CT’s coronavirus transmission rate tops important threshold

A customer gets his temperature taken by security before entering the Apple in Greenwich on June 17.

The coronavirus transmission rate in Connecticut has risen slightly above one, meaning that COVID-19 may have started to spread again in the state, albeit slowly.

“If that is greater than one, the number of cases is going to grow,” Virginia Pitzer, an associate professor of the epidemiology of microbial disease at the Yale School of Public Health, explained about the transmission rate. “If that’s less than one, the number of cases is going to decline. There’s some evidence that suggests that Connecticut cases are maybe growing a little bit right now.”

Three independent tracking sites all show the transmission rate in Connecticut, sometimes denoted as “Rt,” above that threshold. COVID ActNow, which partners with Georgetown and Stanford universities, indicates a transmission rate of 1.18.

Rt.live, built in part by Instagram founder Kevin Systrom, shows a transmission rate slightly lower, 1.03 in Connecticut, the 29th highest in the nation.

Covidestim, the transmission rate tracking tool built by Yale University researchers, Pitzer among them, shows a transmission rate of 1.12, the fourth highest in the United States.

But while the transmission rate can be a leading indicator, and “can be a useful indicator of whether or not we have become complacent in maintaining social distancing measures,” as Pitzer said, it does not mean the coronavirus is beginning to bloom again.

“While an Rt slightly above one may indicate the transmission is starting to increase again, it is not really all that different from having an Rt of 0.99,” Pizer said. “Also, if you are starting from a relatively low number of infections, it does not mean that we are going to see another big wave of cases tomorrow.”

Gov. Ned Lamont’s spokesman, Max Reiss, said the increase in the transmission rate can be attributed to a statistical recalculation.

On Friday, when the state released the updated coronavirus case counts, the release included “a large set of data provided by an out-of-state lab on tests that were conducted on Connecticut residents between May 23 and July 20 and not reported to the state of Connecticut until today. This data set provided by the out-of-state lab includes approximately 12,000 tests, 440 of which were positive.”

“The numbers reported for the one day are skewing the transmission figure,” Reiss said. “Taken as one day, it’s an increase, but over the period the state’s numbers continue to be very low.”

Pitzer, however, said Yale tracking tool, at least, takes those fluctuations into account, estimating transmission rates “based on the inferred number of new infections, which corrects for the inherent delays and biases in the reporting process and the natural history of the disease.”

In fact, Pitzer said she and her colleagues estimate that Connecticut’s transmission rate has been “slightly above one for over a month, although there is a lot of uncertainty in these estimates.”

Pitzer said “the Rt estimate jumps a little bit at the end (which may reflect Friday’s data), but has been pretty consistent in estimating that Rt has been at or slightly above one since mid-June.”

“The method we are using does not really allow for big jumps in Rt (or reported infections), which should help to smooth over ‘data dumps’ such as that,” she said.

Connecticut Media Group