Mask mandates may be slowing Arizona's rate of virus infections, UA professor says

Arizona recently saw its slowest week-to-week increase in coronavirus cases in about a month.

“This is a bit of a subtle point. Things are still going to get worse, just not as quickly as before,” Dr. Joe Gerald, an associate professor with the University of Arizona’s Zuckerman College of Public Health, said in an interview Tuesday. “Absolute counts of new cases will continue to increase, they just won’t be as large as past increases.”

If cases continue to increase at a slower rate, it “provides evidence” that mask-wearing ordinances are effective, Gerald wrote in a report published Saturday.

Although Arizona does not have a statewide mask requirement, Gov. Doug Ducey said in late June that three-fourths of the state, including Pima County, is covered by local mandates that masks be worn in public during the pandemic.

Statewide and countywide cases both increased by less than 50% from one week to the next for the first time since the week after Ducey let his stay-home order expire on May 16, according to data published Tuesday by the Arizona Department of Health Services.

New confirmed cases in Arizona totaled 26,603 from June 21 to June 27. This was an increase of 6,456, or about 32%, from the week of June 14-20. Statewide increases had hovered between 52% and 68% over the previous four weeks.

In Pima County, new cases totaled 2,212 from June 21 to June 27, an increase of 242, or 12%, from the previous week. The four previous week-to-week increases had been between 50% and 87%.

These weekly case totals may still be incomplete due to reporting lags. While it generally takes four to seven days to report new test results, reporting lags often last even longer.

Statewide diagnostic testing is increasing, but at a slower pace than viral transmission, Gerald wrote in the report.

The number of diagnostic tests conducted in Arizona totaled 110,297 from June 21 to June 27. This was an increase of 19,768, or about 22%, from the week of June 14-20, compared with the 32% increase in new cases over the same time frame.

And the percentage of patients testing positive each week has dramatically increased since mid-May, from a low of 5% to 21% for the week that ended on June 27, according to data published Tuesday by the ADHS.

With a positive-test rate of 25% on Tuesday, Arizona had the highest positive rate of any state, according to a seven-day rolling average published by Johns Hopkins University.

The positive rate can help determine if a community is testing enough. A higher rate suggests that a community is mostly testing the sickest patients. A lower rate suggests that a community is testing more people, including those without symptoms.

Ideally this rate would trend downward over a 14-day period, according to official federal recommendations.

The reporting lag for deaths is even longer than the lag for reporting cases, often taking two weeks or longer.

The number of coronavirus deaths in Arizona totaled 202 from June 14 to June 20, the largest number of deaths in a week since the pandemic began, according to the data published Tuesday by ADHS.

“This is consistent with the recent increases in newly diagnosed cases,” Gerald wrote in his report.

“Given that case counts are continuing to increase, a larger number of deaths in the coming weeks is expected.”