California has not seen the surge in coronavirus cases that have overwhelmed cities like New York and Detroit in the past week, which suggests that the state’s early and restrictive shelter-in-place orders could be slowing the virus’s spread. But experts say delays in testing have limited the understanding of the outbreak and have hindered containment efforts.

California implemented one of the earliest and strictest orders to stay at home in the United States in mid-March, and as of Wednesday, there were 8,584 confirmed Covid-19 cases and 183 deaths in the state compared with the 76,000 cases and 1,714 deaths in New York. Dr Deborah Birx, the White House’s coronavirus taskforce coordinator, said on Tuesday that she was “reassured by what California has been able to do” to help control the virus with physical distancing orders.

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Some doctors have said California appears to be succeeding at “flattening the curve”, meaning slowing the spread so hospitals have enough resources and workers to manage the number of cases. The California governor, Gavin Newsom, said on Tuesday that “the current modeling is on the lower end of our projection”. Last month, Newsom had warned that more than half of the state could be infected within two weeks. “We are in a completely different place than the state of New York,” Newsom said at a briefing on Wednesday. “And I hope we continue to be, but we won’t unless people continue to practice physical distancing.”

Indeed, the state’s early and ambitious efforts to enforce shelter-in-place rules do seem to have prevented hospitals from becoming as overwhelmed as New York’s system, Robert Siegel, a professor of microbiology and immunology at Stanford University, told the Guardian. “But it’s difficult to accurately know the impact of your interventions if you don’t have adequate testing,” he said.

As of Tuesday, more than 86,100 tests had been administered in the state, and of those, 57,400 results were still pending. By comparison, New York, which has about half the population of California, has processed more than 200,000 tests. Washington state, which has less than a fifth of California’s population, has processed 65,462 tests.

Testing efforts in California have been set back due to a lack of swabs, vials and media for collecting patient samples, as well as a shortage of kits and bottlenecks at labs.

Across the state, tests are in short supply and currently largely limited to people with severe symptoms and those with underlying health conditions, meaning large swaths of the state’s population are left untested. “The general idea is that if somebody that has been to the hospital, and they have symptoms, then you assume they’re infected,” said Siegel. But by testing more, doctors and health officials could be more strategic and selective about who they isolate, he noted.

Administering more than one type of test could also help California, and the country as a whole, better understand how the coronavirus spreads through communities. The tests being used in the US detect for the presence of viral RNA. Another type of test – called a serology or antibody test – can help detect if a person’s immune system has faced off against Covid-19 and recovered from it. Antibody tests are not currently being done in the US. “It’s really important to test for immunity,” Siegel said, because people who are immune could return to work without endangering themselves or others. “They could more safely work as frontline healthcare providers,” Siegel said.

Facebook Twitter Pinterest A homeless man pushes a cart full of his belongings along an empty street in San Diego. California has the largest homeless population in the US Photograph: Mike Blake/Reuters

Wendy Parmet, a Northeastern University health policy expert, said the testing problems made tracking the virus challenging: “You need testing to make sure you quickly identify new outbreaks and trace contacts. Put out the small sparks before they become another conflagration.” The lack of adequate testing could drag out the sheltering period, she said. “Many of the plans of how you go from where we are now to the next stage rely on testing,” she said.

A bottleneck in the commercial laboratory Quest Diagnostics, which is processing tests, has further exacerbated California’s challenges. Despite initial promises of delivering results within one to two days, the private lab in southern California, which has received tests from hospitals across the country, has not been able to ramp up processing fast enough, meaning some healthcare professionals have had to wait more than a week for results.

And although some in Silicon Valley are working on testing solutions, efforts in the international tech hub have been slow and largely unsuccessful.

“Why California would be lagging I really don’t know,” Siegel said. “Especially because it does strike me that we do have a lot of experts.”

South Korea’s widespread testing of its population, including people who did not have symptoms but might be at risk of spreading, played a major role in allowing the country to control the virus with significantly less disruption than other nations. Widespread, random testing in Iceland has similarly helped epidemiologists better understand how the virus affects people – data from the country found that half of those who tested positive are non-symptomatic, and overall a low population had been infected.

The test shortage not only prevents people suspected of having Covid-19 from getting a diagnosis and being counted and traced, it also hampers officials’ efforts to prevent an outbreak in the most vulnerable and high-risk communities.

California has the largest homeless population in the US, with 40,000 people living in crowded shelters where advocates say testing access has improved over the last week, but continues to fall short.

“It’s impeding the ability of shelters to identify people who have been infected with the virus and remove them from this incredibly dangerous environment, where the virus has the potential to spread like wildfire,” said Eve Garrow, the homelessness policy analyst with the ACLU of Southern California. She argued that all residents and staff should be tested, and noted that she recently heard from one shelter resident who has a fever, but was unable to get a test.

You need testing to make sure you quickly identify new outbreaks and trace contacts. Put out the small sparks before they become another conflagration Wendy Parmet

At one shelter at Skid Row in Los Angeles, where an employee tested positive this week, staff have isolated more than 100 people who may have been exposed, and are working to test as many people as they can. “They were slow to come … but hopefully we get enough tests,” said the Rev Andy Bales, who runs the shelter. He said he hoped health officials would provide enough tests for those potentially exposed and residents with symptoms.

“In New York, they were more aggressive about testing,” Siegel said. “We in California moved ahead with aggressive public health interventions in the absence of testing.” And although testing is crucial, ultimately, distancing measures are more important, he said, adding that California will probably have many more cases, especially in big cities, as testing ramps up. Still, Siegel doesn’t think the state will follow New York’s pattern.

Parmet said when federal and state leaders tout California’s progress, it could encourage people to stay home and distance and pressure other jurisdictions to follow suit: “It’s important for people to see that there are possibilities, that efforts can make a difference.”