COVID-19: Spatial analysis of hospital case-fatality rate in France

Abstract

When the population risk factors and reporting systems are similar, the assessment of the case-fatality (or lethality) rate (ratio of cases to deaths) represents a perfect tool for analyzing, understanding and improving the overall efficiency of the health system. The objective of this article is to estimate the influence of the hospital care system on lethality in metropolitan France during the inception of the COVID-19 epidemic, by analyzing the spatial variability of the hospital case-fatality rate (CFR) between French districts. In theory, the hospital age-standardized CFR should not display significant differences between districts, since hospital lethality depends on the virulence of the pathogen (the SARS-CoV-2 virus), the vulnerability of the population (mainly age-related), the healthcare system quality, and cases and deaths definition and the recording accuracy. We analyzed hospital data on COVID-19 hospitalizations, severity (admission to intensive care units for reanimation or endotracheal intubation) and mortality, from March 19 to May 8 corresponding to the first French lockdown. All rates were age-standardized to eliminate differences in districts age structure. The results show that the higher case-fatality rates observed by districts are mostly related to the level of morbidity. Time analysis shows that the case-fatality rate has decreased over time, globally and in almost all districts, showing an improvement in the management of severe patients during the epidemic. In conclusion, it appears that during the first critical phase of COVID-19 ramping epidemic in metropolitan France, the higher case-fatality rates were generally related to the higher level of hospitalization, then potentially related to the overload of healthcare system. Also, low hospitalization with high case-fatality rates were mostly found in districts with low population density, and could due to some limitation of the local healthcare access. However, the magnitude of this increase of case-fatality rate represents less than 10 per cent of the average case-fatality rate, and this variation is small compared to much greater variation across countries reported in the literature.

Fig 1. Distribution of case-fatality rates calculated by country, based on case and death data from WHO (WHO, May 8, 2020).

Fig 2

COVID-19 timeline of hospitalizations (left) and death (right), March, 19 to May, 8 2020, France.

Fig 3. The 96 districts of metropolitan France.

Fig 4

Hospitalization rate (left) and hospital mortality rate (per 1000 inhabitants) (right) for COVID-19 in metropolitan France for the period March 19 to May 8, 2020.

Fig 5. Cartogram of the standardized hospitalization rate for COVID-19 in France from March 19 to May 8, 2020.

The geometry of the districts in France is shown in the lower left corner.

Fig 6

Case-fatality rate (left) and case-fatality rate adjusted by empirical Bayesian estimator (right) for the COVID-19 epidemic in France from 19 March to 8 May 2020.

Fig 7. Calculated case-fatality rates by 13-day period.

Fig 8. Standardized Lethality Ratio (SLR) for COVID-19 in metropolitan France for the period March 19 to May 8, 2020.

Fig 9

Geographical units (districts) with SLR significance: P-value <0.05 (left), p-value < 0.0005 (right).

Fig 10. Correlation between hospitalization rate and CFR during the COVID-19 epidemic in France for the period of time between March 19 to May 8, 2020.

Fig 11

SLR (symbols) and hospitalization rate (left) and fatality rate (right) during the COVID-19 epidemic in France for the period of time between March 19 to May 8, 2020.

Fig 12. Combination of standardized hospitalization (H) and case-fatality (L) rates in five classes.

Fig 13. Severity ratio during the COVID-19 epidemic in France for the period of time between March 19 to May 8, 2020.