Turn of the coronatide

It may not be the beginning of the end, but in parts of the world that are detecting fewer cases of COVID-19, it is starting to look like the end of the beginning. Maritime metaphors are in heavy demand. Maybe it’s the thought of returning to the beach, as some have already done. The storms that have just battered southern Australia are a rough reminder that nature is unpredictable. These events can come without warning, and may return in waves. You may have noticed talk of a second wave of COVID-19, after a calm interval.

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Ebb tide or false dawn?

If a change is made to test criteria during the shift from response to pandemic recovery, it will affect the bottom line. The ebbing of COVID-19 cases is a real thing only as long as the basis of COVID diagnosis remains constant. But if case selection for laboratory tests change, it can introduce a bias that increases or reduces the odds in favour of detection. It sounds obvious when plainly stated: test everyone with symptoms and you should detect more positive cases than if you only test the sickest patients when admitted to hospital. Clearly, a higher percentage of hospitalised COVID-19 patients are likely to be positive than people who are well enough to stay at home. At the other extreme, inclusion of individuals who are positive without symptoms will add to the total while reducing the apparent mortality rate. This is why other figures can be much more instructive at this stage in the pandemic, as can be seen from metrics such as the effective reproduction number, the gradient of the epidemic curve and the number of days post-epidemic without cases. Experienced epidemiologists look at the whole data set from different angles, and identify trends with caution to avoid over-interpreting the data. No matter how much pressure to put a positive spin on the figures, we don’t want a false dawn.

Catastrophising is a national pastime

Too much time in lockdown fuels introspection and worst case scenario building in which the doomsayer’s prediction of oncoming disaster has the upper hand. The end of life as we know it has not, to the author’s knowledge, happened yet. Some would go so far as to say that the clear and present national threat has thrown us and our leaders together in ways you wouldn’t have picked four months ago. Yes, it is the responsible thing to plan for similar problems over the event horizon. Yes, even in Australia, that may include a second wave of COVID-19 going from the rate of SARS-CoV-2 mutation. But no, a potential second wave does not necessarily have to be a tsunami after the initial wave ebbs. The example so often stated is the 1918-19 influenza pandemic which was followed by a disastrous second wave of infections. Influenza belongs to a different virus family from the coronaviruses. In 1918 Europe was still embroiled in industrial scale warfare at the expense of the health and welfare of the civil population. And health care fell well short of the standards available today. SARS and MERS are much better precedents, though COVID-19 has its own unique features.

Tidelines

The cautious observer will stick to the firm sand between the high and low water marks. COVID-19 may well return in weeks to months, and might even return periodically as a result of continued virus mutation. But the apocalypse tomorrow scenario that came on the back of the northern hemisphere portion of the pandemic lacks plausibility. What we now need is decent mapping of COVID-19’s tidal reach, including the high water mark using properly validated laboratory tests, carefully planned survey methods and robust epidemiological analysis. There are plenty of anecdotal reports and small studies appearing in the rush to publish. Now that the early stages of the pandemic have passed, it should be possible to conduct studies that address some of the big questions about diagnosis, treatment, prevention and surveillance.

Logic in the time of coronavirus

COVID – 5 facts