Testing for Covid-19
Fast, low-cost testing is essential for averting a second wave of Covid-19 by MENACHEM FROMER, PAUL VARGHESE, and ROBERT M. CALIFFSEPTEMBER 23, 2020 notes that Abbot Labs's 5-minute test has a 1.5% false positive rate (a 98.5% "specificity").
CDC Influenza SARS-CoV-2 (Flu SC2) Multiplex Assay|Instructions for Use does not, shamefully, say in any clear way what its false positive and false negative rates are in its 11-page "Performance Characteristics" section. How shameful! I looked around to see if they admit the false positive rate anywhere else. The FDA doesn't on its [FACT SHEET FOR HEALTHCARE PROVIDERS https://www.fda.gov/media/139742/download]. I find that incredible. I should think one of the very most important facts would to be to tell testers to tell subjects the probability that a positive test result indicates you have a possibly deadly disease. They should tell them the false-positive rate, and then also explain Bayes's Rule and gives examples of the posterior probability that someone in a given population with a positive test has covid. For example, they should explain that if the false positive rate is 1%, and only .5% of the population has covid at the time the test is administered, a positive result is wrong with probability 67%; and that if 2% of the population has covid, a positive test wrong with probability 33%. What they do say is this:
What does it mean if the specimen tests positive for SARS-CoV-2, the virus that causes COVID-19? A positive test result for SARS-CoV-2 indicates that RNA from this virus was detected, and therefore the patient is infected with the virus and is presumed to be contagious. Laboratory test results should always be considered in the context of clinical findings and observations and epidemiological data in making a final diagnosis. Patient management decisions should be made by a healthcare provider and follow current CDC guidelines. The Flu SC2 Multiplex Assay has been designed to minimize the likelihood of false-positive test results. However, in the event of a false-positive result, risks to individuals could include the following:
a recommendation for isolation of the patient, monitoring of household or other close contacts for symptoms, patient isolation that might limit contact with family or friends and might increase contact with other individuals with COVID-19, limits in the ability to work, delayed diagnosis and treatment for the actual infection causing the symptoms, and unnecessary prescription of a treatment or therapy.
All laboratories using this test must follow the standard confirmatory testing and reporting guidelines according to their appropriate public health authorities.
