Under-recognition and reporting of dengue in Cambodia: a capture–recapture analysis of the National Dengue Surveillance System

Age-specific case data reveal varying dengue transmission intensity in US states and territories

Dengue viruses (DENV) are endemic in the US territories of Puerto Rico, American Samoa, and the US Virgin Islands, with focal outbreaks also reported in the states of Florida and Hawaii. However, little is known about the intensity of dengue virus transmission over time and how dengue viruses have shaped the level of immunity in these populations, despite the importance of understanding how and why levels of immunity against dengue may change over time. These changes need to be considered when responding to future outbreaks and enacting dengue management strategies, such as guiding vaccine deployment. We used catalytic models fitted to case surveillance data stratified by age from the ArboNET national arboviral surveillance system to reconstruct the history of recent dengue virus transmission in Puerto Rico, American Samoa, US Virgin Islands, Florida, Hawaii, and Guam. We estimated average annual transmission intensity (i.e., force of infection) of DENV between 2010 and 2019 and the level of seroprevalence by age group in each population. We compared models and found that assuming all reported cases are secondary infections generally fit the surveillance data better than assuming all cases are primary infections. Using the secondary case model, we found that force of infection was highly heterogeneous between jurisdictions and over time within jurisdictions, ranging from 0.00008 (95% CrI: 0.00002-0.0004) in Florida to 0.08 (95% CrI: 0.044-0.14) in American Samoa during the 2010-2019 period. For early 2020, we estimated that seropositivity in 10 year-olds ranged from 0.09% (0.02%-0.54%) in Florida to 56.3% (43.7%-69.3%) in American Samoa. In the absence of serological data, age-specific case notification data collected through routine surveillance combined with mathematical modeling are powerful tools to monitor arbovirus circulation, estimate the level of population immunity, and design dengue management strategies.

The feasibility of novel point-of-care diagnostics for febrile illnesses at health centres in Southeast Asia: a mixed-methods study

BACKGROUND

The decline of malaria in Southeast Asia means other causes of fever are increasingly relevant, but often undiagnosed. The objective of this study was to assess the feasibility of point-of-care tests to diagnose acute febrile illnesses in primary care settings.

METHODS

A mixed-methods study was conducted at nine rural health centres in western Cambodia. Workshops introduced health workers to the STANDARD(TM) Q Dengue Duo, STANDARD(TM) Q Malaria/CRP Duo and a multiplex biosensor detecting antibodies and/or antigens of eight pathogens. Sixteen structured observation checklists assessed users' performances and nine focus group discussions explored their opinions.

RESULTS

All three point-of-care tests were performed well under assessment, but sample collection was difficult for the dengue test. Respondents expressed that the diagnostics were useful and could be integrated into routine clinical care, but were not as convenient to perform as standard malaria rapid tests. Health workers recommended that the most valued point-of-care tests would directly inform clinical management (e.g. a decision to refer a patient or to provide/withhold antibiotics).

CONCLUSIONS

Deployment of new point-of-care tests to health centres could be feasible and acceptable if they are user-friendly, selected for locally circulating pathogens and are accompanied by disease-specific education and simple management algorithms.

Dengue in Cambodia 2002-2020: Cases, Characteristics and Capture by National Surveillance

Objective

Data from 19 years of national dengue surveillance in Cambodia (2002-2020) were analyzed to describe trends in dengue case characteristics and incidence.

Methods

Generalized additive models were fitted to dengue case incidence and characteristics (mean age, case phenotype, fatality) over time. Dengue incidence in a pediatric cohort study (2018-2020) was compared to national data during the same period to evaluate disease under-estimation by national surveillance.

Findings

During 2002-2020, there were 353,270 cases of dengue (average age-adjusted incidence 1.75 cases/1,000 persons/year) recorded in Cambodia, with an estimated 2.1-fold increase in case incidence between 2002 and 2020 (slope = 0.0058, SE = 0.0021, p = 0.006). Mean age of infected individuals increased from 5.8 years in 2002 to 9.1 years in 2020 (slope = 0.18, SE = 0.088, p <0.001); case fatality rates decreased from 1.77% in 2002 to 0.10% in 2020 (slope = -0.16, SE = 0.0050, p <0.001). When compared to cohort data, national data under-estimated clinically apparent dengue case incidence by 5.0-fold (95% CI 0.2 - 26.5), and overall dengue case incidence (both apparent and inapparent cases) by 33.6-fold (range: 18.7- 53.6).

Conclusion

Dengue incidence in Cambodia is increasing and disease is shifting to older pediatric populations. National surveillance continues to under-estimate case numbers. Future interventions should account for disease under-estimation and shifting demographics for scaling and to target appropriate age groups.

Temperature, traveling, slums, and housing drive dengue transmission in a non-endemic metropolis

Dengue is steadily increasing worldwide and expanding into higher latitudes. Current non-endemic areas are prone to become endemic soon. To improve understanding of dengue transmission in these settings, we assessed the spatiotemporal dynamics of the hitherto largest outbreak in the non-endemic metropolis of Buenos Aires, Argentina, based on detailed information on the 5,104 georeferenced cases registered during summer-autumn of 2016. The highly seasonal dengue transmission in Buenos Aires was modulated by temperature and triggered by imported cases coming from regions with ongoing outbreaks. However, local transmission was made possible and consolidated heterogeneously in the city due to housing and socioeconomic characteristics of the population, with 32.8% of autochthonous cases occurring in slums, which held only 6.4% of the city population. A hierarchical spatiotemporal model accounting for imperfect detection of cases showed that, outside slums, less-affluent neighborhoods of houses (vs. apartments) favored transmission. Global and local spatiotemporal point-pattern analyses demonstrated that most transmission occurred at or close to home. Additionally, based on these results, a point-pattern analysis was assessed for early identification of transmission foci during the outbreak while accounting for population spatial distribution. Altogether, our results reveal how social, physical, and biological processes shape dengue transmission in Buenos Aires and, likely, other non-endemic cities, and suggest multiple opportunities for control interventions.

Dengue fever is mainly transmitted by a mosquito species that is highly urbanized, and lays eggs and develops mostly in artificial water containers. Dengue transmission is sustained year-round in most tropical regions of the world, but in many subtropical/temperate regions it occurs only in the warmest months. To improve understanding of dengue transmission in these regions, we analyzed one of the largest outbreaks in Buenos Aires city, a subtropical metropolis. Based on information on 5,104 georeferenced cases during summer-autumn 2016, we found that most transmission occurred in or near home, that slums had the highest risk of transmission, and that, outside slums, less-affluent neighborhoods of houses (vs. apartments) favored transmission. We showed that the cumulative effects of temperature over the previous few weeks set the temporal limits for transmission to occur, and that the outbreak was sparked by infected people arriving from regions with ongoing outbreaks. Additionally, we implemented a statistical method to identify transmission foci in real-time that improves targeting control interventions. Our results deepen the understanding of dengue transmission as a result of social, physical, and biological processes, and pose multiple opportunities for improving control of dengue and other mosquito-borne viruses such as Zika, chikungunya, and yellow fever.

Assessing the reporting of Dengue, Chikungunya and Zika to the National Surveillance System in Colombia from 2014-2017: A Capture-recapture analysis accounting for misclassification of arboviral diagnostics

BACKGROUND

Chikungunya, dengue, and Zika are three different arboviruses which have similar symptoms and are a major public health issue in Colombia. Despite the mandatory reporting of these arboviruses to the National Surveillance System in Colombia (SIVIGILA), it has been reported that the system captures less than 10% of diagnosed cases in some cities.

METHODOLOGY/PRINCIPAL FINDINGS

To assess the scope and degree of arboviruses reporting in Colombia between 2014-2017, we conducted an observational study of surveillance data using the capture-recapture approach in three Colombian cities. Using healthcare facility registries (capture data) and surveillance-notified cases (recapture data), we estimated the degree of reporting by clinical diagnosis. We fit robust Poisson regressions to identify predictors of reporting and estimated the predicted probability of reporting by disease and year. To account for the potential misclassification of the clinical diagnosis, we used the simulation extrapolation for misclassification (MC-SIMEX) method. A total of 266,549 registries were examined. Overall arboviruses' reporting ranged from 5.3% to 14.7% and varied in magnitude according to age and year of diagnosis. Dengue was the most notified disease (21-70%) followed by Zika (6-45%). The highest reporting rate was seen in 2016, an epidemic year. The MC-SIMEX corrected rates indicated underestimation of the reporting due to the potential misclassification bias.

CONCLUSIONS

These findings reflect challenges on arboviruses' reporting, and therefore, potential challenges on the estimation of arboviral burden in Colombia and other endemic settings with similar surveillance systems.

Treatment Coverage Estimation for Mass Drug Administration for Malaria with Dihydroartemisinin-Piperaquine in Southern Province, Zambia

Mass drug administration (MDA) is currently being considered as an intervention in low-transmission areas to complement existing malaria control and elimination efforts. The effectiveness of any MDA strategy is dependent on achieving high epidemiologic coverage and participant adherence rates. A community-randomized controlled trial was conducted from November 2014 to March 2016 to evaluate the impact of four rounds of MDA or focal MDA (fMDA)—where treatment was given to all eligible household members if anyone in the household had a positive malaria rapid diagnostic test—on malaria outcomes in Southern Province, Zambia (population approximately 300,000). This study examined epidemiologic coverage and program reach using capture–recapture and satellite enumeration methods to estimate the degree to which the trial reached targeted individuals. Overall, it was found that the percentage of households visited by campaign teams ranged from 62.9% (95% CI: 60.0–65.8) to a high of 77.4% (95% CI: 73.8–81.0) across four rounds of treatment. When the maximum number of visited households across all campaign rounds was used as the numerator, program reach for at least one visit would have been 86.4% (95% CI: 80.8–92.0) in MDA and 83.5% (95% CI: 78.0–89.1) in fMDA trial arms. As per the protocol, the trial provided dihydroartemisinin–piperaquine treatment to an average of 58.8% and 13.3% of the estimated population based on capture–recapture in MDA and fMDA, respectively, across the four rounds.

Mapping global variation in dengue transmission intensity

Intervention planning for dengue requires reliable estimates of dengue transmission intensity. However, current maps of dengue risk provide estimates of disease burden or the boundaries of endemicity rather than transmission intensity. We therefore developed a global high-resolution map of dengue transmission intensity by fitting environmentally driven geospatial models to geolocated force of infection estimates derived from cross-sectional serological surveys and routine case surveillance data. We assessed the impact of interventions on dengue transmission and disease using Wolbachia-infected mosquitoes and the Sanofi-Pasteur vaccine as specific examples. We predicted high transmission intensity in all continents straddling the tropics, with hot spots in South America (Colombia, Venezuela, and Brazil), Africa (western and central African countries), and Southeast Asia (Thailand, Indonesia, and the Philippines). We estimated that 105 [95% confidence interval (CI), 95 to 114] million dengue infections occur each year with 51 (95% CI, 32 to 66) million febrile disease cases. Our analysis suggests that transmission-blocking interventions such as Wolbachia, even at intermediate efficacy (50% transmission reduction), might reduce global annual disease incidence by up to 90%. The Sanofi-Pasteur vaccine, targeting only seropositive recipients, might reduce global annual disease incidence by 20 to 30%, with the greatest impact in high-transmission settings. The transmission intensity map presented here, and made available for download, may help further assessment of the impact of dengue control interventions and prioritization of global public health efforts.

Fostering social innovation and building adaptive capacity for dengue control in Cambodia: a case study

Background

The social-ecological systems theory, with its unique conception of resilience (social-ecological systems & resilience, SESR), provides an operational framework that currently best meets the need for integration and adaptive governance as encouraged by the Sustainable Development Goals. SESR accounts for the complex dynamics of social-ecological systems and operationalizes transdisciplinarity by focusing on community engagement, value co-creation, decentralized leadership and social innovation. Targeting Social Innovation (SI) in the context of implementation research for vector-borne diseases (VBD) control offers a low-cost strategy to contribute to lasting and contextualized community engagement in disease control and health development in low and middle income countries of the global south. In this article we describe the processes of community engagement and transdisciplinary collaboration underpinning community-based dengue management in rural primary schools and households in two districts in Cambodia.

Methods

Multiple student-led and community-based interventions have been implemented focusing on empowering education, communication for behavioral change and participatory epidemiology mapping in order to engage Cambodian communities in dengue control. We describe in particular the significance of the participatory processes that have contributed to the design of SI products that emerged following iterative consultations with community stakeholders to address the dengue problem.

Results

The SI products that emerged following our interaction with community members are 1) adult mosquito traps made locally from solid waste collections, 2) revised dengue curriculum with hands-on activities for transformative learning, 3) guppy distribution systems led by community members, 4) co-design of dengue prevention communication material by students and community members, 5) community mapping.

Conclusions

The initiative described in this article put in motion processes of community engagement towards creating ownership of dengue control interventions tools by community stakeholders, including school children. While the project is ongoing, the project’s interventions so far implemented have contributed to the emergence of culturally relevant SI products and provided initial clues regarding 1) the conditions allowing SI to emerge, 2) specific mechanisms by which it happens and 3) how external parties can facilitate SI emergence. Overall there seems to be a strong argument to be made in supporting SI as a desirable outcome of project implementation towards building adaptive capacity and resilience and to use the protocol supporting this project implementation as an operational guiding document for other VBD adaptive management in the region.

Dengue Outbreak Response and Control in Khyber Pakhtunkhwa, Pakistan: A Mixed Methods Study

Background: Since 2008, dengue fever outbreaks had occurred repeatedly in various districts of Khyber Pakhtunkhwa (KP) province of Pakistan. Most importantly the outbreak of 2017 caused 70 deaths, about 121,083 suspected and 24,938 confirmed cases in 23 districts of KP. In 2018, an abrupt decline in suspected and confirmed dengue cases was observed and 2018 was declared as dengue outbreak free. This study characterizes and explores the control and response measure activities of the outbreak. In addition, we explored the challenges faced and lessons learned for control of future dengue outbreaks from the perspectives of health authorities and dengue response staff in the KP province of Pakistan.

Methods: This was a mixed methods study with quantitative data on dengue outbreaks obtained from health department in KP followed by qualitative study to explore activities and responses that enabled the Dengue Response Unit (DRU) for a successful dengue outbreak control in 2018. In-depth interviews were conducted with the key informants from the department of health and the dengue response unit.

Results: The quantitative data analysis revealed a huge decline of suspected and confirmed dengue cases in comparison with the previous year in most of the KP districts. A similar decline in dengue reported cases was also observed from previously high dengue burden 14 union counsels of Peshawar district. Among the 70 verified deaths in 2017, 44 (63%) were males and 26 (37%) were females. The cases were about 20% each from age groups of 21–30, 41–50, and 51–60 years. The qualitative study findings showed four prominent major themes for successful control: (1) control and response strategy; (2) organizing specific dengue control and response intervention activities; (3) addressing dengue control and response challenges; and (4) generating lesson for future dengue control and response.

A Mapping Review on Urban Landscape Factors of Dengue Retrieved from Earth Observation Data, GIS Techniques, and Survey Questionnaires

To date, there is no effective treatment to cure dengue fever, a mosquito-borne disease which has a major impact on human populations in tropical and sub-tropical regions. Although the characteristics of dengue infection are well known, factors associated with landscape are highly scale dependent in time and space, and therefore difficult to monitor. We propose here a mapping review based on 78 articles that study the relationships between landscape factors and urban dengue cases considering household, neighborhood and administrative levels. Landscape factors were retrieved from survey questionnaires, Geographic Information Systems (GIS), and remote sensing (RS) techniques. We structured these into groups composed of land cover, land use, and housing type and characteristics, as well as subgroups referring to construction material, urban typology, and infrastructure level. We mapped the co-occurrence networks associated with these factors, and analyzed their relevance according to a three-valued interpretation (positive, negative, non significant). From a methodological perspective, coupling RS and GIS techniques with field surveys including entomological observations should be systematically considered, as none digital land use or land cover variables appears to be an univocal determinant of dengue occurrences. Remote sensing urban mapping is however of interest to provide a geographical frame to distribute human population and movement in relation to their activities in the city, and as spatialized input variables for epidemiological and entomological models.

Burden of dengue in the State of Meta, Colombia (2010-2016)

Abstract: In Colombia, dengue is a disease of great impact due to its morbidity and mortality, however, studies on the effects of the economic burden at the local level are scarce. Therefore, our study sought to describe the economic burden of dengue epidemics between 2010 and 2016 in the State of Meta, Colombia. A longitudinal study was performed using information from the records of the epidemiological information system (Sistema Nacional de Vigilancia en Salud Pública - SIVIGILA), and the indicator of disability-adjusted life years (DALYs) was determined as an estimator of the burden of dengue. To assess the economic impact, two assessment scenarios were considered (minimum range and maximum range), which allowed the estimate of the effects of the years of life lost (YLLs). Mortality cases presented heterogeneity in the age groups, mainly affecting groups under 15 years and over 65 years, with YLLs raging between 158.58 and 300.38. In total, 2010 showed the highest medical care costs of the study period, with USD 664,123 for women and USD 740,221 for men. In the epidemic years (2010, 2012-2015) between 91,072.3 and 184,175.1 DALYs were lost per million inhabitants, which generated social burden costs higher than the USD 669.6 million. In conclusion, dengue can be considered a disease of high cost at the local level, economically affecting the General Social Security System in Health and social welfare.

A global model for predicting the arrival of imported dengue infections

With approximately half of the world's population at risk of contracting dengue, this mosquito-borne disease is of global concern. International travellers significantly contribute to dengue's rapid and large-scale spread by importing the disease from endemic into non-endemic countries. To prevent future outbreaks and dengue from establishing in non-endemic countries, knowledge about the arrival time and location of infected travellers is crucial. We propose a network model that predicts the monthly number of dengue-infected air passengers arriving at any given airport. We consider international air travel volumes to construct weighted networks, representing passenger flows between airports. We further calculate the probability of passengers, who travel through the international air transport network, being infected with dengue. The probability of being infected depends on the destination, duration and timing of travel. Our findings shed light onto dengue importation routes and reveal country-specific reporting rates that have been until now largely unknown. This paper provides important new knowledge about the spreading dynamics of dengue that is highly beneficial for public health authorities to strategically allocate the often limited resources to more efficiently prevent the spread of dengue.

Asymptomatic Dengue Virus Infections, Cambodia, 2012-2013

We investigated dengue virus (DENV) and asymptomatic DENV infections in rural villages of Kampong Cham Province, Cambodia, during 2012 and 2013. We conducted perifocal investigations in and around households for 149 DENV index cases identified through hospital and village surveillance. We tested participants 0.5-30 years of age by using nonstructural 1 rapid tests and confirmed DENV infections using quantitative reverse transcription PCR or nonstructural 1-capture ELISA. We used multivariable Poisson regressions to explore links between participants' DENV infection status and household characteristics. Of 7,960 study participants, 346 (4.4%) were infected with DENV, among whom 302 (87.3%) were <15 years of age and 225 (65.0%) were <9 years of age. We identified 26 (7.5%) participants with strictly asymptomatic DENV infection at diagnosis and during follow-up. We linked symptomatic DENV infection status to familial relationships with index cases. During the 2-year study, we saw fewer asymptomatic DENV infections than expected based on the literature.

The PAGODAS protocol: pediatric assessment group of dengue and Aedes saliva protocol to investigate vector-borne determinants of Aedes-transmitted arboviral infections in Cambodia

BACKGROUND

Mosquito-borne arboviruses, like dengue virus, continue to cause significant global morbidity and mortality, particularly in Southeast Asia. When the infectious mosquitoes probe into human skin for a blood meal, they deposit saliva containing a myriad of pharmacologically active compounds, some of which alter the immune response and influence host receptivity to infection, and consequently, the establishment of the virus. Previous reports have highlighted the complexity of mosquito vector-derived factors and immunity in the success of infection. Cumulative evidence from animal models and limited data from humans have identified various vector-derived components, including salivary components, that are co-delivered with the pathogen and play an important role in the dissemination of infection. Much about the roles and effects of these vector-derived factors remain to be discovered.

METHODS/DESIGN

We describe a longitudinal, pagoda (community)-based pediatric cohort study to evaluate the burden of dengue virus infection and document the immune responses to salivary proteins of Aedes aegypti, the mosquito vector of dengue, Zika, and chikungunya viruses. The study includes community-based seroprevalence assessments in the peri-urban town of Chbar Mon in Kampong Speu Province, Cambodia. The study aims to recruit 771 children between the ages of 2 and 9 years for a three year period of longitudinal follow-up, including twice per year (rainy and dry season) serosurveillance for dengue seroconversion and Ae. aegypti salivary gland homogenate antibody intensity determinations by ELISA assays. Diagnostic tests for acute dengue, Zika and chikungunya viral infections will be performed by RT-PCR.

DISCUSSION

This study will serve as a foundation for further understanding of mosquito saliva immunity and its impact on Aedes-transmitted arboviral diseases endemic to Cambodia.

TRIAL REGISTRATION

NCT03534245 registered on 23 May 2018.

Burden of dengue among febrile patients at the time of chikungunya introduction in Piedecuesta, Colombia

OBJECTIVE

To estimate the age-specific incidence of symptomatic dengue and chikungunya in Colombia.

METHOD

A passive facility-based fever surveillance study was conducted among individuals with undifferentiated fever. Confirmatory diagnostics included serological and molecular tests in paired samples, and surveillance's underreporting was assessed using capture-recapture methods.

RESULTS

Of 839 febrile participants 686 completed the study. There were 33.2% (295/839) dengue infections (51% primary infections), and 35.9% (191/532) of negative dengue cases there were chikungunya cases. On average, dengue cases were younger (median = 18 years) than chikungunya cases (median = 25 years). Thrombocytopaenia and abdominal pain were the main dengue predictors, while presence of rash was the main predictor for chikungunya diagnosis. Underreporting of dengue was 31%; the estimated expansion factors indicate an underreporting rate of dengue cases of threefold for all cases and of almost sixfold for inpatients.

CONCLUSIONS

These findings highlight the ongoing coexistence of both arboviruses, a distinct clinical profile of each condition in the study area that could be used by clinicians to generate a differential diagnosis, and the presence of underreporting, mostly among hospitalised cases.

Predicting the severity of dengue fever in children on admission based on clinical features and laboratory indicators: application of classification tree analysis

Background

Dengue fever is a re-emerging viral disease commonly occurring in tropical and subtropical areas. The clinical features and abnormal laboratory test results of dengue infection are similar to those of other febrile illnesses; hence, its accurate and timely diagnosis for providing appropriate treatment is difficult. Delayed diagnosis may be associated with inappropriate treatment and higher risk of death. Early and correct diagnosis can help improve case management and optimise the use of resources such as hospital staff, beds, and intensive care equipment. The goal of this study was to develop a predictive model to characterise dengue severity based on early clinical and laboratory indicators using data mining and statistical tools.

Methods

We retrieved data from a study of febrile illness in children at Angkor Hospital for Children, Cambodia. Of 1225 febrile episodes recorded, 198 patients were confirmed to have dengue. A classification and regression tree (CART) was used to construct a predictive decision tree for severe dengue, while logistic regression analysis was used to independently quantify the significance of each parameter in the decision tree.

Results

A decision tree algorithm using haematocrit, Glasgow Coma Score, urine protein, creatinine, and platelet count predicted severe dengue with a sensitivity, specificity, and accuracy of 60.5%, 65% and 64.1%, respectively.

Conclusions

The decision tree we describe, using five simple clinical and laboratory indicators, can be used to predict severe cases of dengue among paediatric patients on admission. This algorithm is potentially useful for guiding a patient-monitoring plan and outpatient management of fever in resource-poor settings.

Determining the efficacy of guppies and pyriproxyfen (Sumilarv® 2MR) combined with community engagement on dengue vectors in Cambodia: study protocol for a randomized controlled trial

Background

Evidence on the effectiveness of low-cost, sustainable, biological vector-control tools for the Aedes mosquitoes is limited. Therefore, the purpose of this trial is to estimate the impact of guppy fish (guppies), in combination with the use of the larvicide pyriproxyfen (Sumilarv® 2MR), and Communication for Behavioral Impact (COMBI) activities to reduce entomological indices in Cambodia.

Methods/design

In this cluster randomized controlled, superiority trial, 30 clusters comprising one or more villages each (with approximately 170 households) will be allocated, in a 1:1:1 ratio, to receive either (1) three interventions (guppies, Sumilarv® 2MR, and COMBI activities), (2) two interventions (guppies and COMBI activities), or (3) control (standard vector control). Households will be invited to participate, and entomology surveys among 40 randomly selected households per cluster will be carried out quarterly. The primary outcome will be the population density of adult female Aedes mosquitoes (i.e., number per house) trapped using adult resting collections. Secondary outcome measures will include the House Index, Container Index, Breteau Index, Pupae Per House, Pupae Per Person, mosquito infection rate, guppy fish coverage, Sumilarv® 2MR coverage, and percentage of respondents with knowledge about Aedes mosquitoes causing dengue. In the primary analysis, adult female Aedes density and mosquito infection rates will be aggregated over follow-up time points to give a single rate per cluster. This will be analyzed by negative binomial regression, yielding density ratios.

Discussion

This trial is expected to provide robust estimates of the intervention effect. A rigorous evaluation of these vector-control interventions is vital to developing an evidence-based dengue control strategy and to help direct government resources.

Trial registration

Current Controlled Trials, ID: ISRCTN85307778. Registered on 25 October 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-017-2105-2) contains supplementary material, which is available to authorized users.

Disease Burden of Dengue in the Philippines: Adjusting for Underreporting by Comparing Active and Passive Dengue Surveillance in Punta Princesa, Cebu City

AbstractDengue virus (DENV) is a serious threat to public health. Having reliable estimates of the burden of dengue is important to inform policy and research, but surveillance systems are not designed to capture all symptomatic DENV infections. We derived the rate of reporting of dengue by comparing active surveillance of symptomatic DENV infections in a prospective community-based seroepidemiological cohort study (N = 1008) of acute febrile illness in Punta Princesa, Cebu City, Philippines, with passive surveillance data from the Cebu City Health Department. Febrile episodes detected in a weekly follow-up of participants were tested for serotype-specific DENV by hemi-nested reverse transcription-polymerase chain reaction (nested RT-PCR) and acute/convalescent blood samples tested by dengue IgM/IgG enzyme immunoassay. We estimated the burden of dengue in the Philippines in disability-adjusted life years (DALYs), and conducted a probabilistic sensitivity analysis using Monte-Carlo simulations to address uncertainty. The results showed a 21% cumulative reporting rate of symptomatic DENV infections, equivalent to an expansion factor of 4.7 (95% certainty level [CL]: 2.2-15.1). Based on surveillance data in the Philippines for 2010-2014, we estimated 794,255 annual dengue episodes (95% CL: 463,000-2,076,000) and a disease burden of 535 (95% CL: 380-994) DALYs per million population using age weights and time discounting and 997 (95% CL: 681-1,871) DALYs per million population without age and time adjustments. Dengue imposes a substantial burden in the Philippines; almost 10 times higher than estimated for rabies, about twice the burden of intestinal fluke infections, and about 10% of the burden of tuberculosis. Our estimates should inform policy makers and raise awareness among the public.

Dengue Contingency Planning: From Research to Policy and Practice

BACKGROUND

Dengue is an increasingly incident disease across many parts of the world. In response, an evidence-based handbook to translate research into policy and practice was developed. This handbook facilitates contingency planning as well as the development and use of early warning and response systems for dengue fever epidemics, by identifying decision-making processes that contribute to the success or failure of dengue surveillance, as well as triggers that initiate effective responses to incipient outbreaks.

METHODOLOGY/PRINCIPAL FINDINGS

Available evidence was evaluated using a step-wise process that included systematic literature reviews, policymaker and stakeholder interviews, a study to assess dengue contingency planning and outbreak management in 10 countries, and a retrospective logistic regression analysis to identify alarm signals for an outbreak warning system using datasets from five dengue endemic countries. Best practices for managing a dengue outbreak are provided for key elements of a dengue contingency plan including timely contingency planning, the importance of a detailed, context-specific dengue contingency plan that clearly distinguishes between routine and outbreak interventions, surveillance systems for outbreak preparedness, outbreak definitions, alert algorithms, managerial capacity, vector control capacity, and clinical management of large caseloads. Additionally, a computer-assisted early warning system, which enables countries to identify and respond to context-specific variables that predict forthcoming dengue outbreaks, has been developed.

CONCLUSIONS/SIGNIFICANCE

Most countries do not have comprehensive, detailed contingency plans for dengue outbreaks. Countries tend to rely on intensified vector control as their outbreak response, with minimal focus on integrated management of clinical care, epidemiological, laboratory and vector surveillance, and risk communication. The Technical Handbook for Surveillance, Dengue Outbreak Prediction/ Detection and Outbreak Response seeks to provide countries with evidence-based best practices to justify the declaration of an outbreak and the mobilization of the resources required to implement an effective dengue contingency plan.

Symptomatic Dengue Disease in Five Southeast Asian Countries: Epidemiological Evidence from a Dengue Vaccine Trial

Dengue incidence has increased globally, but empirical burden estimates are scarce. Prospective methods are best-able to capture all severities of disease. CYD14 was an observer-blinded dengue vaccine study conducted in children 2-14 years of age in Indonesia, Malaysia, Thailand, the Philippines, and Vietnam. The control group received no vaccine and resembled a prospective, observational study. We calculated the rates of dengue according to different laboratory or clinical criteria to make inferences about dengue burden, and compared with rates reported in the passive surveillance systems to calculate expansion factors which describe under-reporting. Over 6,933 person-years of observation in the control group there were 319 virologically confirmed dengue cases, a crude attack rate of 4.6%/year. Of these, 92 cases (28.8%) were clinically diagnosed as dengue fever or dengue hemorrhagic fever by investigators and 227 were not, indicating that most symptomatic disease fails to satisfy existing case definitions. When examining different case definitions, there was an inverse relationship between clinical severity and observed incidence rates. CYD14's active surveillance system captured a greater proportion of symptomatic dengue than national passive surveillance systems, giving rise to expansion factors ranging from 0.5 to 31.7. This analysis showed substantial, unpredictable and variable under-reporting of symptomatic dengue, even within a controlled clinical trial environment, and emphasizes that burden estimates are highly sensitive to case definitions. These data will assist in generating disease burden estimates and have important policy implications when considering the introduction and health economics of dengue prevention and control interventions.

Sensitivity of the Dengue Surveillance System in Brazil for Detecting Hospitalized Cases

We evaluated the sensitivity of the dengue surveillance system in detecting hospitalized cases in ten capital cities in Brazil from 2008 to 2013 using a probabilistic record linkage of two independent information systems hospitalization (SIH-SUS) adopted as the gold standard and surveillance (SINAN). Sensitivity was defined as the proportion of cases reported to the surveillance system amid the suspected hospitalized cases registered in SIH-SUS. Of the 48,174 hospitalizations registered in SIH-SUS, 24,469 (50.7%) were reported and registered in SINAN, indicating an overall sensitivity of 50.8% (95%CI 50.3–51.2). The observed sensitivity for each of the municipalities included in the study ranged from 22.0% to 99.1%. The combination of the two data sources identified 71,161 hospitalizations, an increase of 97.0% over SINAN itself. Our results allowed establishing the proportion of underreported dengue hospitalizations in the public health system in Brazil, highlighting the use of probabilistic record linkage as a valuable tool for evaluating surveillance systems.

This manuscript address essential issues regarding the current and future challenges of a dengue surveillance system. Dengue fever is one of the major public health threats in a large area of the world, including Brazil which represents around 70% of the cases in the Americas. The dengue surveillance system in Brazil was established in 1986, but evaluations of this surveillance system were rarely conducted. The need for accurate data is of paramount importance due to not only the increase of severe cases in the past decade, but also to monitor the impact of a vaccine as soon as it occurs. The evaluation of the sensitivity of surveillance system is a challenge, due to the lack of a gold standard. In our study, we took advantage of two very well structured and independent information systems with nationwide coverage. The hospitalization information system was defined as the gold standard for hospitalized cases in the public health system and compared to the notifiable diseases information system using a probabilistic record linkage. Therefore, we were able to evaluate the sensitivity of the dengue surveillance system in detecting hospitalized cases in ten capital cities from 2008 to 2013 in Brazil.

Disparities in road crash mortality among pedestrians using wheelchairs in the USA: results of a capture-recapture analysis

OBJECTIVE

This study aims to quantify and describe the burden of fatal pedestrian crashes among persons using wheelchairs in the USA from 2006 to 2012.

DESIGN

The occurrence of fatal pedestrian crashes among pedestrians using wheelchairs was assessed using two-source capture-recapture. Descriptive analysis of fatal crashes was conducted using customary approaches.

SETTING

Two registries were constructed, both of which likely undercounted fatalities among pedestrians who use wheelchairs. The first used data from the Fatality Analysis Reporting System, and the second used a LexisNexis news search.

OUTCOME MEASURES

Mortality rate (per 100 000 person-years) and crash-level, driver-level and pedestrian-level characteristics of fatal crashes.

RESULTS

This study found that, from 2006 to 2012, the mortality rate for pedestrians using wheelchairs was 2.07/100 000 person-years (95% CI 1.60 to 2.54), which was 36% higher than the overall population pedestrian mortality rate (p=0.02). Men's risk was over fivefold higher than women's risk (p<0.001). Compared to the overall population, persons aged 50-64 using wheelchairs had a 38% increased risk (p=0.04), and men who use wheelchairs aged 50-64 had a 75% increased risk over men of the same age in the overall population (p=0.006). Almost half (47.6%; 95% CI 42.8 to 52.5) of fatal crashes occurred in intersections and 38.7% (95% CI 32.0 to 45.0) of intersection crashes occurred at locations without traffic control devices. Among intersection crashes, 47.5% (95% CI 40.6 to 54.5) involved wheelchair users in a crosswalk; no crosswalk was available for 18.3% (95% CI 13.5 to 24.4). Driver failure to yield right-of-way was noted in 21.4% (95% CI 17.7 to 25.7) of crashes, and no crash avoidance manoeuvers were detected in 76.4% (95% CI 71.0 to 81.2).

CONCLUSIONS

Persons who use wheelchairs experience substantial pedestrian mortality disparities calling for behavioural and built environment interventions.

Epidemiological update on the dengue situation in the Western Pacific Region, 2012

Dengue has caused a substantial public health burden in the Western Pacific Region. To assess this burden and regional trends, data were collated and summarized from indicator-based surveillance systems on dengue cases and deaths from countries and areas in the Western Pacific Region. In 2012, dengue notifications continued to increase with 356,838 dengue cases reported in the Region (relative to 244,855 cases reported in 2011) of which 1248 died. In the Asia subregion, the notification rate was highest in Cambodia, the Philippines and the Lao People's Democratic Republic (316.2, 198.9 and 162.4 per 100,000 population, respectively), and in the Pacific island countries and areas, the notification rate was highest in Niue, the Marshall Islands and the Federated States of Micronesia (8556.0, 337.0 and 265.1 per 100,000 population, respectively). All four serotypes were circulating in the Region in 2012 with considerable variabilitiy in distribution. Regional surveillance provides important information to enhance situational awareness, conduct risk assessments and improve preparedness activities.

Dengue epidemiology in selected endemic countries: factors influencing expansion factors as estimates of underreporting

OBJECTIVE

Dengue fever is globally considered underestimated. This study provides expansion factors (EFs) for dengue endemic selected countries and highlights critical issues in the use of EFs.

METHODS

We identified dengue epidemiological cohort studies from 2000 to July 2013 through a literature search using PubMed, Web of Science and Lilacs (Latin American and Caribbean Health Sciences Database), pre-defined keywords and inclusion/exclusion criteria, and included Brazil, Colombia, Nicaragua, Peru, Puerto Rico, Venezuela, Bangladesh, Cambodia, India, Indonesia, Philippines, Singapore, Sri Lanka, Thailand and Vietnam. Dengue national and local passive surveillance data were derived from WHO regional websites, PAHO, SEARO and WPRO. EFs were calculated as CI cohort studies/CI passive data for both national and local levels.

RESULTS

Cohort studies differed in case definition, laboratory test used and surveillance methods. The information on SEARO, PAHO and WPRO websites differed in terms of dengue epidemiological variables, population denominators and completeness. The highest incidence was reported by PAHO countries followed by WPRO and SEARO countries. EFs may vary for the different variables and denominators used for calculation. EFs were the highest in SEARO countries and lowest in PAHO countries. A trend for lower local EFs was observed.

CONCLUSIONS

The use of EFs for quantifying dengue underreporting may be problematic due to lack of uniformity in reporting dengue both active and passive surveillance data. Quality dengue surveillance data are urgently needed for a better estimate of dengue disease burden and to measure the impact of preventive intervention.

Economic and disease burden of dengue in Mexico

BACKGROUND

Dengue imposes a substantial economic and disease burden in most tropical and subtropical countries. Dengue incidence and severity have dramatically increased in Mexico during the past decades. Having objective and comparable estimates of the economic burden of dengue is essential to inform health policy, increase disease awareness, and assess the impact of dengue prevention and control technologies.

METHODS AND FINDINGS

We estimated the annual economic and disease burden of dengue in Mexico for the years 2010-2011. We merged multiple data sources, including a prospective cohort study; patient interviews and macro-costing from major hospitals; surveillance, budget, and health data from the Ministry of Health; WHO cost estimates; and available literature. We conducted a probabilistic sensitivity analysis using Monte Carlo simulations to derive 95% certainty levels (CL) for our estimates. Results suggest that Mexico had about 139,000 (95%CL: 128,000-253,000) symptomatic and 119 (95%CL: 75-171) fatal dengue episodes annually on average (2010-2011), compared to an average of 30,941 symptomatic and 59 fatal dengue episodes reported. The annual cost, including surveillance and vector control, was US$170 (95%CL: 151-292) million, or $1.56 (95%CL: 1.38-2.68) per capita, comparable to other countries in the region. Of this, $87 (95%CL: 87-209) million or $0.80 per capita (95%CL: 0.62-1.12) corresponds to illness. Annual disease burden averaged 65 (95%CL: 36-99) disability-adjusted life years (DALYs) per million population. Inclusion of long-term sequelae, co-morbidities, impact on tourism, and health system disruption during outbreaks would further increase estimated economic and disease burden.

CONCLUSION

With this study, Mexico joins Panama, Puerto Rico, Nicaragua, and Thailand as the only countries or areas worldwide with comprehensive (illness and preventive) empirical estimates of dengue burden. Burden varies annually; during an outbreak, dengue burden may be significantly higher than that of the pre-vaccine level of rotavirus diarrhea. In sum, Mexico's potential economic benefits from dengue control would be substantial.

Co-circulation of dengue virus type 3 genotypes in Vientiane capital, Lao PDR

During the 2012 epidemic of dengue in Vientiane capital, Lao PDR, a major serotype switch from dengue 1 to 3 was observed. A molecular epidemiology study demonstrated that dengue 3 remained the predominant serotype in 2013, but also revealed the co-circulation of two genotypes, supporting the hypothesis of multiple geographic origins of dengue 3 strains circulating in Vientiane capital.

Approaches to refining estimates of global burden and economics of dengue

Dengue presents a formidable and growing global economic and disease burden, with around half the world's population estimated to be at risk of infection. There is wide variation and substantial uncertainty in current estimates of dengue disease burden and, consequently, on economic burden estimates. Dengue disease varies across time, geography and persons affected. Variations in the transmission of four different viruses and interactions among vector density and host's immune status, age, pre-existing medical conditions, all contribute to the disease's complexity. This systematic review aims to identify and examine estimates of dengue disease burden and costs, discuss major sources of uncertainty, and suggest next steps to improve estimates. Economic analysis of dengue is mainly concerned with costs of illness, particularly in estimating total episodes of symptomatic dengue. However, national dengue disease reporting systems show a great diversity in design and implementation, hindering accurate global estimates of dengue episodes and country comparisons. A combination of immediate, short-, and long-term strategies could substantially improve estimates of disease and, consequently, of economic burden of dengue. Suggestions for immediate implementation include refining analysis of currently available data to adjust reported episodes and expanding data collection in empirical studies, such as documenting the number of ambulatory visits before and after hospitalization and including breakdowns by age. Short-term recommendations include merging multiple data sources, such as cohort and surveillance data to evaluate the accuracy of reporting rates (by health sector, treatment, severity, etc.), and using covariates to extrapolate dengue incidence to locations with no or limited reporting. Long-term efforts aim at strengthening capacity to document dengue transmission using serological methods to systematically analyze and relate to epidemiologic data. As promising tools for diagnosis, vaccination, vector control, and treatment are being developed, these recommended steps should improve objective, systematic measures of dengue burden to strengthen health policy decisions.

Dengue disease surveillance: an updated systematic literature review

OBJECTIVES

To review the evidence for the application of tools for dengue outbreak prediction/detection and trend monitoring in passive and active disease surveillance systems in order to develop recommendations for endemic countries and identify important research needs.

METHODS

This systematic literature review followed the protocol of a review from 2008, extending the systematic search from January 2007 to February 2013 on PubMed, EMBASE, CDSR, WHOLIS and Lilacs. Data reporting followed the PRISMA statement. The eligibility criteria comprised (i) population at risk of dengue, (ii) dengue disease surveillance, (iii) outcome of surveillance described and (iv) empirical data evaluated. The analysis classified studies based on the purpose of the surveillance programme. The main limitation of the review was expected publication bias.

RESULTS

A total of 1116 papers were identified of which 36 articles were included in the review. Four cohort-based prospective studies calculated expansion factors demonstrating remarkable levels of underreporting in the surveillance systems. Several studies demonstrated that enhancement methods such as laboratory support, sentinel-based reporting and staff motivation contributed to improvements in dengue reporting. Additional improvements for passive surveillance systems are possible by incorporating simple data forms/entry/electronic-based reporting; defining clear system objectives; performing data analysis at the lowest possible level (e.g. district); seeking regular data feedback. Six studies showed that serotype changes were positively correlated with the number of reported cases or with dengue incidence, with lag times of up to 6 months. Three studies found that data on internet searches and event-based surveillance correlated well with the epidemic curve derived from surveillance data.

CONCLUSIONS

Passive surveillance providing the baseline for outbreak alert should be strengthened and appropriate threshold levels for outbreak alerts investigated. Additional enhancement tools such as syndromic surveillance, laboratory support and motivation strategies can be added. Appropriate alert signals need to be identified and integrated into a risk assessment tool. Shifts in dengue serotypes/genotype or electronic event-based surveillance have also considerable potential as indicator in dengue surveillance. Further research on evidence-based response strategies and cost-effectiveness is needed.

Spatial epidemiology and climatic predictors of paediatric dengue infections captured via sentinel site surveillance, Phnom Penh Cambodia 2011-2012

Background

Dengue is a major contributor to morbidity in children aged twelve and below throughout Cambodia; the 2012 epidemic season was the most severe in the country since 2007, with more than 42,000 reported (suspect or confirmed) cases.

Methods

We report basic epidemiological characteristics in a series of 701 patients at the National Paediatric Hospital in Cambodia, recruited during a prospective clinical study (2011–2012). To more fully explore this cohort, we examined climatic factors using multivariate negative binomial models and spatial clustering of cases using spatial scan statistics to place the clinical study within a larger epidemiological framework.

Results

We identify statistically significant spatial clusters at the urban village scale, and find that the key climatic predictors of increasing cases are weekly minimum temperature, median relative humidity, but find a negative association with rainfall maximum, all at lag times of 1–6 weeks, with significant effects extending to 10 weeks.

Conclusions

Our results identify clustering of infections at the neighbourhood scale, suggesting points for targeted interventions, and we find that the complex interactions of vectors and climatic conditions in this setting may be best captured by rising minimum temperature, and median (as opposed to mean) relative humidity, with complex and limited effects from rainfall. These results suggest that real-time cluster detection during epidemics should be considered in Cambodia, and that improvements in weather data reporting could benefit national control programs by allow greater prioritization of limited health resources to both vulnerable populations and time periods of greatest risk. Finally, these results add to the increasing body of knowledge suggesting complex interactions between climate and dengue cases that require further targeted research.

Burden of dengue infection and disease in a pediatric cohort in urban Sri Lanka

Dengue is the most significant arthropod-borne viral infection of humans. Persons infected with dengue viruses (DENV) have subclinical or clinically apparent infections ranging from undifferentiated fever to dengue hemorrhagic fever/shock syndrome. Although recent studies estimated that the Indian subcontinent has the greatest burden of DENV infection and disease worldwide, we do not have reliable, population-based estimates of the incidence of infection and disease in this region. The goal of this study was to follow-up a cohort of 800 children living in a heavily urbanized area of Colombo, Sri Lanka to obtain accurate estimates of the incidence of DENV infection and disease. Annual blood samples were obtained from all children to estimate dengue seroprevalence at enrollment and to identify children exposed to new DENV infections during the study year. Blood was also obtained from any child in whom fever developed over the course of the study year to identify clinically apparent DENV infections. At enrollment, dengue seroprevalence was 53.07%, which indicated high transmission in this population. Over the study year, the incidence of DENV infection and disease were 8.39 (95% confidence interval = 6.56-10.53) and 3.38 (95% confidence interval = 2.24-4.88), respectively, per 100 children per year. The ratio of clinically inapparent to apparent infections was 1.48. These results will be useful for obtaining more accurate estimates of the burden of dengue in the region and for making decisions about testing and introduction of vaccines.

Estimating the burden of Japanese encephalitis virus and other encephalitides in countries of the mekong region

Diverse aetiologies of viral and bacterial encephalitis are widely recognized as significant yet neglected public health issues in the Mekong region. A robust analysis of the corresponding health burden is lacking. We retrieved 75 articles on encephalitis in the region published in English or in French from 1965 through 2011. Review of available data demonstrated that they are sparse and often derived from hospital-based studies with significant recruitment bias. Almost half (35 of 75) of articles were on Japanese encephalitis virus (JEV) alone or associated with dengue. In the Western Pacific region the WHO reported 30,000-50,000 annual JEV cases (15,000 deaths) between 1966 and 1996 and 4,633 cases (200 deaths) in 2008, a decline likely related to the introduction of JEV vaccination in China, Vietnam, or Thailand since the 1980s. Data on dengue, scrub typhus and rabies encephalitis, among other aetiologies, are also reviewed and discussed. Countries of the Mekong region are undergoing profound demographic, economic and ecological change. As the epidemiological aspects of Japanese encephalitis (JE) are transformed by vaccination in some countries, highly integrated expert collaborative research and objective data are needed to identify and prioritize the human health, animal health and economic burden due to JE and other pathogens associated with encephalitides.

Evaluation of underreporting of salmonellosis and shigellosis hospitalised cases in Greece, 2011: results of a capture-recapture study and a hospital registry review

Background

Salmonellosis and shigellosis are mandatorily notifiable diseases in Greece. Underreporting of both diseases has been postulated but there has not been any national study to quantify it. The objective of this study was to: a) estimate underreporting of hospitalised cases at public Greek hospitals in 2011 with a capture-recapture (C-RC) study, b) evaluate the accuracy of this estimation, c) investigate the possible impact of specific factors on notification rates, and d) estimate community incidence of both diseases.

Methods

The mandatory notification system database and the database of the National Reference Laboratory for Salmonella and Shigella (NRLSS) were used in the C-RC study. The estimated total number of cases was compared with the actual number found by using the hospital records of the microbiological laboratories. Underreporting was also estimated by patients’ age-group, sex, type of hospital, region and month of notification. Assessment of the community incidence was based on the extrapolation of the hospitalisation rate of the diseases in Europe.

Results

The estimated underreporting of salmonellosis and shigellosis cases through the C-RC study was 47.7% and 52.0%, respectively. The reporting rate of salmonellosis significantly varied between the thirteen regions of the country from 8.3% to 95.6% (median: 28.4%). Age and sex were not related to the probability of reporting. The notification rate did not significantly differ between urban and rural areas, however, large university hospitals had a higher underreporting rate than district hospitals (p-value < 0.001). The actual underreporting, based on the hospital records review, was close to the estimated via the C-RC study; 52.8% for salmonellosis and 58.4% for shigellosis. The predicted community incidence of salmonellosis ranged from 312 to 936 and of shigellosis from 35 to 104 cases per 100,000 population.

Conclusions

Underreporting was higher than that reported by other countries and factors associated with underreporting should be further explored. C-RC analysis seems to be a useful tool for the assessment of the underreporting of hospitalised cases. National data on underreporting and under-ascertainment rate are needed for assessing the accuracy of the estimation of the community burden of the diseases.

Use of expansion factors to estimate the burden of dengue in Southeast Asia: a systematic analysis

BACKGROUND

Dengue virus infection is the most common arthropod-borne disease of humans and its geographical range and infection rates are increasing. Health policy decisions require information about the disease burden, but surveillance systems usually underreport the total number of cases. These may be estimated by multiplying reported cases by an expansion factor (EF).

METHODS AND FINDINGS

As a key step to estimate the economic and disease burden of dengue in Southeast Asia (SEA), we projected dengue cases from 2001 through 2010 using EFs. We conducted a systematic literature review (1995-2011) and identified 11 published articles reporting original, empirically derived EFs or the necessary data, and 11 additional relevant studies. To estimate EFs for total cases in countries where no empirical studies were available, we extrapolated data based on the statistically significant inverse relationship between an index of a country's health system quality and its observed reporting rate. We compiled an average 386,000 dengue episodes reported annually to surveillance systems in the region, and projected about 2.92 million dengue episodes. We conducted a probabilistic sensitivity analysis, simultaneously varying the most important parameters in 20,000 Monte Carlo simulations, and derived 95% certainty level of 2.73-3.38 million dengue episodes. We estimated an overall EF in SEA of 7.6 (95% certainty level: 7.0-8.8) dengue cases for every case reported, with an EF range of 3.8 for Malaysia to 19.0 in East Timor.

CONCLUSION

Studies that make no adjustment for underreporting would seriously understate the burden and cost of dengue in SEA and elsewhere. As the sites of the empirical studies we identified were not randomly chosen, the exact extent of underreporting remains uncertain. Nevertheless, the results reported here, based on a systematic analysis of the available literature, show general consistency and provide a reasonable empirical basis to adjust for underreporting.

Estimated global mortality associated with the first 12 months of 2009 pandemic influenza A H1N1 virus circulation: a modelling study

BACKGROUND

18,500 laboratory-confirmed deaths caused by the 2009 pandemic influenza A H1N1 were reported worldwide for the period April, 2009, to August, 2010. This number is likely to be only a fraction of the true number of the deaths associated with 2009 pandemic influenza A H1N1. We aimed to estimate the global number of deaths during the first 12 months of virus circulation in each country.

METHODS

We calculated crude respiratory mortality rates associated with the 2009 pandemic influenza A H1N1 strain by age (0-17 years, 18-64 years, and >64 years) using the cumulative (12 months) virus-associated symptomatic attack rates from 12 countries and symptomatic case fatality ratios (sCFR) from five high-income countries. To adjust crude mortality rates for differences between countries in risk of death from influenza, we developed a respiratory mortality multiplier equal to the ratio of the median lower respiratory tract infection mortality rate in each WHO region mortality stratum to the median in countries with very low mortality. We calculated cardiovascular disease mortality rates associated with 2009 pandemic influenza A H1N1 infection with the ratio of excess deaths from cardiovascular and respiratory diseases during the pandemic in five countries and multiplied these values by the crude respiratory disease mortality rate associated with the virus. Respiratory and cardiovascular mortality rates associated with 2009 pandemic influenza A H1N1 were multiplied by age to calculate the number of associated deaths.

FINDINGS

We estimate that globally there were 201,200 respiratory deaths (range 105,700-395,600) with an additional 83,300 cardiovascular deaths (46,000-179,900) associated with 2009 pandemic influenza A H1N1. 80% of the respiratory and cardiovascular deaths were in people younger than 65 years and 51% occurred in southeast Asia and Africa.

INTERPRETATION

Our estimate of respiratory and cardiovascular mortality associated with the 2009 pandemic influenza A H1N1 was 15 times higher than reported laboratory-confirmed deaths. Although no estimates of sCFRs were available from Africa and southeast Asia, a disproportionate number of estimated pandemic deaths might have occurred in these regions. Therefore, efforts to prevent influenza need to effectively target these regions in future pandemics.

FUNDING

None.