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Opinions of Tuesday, 23 June 2020

Columnist: Dr Justice Kofi Boakye-Appiah

Ghana's two successive negative test regime

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So on our criteria for discharging patients from the isolation centers, I am so glad we have finally decided to scrap the two consecutive negative tests rule. I recall vaguely writing some time ago that it was an overkill and was going to cause needless crowding of the isolation centers as we are seeing now.

Some hospitals are reportedly admitting suspected COVID patients to the general wards due to a shortage of beds in the isolation centers, a very dangerous practice. Up until the end of last week, patients were required to test negative in two successive tests before being discharged and declared recovered. Not just two but two successive negatives so if a second test erroneously (however it remote the chance may be) came out positive, the patient restarted the cycle.

Some very well patients stayed for up to 30 days in isolation because they kept testing positive. Truth is, we were giving a wrong interpretation to the test results. I’ll explain.... There are three ways to test for COVID-19.

VIRAL CULTURES: This is the most specific way of establishing whether or not a person is infected. Samples taken from patients are placed in media prepared to match the most optimal growth environment for the virus. In days to sometimes weeks, the virus multiplies and grows to levels the eye can see.

Only VIABLE viruses grow. This is the best evidence of the presence or absence of the virus but considering how much time and resource is required in addition to the health and safety concerns involved in this method, it is mostly only applicable in research settings and hardly ever done as a routine clinical diagnostic method in hospitals. I am currently growing bacteria which take up to 10 weeks to culture. We can't wait that long.

Ghana does not do this. But I feel we should have done this for some hundreds of the isolated patients just for research purposes as this would have told us exactly how many weeks after infection a person still carries viable forms of the virus and is therefore capable of infecting others. It would have been a good learning point informing policy and management.
The second and newest method is antibody detection. Following infection with the virus, the body produces some antibodies to fight the virus.

Some of these antibodies have neutralising (protective) abilities, other do not. And so though a positive antibody test does not necessarily mean a person is protected, it confirms that the person has been infected. The most widely used antibody method has a specificity and sensitivity of close to 100%. Meaning if it is positive, then the person definitely did catch the virus.

The downside to this is that antibodies may persist for weeks to years after an active infection and so one is unable to as it stands now, tell the difference between a person with an active infection and one cured months ago as both will test positive. With time, we may be able to develop quantitative antibody tests with the ability to distinguish between measured titres in active infections and old ones.

But we are not there yet. This method is therefore not very useful in the clinical setting.

The third and most widely used test is the Real-Time Polymerase chain reaction test. This test basically identifies specific genetic portions of the virus and amplifies them multiple times to identifiable levels. It is an extremely sensitive test.

It is easier to perform in the context of COVID and gives results within a shorter period. Note that the downside to this test is that IT IS UNABLE TO DISTINGUISH BETWEEN LIVING AND DEAD VIRUSES since these genetic fragments can persist in the human body for weeks to years even after all viruses have died and are incapable of causing any disease or being spread. And this is the test Ghana and many other countries are using.

At the beginning of the pandemic, early data showed that patients were generally non-infectious and free of viable viruses 14 days after the onset of symptoms. This formed the basis for the public health recommendation of a 14-day isolation period adopted worldwide especially for the 80% plus of patients who did not need Intensive care treatment.

As time went on, further studies showed that the viral load went so low by day 11 that transmission from an infected person was almost impossible from then on. Countries such as Singapore have adopted this. Following on, three different studies have recently demonstrated that viral cultures (Method 1) performed in infected patients showed almost no growth of viable viruses by day 9.

I have heard the argument of the number of patients used in these studies being too small but that’s not quite accurate. I have looked at all the papers and the sample sizes satisfy the Fisher’s test for statistical significance. That argument is therefore overly simplistic and not solid. As I mentioned earlier, viral culturing remains the most accurate means of determining the presence of viable viruses.

Could these same patients still test positive on say day 16 if tested using PCR (method 3) as we do in Ghana? YES! The viral genetic material a PCR test looks for can last weeks to sometimes months in the body. Obtaining a positive PCR test on even day 21 in such a patient will not necessarily mean that he/she is still infected and can transmit the virus. So going the extra mile of requiring not just one but two successive negative tests is just excessive and a waste of resources. Each test is estimated to cost between $60-80.

Each day spent at an isolation center is an economic cost you and I can only guess. The opportunity cost is that many cured and asymptomatic patients have been in the isolation centers for days beyond the 14-day period and the centers are now full and overcrowded. Some hospitals are reported to be keeping suspected COVID-19 patients on general wards with patients suffering conditions that could predispose them to severe COVID should they get infected. This is risky.

Going forward, we have done a good thing in deciding to establish isolation centres. Even the rich countries didn’t do this but our peculiar housing situation meant we could not have afforded to allow infected patients to self-isolate at home as these countries did.

The last time I checked, up to some 79% of Ghanaians still lived in shared accommodations with shared amenities. But we must also be realistic in admitting the fact that we will not have the capacity to isolate all patients as the figures rise. We need to manage our space and money well. Scrapping the consecutive negative test requirement was a sensible decision.