In 2015, the Zika virus spread rapidly throughout the Americas, including in French departments and overseas collectivities, and revealed new routes of transmission—notably sexual transmission—as well as severe complications, including congenital malformations and neurological syndromes.

It is in this context that a group of representatives from each member country, coordinated by the ECDC, has been working to establish a European surveillance system. Its objectives: early detection and rapid notification of imported and locally acquired cases, particularly those residing in EU areas where the mosquitoes that are potential vectors of the virus—Aedes albopictus or Aedes aegypti—are present, in order to trigger appropriate control measures. This system became effective in March 2016. Protocols for implementing the surveillance system were developed, including investigation guidelines, case definitions, criteria for biological confirmation, and data collection procedures.

Santé publique France contributed significantly to discussions on the implementation of this system, the development of case definitions and criteria for laboratory confirmation, as well as various considerations regarding public health recommendations concerning the Zika virus.

As part of Zika virus surveillance, EU countries were invited to implement this specific surveillance locally. Some countries adopted different approaches depending on their resources and the national risk level.

In France, a national surveillance system was established in January 2016 to rapidly detect imported or locally acquired cases and limit local transmission (during the Aedes albopictus mosquito’s active season, from May to November) through the early implementation of vector control measures.

Between June 2015 and March 2017, 2,133 confirmed cases of Zika virus were reported by 21 EU countries. Most cases were acquired in the Caribbean (71%), primarily in Guadeloupe (489 cases), Martinique (421 cases), and the Dominican Republic (146 cases). The number of cases reported in the EU began to rise, coinciding with the ongoing epidemic in the Americas. During the week of August 15, a peak of 85 imported cases was reported.

Almost all cases (99%) were acquired during travel to areas where the virus is known to circulate, presumably through vector-borne transmission. No cases were infected by Aedes mosquitoes on the European continent. Twenty cases of sexual transmission have been reported in the EU, including 19 cases of transmission from men to women. About 100 women were infected with the Zika virus during their pregnancies. Among the imported cases, only one case of mother-to-child transmission has been reported at the European level.

With 1,141 cases, France is the country with the highest number of detected cases. The majority of these were infected in Guadeloupe, Martinique, and French Guiana, the three French departments and overseas collectivities in the Americas most affected by this outbreak.

This study suggests that the Aedes albopictus mosquito (in Europe) has a low capacity to transmit the virus, given the absence of local transmission despite a significant number of infected travelers returning from epidemic areas to regions within the EU where this mosquito is well established. Nevertheless, this absence of local vector-borne transmission may also be due to the effectiveness of vector control measures implemented at the national level, as is the case in France.

This surveillance has identified a limited number of cases of sexual transmission (1%), although this number may have been underestimated due to a significant proportion of asymptomatic cases following Zika virus infection.

Since the majority of cases are imported, travel advisories—and specifically those for pregnant women—are essential.

This report also demonstrates the system’s ability to identify cases returning from Africa, Asia, and Oceania, thereby enabling the detection of new transmission areas in countries where diagnostic capabilities for the Zika virus may be limited.