Autochthonous Dengue Outbreak, Paris Region, France, September–October 2023

I n Europe, dengue primarily is imported from en- demic countries.However, an increasing number of autochthonous cases and limited outbreaks have been described since 2010.In 2023, a total of 105 autochthonous cases were reported: 66 in Italy, 36 in France; and 3 in Spain (1).We describe an autochthonous outbreak of dengue in the Paris Region of France during September-October 2023. The StudyOn September 13, 2023, a 36-year-old woman from Limeil-Brévannes, a city 15 km south of Paris, who had no consistent medical history started having symptoms of fever (>38°C), malaise, and headache.Her 7-year-old son experienced the same symptoms during September 11-13 and had a maculopapular rash that disappeared 5 days after the onset.Also, the woman's partner had symptoms begin on September 14 and had a fever (>38°C), chills, frontal headache, myalgia, a papular rash, and itching on the trunk and upper limbs.The case-patients reported no travel abroad or to other regions of France.On September 19, the woman continued to be feverish daily and began to have nausea and vomiting.She consulted the emergency department of Hôpital Henri Mondor, Créteil, south of Paris, where blood tests were performed.Tests revealed thrombocytopenia (105,000 cells/μL; reference range 150,000-450,000 cells/μL), leukopenia (700/μL; reference range 1,000-4,000 U/L), and increased alanine aminotransferase (213 U/L; reference range <35 U/L), aspartate aminotransferase (266 U/L; reference range <35 U/L), and gamma-glutamyl transferase (135 U/L; reference range <40 U/L).C-reactive protein was 2.4 mg/L (reference range <5 mg/L).Major and common causes of viral hepatitis were excluded, and serologic tests for hepatitis A-C, HIV, and cytomegalovirus were negatives.Epstein-Barr virus serology was compatible with a previous infection.Because a diagnosis was not made during clinical examination, we performed arbovirus serologic testing, including for dengue virus (DENV), on September 22. DENV serologic results were IgM positive; thus, we performed a retrospective analysis of blood samples collected on September 19.In that analysis, results for DENV nonstructural protein 1 (NS1) antigen in plasma were positive, as was the real-time reverse transcription PCR (RT-PCR), which could identify DENV type 2 (cycle threshold 35), confirming the diagnosis of acute DENV infection.We performed a second serologic test 25 days after symptom onset, which showed seroconversion for DENV, IgM persistence, and apparition of IgG (Table ).The patient's son and partner also had DENV serologic testing on October 13, and results were IgM and IgG positive.All 3 patients fully recovered, and no case was classified as severe dengue.According to national guidelines, we made a notification to the national health authority of France on October 16, which prompted a door-to-door survey in the family's neighborhood during October 19-20.Pesticide spraying for mosquito control was also performed in the neighborhood.