The problem of highly restricted testing in the US
The COVID-19 virus is quite deadly (mortality appears to be between 2 and 10% as discussed in my last post) though since we don’t know how many asymptomatic or mildly symptomatic cases there are, we still can’t be sure of this.
Why don’t we know the number of cases? In the US, so far you can’t order the PCR (or any other test) without CDC approval. Approval is contingent upon meeting a high bar, including known exposure.
Thus we are missing lots of cases, who are not being asked to self-quarantine if the cases are mild, and are thus likely to spread disease.
Why aren’t we testing broadly to get a sense of actual case numbers? The best guess is that CDC does not trust its own test, and that by restricting testing to those who are almost certainly positive to start with, they will make fewer diagnostic errors.
Tests kits were sent to state labs by CDC, then recalled, with the excuse that there was a problem with a “reagent”. A reagent could be any component of the test. CDC has not replaced the reagent or the test kits. States are begging for them.
Dr. Messonier (head of Vaccines and Respiratory Diseases at CDC) says CDC is keeping up with testing, there is no backlog, they can test 400 samples together, and turnaround is overnight. That should clue you in that relatively few are being tested.
Some other countries are reporting large numbers of new cases daily. Do they have better tests? Has any journalist looked into the relative sensitivity and specificity of tests being used around the world?
PCR is a rapid screening test, which when positive almost always connotes a true positive. Negatives may actually be positive if the sample does not contain enough virus or is collected or transported incorrectly.
What is also needed are viral culture tests, which could theoretically pick up cases missed by PCR. Such cultures might also be used to test the effects of drugs on the virus. What work is being done to develop COVID viral culture techniques? Might such tests already exist, since they would probably be very similar to those for SARS and MERS?
Update March 30: FDA says it is not their fault that tests were not available for novel coronavirus. Between the lines, I am reading, “It was the CDC, not us, and we accept none of their blame.”
Update Feb. 27: Australia developed viral cultures; so has CDC:
Akst J. Australian Lab Cultures New Coronavirus as Infections Climb. The Scientist. https://www.the-scientist.com/news-opinion/australian-lab-cultures-new-coronavirus-as-infections-climb-67031.
CDC has grown the COVID-19 virus in cell culture, which is necessary for further studies, including for additional genetic characterization. The cell-grown virus was sent to NIH’s BEI Resources Repository for use by the broad scientific community.
If there is a bat or other animal model for this virus, so much the better for testing drugs that might show efficacy against COVID-19. What work is being done on developing or using animal models?
I assume one gains immunity after infection with COVID-19, which usually occurs after infections, but not always. The next test needed is an antibody or T-cell test that will accurately identify immunity to the virus. People who have recovered should be studied to identify markers of immunity. Then, we will be able to identify those who can safely care for infected individuals without catching the disease themselves.
Let me reiterate: with the limited testing now being performed in the US, we are definitely missing many cases, and missing the opportunity to appropriately use quarantines to limit the rapidity of spread. Slowing spread is critical to producing enough masks, gowns, ventilators, ECMO machines, training hospital staff, building hospitals just for COVID-19 cases, etc.
We need an accurate test, probably a PCR test, NOW. What is holding it up?
Update Feb. 27, from WHO:
Ensuring ongoing test availability. WHO has procured a commercial assay (manufactured under ISO:13485) with strong performance data and shipped to over 150 laboratories globally as an interim measure for Member States requesting support. The main goal is to strengthen global diagnostic capacity for detection of the COVID-19 virus. Support is now also provided to ensure the quality of testing through the implementation of an External Quality Assurance mechanism.
Update March 27: China has a monkey animal model of disease as well as antibody tests.
Update: New CDC Testing Criteria, issued 2/27
Criteria to Guide Evaluation of PUI for COVID-19
Update 2/28: Initial CDC testing info and interpretation protocol:
|2019 nCoV_N1||2019 nCoV_N2||2019 nCoV_N3||RP||Result Interpretationa|
|If only one, or two, of three targets is positive||±||Inconclusive Result|
|–||–||–||+||2019-nCoV not detected|