On ending sheltering from the coronavirus

Comparing the United States and South Korea’s approach to finding new cases shows how reliable estimates can be most quickly obtained. By April 21, both nations had only tested about 1% of their respective populations. Throughout most of the United States, a prerequisite to being tested for the virus was being sick. South Korea, on the other hand, tested contacts of known cases regardless of whether they were sick, quarantining those contacts who tested positive for the virus. That difference explains why the percentage of tests that were positive was so much higher in the United States, 20%, than in South Korea, 1.7%, and why serious cases in those infected with the virus were over three times higher in the United States than in South Korea, 1.7% vs. 0.5%. South Korea’s approach enabled the country to slow the spread of the pandemic, accomplished by testing less than 1% their population. Slowing the spread by only quarantining symptomatic people, while everyone else remains sheltered in place, will take much longer and make it considerably more difficult to justify relaxing sheltering policies.

In the past, contract tracing in the United States was carried out by state and local health departments, but they have been decimated in recent years; following the 2008 recession 50,000 positions were lost. Using public health personnel, Massachusetts has already started contact tracing and San Francisco has started a small pilot study. According to The Daily Journal (April 23), San Mateo County will also begin contact tracing. The $25 billion authorized for testing by Congress on April 23 may enable recruiting the estimated 100,000 workers needed for extensive contact tracing throughout the country.

Contact tracing is arguably the most efficient and effective tool to help us decide when to reopen society, but it is not perfect. Two very recent studies have found that PCR tests for detecting SARS CoV-2 differed in the percentage of false negatives depending on their manufacturer. In both studies, one manufacturer’s test mistook at least 15% of specimens as not containing the virus when in fact it was present. People with these false negative results could infect others if they re-entered society.

It has not yet been proven that antibodies, detected by serological tests, protect people from reinfection with the coronavirus. Until it is, serology tests should not be used to decide on re-entry. Moreover, in one recent study, 7% of specimens with positive serology test results were falsely positive, indicating the presence of antibodies when in reality there were none. People with false positive serology results will be susceptible to infection with the corona virus (The FDA has yet to approve any serology test).

The rates of positive test results for SARS CoV-2 vary by age, race and socioeconomic status and other factors that differ by where people live. Consequently, rates of serious COVID-19 disease vary by county and state so that decisions on ending sheltering should be based on local data, also taking into account that people live and work in different jurisdictions.

More than 16 million workers have already lost their jobs due to COVID-19 and, for many, their health insurance as well. Even with federal assistance, many will live in poverty and without health care until they find work. And many of them will reside in counties with the highest rates of COVID-19. If antibodies prove to protect against reinfection with the virus, serology testing may provide most of those whose test results are positive reassurance that they will not risk reinfection by returning to work. Wherever possible, social distancing, masks and frequent sanitizing may still be necessary.

Contact tracing 5 million people, 1.5% of the entire U.S. population, more than the 5 million already tested, would provide reasonable though not perfect estimates of the rates of SARS CoV-2 infections and of serious COVID-19 disease. The sooner we expand contract tracing, the sooner we will have data on which we can safely reopen society.

Dr. Holtzman is emeritus professor of pediatrics at The Johns Hopkins School of Medicine. From 1995 to 1997 he chaired an NIH Task Force on Genetic Testing. Ensuring the validity of medical tests comprised a key part of the Task Force’s report (genome.gov/10001733/genetic-testing-report). He resides in Menlo Park.