The outbreak remains broadly entrenched, but transmission among those >64 years of age is concerning given this age group’s higher risk of hospitalization, ICU care, and mortality (Figure 2). Cases rates among those >64 years is now 85% higher than during the June peak, 437 versus 235 weekly cases per 100,000 residents.

Note: Data for this report was updated Friday, December 11 allowing 4 working days to adjudicate weekend cases and keep week-over-week backfill <10%. This allows more interpretable comparisons and graphics. All comparisons are week-over-week changes. Future updates will continue to be released on weekends.

Test positivity among those undergoing traditional PCR testing continues to increase, reaching 25.4% this past week (Figure 3). Increasing test positivity indicates that viral transmission continues to increase despite the uncertainty surrounding actual case counts. Test positivity for antigen tests being conducted by the University of Arizona and by some long-term care facilities and retail clinics was 21.1% this week. Test positivity for saliva testing being conducted by Arizona State University for students and other groups was 15.1% this week.

As of December 11th, 3534 (41%) of Arizona’s 8621 general ward beds were occupied by Covid-19 patients, a 21% increase from last week’s 2931 occupied beds (Figure 4 and Figure 5 Panel A). Another 768 (9%) beds were available for use. This is lower than the 861 beds available last week.

At 3534 occupied ward beds, Arizona has now exceeded its prior peak of 3517 beds. Because there are more ward beds now, percent occupancy remains below the July 13th peak of 44.7%. However, this record will fall next week.

As of December 11th, 799 (45%) of Arizona’s 1760 ICU beds were occupied with Covid-19 patients, a 14% increase from last week’s count of 701 patients (Figure 4 and Figure 5 Panel B). An additional 163 (9%) ICU beds remain available. This is higher than last week’s 144 beds. Max Covid-19 ICU occupancy was 970 beds on July 13th. If weekly increases persist, the previous peak will be reached before Friday, December 25th.

Arizona hospitals’ safety margin continues to erode in both the ward and ICU (Figure 6). Most hospitals have now cancelled scheduled procedures to ensure adequate capacity for patients with Covid-19 care. We are now undergoing the great “displacement” such that hospital services are now being rationed so that patients with severe Covid-19 illness are displacing others who have slightly less severe non-Covid medical conditions. As Covid-19 illness continues to increase, delaying others’ care will become ever more difficult. At some point, hospitals will have to expand their physical capacity. Make no mistake, the Covid-19 crisis is now placing a greater share of Arizonans’ health at-risk, not just those unfortunate enough to contract Covid-19.

With 617 deaths, the week ending July 19th remains Arizona’s deadliest week (Figure 7). Weekly Covid-19 mortality reached a nadir of 46 deaths the week ending October 4th. Because cases have been increasing, deaths are now increasing. Sharper rises are expected over the coming weeks as deaths lag new cases by 14-days and are often only made known weeks later. 

However, the case fatality rate has held relatively stable at approximately 1.5% (Figure 8). By Christmas, Arizona will be experiencing >500 deaths per week. However, this toll will not be apparent until mid-January when all deaths are accounted for.

It is difficult to say with certainty why the CFR has fallen over time. Clinicians are now much more experienced at managing Covid-related respiratory failure, relying less on mechanical ventilation and more on high flow oxygen therapy and proning. Treatment protocols are likely more standardized with proven beneficial treatments being more consistently applied, and perhaps more importantly, harmful practices discontinued. Better infection control practices at long-term care facilities has also reduced infections among the most medically frail patients who have so far accounted for 40% of Covid-related deaths in Pima County.

For those keeping score, Arizona has the fastest increasing Covid-19 outbreak as measured by Rt.live. Arizona’s effective viral reproduction number (Rt) is now 1.22, the highest in the nation (Figure 9). However, we are “only” 14^th in the number of daily cases at 81.9 per 100,000 residents (CDC). We can move ahead of Delaware, currently holding 13^th place at 82.4 per 100,000 residents, if we continue to do nothing. Remember, when it comes to Covid less (mitigation) is more (cases)!

For the week ending December 6th, 6326 Pima County residents were diagnosed with Covid-19 (Figure 10). This represents a 68% increase from the 3762 cases initially reported last week. This tally is far higher than the old record of new record for cases in a single week. Test reporting remains relatively timely with reporting delays causing last week’s initial tally of 3660 cases to be upwardly revised by 4% (144 cases) this week.

Increases in viral transmission are occurring across all age groups (Figure 11).

There was no update this week to the ASU Covid-19 model of projected cases, hospitalizations, and deaths through mid-January (full report). The current data continue to track as expected (Figure 11). The main findings are summarized in Figure 11. Assuming current viral transmission rates continue unabated, total Covid-19 hospitalizations in Arizona could exceed the total number of hospital beds by early January (green line). This change does not reflect increases that might occur because of Thanksgiving travel and gatherings.

**A special thank you to the members of the ASU Covid-19 Modeling Group for their efforts to bring greater understanding of the current outbreak and for sharing their report. Readers are encouraged to read the full report which can be found here.