By 30 March 2020, Switzerland had conducted 116,700 tests for Covid-19, a rate of 13,600 per million.
The number of cases continues to rise in Switzerland. On 30 March 2020, Switzerland recorded 1,201 new cases bringing the total to 15,922. However, because of test rationing, Switzerland’s recorded case figure is an unknown percentage of the of the actual number of infections.
South Korea, much praised for its testing, had conducted 7,780 tests per million, only 57% of the rate in Switzerland.
However, not all testing is equal. Early, well-targeted testing, contact tracing and widespread monitoring of symptoms is likely to be more effective. This is what is happening in South Korea. There, they identify epidemiological links on a case by case basis. This has led to a rapid slowdown in new cases. On 30 March 2020, South Korea, a nation of 51 million people, recorded only 78 new cases.
Epidemiological linking involves identifying the source of each infection and testing and isolating accordingly. When a source cannot be found, there is risk that unidentified cases are circulating, continuing to spread the virus, something places like South Korea are working hard to avoid.
In Switzerland, where there is little epidemiological linking and tests have been rationed to high risk and serious cases, there are many unidentified cases, off the radar, that could be spreading the virus. An uncontrolled approach like this makes it very difficult to contain the spread. And ramping up the number of tests once there are large numbers of unidentified cases circulating can become an unwinnable game of catch up. The virus continues to spread and it becomes increasingly more difficult to identify everyone infected with it.
Widespread reduction in human contact is then the only real tool left to reduce spread. Essentially, if you don’t know who has it, you are left having to assume everyone has it.
One indicator of how well testing is capturing infections is the rate of positives. In South Korea, the percentage of tests yielding a positive result was 2.4%. This suggests they were proactively testing more suspected cases. The rate of positives in Switzerland was 13.2%. In Italy (15.8%) and the UK (16.4%) the percentages were far higher than in South Korea too. In Lombardia, the region of Italy hardest hit by the virus, the percentage testing positive was 22.5%.
Higher positive percentages among those tested suggests fewer suspected cases are being tested and more unidentified cases are slipping through the net and potentially continuing to spread the virus.