Summary

The enhanced surveillance system for dengue, chikungunya, and Zika was activated from May 1 to November 30, the period of activity for the Asian tiger mosquito (Ae. albopictus) in mainland France.

As was the case last year, import pressure was particularly high for dengue this season, linked to very active viral circulation in Guadeloupe and Martinique. Thus, from May 1 to November 30, 2024, 2,107 cases of dengue were imported into mainland France (55% of which originated in the French Antilles).

In Occitanie, from May 1 to November 30, 2024, the following were identified:

• 178 imported cases of dengue, 3 imported cases of chikungunya, and 1 imported case of Zika;

• Three outbreaks of locally transmitted dengue (5 cases):

  • 1 case in Hérault residing in Montpellier (serotype undetermined) with possible exposure in the town of Pérols (date of onset of symptoms (DDS) on 06/17);

  • 2 intrafamilial cases in the Pyrénées-Orientales (serotype undetermined) residing in the municipality of Baho with possible exposure in Florac in Lozère (onset of symptoms on 07/16 and 07/19);

  • 2 cases of DENV-1 in the Hérault department residing in Vendargues (onset of symptoms on 09/08 and 09/09).

Each identified case, whether imported or autochthonous, prompted an epidemiological investigation by the Regional Health Agency and triggered a rapid response by vector control services (LAV) around the 163 cases that were viremic in Occitanie (88% of identified cases), in order to limit the risk of autochthonous transmission of the virus. In total, 216 entomological surveys and 189 vector control treatments were carried out in the region.

Active case finding was implemented around clusters of locally acquired cases to determine the extent of local transmission and adjust the scope of LAV treatment as needed: awareness-raising among healthcare professionals and press releases to inform the general public, and, depending on the context, door-to-door surveys within a 150- to 250-meter radius.

During this surveillance season, 72% of cases were identified through reporting by healthcare professionals; 27% had not been reported and were identified using catch-up data from the laboratory network (automated transfer of results from Eurofins Biomnis and Cerba laboratories to Santé publique France), and 1% resulted from active case finding around local transmission clusters.

As in the previous season, reporting by a healthcare professional reduced the median time between the onset of symptoms and case identification by 4 days (median time of 12 days via laboratory catch-up vs. 8 days via a healthcare professional). Healthcare professionals thus have a key role to play: by diagnosing and reporting cases of dengue, chikungunya, and Zika, they enable early intervention by mosquito control operators and reduce the risk of local transmission.
The year 2024 was a record year for dengue transmission in France, with 8 episodes of local dengue transmission identified in other regions, totaling 78 cases: 7 outbreaks in the Provence-Alpes-Côte d’Azur region (17 cases in the Alpes-Maritimes, 18 cases in the Vaucluse, and 41 cases in the Var) and 1 outbreak in the Auvergne-Rhône-Alpes region (2 cases in the Drôme). A locally transmitted case of chikungunya was also identified in the Île-de-France region.