Spatial point analysis based on dengue surveys at household level in central Brazil

<p>Abstract</p> <p>Background</p> <p>Dengue virus (DENV) affects nonimunne human populations in tropical and subtropical regions. In the Americas, dengue has drastically increased in the last two decades and Brazil is considered one of the most affected countries. The high frequency of asymptomatic infection makes difficult to estimate prevalence of infection using registered cases and to locate high risk intra-urban area at population level. The goal of this spatial point analysis was to identify potential high-risk intra-urban areas of dengue, using data collected at household level from surveys.</p> <p>Methods</p> <p>Two household surveys took place in the city of Goiania (~1.1 million population), Central Brazil in the year 2001 and 2002. First survey screened 1,586 asymptomatic individuals older than 5 years of age. Second survey 2,906 asymptomatic volunteers, same age-groups, were selected by multistage sampling (census tracts; blocks; households) using available digital maps. Sera from participants were tested by dengue virus-specific IgM/IgG by EIA. A Generalized Additive Model (GAM) was used to detect the spatial varying risk over the region. Initially without any fixed covariates, to depict the overall risk map, followed by a model including the main covariates and the year, where the resulting maps show the risk associated with living place, controlled for the individual risk factors. This method has the advantage to generate smoothed risk factors maps, adjusted by socio-demographic covariates.</p> <p>Results</p> <p>The prevalence of antibody against dengue infection was 37.3% (95%CI [35.5–39.1]) in the year 2002; 7.8% increase in one-year interval. The spatial variation in risk of dengue infection significantly changed when comparing 2001 with 2002, (ORadjusted = 1.35; p < 0.001), while controlling for potential confounders using GAM model. Also increasing age and low education levels were associated with dengue infection.</p> <p>Conclusion</p> <p>This study showed spatial heterogeneity in the risk areas of dengue when using a spatial multivariate approach in a short time interval. Data from household surveys pointed out that low prevalence areas in 2001 surveys shifted to high-risk area in consecutive year. This mapping of dengue risks should give insights for control interventions in urban areas.</p

Dengue endêmico: o desafio das estratégias de vigilância Endemic dengue: surveillance strategy challenges

A interação entre infecção clínica, vetor e imunidade sorotípica da população define o risco de epidemia por dengue. A situação epidemiológica endêmico-esporádica seria meta aceitável de controle em regiões metropolitanas ante deficiências de urbanização, saneamento, acesso às residências por agentes sanitários, baixo poder residual de inseticidas biológicos e mobilização social. A Vigilância, então, requererá continuidade das ações públicas e da sociedade em geral, estimuladas na medida inversa da redução de casos, e propostas adequadas. Visando constituir sistema de Vigilância sensível e específico, sobretudo em períodos endêmicos, propõe-se que o componente clínico sentinela deve integrar tanto a assistência emergencial aberta preconizada, detectando casos graves - ponta do iceberg, como serviços de referência para doenças febris agudas, definindo diferentes formas clínicas e propiciando confirmação diagnóstica. Em regiões estratégicas, paralelamente, inquéritos sorotipicos amostrais, embora complexos, devem ser buscados, avaliando imunidade e suscetibilidade de grupos etários aos sorotipos circulantes, estimativa de casos subclínicos e alcance do Sistema de Vigilância e Controle.<br>Interaction between clinical infection, vector, and population serotype immunity defines dengue epidemic risk. An endemic-sporadic epidemiological situation is an acceptable control target in metropolitan regions deficient in urban upgrading, sanitation, and health agents' access to residences, besides low residual power of biological insecticides and social mobilization problems. Surveillance requires continued action by government and society (particularly when incidence decreases) and adequate proposals. To establish a sensitive and specific surveillance system for endemic periods, the authors propose the sentinel clinical component as part of emergency care (detecting serious tip-of-the-iceberg cases) and reference services for acute febrile diseases, defining clinical forms and providing diagnostic confirmation. Although complex, sample serotype surveys should be conducted in strategic areas, evaluating: immunity and susceptibility of age groups to circulating serotypes; estimation of sub-clinical cases; and Surveillance and Control System reach

Confiabilidade do diagnóstico final de dengue na epidemia 2001-2002 no Município do Rio de Janeiro, Brasil Reliability of the final dengue diagnosis in the epidemic occurring in Rio de Janeiro, Brazil, 2001-2002

Este estudo analisou a confiabilidade do diagnóstico final das 155.242 notificações de dengue da epidemia 2001-2002 no Município do Rio de Janeiro, fornecidas pela Secretaria Municipal de Saúde do Rio de Janeiro, por meio do Sistema de Informação de Agravos de Notificação (SINAN). O diagnóstico final possui como opções de preenchimento: dengue clássico, febre hemorrágica do dengue, descartado, inconclusivo e ignorado. Foi construída uma rotina em Epi Info para comparar o diagnóstico final digitado no SINAN com os critérios do Ministério da Saúde (MS), agrupando os casos como dengue clássico, dengue hemorrágico, descartado e inconclusivo (inclui ignorado). O diagnóstico final mostrou 52,4% dengue clássico, 0,6% dengue hemorrágico, 0,9% descartado e 46% de inconclusivo e ignorado, sendo que 78% de dengue clássico, 69% de dengue hemorrágico e 21,1% dos descartados preencheram os critérios do MS. A confiabilidade do diagnóstico final digitado foi em geral satisfatória (kappa = 0,681; IC95%: 0,685-0,677), porém baixa para os óbitos (kappa = 0,152; IC95%: 0,046-0,258). Considerando-se o volume da epidemia, o diagnóstico final de dengue clássico e dengue hemorrágico foi satisfatório, porém a alta proporção de casos ignorados e inconclusivos e a baixa qualidade da informação nos óbitos limitam o uso do SINAN nesse contexto.<br>This study analyzed the reliability of the final diagnosis in the 155,242 dengue reports during the 2001-2002 epidemic in the city of Rio de Janeiro, Brazil, using the official information system on communicable diseases (SINAN). The system allows the following options for the final diagnosis: classic dengue, dengue hemorrhagic fever, discarded, inconclusive, and unknown. We built a classification routine in Epi Info to compare the final diagnosis from SINAN with Ministry of Health criteria. According to the final diagnosis, the case breakdown was: 52.4% classic dengue; 0.6% dengue hemorrhagic fever; 0.9% discarded; 46% inconclusive and unknown. The revised diagnosis showed that 78% of classic dengue, 69% of dengue hemorrhagic fever, and 21.1% of discarded cases met the classification criteria. Although the reliability of the SINAN final diagnosis was generally satisfactory (kappa = 0.681; 95%CI: 0.685-0.677), it was worse for fatal cases (kappa = 0.152; 95%CI: 0.046-0.258). Considering the epidemic's magnitude, the final diagnosis of classic dengue and dengue hemorrhagic fever was satisfactory, but the high proportion of inconclusive or unknown cases and the poor quality of information for fatal cases limit the usefulness of SINAN in this context