Ducking the Western Cape’s Covid-19 bullet

I must declare my interest in curating this story. It also happens to be the interest of thousands of immune-compromised people in the Western Cape, which has just seen a massive rise in the seven-day average of 'new' Covid-19 positivity ratios (daily cases/tests); from 12.7% to 17.3%. By comparison, the rest of the country stands at 1.5% to 2.6%. You see, along with hypertensives, diabetics, obese people and the elderly, (some at-risk categories), I'm a 63-year old cancer survivor (just off 18 sessions of chemo). My immune system is so compromised that if I catch the coronavirus, my chances of dying are above normal. The Western Cape, in particular the Cape Metro, also carries the country's largest burden of TB due to wet Winters (not to mention drug-resistant TB), far greater killers than the coronavirus. Ironically, tourism, the industry responsible for our relative prosperity, brought with it Covid-19-seeding visitors. Now we can't get lab tests back quickly enough to speed up self-isolation, tracing and treatment – vital if the flow towards private hospitals backing fast-filling public hospital ICUs is to be reduced. I'm finally ready for a CT scan and hopefully, my curative operation. However, if my private hospital's ICUs are full by month's end, I'll have a problem. My hospital allows each surgeon one serious non-Covid patient bed at a time. Wish me luck. – Chris Bateman

By Dave de Klerk*

It is generally agreed throughout the world, that the more testing that is done the better the virus can be "managed".

In table 1 this week, I have therefore only included those 27 countries (out of the 215 that have reported infections) that have done more than 500 000 tests to date.

They are ranked in decreasing order of mortality, deaths being presumed to be the most accurately reported data.

South Africa currently lies towards the bottom of the table with a ratio of deaths to positive cases found of 1.9% and deaths per million population of 7, both still very low. We have to date (23 May) had 407 fatalities.

Various projections have suggested that South Africa could ultimately have deaths in the tens of thousands. A reputable international actuarial consulting firm, NMG, predicted on 1 May that there would ultimately be 61 500 deaths caused by Covid-19 in South Africa. But how likely is this?? Our mortality rate of deaths to positive cases has held very steady at around 2%. So if we even look at an eventual total of 10 000 deaths, this would imply that we find a total of about 500 000 positive cases and, assuming our positivity ratio never exceeds 20 (about the highest any country experienced at its peak), we would need to do 2 500 000 tests to find all these cases. We've done approximately 500 000 tests over the last month and a half. How long will we take to do another 2 million?

Based on other countries' experiences of time taken to reach their peaks of daily deaths, it doesn't look at all likely to me, that we will even approach 10 000 deaths.

In addition, that level would imply 172 deaths per million population and, looking at Table 1 again, that would put us up to number 7 on that chart. Could we really be so very "far behind" other countries that our current  7 per million eventually grows to 172 per million population?  Common sense tells me that's very unlikely.

I've also updated Table 2 from last week.

There, the picture for the Western Cape looks considerably "less rosy".

The running seven day average of "new" positivity ratios (Daily cases/tests) has increased for the Western Cape from 12.7% to 17.3 %, a massive increase.

For the rest of South Africa the corresponding figures are 1.5% and 2.6%, still low but also increasing.

One point that is relevant though is that the tests for the latest week did not increase significantly from the previous week, still averaging about 4 000 per day.

The reason for this is clear from an extract from Western Cape Premier, Alan Winde's weekly press conference on 20 May.

"Testing/lab capacity is under severe strain. The National Health Laboratory , which is mandated to perform all public tests, simply doesn't have the capacity to test enough, and return tests quickly enough , for us to intervene with speed as these numbers grow."

If the limited tests available are being used mainly for people more likely to test positive, eg hospital admissions, this may partly explain the significant increase in positivity ratios- but there does seem to be, independently of this, a very significant real increase in infection rates in the Western Cape.

These running 7 day-average positivity ratios will continue to be monitored.

• Dave de Klerk is a retired actuary living in, or rather locked in, Cape Town.