The outbreak remains broadly entrenched including among those >64 years of age who are at highest risk of hospitalization, ICU admission, and mortality (Figure 2). For this reason, we can expect hospitals to continue to experience increasing occupancy at least through New Year’s Day.

Note: Data for this report was updated Friday, December 18 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 set a record this past week at 26.3% (Figure 3). Increasing test positivity indicates that viral transmission is increasing despite the uncertainty surrounding the precise case count. I am withholding the test positivity for antigen tests being conducted by the University of Arizona and by some long-term care facilities and retail clinics for quality reasons. Test positivity for saliva testing being conducted by Arizona State University for students and other groups was 16.8% this week.

As of December 18th, 4014 (47%) of Arizona’s 8548 general ward beds were occupied by Covid-19 patients, a 14% increase from last week’s 3534 occupied beds (Figure 4 and Figure 5 Panel A). Another 666 (8%) beds remained available for use. The number of available beds is lower than last week’s 768 beds.

At 4014 occupied ward beds, Arizona has exceeded its July peak of 3517 beds. At 47% occupancy, Arizona has also exceeded its July 13th occupancy peak of 45%.

As of December 18th, 939 (53%) of Arizona’s 1763 ICU beds were occupied with Covid-19 patients, a 18% increase from last week’s count of 799 patients (Figure 4 and Figure 5 Panel B). An additional 136 (8%) ICU beds remain available. This is lower than last week’s 163 beds. Max Covid-19 ICU occupancy was 970 (57%) beds on July 13th. These records should fall in the coming week.

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’ 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 also 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. By Christmas, Arizona will be experiencing >500 deaths per week. However, this toll will not be apparent until mid-January once all deaths are accounted for. As a rule of thumb, multiply the number of weekly deaths by 1.5% (approximate case fatality rate) to estimate the number of expected deaths in 2 – 3 weeks time.

For those keeping score, Arizona has the 7^th fastest increasing Covid-19 outbreak as measured by Rt.live. Arizona’s effective viral reproduction number (Rt) is now 1.11 (Figure 8).

Arizona ranks 4^th in the number of daily reported cases at 92.9 per 100,000 residents (Figure 9, CDC). We should move ahead of Rhode Island, 93.7 per 100,000 residents, this week.

For the week ending December 13th, 7237 Pima County residents were diagnosed with Covid-19 (Figure 10). This represents a 14% increase from the 6326 cases initially reported last week. This tally once again sets a record for cases in a single week.

Test reporting remains relatively timely with reporting delays causing last week’s initial tally of 6326 cases to be upwardly revised by 2% (98 cases) this week. Increases in viral transmission are occurring across all age groups (Figure 11).

Once again, there was no update to the ASU Covid-19 model of projected cases, hospitalizations, and deaths through mid-January (full report). The most recent projections are shown in Figure 11. Assuming current viral transmission rates match those predicted, total Covid-19 hospitalizations in Arizona could exceed the total number of hospital beds by early January (green line).

However, actual increases in hospitalizations and ICU admissions are beginning to deviate from this track. For example, total hospital occupancy on December 18^th was 4813 patients. According to the model projections, we would expect approximately 7000 hospitalized patients by Christmas Day, an increase of 2200 patients in one week’s time. This would be more than 3X the 620 patient increase observed from December 11 – December 18. For this reason, I expect the ASU model to be updated in the near future.

There are a number of reasons why Arizona may not realize the projected number of hospitalizations. The most obvious is that cases will not increase as fast as expected. However, it is also possible that hospitals are adjusting their admission criteria such that sicker patients are sent home. For example, a patient with low oxygen saturation who might have been admitted several weeks ago is now being discharged from the ED or the floor with a pulse oximeter and prescription for home oxygen therapy. Of course, both explanations could be happening simultaneously. Even if hospitalizations do not reach the heights projected as soon as projected, they are still going to reach unprecedented levels.

**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.