[An epidemic risk of yellow fever in Burkina Faso despite a rapid immunisation riposte: role of a multidisciplinary investigation team].

UNLABELLED: On October 8, 1999, one yellow fever (YF) case is confirmed in the South West of Burkina Faso by the Centre Muraz' virology unit. Epidemic extension is suspected as large movements of population are occurring due to troubles in Côte d'Ivoire nearby and as the Aedes vector is endemic in the region. On October 23, the Gaoua's Health Regional Head immunizes 1,000 people around the detected YF case, i.e. 70% of the estimated population and requests an epidemiological investigation. A multidisciplinary team (epidemiologist, entomologist, virologist) from the Centre Muraz, a medical research centre based in Bobo Dioulasso investigate in order to answer the following questions: are there any other or asymptomatic cases of YF? How far is the epidemic risk? Is a paper filter a valuable method for collecting blood samples? What benefit can be gained from a multidisciplinary team?

METHOD: An epidemiological analysis of the patient, a research of asymptomatic or ignored patient is performed (Health Centre registers, interview of the population). This includes the research of people missing the immunisation campaign. Blood samples are collected through 5 ml EDTA glass tubes or through filter paper in order to measure immunoglobuline M. A classical entomological prospecting completes the investigation.

RESULTS: Two possible cases are suspected in the patient's home. History of the patient's is in agreement with a local contamination. In the village 110 people missed the immunisation campaign and samples were collected in 58 people including 26 children. Among them, four (15.3%) were positive with immunoglobuline M, while there were none in the adults. Aedes Luteocephalus, a potential vector is collected through night-captures but is absent of home-water collection. Paper filter assays shows a 100% concordance with classical method.

CONCLUSION: The team could determine the persistency of a yellow fever epidemic risk in the region despite a rapid and adequate immunisation riposte. Due to iterative sporadic cases and due to population movement, a routine survey of YF has to be promoted as the immune status of the population, particularly in the youth, do not protect them. Collection of blood through paper filter will greatly help the routine survey and shall be confirmed during the following investigations.