Less than 50% of new Covid cases in isolation at time of test

The SwissCovid app is one arm of the Swiss contact tracing effort; the other is physical follow-ups by the cantons. Keystone / Jean-christophe Bott

National statistics show that just under half of new Covid-19 cases are already in quarantine when they test positive. Regional figures suggest the number could be even lower.

The NZZ am Sonntag reports that the most recent numbers provided by the Federal Office of Public Health (FOPH) show that 44% of people testing positive since May 11 were already in isolation as a result of precautions taken after contact tracing.

The FOPH’s numbers are based on medical questionnaires filled out by patients – forms which since May include the question of whether the patient is already in quarantine. Some 30% of the patients said that they weren’t in isolation, while the remaining 26% didn’t answer the question.

However, the newspaper writes that the questionnaires were available for less than half of the 9,000 Covid-19 cases reported since mid-May. “The FOPH estimate is thus a bit limited,” it writes.

Figures from Vaud and Geneva, two cantons particularly affected by the virus and where contact tracing is widely developed, suggest the figure could be even lower than that reported nationally.

For the first week in August, 26% of new positive cases in Geneva were already in quarantine, the NZZ am Sonntag writes; in canton Vaud over the past week, the figure was 30%.

And though Vaud authorities told the newspaper this shows a certain impact of contact tracing in preempting cases, University of Bern epidemiologist Nicola Low says the figure is too low.

Ideally, some 80% of confirmed cases should already be in quarantine, in order for contact tracing regimes to really be working well, Low said. “If this percentage [currently seen in Switzerland] doesn’t increase, it’s not a good sign for efforts to control the virus.”

Contact tracing, through the SwissCovid app and the physical efforts of cantonal authorities, has been one of the major planks of the effort to combat the spread of coronavirus in Switzerland since lockdown measures were eased.

On Saturday and Sunday, Switzerland recorded a total of 571 new cases – a rise of 118 compared with last weekend, and a continuation of the upward trend seen since the end of June.

Daily case numbers this week climbed twice above 300, a figure that hasn’t been recorded since the height of the pandemic in April.