Capture–Recapture Method for Estimating Annual Incidence of Imported Dengue, France, 2007–2010

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Imported dengue cases pose the public health risk for local circulation in European areas, especially southeast France, where the Aedes mosquito is established.Using a capture-recapture method with Chao's estimator, we estimated the annual incidence of dengue fever and the completeness of existing mandatory notification and laboratory network surveillance systems.During 2007-2010, >8,300 cases with laboratory evidence of recent dengue infection were diagnosed.Of these cases, 4,500 occurred in 2010, coinciding with intense epidemics in the French West Indies.Over this 4-year period, 327 cases occurred in southeast France during the vector activity period.Of these, 234 cases occurred in 2010, most of them potentially viremic.Completeness of the mandatory notification and laboratory network systems were ≈10% and 40%, respectively, but higher in southeast areas during May-November (32% and 69%, respectively).Dengue surveillance systems in France provide complementary information that is essential to the implementation of control measures.D engue fever, caused by 4 virus serotypes, is the most common mosquito-borne viral disease in the world: an estimated 50 million cases occur annually (1).During the past 50 years, incidence has increased 30-fold with increasing geographic expansion (1).In Europe, imported cases among travelers returning from endemic or epidemic countries have been reported frequently during recent years.Considering the risk for a local cycle of transmission and subsequent epidemic, imported dengue cases pose a potential public health problem in European areas where a competent vector is established.Since 2004, the Aedes albopictus mosquito has been established in southeast France (2,3).During 2010, the first 2 known cases of autochthonous dengue fever were diagnosed in persons in metropolitan France (4), which comprises continental France and the island of Corsica, located southeast of mainland France (Figure 1).Two cases were also reported in Croatia during 2010 (5), demonstrating that local transmission in continental Europe is a reality.Accordingly, in the context of implementing appropriate public health measures, dengue surveillance systems should be able to estimate the incidence of imported symptomatic cases, describe their geographic distribution in areas already or potentially colonized by the competent vector, and identify the countries where infection occurred.Using a capture-recapture method, we estimate the annual incidence of imported dengue cases and the completeness of the existing surveillance systems in metropolitan France during 2007-2010. Methods Dengue Surveillance SystemsAs of 2010, the Ae.albopictus mosquito was designated as permanently established in 6 southeast departments (administrative districts) in metropolitan France as follows: Alpes-Maritimes (2004), the 2 departments that comprise Corsica, Haute-Corse (2006) and Corse-du-Sud ( 2007), Var (2007), Bouches-du-Rhône (2009), and Capture-Recapture Method for Estimating Annual Incidence of Imported Dengue, France,