Which provinces are not doing enough covid-19 tests?
The first covid-19 case in South Africa was confirmed at the beginning of March in KwaZulu-Natal. Now, three months later, the country has accumulated over 50 000 confirmed cases across its nine provinces. All provinces have now crossed the 100 case mark, the commonly used starting point for cross region covid-19 statistical comparisons. The distribution of cases across provinces, and therefore the location of hotspots, is well documented. However, the relative performance of provinces in terms of infections and tests has not been explored to as great an extent.
In one of their March press briefings, the WHO suggested that as a general benchmark there should be 10 negative tests for every 1 positive test, if a country is doing enough tests¹. This equates to just over 9% of all tests returning positive. Anymore and the country is likely not testing enough. Rounding up to 10% for simplicity, another way of looking at this would be to say that tests should be increasing at 10 times the rate that infections are increasing. For example, if a country records 60 new infections during a week, the number of tests in that week would need to have increased by 600 in order for the country to be meeting the rough guideline for doing enough tests. With this in mind, the rate of increase in both tests and infections can be compared to provide some insight into whether or not enough tests are being conducted.
Since the 27th of April, South Africa’s National Institute for Communicable Diseases (NICD) has been publishing a weekly epidemiological brief ². The briefs contain several pages of tables and graphs on covid-19 statistics at a national and provincial level. The data of interest here is the cumulative number of both cases and tests per 100 000 persons. On the basis of this data, for the 5-week period from 27 April to 30 May, a closer look at each of the nine provinces reveals that only the Western Cape had their number of new cases more than 10 times greater than their number of new tests. In other words, by the 10% threshold discussed above, only the Western Cape is not testing enough.
In the first week of May, the period from 27 April to 3 May, the Western Cape conducted enough covid-19 tests, but for the rest of the month they fell short of the guideline. The second week of May saw fewer tests than first as the province registered 29 fewer tests per 100 000 than would be required to ensure that at most 10% of new tests returned positive. In the third week the number of new tests almost doubled. However, in subsequent weeks the change was minimal. The percentage of tests returning positive has increased every week in May from 8.8% in the first week all the way to 20.2% in the fifth week.
Gauteng, the Eastern Cape and KwaZulu-Natal collectively accounted for 30% of the country’s cumulative infections at the end of May and all three provinces saw fewer than 10% of tests in May return positive. The provinces have consistently seen significantly less than 10% of their tests return positive. During the last week of May, Gauteng was ahead in terms of tests, with only 2.7% of new tests returning positive. They were followed by KwaZulu-Natal (3.3%) and then the Eastern Cape (3.9%). Unlike the other two provinces, the Eastern Cape saw more than 5% of tests returning positive on two occasions in the month.
The remaining five provinces have each registered fewer than 300 cases and have a very low number of their tests returning positive. For the Free State and Mpumalanga (bar the first week of May), fewer than 1% of tests returned positive each week. The North West only just exceeded 1% in the last week of the month, while Limpopo approached the 3% mark. The Northern Cape however appears to have seen a surge in cases in the last week of May, with a lagging rise in tests. The 8.2% of tests that returned positive in the last week of May ranks the Northern Cape below only their neighbours in the Western Cape.
Looking at the country as a whole, fewer than 10% of tests in May returned positive, although the country is fast approaching the 10% threshold. The increase is largely driven by the slow increase in tests in the hardest hit province, the Western Cape. Though merely one indicator, the high positivity rate in the Western Cape is clearly a reason for concern. As the virus continues to spread, testing across the country in general and in the Western Cape in particular needs to be more extensive. An extensive testing regime will help ensure that the country identifies most of the covid-19 cases present and aid in controlling the spread of the virus.
* An error in the NICD number of cumulative tests per 100 000 in the Northern Cape which saw a decline between 27 April and 3 May is the reason for the negative result in the first week.
[1] M.Van Kerkhove, COVID-19 — virtual press conference — 30 March 2020 (2020), World Health Organization (WHO) press conference transcript
[2] COVID-19 SURVEILLANCE REPORTS (2020), National Institute for Communicable Diseases (NICD) website
