Surveillance of dengue: evolution of surveillance strategies during a large outbreak, Réunion, France

Abstract

Issue After a period of low-level circulation of a few cases per week during 2017, La Réunion experienced an outbreak of dengue in 2018 followed by a second and ongoing larger epidemic wave in 2019. Various surveillance systems have been progressively implemented to monitor and characterize the outbreak. Methods All laboratory diagnoses of dengue are routinely notified to the regional health authority (RHA) for investigation. With the outbreak onset additional programmes were implemented including the monitoring of presentations to emergency departments (EDs) and hospitalisations of dengue cases. In addition, all death notifications to the RHA which cite dengue are reviewed by an expert committee and the cause of death classified as directly, indirectly or unrelated to dengue. Finally, weekly data from a sentinel network of general practitioners is used to estimate the number of community consultations with dengue-like illness across the island. Results In 2017, 97 dengue cases were notified, with low level circulation continuing through the austral winter. In 2018, 6,679 cases (exclusively serotype 2) were notified. Western and southern regions of the island were most affected. The supplementary surveillance identified over 500 ED presentations for dengue-like illness and 160 hospitalisations. Three deaths were determined to be directly due to dengue, while 3 were indirectly related. Finally, there was an estimated 26,000 consultations for dengue-like illness in the community. After a second winter of persistent circulation, a second epidemic wave commenced in December 2018, and is still ongoing. Lessons The implementation of additional surveillance systems enabled a better understanding of the magnitude and impact of the outbreak. The use of sentinel network allowed the estimation of the number of people affected in the community without a laboratory diagnosis. The ongoing viral circulation since 2017 suggests a high risk of endemisation of dengue on the island. Key messages The outbreak has had a significant impact of health and community health services, and on the wider population. The second consecutive austral winter with interrupted transmission suggest a high risk of endemisation.