Global Alert and Response (GAR)

WHO Report on Global Surveillance of Epidemic-prone Infectious Diseases - Dengue and dengue haemorrhagic fever

Description of the data

For Asia, WHO has reports of cases and deaths from dengue from 1995-1998. Case reporting from the Americas is available from 1960, and reporting of deaths from 1989. There are separate reports for DF and DHF from the Americas but not from other continents. Although dengue infections occur in Africa they are not routinely reported from Africa.

Strengths and weaknesses of dengue surveillance

Dengue surveillance is difficult to establish and maintain. DF is a complex disease whose symptoms are difficult to distinguish from other common febrile illnesses. Surveillance for DHF holds special problems. First, there are many places where DHF is a rare occurrence. In these places DHF may not be suspected as a cause of particular symptoms. Second, diagnosing DHF cannot be done by clinical judgement alone. Correctly identifying a case of DHF requires laboratory tests (hemotocrits, platelet counts, virologic or serologic tests) of samples of blood collected from patients with haemorrhagic symptoms. Laboratory equipment to perform these tests are not always available in health centres.

As in other diseases the case definitions used for reporting differ among countries, and some countries report only laboratory confirmed cases whereas other report suspected cases as well. Finally, some countries report cases and deaths from DF and DHF/DSS separately, whereas in other countries reports of DF and DHF are combined. Problems of under-diagnosis, incomplete reporting and reporting delay also weaken surveillance.

Laboratories play a very important role in surveillance of dengue - not only in confirming DF and DHF cases but also in monitoring serotypes and strains circulating in the population. For example, the introduction of a new serotype may be an important indicator of future epidemics of DHF/DSS. In many countries laboratories need considerable strengthening to conduct adequate surveillance of dengue.

The lack of any systematic reports of dengue cases from Africa is a clear weakness in global surveillance efforts for dengue.