While COVID-19 positivity rates soon will play a role in whether Iowa students physically attend classes, state officials disclosed Tuesday that their 14-day averages are not based on the number of total new cases and tests in that time period.
Meanwhile, public health leaders cannot explain consistent discrepancies between their reported rates and those calculated using the state’s own figures.
The Telegraph Herald’s daily reporting of new COVID-19 tests and confirmed cases — taken from the state’s real-time, online dashboard — recently have consistently yielded both daily and two-week positivity rates that are different than those reported by the state.
The disparities were apparent again on the state’s coronavirus site Tuesday, when the state reported Dubuque County’s 14-day positivity rate as 11% and the county’s positivity rate on Monday as 6.9%.
The state previously had reported, as of 5 p.m. July 27, that 18,522 tests had been conducted in Dubuque County, with 1,362 cases of COVID-19 confirmed. Fourteen days later, at 5 p.m. Monday, the state website reported 20,852 tests and 1,684 cases in the county.
Based on the figures shared by the state, there were 322 new cases and 2,330 new tests in that 14-day stretch — a positivity rate of 13.8%.
Also based on state figures, Dubuque County had a positivity rate of 8.4% from 5 p.m. Sunday to 5 p.m. Monday. New results rarely are reported on the state website after 5 p.m. on weekdays.
Iowa Department of Public Health spokeswoman Amy McCoy told the Telegraph Herald on Tuesday that state officials are using a different method for calculating their 14-day positivity rate rather than taking the number of new confirmed cases and dividing it by the number of new tests in that span.
“My understanding is we are looking at the daily percentage of individuals positive, then doing the 14-day-average time frame from that,” she said. “So, not necessarily the case totals individually, from each day, but the actual percentages from each day over the 14 days, divided by 14.”
But with this approach, the positivity rates on any given day are weighted equally, even if there are large disparities in the number of new tests.
For example, if 5% — or 5 tests — out of 100 tests were positive one day and 15% — or 60 tests — of 400 tests were positive the next day, the two-day positivity rate would be 10% under the state’s method of calculating averages.
However, 65 confirmed cases out of 500 tests produces a positivity rate of 13%.
In the other Iowa counties in the TH coverage area, the newspaper’s calculations — based on the number of new cases and new tests during the 14-day period — all were higher than those reported by the state.
Clayton County had an 8.5% positivity rate using the figures, compared to the state-reported 6%; Jackson County had a 9.1% calculated rate, compared to a state-reported 8%; Delaware County had a 6.7% calculated rate, compared to the state-reported 6%; and Jones County had a 5.9% calculated rate, while state data reported 5% positivity.
And a discrepancy remains even when the TH used the state’s method for calculating an average for Dubuque County. Based on the newspaper’s daily reporting of state figures, the positivity rate during this 14-day span — using the state’s method — still averaged 14.5%.
McCoy acknowledged that the state’s method could influence the 14-day average, then noted that the two-week average itself is not the only factor influencing how schools operate.
“That is why we are pairing that 14-day rolling total along with the absenteeism (total) and then having conversations about what is happening in the community,” she said.
Two-week positivity rates reported on the state level are a critical factor in determining if schools can move to all-virtual instruction during the pandemic.
State officials said late last month that school leaders only can ask for permission to close buildings or districts if their counties have a 14-day average positivity rate of at least 15% and at least 10% of students are absent, or if the county has a 20% positivity rate over 14 days.
A call seeking comment to Iowa Gov. Kim Reynolds’ office on Tuesday was not returned.
Students in the Dubuque and Western Dubuque school districts will go back to school on Aug. 24. The nature of their educational experience could vary significantly based on the calculation of positivity rates.
Dubuque Community Schools Superintendent Stan Rheingans said the district is monitoring the 14-day average “on a daily basis” since it has been identified by the state as the “key indicator” for schools.
“The state has told districts that they will not consider a request to transition to fully online instruction for a school or district until the positivity rate reaches at least 15 percent and is accompanied by 10 percent of students in a school being absent,” Rheingans wrote in an email to the Telegraph Herald. “Locally, we are working to develop our own metrics on both ends of the scale to determine when we will look at students returning to school fully or when we would need to consider a move to fully remote education.”
Rheingans also acknowledged that he was aware of discrepancies in the way the 14-day average was calculated.
“We understand that there are some differences in how the positivity rate is calculated by various sources and look forward to clarification on those variations to determine the most appropriate metric to use,” he said.
Western Dubuque Superintendent Rick Colpitts said his district is not in direct communication with the state but is keeping a close eye on positivity trends.
“The proclamation (issued by the state in late July) directs us to work with local officials so we are in communication with the county health department, and they are probably using the numbers the state gives them,” Colpitts said.
Colpitts said he will continue to seek clarity on the metrics.
In the event that Dubuque County surpasses key positivity thresholds, districts would initiate the process of shutting down by applying for a waiver. He said state officials then would have to rule on waiver requests.
Given the importance of he county’s positivity rates, Colpitts resolved to learn more about how the figures are calculated.
“We have to dig into this,” he said.
In repeated conversations in recent weeks with the TH, McCoy also said the state reports both tests and their results simultaneously. Those figures are used by the TH to calculate 24-hour positivity rates, which also have repeatedly differed from state figures. No explanation for those discrepancies has been provided by state officials.