Much of what we know about the coronavirus has been revealed by testing: who has it, how widespread it is and where hot spots are. And testing enables contact tracing, a crucial public health tool that helps prevent small clusters of cases from becoming large outbreaks.
Yet our understanding of the pandemic and how best to control it is hamstrung by the fundamental limitations of testing.
Only a fraction of those believed to be infected with the virus have had their diagnosis confirmed by testing. Testing cannot catch all asymptomatic cases, since many people without symptoms never seek testing unless they work in high-risk locations like hospitals, nursing homes or prisons, where employees are tested regularly. And both kinds of tests — diagnostic, which determines if someone is infected with the virus, and antibody, which verifies a past infection — are fallible, with research showing some problems with false negatives and false positives.
We’ve come a long way with testing since the beginning of shelter-in-place 100 days ago, when California lagged behind other populous states in per capita testing. But there is still much left to do across the state. Here are four milestones we’ve reached, and four obstacles we still have to overcome.
Achievements
1. Anyone can get tested, symptoms or not. Back in mid-March, when shelter-in-place began, hospitals denied testing to many patients — even those with telltale symptoms of COVID-19, such as fever and shortness of breath — because of a severe shortage of tests nationwide. Health care providers and health officials worked furiously to erect drive-through testing sites in parking lots, event centers, fire stations, stadiums and, eventually, pharmacies. What began as just a handful of testing sites has grown to several hundred. And many state- and county-run sites now offer free tests for residents.
2. The state goal of 60,000 daily tests? We’re there. To understand how far the coronavirus has spread in a community, every day there needs to be 150 tests conducted for every 100,000 people, say Harvard researchers. In California, that’s about 60,000 a day. In late March, that was hard. The state went from conducting only a few thousand tests a day at that time to an average of about 70,000 a day now, according to a seven-day average of daily testing figures provided each day by the state public health department. Most people can also get tested relatively quickly, though not all can be tested at their own health care provider.
3. Some runaway contagions were averted. Testing and contact tracing have been used to identify and prevent some flareups of positive cases from becoming widespread, although most Bay Area counties have yet to hire as many contact tracers as they would like. At Laguna Honda, the first skilled nursing facility in San Francisco to test all residents and staff, testing identified four people who were positive for the virus in May. Health officials then tested the people those four had contact with and identified an additional four cases. Similarly, in April, after city officials identified two people who tested positive at San Francisco’s largest homeless shelter, contact tracing and widespread testing identified 93 other homeless people who tested positive.
4. People can get test results quickly. In the early days of shelter in place, labs processed coronavirus tests so slowly that people had to wait up to 10 days to learn whether they had the virus. But California’s enormous backlog of pending tests was cleared at the end of April. Now most people learn their results within days.
Hurdles still to overcome
1. Too few tests in nursing homes. Older residents are more likely than younger, healthier people to become very ill or die if they contract the virus. About 50% of the state’s deaths from COVID-19 involve residents and workers at nursing homes and other residential care facilities for the elderly. And while a few California counties, including San Francisco, recently began requiring nursing homes to test all residents and staff, the vast majority have not. As of June 17, just 21% of the state’s 1,223 nursing homes — 256 sites — had submitted the results of baseline testing for their residents and workers, according to the state department of public health, which requires all such facilities to complete baseline testing by the end of June.
2. Limits to testing technology. A diagnostic test can capture only one moment in time, and it’s difficult to pinpoint the perfect time to test. Some people test negative, then positive, then negative — all within a few days. This is because virus levels fluctuate throughout the course of infection. Getting tested too early, before the virus is circulating at levels high enough to be detected in a test, can generate a false negative result.
3. Antibody testing obstacles. Antibody tests are supposed to reveal whether a person has been exposed to the coronavirus. Although the U.S. Food and Drug Administration cracked down on sales of shoddy tests, some still have accuracy issues. They also can’t reveal whether a person is immune to reinfection.
4. Public data on testing is insufficient and inconsistent. The daily testing numbers reported by the state don’t include where tests are being done, or demographic information on who is being tested. The lack of details makes it difficult for the public to easily understand whether certain groups are being missed. County-level testing data is also inconsistent between jurisdictions.
Catherine Ho and Cynthia Dizikes are San Francisco Chronicle staff writers. Email: [email protected], [email protected] Twitter: @Cat_Ho, @CDizikes
