(The author, Dr. Jerald Mark Garcia, is a Cebuano, an anesthesiologist practising in Honolulu, Hawaii.)
TO understand what Cebu is doing, you have to consider the rapid antibody diagnostic test (RDT) and the polymerase chain reaction test (PCR) as two completely different tests.
RDT is being used as a STRATEGIC test to determine what to do about the COMMUNITY (ex.: extend ECQ, lift quarantine restrictions). Whereas, the PCR test is used as a DIAGNOSTIC test to determine what to do about an INDIVIDUAL (ex.: isolate, treat, contact trace). Another way to put it would be that RDT helps leaders decide how to reopen the economy while PCR helps clinicians decide how to treat a patient. The results of each test help determine different things. One does not replace the other.
Rapid antibody test results are being used as a collective in order to determine Cebu’s prevalence or exposure to the coronavirus disease (Covid-19). Having this extra information will then help leaders decide whether or not Cebu as a community is ready to transition to general community quarantine (GCQ) by May 15.
It is conducted the same way SWS or Pulse Asia does a survey. They take a random representative sample of different population sets (example, per province or barangay) and ask the same question, such as “Do you approve of the job President Duterte is doing?” They then apply the collective result of that question to the entire Philippines. So, when SWS says, with a certain degree of confidence, that 94 percent of Filipinos approve of the job that President Duterte is doing, it doesn’t mean that they asked all 106 million Filipinos the question, they merely extrapolated from their sample size of a couple thousand respondents.
Cebu is essentially doing something similar because it is also impossible to test the million or so Cebuanos. However, the question that will be “asked” is: “Have you been exposed to Covid?” And the answer is not obtained verbally or in writing, it is obtained through the rapid antibody test (which is a blood test, NOT a mucosal swab test).
The results of that “survey” can then be extrapolated to give our leaders an idea of the prevalence of Covid exposure in Cebu, barangay per barangay. Depending on those outcomes, they may then decide to lift restrictions for certain barangays where prevalence is low and tighten restrictions for others.
Making these decisions based on this extra piece of information obtained through the RDT is much better than just blindly lifting or extending quarantine restrictions based on arbitrary dates, as will be done most everywhere else in the country. We know of other countries who’ve lifted restrictions only to place them back a few weeks later as their cases spiked again. Cebu hopes to avoid that scenario.
The PCR tests, on the other hand, remain the gold standard for diagnosis because it is the only way to tell if someone has the virus. PCR tests will continue to be used for:
1) People with Covid symptoms
2) Contacts of people with Covid symptoms
3) Frontliners who have contacts with too many people to know the extent of their exposure
The contact tracing and aggressive targeted massive testing that is currently being done using PCR tests will continue to be used the same way.
This part will not change for Cebu because the results of the PCR test determines what to do for individuals – should we isolate, treat and/or contact trace? It is also only the results of the PCR test that will count in the DOH tally.
The justification for following up a positive RDT with a confirmatory PCR test is best explained by the graph (grabbed from my alma mater, the University of Minnesota Medical School’s FB page). A positive antibody test can mean one of two things:
1) You have the antibody but not the virus because you have already fought it off. You are not contagious and do not need to be isolated. (So, there is no need to panic should the antibody test yield many positives. In fact, it might mean a significant amount of herd immunity which could be a good thing!)
2) You have the antibody but are still in the midst of fighting the virus, in which case you still have a significant viral load, enough to be contagious. Therefore, you will need to be isolated.
The decision to isolate cannot just simply be based on a positive rapid antibody test.
Remember, rapid antibody test = decision for community, PCR = decision for individual.
(Dr. Jerald Mark Garcia graduated suma cum laude from the University of Minnesota, finished Medicine at the University of Minnesota Medical School, and trained and did his fellowship in Interventional Pain Medicine at Case Western University in Cleveland, Ohio. He is the son of former Cebu City mayor Alvin Garcia and wife Ninette.)