Arizona’s reports of new COVID-19 cases jumped by at least 1,105 last week, but at least the rate of increase may be slowing as the effect of stay-at-home and social distancing orders take effect, according to numbers posted Thursday on the state health department website.

Statewide, cases of new infections continue to climb, hitting 3,018 cases and 89 deaths on Thursday. (see https://www.azdhs. gov/) Those totals represent the tip of the iceberg, since only people with serious symptoms are getting tests — which remain in short supply. Studies elsewhere now suggest 25% to 50% of those infected may show few if any symptoms, but can still spread the virus. Some studies indicate people can infect others at least 48 hours before any symptoms appear.

Those studies show the continued importance of social distancing as well as the federal Centers of Disease Control’s latest recommendation that people wear masks when they mingle with other people in public.

However, Arizona’s figures at the moment don’t show the exponential rate of increase in new infections seen elsewhere. The state documented 45 new cases the week of March 8. The next week cases increased tenfold and doubled the week after to 989. For that three-week period, the rate of increase followed the exponential curve of the early infection in many hard-hit areas.

However, the site reported 1,105 new cases last week, a small increase from the previous week. Most of the tests are now being conducted in private labs, many of which have backlogs. Therefore, more cases might still show up from tests done in the week of March 29.

The number of tests has followed a similar pattern, rising from 55 the week March 1 and hitting 32,500 the week of March 29 and 34,564 for the not yet complete week of April 5.

Interestingly, more than 2,302 children have been tested, with just 83 infections detected — a 3.6% infection rate. Some 14,900 people in the 20-44 age group have been tested, with just 1,099 cases detected. But of the 6,100 tests among those older that 65, 726 have tested positive. This probably reflects the tendency toward much more serious symptoms in the elderly, prompting a larger share of those infected to seek a test.

Those tests don’t represent the presence of the virus in the population — just the percentage of people in each age group with symptoms who tested positive.

Still, with those very preliminary numbers, the rate of increase may be at least slowing in some areas.

It takes one to two weeks after infection for symptoms to develop. That means people diagnosed last week probably were infected in the weeks of March 8 or March 15, when the state had only a handful of cases and before the state had started to impose social distancing recommendations and closures. The effects of those closures are just starting to show up in the statistics tracking the spread of the virus.

Unfortunately, that slowdown in the rate of new infections doesn’t apply everywhere. For instance, the rate of increase continues to accelerate in Navajo County, even in these preliminary figures. Navajo County went from 8 cases documented during the week of March 8, to 35 cases the week of March 15, 63 cases the week of March 22 and 124 cases the week of March 29. The county now has 286 documented cases, behind only Maricopa and Pima counties — both with vastly larger populations.

Other counties have been more consistent. The positive tests went from 7 to 10 to 16 and then 52 in Apache County.

Cases went from 32 to 71 to 73 then to 210 in Coconino County.

Those numbers are all so small that the lag in reporting of positive results to the state could change the picture as more results come in for the week in question.

The rate of increase isn’t tracked on the website for counties with a low number of cases like Gila, Greenlee, Cochise, Graham and La Paz. Gila County now has three confirmed cases.

Maricopa County has the most cases overall and may be showing a decline in the rate of increase. The documented cases went from 21 during the week of March 8, to 290 during the week of March 15, and then 588 during the week of March 22. As of Thursday morning, the total of number cases was 1,689.

The rate of new reports in Pima County has also slowed, rising from 61 during the week of March 15, to 169 in the week of March 22, to 205 in the week of March 29. As of Thursday morning, Pima had a total number of 512 confirmed cases.

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