Paris | Nine out of ten symptomatic cases were not detected in France shortly after the end of the first national confinement in May, believe researchers in the scientific journal Nature, which points to a failure of the surveillance system.
The screening capacity “has remained insufficient, even at the low levels of viral circulation reached after this confinement” and it was foreseeable that it “will deteriorate rapidly with the increase in epidemic activity”, note its authors.
Giulia Pullano, Vittoria Colizza, of the French Institute for Public Research Inserm, and their colleagues did not include asymptomatic infections (without symptoms) in their calculation, which points to the failure of the surveillance system, with an “under-detection cases of COVID-19 in France which threatens the fight against the epidemic ”.
Including the asymptomatic infection rate estimated by the researchers, “only one in twelve Sars-CoV-2 infection was identified, during the study period” of seven weeks following confinement, from May 11 to June 28, Jeffrey Shaman of the Mailman School of Public Health at Columbia University (New York) points out in a commentary on this research, also published in Nature.
The screening system has not achieved the detection rates needed to contain the pandemic, despite improving over time.
Between 250,000 and 280,000 tests per week were carried out in France over the period studied, according to the Public Health France database.
Strategies for detecting and monitoring the spread of Sars-CoV-2 are considered essential so that cases can be identified and isolated to prevent transmission within a community – especially at low levels of prevalence of Sars-CoV-2. disease after long and expensive confinements.
The researchers estimated the number of symptomatic infections of the new coronavirus that occurred in France during the period studied using mathematical models.
To develop these models, they used regional data from hospital admissions as well as serological studies (blood tests for the presence of antibodies, evidence of coronavirus infection) and estimates from ” a self-reported symptom tracking database.
Result: nearly 104,000 symptomatic infections occurred during the study period, against just over 14,000 officially recorded cases.
Only 5 of the 12 regions studied exceeded a median detection rate of 50% by the end of June and less than a third (31%) of people with COVID-19-like symptoms saw a doctor despite recommendations.
Taken together, these results suggest that the majority of SarS-CoV-2 infections were not detected during the first few weeks after this confinement. For the authors, the strategies to test, trace and isolate must be considerably improved to control the spread of COVID-19 and allow the lifting of the restrictive measures applied to slow down the second wave in Europe and “avoid a third wave”.