Summary

Arbovirus surveillance in 2020 was marked by the implementation of regulatory changes requiring the reporting of only confirmed cases of dengue, chikungunya, and Zika in mainland France during the enhanced surveillance period corresponding to the vector’s activity period from May to November. It was also impacted by the COVID-19 pandemic, which significantly reduced travel and movement abroad.

Despite the partial closure of borders in this context, 110 imported cases of arbovirus disease were reported in Auvergne-Rhône-Alpes (ARA), a number higher than in the previous three years (an average of 60 cases between 2017 and 2019). Large-scale dengue outbreaks in the French West Indies during the enhanced surveillance season and continued travel to and from French overseas territories accounted for 97% of imported cases. The peak of the dengue outbreaks in Martinique and Guadeloupe occurred in October, leading to an unusual increase in the number of imported cases during this period in mainland France, linked to the return from the All Saints’ Day holidays when travel was still possible. Furthermore, communication that was heavily focused on the risk of COVID-19 and pre-travel testing may have pushed the risk of dengue importation into mainland France by these travelers into the background.

The COVID-19 pandemic also impacted the surveillance and reporting of arbovirus cases, as the time between the onset of symptoms and reporting increased due to laboratory backlogs, leading to difficulties in accessing testing and analysis—which were likely considered less of a priority compared to the risk of SARS-CoV-2 transmission.

The risk of local dengue transmission remains present in our territory. Although no locally acquired cases were identified in the ARA in 2020, six local dengue outbreaks were identified in the PACA and Occitanie regions, totaling 13 cases. This represents the highest number of outbreaks ever recorded in a single season.

In 2021, enhanced surveillance of arboviruses will continue to be based on the reporting of biologically confirmed cases. For the first time, it will be extended to all 12 departments in the region. Vector control measures will be implemented based on the presence of the Aedes albopictus mosquito and field surveys conducted by EIRAD in areas where individuals have stayed during the viremic period.

The current COVID-19 situation and the partial closure of borders continue to limit the risk of arbovirus importation into mainland France and impact surveillance. However, although reduced, travel to and from the intertropical zone continues, where dengue epidemics are ongoing, particularly in Réunion, where a third wave of the epidemic is being observed (more information in the Epidemiological Update). Even if it is lower in this context, the risk of dengue importation during the summer vacation period remains a reality.

Therefore, it is essential to maintain vector control efforts and community engagement in the fight against the tiger mosquito to limit the risk of new outbreaks of locally transmitted cases this season in the ARA. Furthermore, prevention messages must continue to be communicated despite the ongoing prominence of COVID-19.