Severe dengue: the need for new case definitions

Dengue fever imposes a societal burden that is difficult to measure because of the disease's non-specific symptoms and the lack of easily applied case definitions for its more severe manifestations. An efficacy trial of a tetravalent vaccine is expected in the near future, but only one of the severe dengue syndromes-the continuum of dengue haemorrhagic fever and dengue shock syndrome-is well defined. One of the results of the focus on dengue haemorrhagic fever is the false perception of low disease burden in the Americas, which is an obstacle to the mobilisation of political and economic resources to fight the disease. Three improvements are necessary to standardise the dengue haemorrhagic fever definition and to allow it to do well in different populations: (1) redefine the threshold for thrombocytopenia, (2) clarify the standard practice and value of the tourniquet test, and (3) incorporate a criterion to measure intravenous fluid replacement. In addition, for an accurate estimation of dengue burden, locally appropriate definitions of severe dengue must be devised and standardised so they will be considered valid in the global research community.