Key Points

COVID-19: Continued Acceleration of the Epidemic

The near-saturation of diagnostic capacity that has affected the Île-de-France region for several weeks is affecting the estimate of the virological incidence rate. The receipt of delayed results now allows for an update of the incidence rate, significantly raising it. Despite this initial underestimation, the regional incidence rate for week 39, calculated using available data, is still higher than the updated rate for week 38, indicating an increasing intensity of SARS-CoV-2 circulation.

The positivity rate shows a very clear increase, reaching 11% of tests performed. Two departments exceeded the 10% threshold the previous week; now only Seine-et-Marne remains below this threshold, rising from 7.4% in Week 38 to 9.2% in Week 39. This increase is rapid, and it is not possible to distinguish the portion attributable to actual viral circulation from the effect of targeting priority populations. Recommendations to prioritize testing for the most at-risk populations can only partially explain this increase. A comparison of positivity rates between tested individuals with symptoms (22%) versus those tested without symptoms (6%), in a context of strained testing capacity, supports this strategy of prioritizing testing.

The establishment of testing centers dedicated to priority groups
(symptomatic individuals, close contacts, and healthcare workers) is a key strategy for rationalizing the use of tests, which, combined with expanding contact tracing capabilities, helps curb viral circulation. The deployment this summer of mobile testing centers also made it possible to target specific geographic areas with the aim of addressing inequalities in access to care in the Île-de-France region. The circulation of the virus is also evident in the detection of clusters, with schools and universities being the primary source since September. This phenomenon logically reflects the effect of students returning to the classroom, while the high severity of clusters identified in higher education is primarily linked to the size of these gatherings.

The number of clusters is also underestimated due to increasing delays in reporting and validating these cases. Only 3% of confirmed cases recorded since May 13 originated from an identified cluster, raising questions about the relevance of this indicator for tracking the epidemic’s dynamics. At the hospital level, the proportion of emergency room visits for suspected COVID-19 that subsequently lead to hospitalization is steadily increasing, rising from 16% in Week 37, to 20% in Week 38, and to 29% in Week 39. This increase primarily concerns people over the age of 45, among whom the epidemic is spreading. Regarding hospitalizations, 1,208 new admissions were reported in Week 39 compared to 1,352 in Week 38, representing a one-time decrease of 10%, while intensive care units recorded a 42% increase with 244 new admissions in Week 39, indicating a sustained rise.