The findings of the outbreak investigations presented in the London-based article caught our attention. They once again confirm the significant potential impact of SARS-CoV-2 in terms of morbidity and mortality in nursing homes. The investigations showed that 60% of residents who tested positive for the virus in the four nursing homes involved were asymptomatic, making it difficult to identify them and implement management measures within the facility. Furthermore, 4% of staff working in these facilities at the time of testing and showing no symptoms also tested positive for SARS-CoV-2. These findings point to the presence of a silent reservoir of SARS-CoV-2 within nursing homes, raising questions about the management of outbreaks. In light of these results and given the potential impact of this virus on older adults, the authors recommend systematic and regular screening coupled with enhanced surveillance to minimize the impact of future outbreaks within these facilities.

In the Vendée region, health authorities have recommended since May that all residents and staff undergo systematic testing as soon as a case is identified. In addition, some facilities have, on a voluntary basis and following the end of lockdown, implemented systematic testing to assess the “invisible reservoir” of the virus.

The results of our data analysis in the Vendée region are consistent with the findings of the London study regarding the presence of a silent reservoir of SARS-CoV-2 in nursing homes.

We observed that testing only staff members when a resident or staff member tests positive in a facility may lead to the failure to identify infected, asymptomatic residents. At the same time, 6% of nursing homes that conducted universal testing in the absence of a confirmed case triggering the process identified one or more infected individuals—cases that would have gone unnoticed without this testing.

Our analysis, conducted after the national lockdown—that is, in an epidemiological context of low COVID-19 incidence—shows a higher percentage of asymptomatic individuals in the Vendée region (82%) than what is reported in the literature (40.7% to 57%). We therefore conclude that surveillance based on the presence of “classic” COVID-19 symptoms (fever, cough, difficulty breathing, sore throat, fatigue/malaise, headache, muscle pain, nausea/vomiting, diarrhea, anosmia, ageusia) carries the risk of overlooking infected individuals and may thereby hinder effective management of a SARS-CoV-2 outbreak, as asymptomatic individuals or those presenting with symptoms other than the ‘classic’ symptoms can contribute to viral transmission.

Given the epidemiological situation in the Vendée region (low incidence of COVID-19) and during the post-lockdown period as testing capacity is ramped up, universal testing in the absence of a first confirmed case does not appear to be an efficient approach, given the resources required and the invasive nature of the testing procedure for residents and staff. On the other hand, systematic testing in response to the presence of a first confirmed case seems advisable to us for investigating and managing the presence of potential asymptomatic infections. However, the strategy must be subject to a contextual assessment of exposure, compliance with barrier measures, and the risk of transmission. The Centers for Support in the Prevention of Healthcare-Associated Infections (CPias) possess this expertise and are available to assist facilities. More generally, the current national strategy—which is based on systematic testing of all staff and residents in connection with a case—will need to undergo cost-effectiveness evaluations and adjustments.