SA Covid-19 stats ‘still looking good’, but winter is coming – Dave de Klerk

South Africa’s battle plan against Covid-19 has been described as being ‘ruthlessly efficient’ and it has been hailed by the WHO Health Emergencies Programme’s Executive Director Michael Ryan, saying the country has done “an impressive job” in bringing the spread of the virus under control. Seasoned analyst Dave de Klerk takes a look at the latest figures and how South Africa compares to the rest of the world and says the country “is still looking good” and added that testing is increasing at a good rate. But as tempting as it is to breathe a sigh of relief; the lockdown which has been more severe than in most other countries with the curious addition of a ban on the sale of alcohol and cigarettes, will be partially lifted at the beginning of next week, which would mean more people will come into closer contact with each other and the flu season is upon us. De Klerk says many countries ratios seem to correlate to some extent with ‘temperature’. – Linda van Tilburg

By Dave de Klerk*

Even though the absolute number of positive cases in South Africa has increased significantly over the past week, on the basis used in the table below (The ratio of positive cases to total tests) South Africa is still looking good with an unaltered ratio of 2.7%. This very low ratio was also applauded by Dr Michael Ryan, an executive director of the World Health Organisation at a media briefing on the 22nd April.

Coronavirus  Statistics.
A B C D E F G H
positives/ positives/ positives/ Change Deaths/ Average Average Increase
Country. tests % tests % tests % 11.04 to Positives% daily tests daily tests in tests
at 11.04 at 18.04 at 25.04 25.04 to 18.4 11.4-18.4 18.4-25.4 Per cent
USA 19.8 19.9 18.2 -1.6 5.3 146922 222433 51.4
Italy 15.8 13.5 11.4 -4.4 13.2 48909 57416 17.4
Germany 9.5 8.3 7.6 -1.9 3.2 58639 49187 -16.1
UK 23.6 24.8 23.2 -0.4 13.5 17923 25765 43.8
Iran 27.8 24.5 21.8 -6.0 6.2 11205 11420 1.9
Turkey 15.3 13.7 12.4 -2.9 2.3 36936 38519 4.3
Belgium 27.4 25.5 24.0 -3.4 14.7 6264 6153 -1.8
Canada 5.8 6.5 6.6 0.8 4.4 16381 24008 46.6
Switzerland 13.2 12.7 11.8 -1.4 5.0 3771 4129 9.5
Russia 1.1 2 2.7 1.6 0.9 92493 127087 37.4
Portugal 9.8 8.3 7.1 -2.7 3.5 10440 13519 29.5
Austria 9.8 8.3 6.9 -2.9 3.0 4994 6452 29.2
Israel 9.2 7.1 5.1 -4.1 1.2 9987 16492 65.1
India 4.5 4.4 4.5 0.0 3.2 26145 29691 13.6
S Korea 2.1 1.9 1.8 -0.3 2.2 6355 5597 -11.9
Japan 9.8 9.2 9.0 -0.8 2.2 6079 5161 -15.1
Chile 9.1 8.9 8.6 -0.5 1.3 4645 5760 24.0
Poland 4.9 4.5 4.0 -0.9 4.0 9057 12291 35.7
Denmark 8.8 7.9 6.2 -2.6 4.8 3381 6471 91.4
Australia 1.8 1.6 1.3 -0.5 1.1 7876 13213 67.8
Pakistan 8.2 8.3 8.8 0.6 1.9 4392 7402 68.5
Malaysia 6.3 5.3 4.5 -1.8 1.7 4128 3739 -9.4
UAE 0.6 0.8 1.0 0.4 0.6 16972 36475 114.9
Singapore 3.2 6.3 10.4 7.2 0.2 3159 3854 22.0
Thailand 3.5 2.7 2.0 -1.5 1.7 4091 6013 47.0
Argentina 11.9 9.2 8.0 -3.9 4.7 1845 2352 27.5
South Africa 2.7 2.8 2.7 0.0 1.7 4710 7569 60.7
Iceland 4.9 4.3 3.9 -1.0 0.5 922 697 -24.4
New Zealand 2.2 1.7 1.2 -1.0 0.8 3151 5394 71.2

A, B, C, D above. The demand for tests everywhere far exceeds the supply and it is assumed that mainly people with strong symptoms would generally be tested. The population infection rate would likely be much lower than these rates. Because of the strong motivation to find cases, improvement in this ratio should give some indication of a reduction in infection rates in a population and vice versa.

Column E above gives an indication of mortality rates of people testing positive for the virus. There are obviously time lags and the ultimate mortality rates may be higher. However positive test results take some days to process and this offsets to some extent the average times to death after being tested positive.

All data obtained from www.worldometers.info. Data for China, France, Spain, Netherlands, Sweden, Brazil and Mexico have been excluded because the daily number of tests are not updated regularly, if at all.

However in the Western Cape our infection rate is significantly higher than the national average, at approximately 6%, which is, however, by international standards still fairly low. Using some 150 000 door to door screenings to really focus on finding positive cases may have possibly had some influence on this higher rate.

The rationale for looking at a ratio of positives to total tests is based on the assumption that the organisations looking for cases (Screeners, medics, testers etc) are highly motivated to find as many positive cases as possible – in order to isolate/quarantine carriers so as to slow the spread of the disease through the country. Their “percentage success” in finding cases could therefore be regarded as a rough measure of infection rates in the populations. Assuming testing protocols are kept roughly the same, the trend of this metric over time can give an indication of a worsening or improving situation.

Whereas certain other countries can find 20 or more positive cases out of each 100 they test, we can’t even find 3 out of each 100 !- as the WHO complimented us on last week.

Most countries’ ratios are dropping which probably indicates that lockdowns are working. There are a few exceptions however. The UK remains very high. Singapore is looking particularly bad on this metric and Russia is looking steadily worse.

Read also: Covid-19 deaths; some sage historical perspective

In certain countries the number of tests is not as reliably reported as the numbers of positives. In some countries the test number are infrequently, if ever, updated. France, Spain, Netherlands, Sweden, Brazil and Mexico had to be excluded for this reason. The USA interestingly, after averaging about 150 000 tests a day for  weeks, “spectacularly” increased this to about 450 000 on Thursday 23rd last week without any noticeable increase in positive cases found? The next two days’ tests reported an average of about 250 000 per day. A beneficial result of this would be to counter the mounting criticism that the US should be doing more testing as well as bringing their ratio down to closer to the upper limit (12%) that the World Health Organisation recommends should be achieved by each country before it should relax its restrictions.

The other countries included in the table do seem to update their cumulative tests on a daily basis, by numbers that look reasonable.

Furthermore, as countries open their economies I would expect more “routine tests”-eg to test company employees-to be done, without the likelihood of finding too many positives.

This will probably have an effect on this “ratio approach” but will probably not have too much of an immediate effect.

Another observation in looking at many countries’ ratios is that, to date, their experiences seem to correlate to some extent with “temperature”. Colder climates are associated with higher ratios and vice versa.

Read also: Political point-scoring with SA Covid-19 stats is dangerous – Wits Prof David Everatt

If this proves to be a correct interpretation, South Africa will experience more “virus pressure” as winter approaches. Seasonal influenza statistics show that there is a rapid increase in June in the southern hemisphere until a peak is reached in August- then tapering off in spring.

Furthermore based purely on anecdotal evidence (I’m not aware of any rigorous analyses having been done yet) Covid-19 mortality may be associated at least as much with co-morbidity or pre-existing health conditions as with purely advancing age, although the latter is itself often associated with co-morbidity anyway. This may also be effecting the classification of deaths by cause and therefore could possibly understate the Covid-19 deaths being recorded.

South Africa’s high prevalence of co-morbidity-particularly in the townships-may unfortunately more than counter the relatively young average age in South Africa.

Looking at South Africa’s experience again, we continue to show a very low ratio of positive cases to tests (Even slightly below the World Health Organisation’s lower limit of their recommended range before considering relaxing restrictions). Only South Korea, UAE, Australia and New Zealand are below us! Our mortality rates to date are also some of the lowest and our testing is increasing at a good rate.

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