Dengue Type 3 Virus, Saint Mar tin, 2003–2004 Christophe N. Peyrefitte,*† Boris A.M. Pastorino,* Maël Bessaud,* Patrick Gravier,* Fabienne Tock,* Patricia Couissinier-Paris,* Jenny Martial,‡ Patricia Huc-Anais,§ Raymond Césaire,‡ Marc Grandadam,* and Hugues J. Tolou* We describe the spread of a dengue virus during an outbreak in Saint Martin island (French West Indies) during winter 2003–2004. Dengue type 3 viruses were isolated from 6 patients exhibiting clinical symptoms. This serotype had not been detected on the island during the preceding 3 years. Genome sequence determinations and analyses showed a common origin with dengue type 3 viruses iso- lated in Martinique 2 years earlier. Dmajor public health problem; >50 million persons are engue virus (DENV) infection is recognized as a infected each year worldwide (1), and the incidence of severe, sometimes lethal, forms of the disease is increasing (2). Dengue viruses are mosquitoborne flaviviruses with a single-stranded, nonsegmented, positive-sense RNA genome ≈11 kb in length. Four antigenically distinct serotypes, DENV types 1 to 4, exist (3). Infection with any serotype can lead to disease, ranging from mild infection, dengue fever (a generally mild disease with complete recovery), to severe forms (dengue hemorrhagic fever and dengue shock syndrome). Molecular epidemiologic studies have investigated the possibility of a link between particu- lar DENV genotypes or clusters and particular clinical forms of disease (4,5). Consequently, finding new viral genotypes in areas where they had been absent could be of epidemiologic and clinical interest. A recent work described the emergence and the global spread of DENV-3 subtype III (5). Originating from the Sri Lankan/Indian subcontinent, the new variant likely spread to eastern Africa in the 1980s, then to Latin America in the mid-1990s (5). Previous work in our laboratory identified *Institut de Médecine Tropicale du Service de Santé des Armées, Marseille Armées, France; †Université de la Méditerranée, Marseille, France; ‡Centre Hospitalier Universitaire de Fort de France, Martinique, France; and §Laboratoire d’Analyse Médicale Lepers, Marigot, Saint Martin, France a DENV-3 subtype 3 of the same origin in Martinique in 1999 (6). Whereas other Caribbean islands had annual dengue epidemics, the last outbreak reported in Saint Martin (French West Indies) (Figure 1) was in 1977 (7). Only DENV-1 was isolated during this epidemic, while Figure 1. Map of Saint Martin, an island in the Caribbean. The lower map represents the Caribbean subregion. The year of dengue virus type 3 subtype III detection is indicated under the concerned island or country. The upper map is a close-up of Saint Martin. Source: Centre de documentation de l’Institut de Médecine Tropicale du Service de Santé des Armées. Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 11, No. 5, May 2005 757