means.
We're talking about R0 value, also referred to as R-naught, which a Colorado Department of Public Health spokesperson describes as "the average number of new cases generated per infected person. It is the rate of infection." And like so many other numbers in Colorado right now, the state's R-naught is bad and will likely get worse before it improves.
The "R" in R-naught stands for "reproduction." If the number is one, it means a person with a communicable disease such as COVID-19 is passing it on average to one other person. An R-naught below 1 causes the infection rate to go down, while a value higher than 1 translates to exponential growth. As of this week, Colorado's R-naught is edging toward 2 — and surpassing it in some places.
We asked the health department to explain R-naught, and why folks there are trying so desperately to drive it down. Here's that Q&A, conducted via email:
Westword: What is the current R-naught value for Colorado right now?
CDPHE: The current statewide R-naught value is estimated at 1.7.
The R-naught value has exceeded 1 in every Local Public Health Agency region, with the Central Mountains, Northwest and West Central Partnership all exceeding 2.
How does the current value compare to the typical value over the summer months, when COVID-19 cases and hospitalizations seemed to have stabilized at a manageable level?
The R-naught number was suppressed to below 1 for much of the summer. The rising R-naught number demonstrates how the virus is spreading exponentially.
Has the R-naught value in Colorado been on the rise over the past month or so, and if so, what concerns do the increases spark?
In the past month, the reproductive number, or the R-naught value, has increased. There are some more details of this increase on page 3 of the most recent modeling report.
Is there an R-naught value equivalent to the 5 percent positivity rate, which the World Health Organization has identified as a warning sign, and if so, what is it?
Just as we try to keep the positivity rate below 5 percent, we try to keep the R-naught value below 1.
Should the R-naught value in Colorado continue to climb, what are the risks to public health in terms of COVID-19 cases, hospitalizations and deaths?
As long as the R-naught value is increasing, we will likely see increased transmission overall. Increases in cases are normally followed by an increase in hospitalizations and deaths.
Are there any indications that the R-naught value in Colorado is about to peak, or do current trends point to continued increases?
If Coloradans don’t take bold actions to avoid gatherings during the month of November, we can expect the R-naught to continue to climb. To reverse course, we need everyone to know that the virus is spreading quicker than we have seen — and now is not the time to let up.
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