BizHealthcare - 14 April 2020
BY: MARCUS LOW & NATHAN GEFFEN
"Most of the Covid-19 numbers we have paint only part of the picture and can easily be misinterpreted. Here are some tips on understanding the numbers.
Confirmed versus actual cases
Every day Minister of Health Dr Zweli Mkhize provides the total confirmed cases and the increase in confirmed cases since the previous day. But how much can we really tell from these numbers?
Confirmed cases are only a fraction of the total cases in the country. Maybe the real number of cases is twice or maybe it is ten times the reported cases; we simply don’t know. As testing scales up, the picture may become a bit clearer. Unfortunately, in the past ten days or so the number of tests has declined from a peak of 8,066 on 27 March to 1,225 on 6 April. (Hopefully this will improve in the next few days if the government successfully rolls out the 45-minute GeneXpert testing machines.)
The number of confirmed cases depends on the number of tests done and how well those tests are targeted. All other things being equal, a sudden increase in testing capacity might result in a sudden increase in confirmed cases. This would not mean that there is definitely explosive growth in the number of cases; only that we would be finding more of them.
Similarly, it can become easier or harder over time to know who to test. Most of South Africa’s early Covid-19 cases were people travelling back from overseas, where they probably contracted the virus. It made sense to focus testing on people with Covid-19 symptoms and who had travelled to affected countries. South Africa’s travel ban came into effect on 18 March – effectively turning off this source of new infections. Now, as recent overseas travel has become a less important indicator of possible infection, it is becoming harder to know who to test.
All this probably explains why the daily increases haven’t been that high in recent days. Everyday from 23 to 27 March, over a hundred new cases were reported in South Africa – from 28 March to 6 April the daily increases were under 100.
Apart from all this, there will also be random fluctuations in the data. By chance you may find 80 confirmed cases one day and 60 the next day. In itself a decrease in confirmed cases like this means nothing.
For all these reasons it’s best to be cautious about how you interpret day-to-day changes in confirmed cases."
Read more:
