Vincent Pierre

Post-Epidemic Chikungunya Disease on Reunion Island: Course of Rheumatic Manifestations and Associated Factors over a 15-Month Period

Although the acute manifestations of Chikungunya virus (CHIKV) illness are well-documented, few data exist about the long-term rheumatic outcomes of CHIKV-infected patients. We undertook between June and September 2006 a retrospective cohort study aimed at assessing the course of late rheumatic manifestations and investigating potential risk factors associated with the persistence of these rheumatic manifestations over 15 months. 147 participants (>16 yrs) with laboratory-confirmed CHIKV disease diagnosed between March 1 and June 30, 2005, were identified through a surveillance database and interviewed by telephone. At the 15-month-period evaluation after diagnosis, 84 of 147 participants (57%) self-reported rheumatic symptoms. Of these 84 patients, 53 (63%) reported permanent trouble while 31 (37%) had recurrent symptoms. Age ≥45 years (OR = 3.9, 95% CI 1.7–9.7), severe initial joint pain (OR = 4.8, 95% CI 1.9–12.1), and presence of underlying osteoarthritis comorbidity (OR = 2.9, 95% CI 1.1–7.4) were predictors of nonrecovery. Our findings suggest that long-term CHIKV rheumatic manifestations seem to be a frequent underlying post-epidemic condition. Three independent risk factors that may aid in early recognition of patients with the highest risk of presenting prolonged CHIKV illness were identified. Such findings may be particularly useful in the development of future prevention and care strategies for this emerging virus infection.

Seroprevalence and Risk Factors of Chikungunya Virus Infection in Mayotte, Indian Ocean, 2005-2006: A Population-Based Survey

Background Since 2006, Chikungunya virus (CHIKV) has re-emerged as an important pathogen of global concern. However, individual and household factors associated with the acquisition and the magnitude of clinically silent CHIKV infections remain poorly understood. In this present study, we aimed to investigate the seroprevalence, estimate the proportion of symptomatic illness and identify the risk factors for CHIKV infection in the primo-exposed population of Mayotte. Methods/ Principal Findings We conducted a household-based cross sectional serosurvey in Mayotte in November and December 2006 using complex multistage cluster sampling. To produce the results representative of the island population aged 2 years or older, sample data were adjusted with sample weights. Explanatory and multiple logistic regression analyses were performed to investigate associations between CHIKV infection seropositivity (presence of IgM and/or IgG to CHIKV by enzyme-linked immunoabsorbent assay) and risk factors. A total of 1154 individuals were analyzed. The overall seroprevalence of CHIKV infection was 37·2% (95% CI = 33·9–40·5), 318 (72·3%) of the seropositive participants reported symptoms consistent with a CHIKV infection during the epidemic period. Risk factors for CHIKV seropositivity among adults (aged 15 years and older) were male gender, low socioeconomic index, schooling ≤6 years and living in makeshift housing. Conclusions Our findings indicate that roughly one out of four CHIKV infections is asymptomatic. Conditions associated with poverty may be considered as critical in CHIKV acquisition. Thus, these conditions should be taken into account in the development of future prevention strategies of CHIKV disease.

Rift Valley Fever, Mayotte, 2007–2008

After the 2006–2007 epidemic wave of Rift Valley fever (RVF) in East Africa and its circulation in the Comoros, laboratory case-finding of RVF was conducted in Mayotte from September 2007 through May 2008. Ten recent human RVF cases were detected, which confirms the indigenous transmission of RFV virus in Mayotte.

Outbreak of Chikungunya fever in Mayotte, Comoros archipelago, 2005–2006

In 2005-2006, a large outbreak of Chikungunya (CHIK) fever occurred on the western Indian Ocean Islands. In Mayotte, concurrent with an enhanced passive case notification system, we carried out two surveys. A seroprevalence survey designed to document recent CHIK infection was conducted on serum samples collected from pregnant women in October 2005 (n=316) and in March-April 2006 (n=629). A cross-sectional clinical community survey carried out from 2 to 10 May 2006 among 2235 individuals was designed to determine the cumulative incidence of presumptive CHIK fever cases. The seroprevalence of recent infection among pregnant women was 1.6% in October 2005 and rose to 26% in April 2006. The clinical community survey showed that nearly 26% of respondents had experienced presumptive CHIK fever between January and May 2006. Extrapolated to the overall population of Mayotte, these figures lead to an estimated attack rate of 249.5 cases per 1000 population as of early May 2006. Nine patients with the maternofetal form and six subjects with the severe form were recorded. This first emergence of CHIK fever in Mayotte lead to a very large outbreak. Efforts to strengthen surveillance and prevention of arbovirus infection are needed at country and regional levels.

Chikungunya-related Fatality Rates, Mauritius, India, and Reunion Island

To the Editor: During the epidemic of chikungunya virus infection that occurred on Reunion Island in 2005–06, we reported an overmortality corresponding to the epidemic peak, which was estimated by comparing observed and expected deaths (1). The excess was similar to the number of deaths related to chikungunya infection reported by death certificates (2). The case-fatality rate (CFR) on Reunion Island was estimated to be 1/1,000 population. According to Beesoon et al. (3), the fatality rate attributable to chikungunya infection was much higher on Mauritius: 743 deaths in excess of expected deaths led to a CFR of ≈4.5%, with 15,760 confirmed or suspected cases for 2005 and 2006 as reported in this letter. A similar CFR of 4.9% can be calculated for the city of Ahmedabad, India, during the 2006 chikungunya epidemic (4). This 45- to 49-fold difference could be explained by a greater severity of chikungunya infection in Mauritius or Ahmedabad that could be due to a mutating strain, differences in the preexisting conditions of patients, differences in the management of patients, or by coincident deaths in excess from other causes. However, the most probable explanation can be attributed to the surveillance systems of chikungunya cases. On Reunion Island, surveillance was highly sensitive and relied either on active case finding or on estimates of suspected cases. Results have been assessed by iterative external studies and serosurveys, and the CFR we found is likely consistent. If we apply this rate to Mauritius, ≈60% of the population would have contracted chikungunya infection during this epidemic. If so, the risk of epidemic resurgence could be much lower than previously expected. This point raises the need to conduct seroprevalence studies in those territories, the only way to evaluate the herd immunity level of the population.

Transmission télématique de données épidémiologiques et surveillance de l’épidémie de chikungunya à la Réunion en 2006

INTRODUCTION When the first cases of the 2005-2006 chikungunya epidemic struck Reunion Island, local health authorities set up an island-wide operational epidemiologic surveillance system for these infections. This system relied on vector control teams, which conducted active case-finding around the reported cases, and on a sentinel physician network. In addition, in March 2006, the Sephira and Reunion-Telecom companies, in partnership with the Reunion-Mayotte interregional epidemiology bureau (CIRE), developed an innovative system of epidemiologic monitoring by electronic data transmission. METHODS This system relied on the participation of volunteer physicians who transmitted epidemiologic data through the data terminals used for the transmission of electronic treatment forms to the health insurance funds. Using the patients insurance identification card, each physician provided information about consultations related to chikungunya. This information was transmitted, via the Sephira server in France to Reunion-Telecom, which processed, aggregated and transmitted these data weekly to the CIRE. This network was separate from and independent of the sentinel physician network, RESULTS In all, 44 physicians, accounting for 6% of the general practitioners in Reunion, participated in this system, which went into operation during week 14 of 2006. The data collected allowed an assessment of the trends in the epidemic incidence rate by calculating the percentage of consultations related to chikungunya among all consultations (office visits and house calls). For weeks 14-26 of 2006, when the epidemic transmission had spread across the entire island, the Reunion-Telecom health network data proved to be closely correlated with the results of the sentinel physician network surveillance system used to monitor the epidemic trends (correlation coefficient=0.97). CONCLUSION The system provided very encouraging results in monitoring disease time trends in a period of massive epidemic. Its simplicity of use and the speed of data transmission are undeniable assets for its future development. Because it offers the possibility of monitoring other diseases with epidemic potential, such as dengue and influenza, it opens new prospects for infectious disease surveillance.

COL7-04 Paludisme d’importation à la Réunion (2003-2007) et risque de réémergence de cas autochtone

Objectif L’eradication du paludisme a La Reunion etait declaree en 1979. Ce travail devait evaluer le risque de reemergence de cas autochtone par l’analyse des donnees epidemiologiques (declarations obligatoires 2003-2007) et entomologiques (releves d’indices d’ Anopheles arabiensis depuis 1985). Resultats Entre 2003 et 2007, 619 cas de paludisme d’importation ont ete notifies (163 en 2003, 76 en 2007). L’âge median des patients etait de 34 ans et le sex-ratio H/F de 2. La moitie des patients etaient immigrants de 1 re generation et 47,8 % etaient nes dans une zone d’endemie palustre (Madagascar, Comores ou Mayotte). Plasmodium falciparum etait responsable de 84,3 % des acces. Les pays de contamination etaient Madagascar dans 40,5 % des cas, les Comores ou Mayotte dans 29 %, et un autre pays africain dans 6,1 % des cas. Aucune chimioprophylaxie n’a ete suivie dans 45,2 % des cas. Le delai median entre le retour de la zone endemique et le diagnostic etait de 11 jours. Plus de la moitie des cas (59,4 %) ont ete hospitalises et 4 deces ont ete signales. Conclusion La presence et l’extension geographique d’ Anopheles arabiensis et l’importation de Plasmodium via des voyageurs en provenance de pays impaludes impose une surveillance entomologique et epidemiologique renforcee pour prevenir la reemergence de cette maladie a La Reunion. L’existence de gites naturels dans l’Est proche de zones residentielles (zone des 2 derniers cas autochtones) et la future creation de zones irriguees dans l’Ouest ou la proliferation vectorielle est continue toute l’annee montre que le risque de cas autochtone secondaire est toujours bien reel.