Key Points

SARS-CoV-2 continues to circulate in Nouvelle-Aquitaine, with a steady increase in the positivity rate and an incidence rate that rose again during week 41.

A decrease in the incidence rate had been observed during the previous two weeks (W39 and W40). Several factors may have contributed to this downward trend, including the change in testing strategy initiated in early September. Indeed, due to laboratory capacity constraints, priorities were established so that symptomatic individuals, contacts of a confirmed case, and those with risk factors could be tested first. As summarized in the table below, this resulted in a sharp decrease in the testing rate starting in mid-September, which also led to a decrease in the number of positive cases and, consequently, in the incidence rate.

The incidence rate is, in fact, the product of the positivity rate (Tp) and the testing rate (Td), and interpreting a single indicator at a given moment must be done with caution. It is important that these three indicators be described together and in terms of long-term trends in order to interpret the epidemiological situation.

While transmission remains most active among those aged 15–44, the incidence rate is now rising among people aged 65 and older. The positivity rate is also steadily increasing in this age group, with a more pronounced trend than among younger people. New infections, which primarily affected young people during the summer, are now spreading to older adults—and thus the most vulnerable. If this trend continues in the coming weeks, we could face a greater health impact in terms
of hospitalizations and ICU admissions.