27 March 2020 – Policy Brief
Analysis of Swiss Epidemic as of 27 March 20
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At 3 PM yesterday the Federal Office of Public Health (FOPH) shared line-listed data of the confirmed daily COVID-19 cases in Switzerland by canton, age and sex, and the daily number of negative tests for the whole country. The FOPH asked the academic community to address four questions. The expert panel undertook descriptive analyses and modelling to address the questions, to which we provide answers below.
Question 1. How should the epidemic curve be interpreted? Increasing, decreasing, stable trend?
The data provided are not themselves the epidemic curve, which would include all SARS-CoV-2 infections, but rather only the confirmed COVID-19 cases. The main difficulty in making inferences is the intrinsic biology of the virus, which means that the confirmed cases today reflect transmission 2-3 weeks ago. Furthermore, due to delays in updating the number of reported cases, the last three days should be interpreted with caution.
From the observed data, it is too early to infer either the trend of the epidemic curve or the magnitude of the effect of the control measures implemented since 13 March. A transmission model, developed for this report, also shows that, with the available data, the future trajectory of the epidemic in Switzerland is still uncertain. The uncertainty implies that we need to be prepared for the continued growth of the epidemic. Addition of data from new cases in the immediate future will considerably improve our ability to predict the effectiveness of the interventions and of the final size of the epidemic.
Question 2. Do you think that the data allow to evaluate the effect of the measures taken, and if so, how? If not why?
The data shared by FOPH are a vital information source that should make it possible to estimate the intervention effectiveness, but this will require at least a week’s more data. Additional parameters, including more complete data on the date of onset of symptoms in confirmed cases, would make it possible to stimate the trends with more confidence and to determine the impact of the control measures sooner. Variations in testing rates may be masking some of the trends in the data. These trends would be clearer if the numbers of negative test results were available disaggregated by canton and ideally, age and sex. The analysis by canton indicates that the most intense outbreaks are in a small number of cantons and that, in much of Switzerland, it might still be possible to avert a major outbreak by intensive case finding, contact tracing and isolation, if this strategy is implemented very soon with a stateof-the-art information system.
Question 3. What can be learned from the data despite these quality problems?
Data collection and curation is clearly challenging, and we are unsure what specific quality problems are referred to here. Despite the inevitable noise in the data and delays in reporting, our initial analyses highlight several important trends:
- The rate of confirmed cases per 10,000 population varies substantially by canton.
- The average age of confirmed cases has increased as the epidemic has developed. This trend is compatible with a pattern of initial cases being imported or detected by contact tracing, and later cases being ascertained in the clinic, when community transmission became established.
- The mean age of confirmed cases has remained constant since March 3, implying that eligibility criteria in the later increase in testing did not expand.
- There is evidence for an age-gender interaction. In younger age groups, women account for a larger proportion of confirmed cases, and in the older age groups confirmed cases are predominantly male. This pattern cannot be further interpreted without data on the distribution of testing by age and sex.
- The proportion of tests with a positive result appears to be increasing. This pattern is consistent with incomplete ascertainment in case detection. This is of concern because of the potential for continued transmission, despite social distancing measures.
Question 4. What would be your reply if you were asked how this epidemic will evolve in the near futur especially with regard to the capacities in the medical system?
The observed data and model predictions show that future course of the epidemic remains uncertain. We must prepare for the case where the epidemic grows to levels that will severely strain the capacity of our health system. The panel currently lacks data on which to base judgements on the adequacy of the supply of ICU beds, ventilators, protective clothing, or trained and uninfected staff. The question does not specify which capacities are referred to.
Disclaimer: The answers to the four questions are based on interpretation of descriptive analyses and modelling that were conducted under extreme time pressure. The findings of the analyses are subject to change. Changes in the findings could affect the interpretation.
Background on panel assembly and structure of the report
This document is the response of this panel to the questions raised by Brigitte Meier, structured as follows: in part 1 (pages 3-10), we present preliminary analyses and modelling of the data provided by FOPH, highlighting some key insights from these data. All data analyses were carried out by the team at ISPM Bern. In part 2 (pages 11-13), we address each of the four questions posed by the FOPH, based on the limited analyses that we were able to conduct in the short time frame. A short outlook is provided.