Updated on September 7th, 2020
All medical investigations involve a cost benefit analysis. This is not only financial cost. It is well recognized that excessive medical investigations have the potential to increase not only anxiety but also create complications and illness from subsequent tests and procedures. Testing is a key component of the strategy for controlling the COVID-19 epidemic and is likely to be so for some time. Testing healthy populations to screen for medical illness involves logistical and ethical challenges. As always information is key to resolving this dilemma.
Tests which may be performed for COVID-19 can be divided as follows:
- Tests which specifically look for the virus.
- Tests on the blood that look for evidence of antibodies which suggest current (IGM) or previous (IGG) infection.
There are several tests available which check for the COVID-19 virus. Hong Kong has increased the capacity for testing and is now actively undertaking a mass screening program. We recently undertook a survey of patient perceptions of this program. There is a genuine academic debate about the impact of testing an entire population rather than selective samples of higher risk cohorts. There are also questions about the positive predictive value of widespread testing when the prevalence is low. This is a technical issue that means even with the best currently available testing, the likelihood of a positive result being a false positive increases as any condition becomes less common. There is general agreement amongst medical experts that more testing is good and the tests which are used are valid and appropriate. The medical arguments are really over population selection, timing of testing and cost benefit.
In a community setting these tests are now being performed at home. At OT&P we use home saliva testing. The Government testing program uses nasopharyngeal and throat swabs. The swabs used in the Government program will, if anything, have a higher sensitivity and specificity than home saliva testing. Swab testing requires staff to wear full protective equipment as it carries a higher risk of infection. The decision on which test is used therefore depends on the setting. Government outpatients also use saliva tests on low risk patients. The key message is that testing in Government testing centres, outpatient clinics and private clinics is similar in accuracy.
A number of countries already require evidence of a negative test within a fixed period before arrival. Hong Kong will also require such testing for all individuals from higher risk destinations in addition to the on-arrival testing within Hong Kong. It is likely that evidence of a negative test will be required for many destinations outside of Hong Kong for some time.
There is also a blood test which measures antibodies against COVID-19 IGG. The IGG test becomes positive within the first few weeks of the illness. A number of reliable antibody tests are now available. The incidence of infection in Hong Kong is very low. In the study that OT&P conducted in partnership with the University of Hong Kong the seroprevelance in our population was only 1%. Even in countries with widespread infection, the antibody studies suggest antibody levels which are below those needed for herd immunity. We do not yet fully understand how many infected people get antibodies, how effective they are in protection and how long they are likely to last. We are also beginning to understand the importance of the T-Cell response in immunity in COVID-19. There is no simple test which allows us to measure effective immunity. For this reason, the concept of an antibody test as an ‘immunity passport’ is still some way off. It is likely that PCR testing will be the mainstay of control for some time yet.
We are aware that there is an increasing discussion about COVID-19 testing and we fully expect that our patients wish to make informed decisions on matters regarding their health. We are able perform testing both for the virus and for antibodies. Before considering testing it should be recognized that:
- The majority of patients contracting COVID-19 have a relatively mild illness and make a full recovery.
- If a PCR test is positive, the doctor will have an obligation to inform the Department of Health, and you will be admitted to hospital for quarantine and any close contacts may be asked to quarantined in a government facility.
- There are no mandatory reporting obligations regarding a COVID-19 IGG test. That is to say your doctor will not inform the health department. Clearly there are public health implications and you should discuss any positive test with a medical professional to decide the implications in context.
- PCR tests are point in time tests. A negative today does not guarantee that you will not become infected or develop symptoms in the future.
- The incidence of COVID-19 remains low in our population. Whilst that may change currently it is statistically most likely that in low risk cases symptoms are likely to be caused by another form of infection.
Hong Kong has instituted a policy of testing, case identification and quarantine. Hong Kong has world-class systems and expertise in the management of infectious disease. This has been reflected in the number of COVID-19 cases in comparison to other countries which were hit later by the epidemic. All OT&P clinics have been fully operational throughout this process. We are supporting the Hong Kong public health strategy and have been working closely with the Department of Health. Including PCR and serology we have performed more than 3,000 tests for COVID-19 with the vast majority being negative. We have enhanced infection control procedures in compliance with CHP recommendations and our ongoing accreditation with ACHS. We will continue to care for all our patients.
If you have any concerns or specific questions regarding this issue or if you wish to discuss the implications or logistics of testing for COVID-19, please arrange an appointment to discuss with your doctor.
1. Harris, R. (2020, February 28). How A Coronavirus Blood Test Could Solve Some Medical Mysteries. Retrieved from https://www.npr.org/sections/health-shots/2020/02/28/810131079/how-a-coronavirus-blood-test-could-solve-some-medical-mysteries