Some states have seen increases in the last 14 days. Upticks in Arizona have health experts particularly worried.
An ABC News analysis of New York Times data found that new positive cases, hospitalizations and deaths have all increased in Arizona. While testing in the state also increased, that uptick cannot be attributed to more testing.
On May 15, when Arizona reopened, it reported 495 new cases. On June 23, the state reported 3,591 new cases.
By contrast, New York, once the epicenter of the coronavirus outbreak in the U.S., 597 new cases on June 23. Hawaii reported 2 new cases, though it had reported 27 new cases just three days ago.
Current hospitalizations also rose in Arizona, from 808 hospitalizations on May 15 to 2,136 hospitalizations on June 23.
The rate of positive tests in Arizona has fallen to 8.5% since late May. Experts say the percentage of positive COVID cases found during testing should be well below 10%.
But that number is still well above the rate in South Korea, considered a global leader for its COVID-19 response, which never had rates of positivity in testing above 1% or 2%. In New Zealand, which has all but eradicated the virus, the nationwide positivity rate averaged 0.5% from January through May.
New York City's positivity rate, which has fallen consistently since the city's peak, now stands at about 2%.
A high positivity rate can be a sign that a state is only testing its sickest patients and failing to cast a net wide enough to accurately capture community transmission, according to Johns Hopkins University, which has been tracking cases around the globe.
As to what's behind Arizona's rise, "it is hard to say with certainty," said Kacey Ernst, an infectious disease epidemiologist at the University of Arizona. While it's possible localized outbreaks in long-term care facilities are driving the numbers, Ernst suspects it's more likely that loosening state restrictions lead to increased community transmission.
"Many people equate reopening with being safe," Ernst said. "While there is certainly some uptake of masks and physical distancing, it is not ubiquitous."
Ernst also pointed to disparities within Arizona, where the indigenous population is disproportionately being hospitalized for and dying of COVID-19.
"While we are all experiencing a pandemic, it is broken into broad community transmission and many smaller defined outbreaks that have unique circumstances to be addressed. We are not yet in the place where we have well-developed capacity to test and do contact tracing for all of our cases," she said.
Will Humble, executive director of the Arizona Public Health Association, an organization for health professionals and former director of the Arizona Department of Health Services, pointed to Arizona's re-opening as the culprit.
In Arizona, "new cases were slowly declining throughout most of May, until the 26th," Humble said.
"Then there was a bounce-back, where it really starts to ramp up. There’s a rebound effect that began on May 26."
In response to the influx of cases and hospitalizations, Arizona has recruited traveling nurses to help treat coronavirus patients.
Bridget Harrigan, a traveling nurse, finished a COVID-19 hospital stint in New York City and has since been reassigned to Arizona.
So far Harrigan's one Arizona hospital shift hasn't been as rough as her shifts in New York, she said, but she's under no illusion that it will stay that way.
"It has every capability of getting there," she said, adding, "I'm hoping that that doesn't happen while I'm here. But if it is, that's what I'm here for."
As of June 23, Arizona had reported more than 58,000 cases and 1,380 deaths, according to the state health department.
Phoenix, one of the state's COVID-19 hotspots, is only in the beginning of its surge, Dr. Sam Durrani, chair of COVID-19 response at Arizona's Honor Care Health System, told ABC News.
Absolutely no one should be gathering right now, he added.
ABC News' Matt Gutman, Soorin Kim, Brian Hartman, Benjamin Bell, Terrance Smith, Kate Holland and Arielle Mitropoulos contributed to this report.
This report was featured in the Wednesday, June 24, 2020, episode of “Start Here,” ABC News’ daily news podcast.
"Start Here" offers a straightforward look at the day's top stories in 20 minutes. Listen for free every weekday on Apple Podcasts, Google Podcasts, Spotify, the ABC News app or wherever you get your podcasts.
What to know about the coronavirus:
- How it started and how to protect yourself: Coronavirus explained
- What to do if you have symptoms: Coronavirus symptoms
- Tracking the spread in the U.S. and worldwide: Coronavirus map
Tune into ABC at 1 p.m. ET and ABC News Live at 4 p.m. ET every weekday for special coverage of the novel coronavirus with the full ABC News team, including the latest news, context and analysis.