ROCHESTER, Minn. — A new study is issuing a stern warning regarding coronavirus tests: they’re not infallible and false-negatives are bound to happen. Up until now the main problem with these tests was just making sure they’re available. While there are still millions who can’t find a test, availability is slowly increasing. That’s a great development, but the study’s authors caution that medical workers, public health officials, and the public in general all need to understand that these tests aren’t going to be 100% accurate 100% of the time.
They recommend that clinical and public health decisions be based on more considerations than just the number of confirmed COVID-19 cases via test. If social distancing measures are lifted too early due to an over reliance on test results, it could cause a catastrophic relapse of infections.
Right now, reverse transcriptase-polymerase chain reaction (RT-PCR) tests are universally being used to test for coronavirus. Unfortunately, the research team behind this study from the Mayo Clinic say that thus far, the sensitivity and overall performance of (RT-PCR) tests have not been accurately disclosed in medical reports.
Health care officials should already be planning on a “less visible second wave of infection from people with false-negative test results,” says study co-author Dr. Priya Sampathkumar, an infectious diseases specialist at Mayo Clinic, in a statement.
“RT-PCR testing is most useful when it is positive,” Dr. Sampathkumar adds. “It is less useful in ruling out COVID-19. A negative test often does not mean the person does not have the disease, and test results need to be considered in the context of patient characteristics and exposure.”
These tests are estimated to be about 90% accurate, but the number of false-negatives will assuredly grow each day as more and more people are tested all over the world.
“In California, estimates say the rate of COVID-19 infection may exceed 50% by mid-May 2020,” Dr. Sampathkumar explains. “With a population of 40 million people, 2 million false-negative results would be expected in California with comprehensive testing. Even if only 1% of the population was tested, 20,000 false-negative results would be expected.”
Right now there are over 4 million health care workers providing direct care to coronavirus patients in the United States. If every single one of those physicians were tested, and 10% were infected, that would mean over 40,000 false-negative results would appear. Unsettlingly, 10% is far below projections for physician infections.
“Currently, CDC (Centers for Disease Control and Prevention) guidelines for asymptomatic health care workers with negative testing could lead to their immediate return to work in routine clinical care, which risks spreading disease,” says first study author Colin West, M.D., Ph.D., a Mayo Clinic physician.
So, what can be done? The study’s authors have some recommendations.
First, measures like social distancing, PPE, hand washing, and surface disinfection should still be followed strictly regardless of test results. Universal masking among patients and health care workers is ideal across all scenarios.
More sensitive and accurate tests should also be developed as soon as possible. More specifically, blood tests that quickly identify COVID-19 antibodies are badly needed. Also, negative test results right now should always be taken with a grain of salt, especially among those in high risk groups.
“For truly low-risk individuals, negative test results may be sufficiently reassuring,” Dr. West comments. “For higher-risk individuals, even those without symptoms, the risk of false-negative test results requires additional measures to protect against the spread of disease, such as extended self-isolation.”
At the Mayo Clinic, testing is just “one of many factors we take into account in deciding whether the patient meets criteria for COVID-19,” according to Dr. Sampathkumar. Even if a person’s test comes back negative, if that patient was in close contact with a confirmed coronavirus case, or their chest X-ray appears even slightly abnormal, that patient is treated as if he or she has COVID-19.
“We need to continue to refine protocols for asymptomatic patients and exposed health care workers,” Dr. Sampathkumar concludes.
The study is published in Mayo Clinic Proceedings.