[Epidemiology of dengue infection in Ribeirão Preto, SP, Brazil]

Asymptomatic dengue infection rate: A systematic literature review

Objectives

Dengue infection is spreading worldwide. The clinical spectrum is broad and includes asymptomatic infections. This review provides an overview of the different proportions of asymptomatic infections described in epidemiological studies according to definitions, study designs, and detection methods.

Methods

Medline and Embase databases were searched without restriction of date or language. Studies were included if they reported data on the incidence or prevalence of asymptomatic dengue infections. The data were summarized and classified according to the definitions of the term 'asymptomatic'.

Results

A total of 74 studies were included. The mean proportion of asymptomatic infections among dengue-infected persons was 54% in 50 included studies. The prevalence of dengue infections detected in healthy persons was 0.2% in 24 included studies. The term 'asymptomatic' has been used to refer to 'clinically undetectable infection', but also to 'undiagnosed infection' or 'mild infection'. Only 8% were clinically undetectable laboratory-confirmed dengue infections.

Conclusion

The proportion of asymptomatic dengue infections varied greatly. Studies proving data on clinically undetectable laboratory-confirmed dengue infections were very few, but provided consistent results of low proportions of asymptomatic infections. These data challenge the assumption that the majority of dengue cases are asymptomatic.

Fine-scale heterogeneity in population density predicts wave dynamics in dengue epidemics

The spread of dengue and other arboviruses constitutes an expanding global health threat. The extensive heterogeneity in population distribution and potential complexity of movement in megacities of low and middle-income countries challenges predictive modeling, even as its importance to disease spread is clearer than ever. Using surveillance data at fine resolution from Rio de Janeiro, we document a scale-invariant pattern in the size of successive epidemics following DENV4 emergence. Using surveillance data at fine resolution following the emergence of the DENV4 dengue serotype in Rio de Janeiro, we document a pattern in the size of successive epidemics that is invariant to the scale of spatial aggregation. This pattern emerges from the combined effect of herd immunity and seasonal transmission, and is strongly driven by variation in population density at sub-kilometer scales. It is apparent only when the landscape is stratified by population density and not by spatial proximity as has been common practice. Models that exploit this emergent simplicity should afford improved predictions of the local size of successive epidemic waves.

Quantifying the spatial spread of dengue in a non-endemic Brazilian metropolis via transmission chain reconstruction

The ongoing geographical expansion of dengue is inducing an epidemiological transition in many previously transmission-free urban areas, which are now prone to annual epidemics. To analyze the spatiotemporal dynamics of dengue in these settings, we reconstruct transmission chains in Porto Alegre, Brazil, by applying a Bayesian inference model to geo-located dengue cases from 2013 to 2016. We found that transmission clusters expand by linearly increasing their diameter with time, at an average rate of about 600 m month⁻¹. The majority (70.4%, 95% CI: 58.2–79.8%) of individual transmission events occur within a distance of 500 m. Cluster diameter, duration, and epidemic size are proportionally smaller when control interventions were more timely and intense. The results suggest that a large proportion of cases are transmitted via short-distance human movement (<1 km) and a limited contribution of long distance commuting within the city. These results can assist the design of control policies, including insecticide spraying and strategies for active case finding.

There is increasing urgency to understand the spatiotemporal dynamics of dengue in non-endemic regions. Here, the authors reconstruct likely dengue transmission chains in the city of Porto Alegre based on geo-located cases only, and find that most transmission events occur over short-distances.

Quantifying the spatial spread of dengue in a non-endemic Brazilian metropolis via transmission chain reconstruction

The ongoing geographical expansion of dengue is inducing an epidemiological transition in many previously transmission-free urban areas, which are now prone to annual epidemics. To analyze the spatiotemporal dynamics of dengue in these settings, we reconstruct transmission chains in Porto Alegre, Brazil, by applying a Bayesian inference model to geo-located dengue cases from 2013 to 2016. We found that transmission clusters expand by linearly increasing their diameter with time, at an average rate of about 600 m month^-1. The majority (70.4%, 95% CI: 58.2-79.8%) of individual transmission events occur within a distance of 500 m. Cluster diameter, duration, and epidemic size are proportionally smaller when control interventions were more timely and intense. The results suggest that a large proportion of cases are transmitted via short-distance human movement (<1 km) and a limited contribution of long distance commuting within the city. These results can assist the design of control policies, including insecticide spraying and strategies for active case finding.

Immune status alters the probability of apparent illness due to dengue virus infection: Evidence from a pooled analysis across multiple cohort and cluster studies

Dengue is an important vector-borne pathogen found across much of the world. Many factors complicate our understanding of the relationship between infection with one of the four dengue virus serotypes, and the observed incidence of disease. One of the factors is a large proportion of infections appear to result in no or few symptoms, while others result in severe infections. Estimates of the proportion of infections that result in no symptoms (inapparent) vary widely from 8% to 100%, depending on study and setting. To investigate the sources of variation of these estimates, we used a flexible framework to combine data from multiple cohort studies and cluster studies (follow-up around index cases). Building on previous observations that the immune status of individuals affects their probability of apparent disease, we estimated the probability of apparent disease among individuals with different exposure histories. In cohort studies mostly assessing infection in children, we estimated the proportion of infections that are apparent as 0.18 (95% Credible Interval, CI: 0.16, 0.20) for primary infections, 0.13 (95% CI: 0.05, 0.17) for individuals infected in the year following a first infection (cross-immune period), and 0.41 (95% CI: 0.36, 0.45) for those experiencing secondary infections after this first year. Estimates of the proportion of infections that are apparent from cluster studies were slightly higher than those from cohort studies for both primary and secondary infections, 0.22 (95% CI: 0.15, 0.29) and 0.57 (95% CI: 0.49, 0.68) respectively. We attempted to estimate the apparent proportion by serotype, but current published data were too limited to distinguish the presence or absence of serotype-specific differences. These estimates are critical for understanding dengue epidemiology. Most dengue data come from passive surveillance systems which not only miss most infections because they are asymptomatic and often underreported, but will also vary in sensitivity over time due to the interaction between previous incidence and the symptomatic proportion, as shown here. Nonetheless the underlying incidence of infection is critical to understanding susceptibility of the population and estimating the true burden of disease, key factors for effectively targeting interventions. The estimates shown here help clarify the link between past infection, observed disease, and current transmission intensity.

Dengue disease severity is known to vary widely from the very severe to asymptomatic. There is a wide range of estimates of how many infections result in each of these outcomes. It is known that after a first infection the outcome of a second infection with a different serotype varies over time, but this has not been taken into account in these previous estimates. In this paper, we use modelling methods, combined with information from published dengue research in which individuals are followed over time, to estimate the proportion of infections that result in symptoms at different times after infection. We estimated the proportion of infections that are symptomatic for first infections as 0.18 (95% Credible Interval, CI: 0.16, 0.20), 0.13 (95% CI: 0.05, 0.17) for individuals infected in the year following a first infection and 0.41 (95% CI: 0.36, 0.45) for those experiencing secondary infections after this first year. The estimates here will help understand how cases relate to underlying transmission, which is vital for understanding how much of the population are susceptible to infection and for effectively targeting interventions.

High prevalence of clinically unsuspected dengue disease among children in Ribeirao Preto city, Brazil

The aim of this study was to analyze the characteristics of Dengue virus (DENV)-infected children and the accuracy of dengue diagnosis based on clinical presentations. The inclusion criteria were children ≥1-year-old presenting febrile illness with 1-7 days of onset. Children (n = 110) aged 2-15 years were included in this study. DENV infection was confirmed with virological tests using serum, salvia, and/or urine samples. The attending pediatricians classified 56/110 (50.91%) of the children as suspected dengue cases. The DENV infection was confirmed by specific laboratory tests in 52/56 (92.9%) of the suspected dengue cases but also in 44/54 (81.5%) of the unsuspected dengue cases; total of 96/110 (87.27%) confirmed dengue cases. The clinical diagnosis gave an overall sensitivity of 54.2% (52/96) and a specificity of 71.4% (10/14). The positive predictive value of the clinical diagnosis was 92.8% and negative predictive value was 18.5%. After the third day of onset of symptoms, the DENV genome detection rate was similar in serum and saliva samples, suggesting that saliva samples represent an alternative to blood samples for early dengue diagnosis. Vaccination against Yellow fever virus did not influence the antibody response against DENV-1, DENV-2, and DENV-3, which circulated during the study period. Although the signs and symptoms were compatible with dengue, the attending pediatricians did not suspect the disease in several children. Therefore, the inclusion of virological tests for early diagnosis in the protocols for dengue surveillance would help in the implementation of prompt treatment of patients and epidemic containment strategies. J. Med. Virol. 88:1711-1719, 2016. © 2016 Wiley Periodicals, Inc.

Peridomestic Infection as a Determining Factor of Dengue Transmission

Background

The study of endemic dengue transmission is essential for proposing alternatives to impact its burden. The traditional paradigm establishes that transmission starts around cases, but there are few studies that determine the risk.

Methods

To assess the association between the peridomestic dengue infection and the exposure to a dengue index case (IC), a cohort was carried out in two Mexican endemic communities. People cohabitating with IC or living within a 50-meter radius (exposed cohort) and subjects of areas with no ICs in a 200-meter radius (unexposed cohort) were included.

Results

Exposure was associated with DENV infection in cohabitants (PRa 3.55; 95%CI 2.37–5.31) or neighbors (PRa 1.82; 95%CI 1.29–2.58). Age, location, toilets with no direct water discharge, families with children younger than 5 and the House Index, were associated with infection. Families with older than 13 were associated with a decreased frequency. After a month since the IC fever onset, the infection incidence was not influenced by exposure to an IC or vector density; it was influenced by the local seasonal behavior of dengue and the age. Additionally, we found asymptomatic infections accounted for 60% and a greater age was a protective factor for the presence of symptoms (RR 0.98; 95%CI 0.97–0.99).

Conclusion

The evidence suggests that dengue endemic transmission in these locations is initially peridomestic, around an infected subject who may be asymptomatic due to demographic structure and endemicity, and it is influenced by other characteristics of the individual, the neighborhood and the location. Once the transmission chain has been established, dengue spreads in the community probably by the adults who, despite being the group with lower infection frequency, mostly suffer asymptomatic infections and have higher mobility. This scenario complicates the opportunity and the effectiveness of control programs and highlights the need to apply multiple measures for dengue control.

The study of dengue transmission is essential for proposing alternatives to diminish the cases and the cost of dengue treatment and control. The traditional paradigm establishes that transmission chain starts around a case, but there are few studies that determine the risk, therefore, we studied if to live around a dengue case increases the risk to get infected by Dengue virus. We interviewed and took blood samples from people cohabitating with dengue cases and neighbors in two Mexican communities, to compare we interviewed and took blood samples from subjects of areas without dengue cases in these communities. We found that people cohabitating and neighbors had more risk to get infected. Younger and older person, the workers, families with children younger than 5, houses with toilets with no direct water discharge, and areas with more mosquitoes, also had increased infection risk until one month after the fever onset of dengue case. After this month the frequency of dengue infections was only influenced by the seasonal behavior of dengue and the age of the subjects. Also, we found that 60% of infections are asymptomatic and older people have less risk to develop symptoms. This study suggests that dengue transmission in these locations is initially peridomestic, around the houses of infected subject who may be asymptomatic (without symptoms), and it is influenced by other characteristics of the individual, the neighborhood and the community. After this peridomestic transmission, dengue spreads in the community probably by adults who mostly suffer asymptomatic infections and have higher mobility, which complicates the application and affects the results of vector control programs.

Mídia, saúde e poder: um jogo de representações sobre dengue

O objetivo desta pesquisa foi construir discursos que representem como a primeira epidemia de dengue em Ribeirão Preto-SP foi abordada pela mídia impressa e trazer para reflexão desdobramentos sobre mídia e poder. Foram reunidas 126 reportagens de novembro de 1990 a março de 1991 dos jornais Folha de S. Paulo, O Estado de S. Paulo e A Cidade, e das revistas Veja e Revide. Utilizou-se o método do Discurso do Sujeito Coletivo, fundamentado na Teoria das Representações Sociais. A mídia polemizou com a discussão sobre quem seria o grande vilão da epidemia em vez de esclarecer sobre a epidemia em si. Comprovou-se a defasagem da informação disponibilizada. O jogo de representações e a relação mídia/poder ficaram nítidas. Temos como problema não somente a possibilidade de acesso adequado e suficiente às informações produzidas, mas, também, a dificuldade de decidir o que deve ser discutido nos jornais diários para enriquecer, de fato, o arcabouço informacional da população. Para isso, os profissionais que lidam com informação e comunicação em saúde, na mídia impressa, precisam ser capacitados para provocar a aproximação da linguagem técnica à linguagem popular. Para que haja circulação e apropriação da informação em Saúde Pública, é necessário abrir a discussão para a comunidade e capacitá-la para que consiga se expressar. É importante discutir a qual tipo de informação o cidadão tem acesso durante os processos epidêmicos: Informação política ou epidemiológica? Questões políticas não podem se sobrepor a questões prioritárias de saúde nos meios de comunicação presentes no cotidiano das famílias brasileiras.

Epidemiological risk factors associated with high global frequency of inapparent dengue virus infections

Dengue is a major international public health concern, and the number of outbreaks has escalated greatly. Human migration and international trade and travel are constantly introducing new vectors and pathogens into novel geographic areas. Of particular interest is the extent to which dengue virus (DENV) infections are subclinical or inapparent. Not only may such infections contribute to the global spread of DENV by human migration, but also seroprevalence rates in naïve populations may be initially high despite minimal numbers of detectable clinical cases. As the probability of severe disease is increased in secondary infections, populations may thus be primed, with serious public health consequences following introduction of a new serotype. In addition, pre-existing immunity from inapparent infections may affect vaccine uptake, and the ratio of clinically apparent to inapparent infection could affect the interpretation of vaccine trials. We performed a literature search for inapparent DENV infections and provide an analytical review of their frequency and associated risk factors. Inapparent rates were highly variable, but “inapparent” was the major outcome of infection in all prospective studies. Differences in the epidemiological context and type of surveillance account for much of the variability in inapparent infection rates. However, one particular epidemiological pattern was shared by four longitudinal cohort studies: the rate of inapparent DENV infections was positively correlated with the incidence of disease the previous year, strongly supporting an important role for short-term heterotypic immunity in determining the outcome of infection. Primary and secondary infections were equally likely to be inapparent. Knowledge of the extent to which viruses from inapparent infections are transmissible to mosquitoes is urgently needed. Inapparent infections need to be considered for their impact on disease severity, transmission dynamics, and vaccine efficacy and uptake.

Representações sociais sobre dengue: reflexões sobre a mediação da informação em saúde pública

O objetivo do trabalho é trazer subsídios para o debate sobre as relações entre saúde pública, meios de comunicação e a formulação e divulgação da informação sobre saúde para os cidadãos. O foco da pesquisa é a divulgação de informações sobre dengue e processos epidêmicos em Ribeirão Preto, SP. Foi utilizada como principal referencial para a pesquisa a Teoria das Representações Sociais, a qual busca captar o imaginário social da população sobre a doença a ser abordada. O método utilizado foi o Discurso do Sujeito Coletivo (DSC), caracterizado pela organização e tabulação de dados qualitativos de natureza verbal. Questionários foram aplicados para a coleta de dados. Para analisar e contextualizar os dados obtidos foram feitas referências a algumas teorias acerca da reflexividade, do risco epidemiológico e da Sociedade da Informação. Salienta-se, ao final, a importância dos mediadores para que haja bom desempenho do processo de mediar informações sobre saúde, e sobre dengue especificamente.

A prospective cohort study to evaluate peridomestic infection as a determinant of dengue transmission: protocol

Background

Vector control programs, which have focused mainly on the patient house and peridomestic areas around dengue cases, have not produced the expected impact on transmission. This project will evaluate the assumption that the endemic/epidemic transmission of dengue begins around peridomestic vicinities of the primary cases. Its objective is to assess the relationship between symptomatic dengue case exposure and peridomestic infection incidence.

Methods/Design

A prospective cohort study will be conducted (in Tepalcingo and Axochiapan, in the state of Morelos, Mexico), using the state surveillance system for the detection of incident cases. Paired blood specimens will be collected from both the individuals who live with the incident cases and a sample of subjects residing within a 25-meter radius of such cases (exposed cohort), in order to measure dengue-specific antibodies. Other subjects will be selected from areas which have not presented any incident cases within 200 meters, during the two months preceding the sampling (non-exposed cohort). Symptomatic/asymptomatic incident infection will be considered as the dependent variable, exposure to confirmed dengue cases, as the principal variable, and the socio-demographic, environmental and socio-cultural conditions of the subjects, as additional explanatory variables.

Discussion

Results indicating a high infection rate among the exposed subjects would justify the application of peridomestic control measures and call for an evaluation of alternate causes for insufficient program impact. On the other hand, a low incidence of peridomestic-infected subjects would support the hypothesis that infection occurs outside the domicile, and would thus explain why the vector control measures applied in the past have exerted such a limited impact on cases incidence rates. The results of the present study may therefore serve to reassess site selection for interventions of this type.

Clinical and epidemiological characterization of dengue hemorrhagic fever cases in northeastern, Brazil

INTRODUCTION

The dengue hemorrhagic dengue (DHF) remains an important public health problem in Brazil. The objective of this study was to analyze the epidemiological characteristics of DHF cases during the 2003 epidemic in Ceará.

METHODS

Suspected DHF cases with onset of symptoms between January and December 2003 were investigated.

RESULTS

37,964 classic dengue cases and 291 DHF cases were reported. Among the cases discarded, 75.5% were serologically positive but did not meet the criteria recommended by the World Health Organization (WHO). The DHF patients' median age was 30 years (2 - 88). Among the hemorrhagic manifestations, petechiae were the most (32.6%) frequent. Cases of gastrointestinal bleeding, ascites, pericardial pleural effusion, hepatomegaly, hypotension and shock showed higher risk of progression to death (p <0.05).

CONCLUSIONS

The introduction of a new serotype (DENV-3) in Ceará, which encountered a susceptible population and high vector density, may have been the primary agent responsible for the magnitude of the epidemic. Timely and appropriate medical care, along with an organized care structure are essential for reducing its lethality.

Evolução temporal da dengue no município de Ribeirão Preto, São Paulo, 1994 a 2003

Este estudo caracteriza-se epidemiológico-descritivo com objetivo de descrever a evolução temporal dos casos de dengue em Ribeirão Preto, São Paulo, no período de 1994 a 2003, segundo mês de ocorrência e sexo. Os dados foram obtidos junto às fichas de notificação compulsória fornecidas pela Vigilância Epidemiológica da Secretaria Municipal de Saúde do município. Foram obtidos os coeficientes de incidência por 100.000 habitantes, segundo estimativas populacionais do Instituto Brasileiro de Geografia e Estatística. O município viveu uma epidemia de dengue no ano de 2001, quando o coeficiente de incidência chegou a 619,65 casos/100.000 habitantes, sendo que dentre os 5.553 casos encontrados no período estudado, 0,07% ocorreram no ano de 1994, 3,68% em 1995, 4,52% em 1996, 2,40% em 1997, 1,82% em 1998, 5,73% em 1999, 3,75% em 2000, 57,37% em 2001, 6,25% em 2002 e, 14,39% em 2003 . Os meses do ano de maior ocorrência da doença foram de janeiro a maio. Em relação à variável sexo, a proporção entre o número de casos foi de aproximadamente 1:1, mostrando pequenas flutuações de casos de dengue entre homens e mulheres, para todo período estudado. Os resultados apontam a necessidade do desenvolvimento de estudos sobre a temática e reforçam o papel das instituições de ensino na questão da dengue no nosso país.

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

Background

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.

Methods

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.

Results

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.

Conclusion

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.

Dengue vector prevalence and virus infection in a rural area in south India

We conducted a 2-year (1997-1999) longitudinal, entomological and virological study in three dengue endemic villages in Vellore district, Tamil Nadu, to understand the dynamics of dengue transmission. Aedes aegypti (Linn.), Ae. albopictus (Skuse) and Ae. vittatus (Bigot) were the prevalent vector species. Aedes aegypti was breeding throughout the year with a Breteau index ranging from 9.05 to 45.49. Aedes albopictus and Ae. vittatus were prevalent mainly in the rainy season. Small water holding containers (cemented tanks/cisterns) were the perennial breeding source of Ae. aegypti, and its abundance was significantly higher in semi-urbanized central areas than the peripheral areas of the villages. From 271 pools (4016 specimens) of adult females, eight dengue virus (DENV) isolates were obtained of which seven were from Ae. aegypti and one from Ae. albopictus. This is the first report of DENV isolation from Ae. albopictus in rural India. Infection rates in the two species were comparable. However, due to higher and perennial prevalence, Ae. aegypti is considered as primary vector with Ae. albopictus playing a secondary role. Despite circulation of all four serotypes (DENV 1-4) detected mainly during the transmission season, the high anthropophilic index of the vectors and their abundance, no human dengue case was reported, suggesting silent dengue transmission.