Report: Up to 90% of confirmed COVID-19 cases might not be contagious

Widely used tests may be detecting 'relatively insignificant amounts' of the virus.

Updated: September 1, 2020 - 1:52pm

Nearly 90 % of confirmed COVID-19 cases in the United States could be clinically insignificant and non-contagious, according to a recent newspaper analysis of laboratory data, raising the possibility that the widespread coronavirus mitigation measures put in place over the last several months may have been based in part on overstated viral test results. 

Public health experts throughout the U.S. are raising concerns that "standard [COVID-19] tests are diagnosing huge numbers of people who may be carrying relatively insignificant amounts of the virus," the New York Times reported on Saturday. A significant majority of the individuals who test positive "are not likely to be contagious," the paper says. 

At issue is the type of test often used to detect the novel coronavirus, one known as polymerase chain reaction or PCR. That type of test amplifies the viral genetic material in a sample, allowing testing machines to detect its presence.

The number of amplification cycles needed to detect the virus is directly correlated to a patient's viral load: The more cycles needed to get a positive result, the smaller the viral load in the patient. 

The Times reviewed "three sets of testing data" from New York, Massachusetts and Nevada. The paper found that "up to 90 percent of people testing positive carried barely any virus."

Citing a recent 24-hour U.S. tally of over 45,000 positive coronavirus cases, the paper said that "if the rates of contagiousness in Massachusetts and New York were to apply nationwide, then perhaps only 4,500 of those people may actually need to isolate and submit to contact tracing."

One virologist told the paper that it was "mind-blowing" that coronavirus tests are generally "just returning a positive or a negative" rather than detailing the actual viral load of the patient's sample. 

The Times's analysis, meanwhile, comes shortly on the heels of new research suggesting that asymptomatic spread of COVID-19 is comparatively rarer than earlier estimates. Scientists in China found that, among individuals with coronavirus infections, "asymptomatic cases were least likely to infect their close contacts."

Just the News Spotlight