California, whose coronavirus response was hailed as a success story, is now seeing 5,000-plus cases each day. Here's what went wrong.

• California was praised for its successful early response to the coronavirus, which kept the state's epidemic curve relatively flat — until recently.
• The state set new records for daily infections over the past week.
• Experts say parts of the state reopened too early.
• Racial and income disparities have also led outbreaks to grow in some Southern California communities.

California was the first state to issue a stay-at-home order to stop the coronavirus' spread. And it worked: For a few months after that mid-March directive, California's curve remained flat, with fewer than 2,000 new cases reported each day.

But in the past two weeks, California has ceased to be the country's shining example. The state hit its record number of new cases in a single day — more than 7,000 — on June 23, according to government data. California has also recorded more than 40,000 new COVID-19 cases since June 20, which pushed its case total over 215,000.

"In the last seven days, we've seen a 45% increase in the total number of cases that have tested positive in the state of California," Gov. Gavin Newsom said at a press conference on Monday.

On Sunday Newsom ordered bars in seven Southern California counties to close and recommended that health officials in eight additional counties do the same. He had mandated the use of face masks statewide starting June 18.

"What we did wrong was to start to open things back up too soon," John Swartzberg, a professor of infectious diseases at UC Berkeley, told Business Insider.

California lifted statewide restrictions while daily case numbers were still rising. The state didn't see either of the downward trends recommended in White House guidelines — a two-week decline in cases or a two-week decline in the share of tests coming back positive — before reopening.

The state's surge has mirrored trends in many other states that also reopened without seeing a steady decline in cases. The US recorded an all-time high of more than 45,000 new coronavirus infections on Friday, according to Johns Hopkins University data.

California's challenges have also been complicated by a patchwork of differing local rules among counties. Specifically, Southern California locked down later than the San Francisco Bay Area, then reopened businesses earlier, so the state's cases are disproportionately concentrated around Los Angeles and San Diego.

"What happened to California? It's called a pandemic," Swartzberg said.

California took early action to shut down but reopened too soon

Some of the US's first coronavirus cases were detected in the Bay Area in February. The region's six counties took the country's quickest, most decisive action, issuing a joint shelter-in-place order on March 17. The rest of California followed suit within days.

"We were cautious by wearing masks and social distancing — it really helped," Swartzberg said.

But days make a difference when a virus is spreading exponentially, and the three-day delay in Southern California's lockdown after the Bay Area's partially explains why its outbreak has been worse since the beginning.

"The problem is COVID-19 replicates quite quickly," George Rutherford, a professor of epidemiology at the University of California, San Francisco, told The Wall Street Journal. "Even delays by as much as a couple of days mean you get four times the cases."

The Bay Area and Sacramento hold 25% of the state's population but had only 16% of its COVID-19 cases and 14% of its deaths in mid-May, according to The Journal. The Bay Area has about 24,101 of the state's 215,000 cases, according to SFist. Los Angeles County, meanwhile, has recorded about 98,000 total cases. Its surrounding counties have another 32,000.

California shifted into phase two of its reopening on May 8, which allowed "lower-risk businesses," such as nonessential retail and childcare, to reopen with social distancing. The Bay Area remained under stricter local rules, however, while Los Angeles reopened gyms, outdoor recreation areas, and museums. Some of the state's rural counties with low case totals reopened retail and dine-in restaurants around that time too.

But the state's cases were still rising as those reopenings started, and its rate of positive test results remained the same — which suggests that the virus was still spreading undetected.

"By the second week of May, things were starting to clearly open up, and we really opened up around Memorial Day," Swartzberg said. He added, "Southern California has been too liberal in terms of opening things up."

Why Southern and Northern California are seeing different outbreaks

Since June 15, LA County has recorded 39% of the new cases in California, though it's home to only a quarter of the state's population, according to the Los Angeles Times.

In addition to the timing of LA's lockdown and reopening, another reason for the disparity between outbreaks in Northern and Southern California is that the LA area has more facilities that house elderly people and low-income residents — both groups are especially vulnerable to the virus.

Furthermore, Los Angeles has significantly more Black and Latino residents than San Francisco, and those communities have been hit disproportionately hard by the coronavirus. In California, Latino patients account for 57% of all coronavirus cases despite making up only 39% of the population, according to The Guardian.

The reason for this disparity is that Black and Latino people are more likely than white people to have preexisting health conditions that put them at risk for severe cases. Those underlying health inequalities are the result of systemic inequality and long-term discriminatory public policies. People of color are also more likely to be essential workers with jobs in factories and on farms.

One outbreak in San Diego County was among a migrant-worker center. Two major outbreaks at California prisons in May — Avenal State Prison and the California Institution for Men – killed inmates and spread the virus through staff into surrounding communities.

Testing has increased, but it's not the reason cases are spiking

While California has increased its testing capacity — testing more than 80,000 people a day — the share of tests coming back positive has also grown, suggesting increased testing is not the primary reason for the surge.

Newsom said on Monday that California's seven-day positivity rate was 5.9%. That's a rise from prior weeks — from May 14 through June 21, the state's positivity rate was between 4 and 5%, but never more than 5%, according to Johns Hopkins University.

The World Health Organization recommends that regions should be under a stay-at-home order if more than 5% of tests are coming back positive.

California has hired nearly 10,000 contact tracers, but Dr. Art Reingold, the head of epidemiology at the UC Berkeley School of Public Health, told Healthline that contact tracing alone would not fix the state's outbreak.

"The fact is that even under optimal circumstances, this would be an incredibly difficult virus to contain — and we're not doing a very good job in some parts of California or in the US, frankly," Reingold said.

Swartzberg believes the state can still prevent the situation from getting worse, though.

"We're going to do the best we can," he said. "We can't predict the future, but we're going to look at these daily numbers really carefully, do as much testing as we can, and let that inform decisions so that we can self-correct."