Key Points

• This outbreak is characterized by an exceptionally high number of cases, with an estimated 21,340 clinically suggestive cases during the 14-and-a-half-month outbreak, which lasted from June 2023 to August 2024.

• At the peak of the outbreak, in January 2024, more than 1,000 cases were estimated each week for a month.

• Such a scale had not been observed in the region for nearly 20 years, since the 2005–2006 outbreak: the overall incidence rate stood at 71 cases per 1,000 inhabitants in 2023–2024, compared to 85 cases per 1,000 inhabitants in 2005–2006 and 55 cases per 1,000 inhabitants during the 2012–2013 epidemic.

• This intensity is explained by the predominant circulation of the DENV-3 serotype, which had not caused an outbreak in French Guiana since the 2005–2006 outbreak: we can therefore assume that the population had little immunity to this serotype.

• During the outbreak, 711 people were hospitalized: among them, nearly 30% were under 15 years of age, 39% had at least one risk factor, and 8% were pregnant women.

• Among the hospitalized cases, 7% were classified as severe. In total, 35 people were admitted to intensive care, and 11 people died in the hospital. Of the 11 deaths, 7 were classified as directly related to dengue.

• The 2023–2024 epidemic was less severe than in 2012–2013, meaning that the proportion of severe cases among clinically suggestive cases was significantly lower: 2 severe cases per 1,000 cases versus 5 per 1,000 in 2012–2013.

• During the most recent epidemic, 11 people died in the hospital. The case-fatality rate among hospitalized cases and among clinically suggestive cases was not significantly different from that of the 2005–2006 (4 deaths) and 2012–2013 (6 deaths) epidemics. This also supports the conclusion that the outbreak was no more severe than that of 2012–2013.

• The outbreak began in the Savanes sector, which experienced two waves of the outbreak in June 2023 and January 2024: this is the sector where the outbreak lasted the longest (14 months).

• The Savanes, Maroni, and West Coast were characterized by predominant circulation of the DENV-3 serotype (approximately 80% of serotyped samples in each sector), while a more balanced co-circulation was observed in the Cayenne Island (56% DENV-3 and 44% DENV-2) and East Interior sectors.

• The Oyapock sector is the only sector where serotype DENV-1 circulated significantly (24% of serotyped samples) due to its geographical location on the border with Brazil, where this serotype was circulating at that time. This sector is also the one where the epidemic was the shortest (approximately 6 months) but where the weekly incidence rate of clinically suggestive cases at the peak of the epidemic was the highest.