SUMMARYIn April 2005, an outbreak of Chikungunya fever occurred on the island of Re´union in the Indian Ocean. During winter 2005, six patients developed meningoencephalitis and acute hepatitis due to Chikungunya virus. Our objectives were to determine the incidence and mortality of atypical Chikungunya viral infections and to identify risk factors for severe disease. A hospital-based surveillance system was established to collect data on atypical Chikungunya cases. Case reports, medical records and laboratory results were reviewed and analysed. We defined an atypical case as one in which a patient with laboratory-confirmed Chikungunya virus infection developed symptoms other than fever and arthralgia. We defined a severe atypical case as one which required maintenance of at least one vital function. We recorded 610 atypical cases of Chikungunya fever : 222 were severe cases, 65 affected patients died. Five hundred and forty-six cases had underlying medical conditions (of which 226 suffered from cardiovascular, 147 from neurological and 150 from respiratory disorders). Clinical features that had never been associated with Chikungunya fever were recorded, such as bullous dermatosis, pneumonia, and diabetes mellitus. Hypertension, and underlying respiratory or cardiological conditions were independent risk factors for disease severity. The overall mortality rate was 10 . 6 % and it increased with age. This is the first time that severe cases and deaths due to Chikungunya fever have been documented. The information presented in this article may assist clinicians in identifying the disease, selecting the treatment strategy, and anticipating the course of illness.

In January 2005, an epidemic of chikungunya fever broke out in the Comoro Islands and lasted until May 2005. In April, cases were also reported in Mayotte and Mauritius. On Réunion Island, the first cases were reported at the end of April. Surveillance of this epidemic required an adaptive system, which at first was based on active and retrospective case detection around the cases reported, then relied on a sentinel network when the incidence increased. Emerging and severe forms of infection were investigated. Death certificates were monitored. By April 2006, the surveillance estimate was 244,000 cases of chikungunya virus infection, including 123 severe cases and 41 of maternoneonatal transmission, with an overall attack rate of 35%. Chikungunya infection was mentioned on 203 death certificates and significant mortality was observed. This epidemic highlighted the need for a mutual strategy of providing information on arboviral diseases and their prevention and control between countries in the southwestern Indian Ocean.

During this large outbreak, the estimated risk of viremic blood donation was high, but low compared to the risk of mosquito-borne CHIKV transmission. The estimated risk was corroborated by the concordant results with the observed risk.

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We report a situation update of imported chinkungunya infections in metropolitan France (the part of France that is in Europe, including the Mediterranean island of Corsica), from April 2005 to June 2006

By 9 April 2006, 241 000 cases of chikungunya had been reported on the island of Reunion, and 5339 cases on the island of Mayotte. The islands of Mauritius, Seychelles, Madagascar, and Comoros are also affected

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In the department of Puy-de-Dôme, France, 17 cases of invasive meningococcal disease C were notified between March 2001 and the first week of 2002. Among the 15 confirmed cases, 11 (73%) were serogroup C, 2 (13%) serogroup B, and 2 could not be identified. The rapid increase in the number of cases in a period of low endemicity for the rest of the country and the severity of the disease (case fatality ratio 27%, purpura fulminans 64%) led the health authorities to initiate a vaccination campaign targeting children and young adults from 2 months up to 20 years living in a limited area of the department. Around 80 000 people were immunised between 16/01/02 and 09/02/02. More than half of the 1390 immediate side effects were headache and dizziness. As of mid-March, no further case of meningococcal disease has been notified since 6 January.