Miami-Dade changes COVID reporting calculations to align with state
After months of posting a higher rate of positive test results for COVID-19 than the state, Miami-Dade County officials have changed the way they calculate and report the metric — a key measure that gauges the level of testing and can show whether infections are rising or falling in the area.
The county changed the way it calculates the rate in order to more closely align with the Florida Department of Health’s method of arriving at the local positive test rate for new cases. The county’s rate has been higher than the state’s for months, a discrepancy that caused difficulty for local leaders trying to determine whether to impose closures and other safety measures.
The changes to the county’s New Normal dashboard began Saturday with the removal of two pages: one titled “Daily Positive Cases out of Total Tests” showing a two-week trend of local tests that were positive for COVID-19 and a second titled “New Positive Cases” reflecting the number of new tests and new positive results by day.
Miami-Dade officials also removed a page showing influenza-like illness data from the state. And they added a new measure: the positivity rate for Jackson Health System, Miami-Dade’s taxpayer-owned hospital network.
On Tuesday, the New Normal dashboard again was changed to add a page showing the state’s positivity rate chart for Miami-Dade. Miami-Dade has more cases, hospitalizations and deaths due to COVID-19 than any other county in Florida.
The revised New Normal dashboard also includes a statement that beginning on Tuesday, Miami-Dade will report four separate positivity rates each day along with an explanation of the previous differences in positivity rates between the state and county.
Jennifer Moon, Miami-Dade’s budget director and deputy mayor overseeing the county’s COVID-19 response, said in an email Tuesday that she was pleased the county and state were now in agreement over the local positivity rate.
She said that until Monday, the state hadn’t made clear what information it was using to create the state report, “despite multiple requests for an explanation. ... So we were reporting what we understood to be the number of tests for which results were received each day and the percentage of those tests that were positive,” Moon said. “I’m glad that we are all on the same page now.”
On Monday, Moon met with Yesenia Villalta, administrator of the Florida health department’s Miami office, to review their methods for calculating the local positive test rate. On Tuesday, Moon provided the Miami Herald with a two-page summary explaining the differences in the state’s and county’s methods for calculating the local positive test rate, and changes to Miami-Dade’s New Normal dashboard.
Miami-Dade draws its raw data on COVID-19 testing from the health department. The state calculates and reports at least three different positivity rates each day: a statewide rate based on all tests taken the prior day, including retests; a statewide rate for first-time positive tests only, excluding retests; and a cumulative positivity rate for everyone tested since March. All those rates are available daily on Florida’s COVID-19 report.
The state also produces a daily report by county that shows the daily positivity rate for new cases only — which excludes all retests of anyone who had previously tested positive.
Miami-Dade’s New Normal dashboard, however, had been calculating the local positivity rate for new cases by using numbers that represented only the people tested, and not those tested plus retests. The state, however, includes the retests in their calculation as long as the person had not been counted as positive before.
The county will no longer calculate its own local positivity rates, Moon said. Instead, the New Normal dashboard will now report three different positive test rates based on the state’s calculations: the cumulative positivity rate as reported by the state’s daily report; the daily positivity rate as reported in the state’s county report; and the 14-day average of the positivity rate reported in the state’s county-level report.
The New Normal dashboard will also report the positivity rate for Jackson Health System.
“This should serve as a leading indicator for JHS hospital resource needs,” according to the summary Miami-Dade provided to explain the differences in the state’s and county’s reporting.
The new, separate positivity rate for Jackson’s patients and staff that will now be listed by the county “is not necessarily indicative of what’s happening in the broader community,” a spokesperson said Tuesday.
“A large share of our tests are performed on symptomatic people, so we would expect a higher positivity rate than community testing sites and other locations,” the spokesperson said. “Also, because we have stopped elective procedures and other non-emergent treatments, we are seeing fewer patients coming to our hospitals for non-COVID issues, so naturally our numbers will be higher.”
Miami-Dade stopped reporting the 14-day average of local COVID-19 tests on Saturday after the Miami Herald reported on the long-running difference in the numbers, and efforts by county and state officials to resolve the matter.
On Friday, the rate of positive test results in Miami-Dade on the county’s New Normal dashboard reflected a 14-day average of 27.05%. The state health department does not report a two-week average, but it does provide daily positive rates for the prior 14 days in Miami-Dade. The rate on Friday was much lower than the county’s: 20.5%.
Both numbers are far above the 5% that public health officials say would indicate the virus is being suppressed.
Public health experts and epidemiologists say the positivity rate can be calculated in different ways depending on what someone wants to measure. The cumulative rate of positivity can provide insight into the extent of the pandemic, for instance.
But many epidemiologists believe the most accepted way to look at positivity rates is the way the state has been doing it — by dividing the number of newly positive test results each day by the total number of tests on the same day, excluding those who previously tested positive.
“It would answer the question: Is the pandemic increasing in your area, or decreasing in your area,” said Brittany Kmush, an infectious disease epidemiologist and assistant professor of public health at Syracuse University in New York. “That’s the one I’ve been kind of focusing most on — that kind of instantaneous positivity rate.”
Florida has tested more people for COVID-19 in the past two weeks than at any other time during the pandemic, an average of 92,630 people a day, representing an increase of nearly 59% over the prior two-week period.
But even with such a dramatic increase in testing, public health experts say Florida’s high positivity rate strongly suggests that the state may not be casting a wide enough net to know how much the virus is spreading.
The 9,440 new cases confirmed by the state on Tuesday represent a positivity rate of 13.62% for new cases.
This story has been updated to reflect new information regarding the state’s and county’s calculation of the daily positive rate for new cases.
This story was originally published July 21, 2020 at 2:03 PM.
