Public Transit Development Predicts Spatial Distribution of Dengue Virus Incidence in Medellín, Colombia

Dengue is a growing global threat in some of the world’s most rapidly growing landscapes. Urbanization and human movement affect the spatial dynamics and magnitude of dengue outbreaks; however, precise effects of urban growth on dengue is not well understood because of a lack of sufficiently fine-scaled data. We analyzed nine years of address-level dengue case data in Medellin, Colombia during a period of public transit expansion. We correlate changes in the spread and magnitude of localized outbreaks to changes in accessibility and usage of public transit. Locations closer to and with a greater utilization of public transit had greater dengue incidence. This relationship was modulated by socioeconomic status; lower socioeconomic status locations experienced stronger effects of public transit accessibility and usage on dengue incidence. Public transit is a vital urban resource, particularly among low socioeconomic populations; these results highlight the importance of public health services concurrent with urban growth.

Climate Suitable Conditions Index and Autochthonous Dengue Infections: an Early Warning Index

Background: Aedes aegypti is the primary vector of dengue and contributes to most major epidemics of this virus worldwide. Aedes albopictus is also blamed for certain epidemics, as the 2014 Guangdong dengue outbreak. In Guangdong province, Ae. albopictus is thought to be the dominant vector species, with Ae. aegypti absent from most areas. Whether or not primary mosquito vectors are present, optimal climatic conditions for dengue vector species may play a substantial role in epidemics of the virus. We hypothesise that although vector species are required to initiate and establish an outbreak, favourable weather conditions may then grow and perpetuate the outbreak via complex effects on vector sympatry or interactions.Methods: Vector spices-specific suitable conditions index (SCI) and autochthonous dengue case data were fitted to negative binomial (NB) regression models. After accounting for potential confounders, we assessed the relationship between SCI and autochthonous dengue cases. We assumed SCI interaction was a proxy for vector species sympatry and SCI difference a proxy for interspecies competition. Finally, we explored the relationship between these assumed conditions and the autochthonous dengue case. Results: Autochthonous dengue cases are associated negatively with SCI for Ae.albopictus and positively with SCI for Ae.aegypti. According to the NB regression models, autochthonous dengue cases increased 4% (Incident Rate Ratio (IRR): 1.04, 95% CI: 1.02, 1.06) for every unit increase in SCI for Ae. aegypti, but decreased by 3% (IRR: 0.97, 95% CI: 0.96, 0.99) for Ae. albopictus SCI. There was also an interaction between two SCIs and a positive effect of the difference in SCIs on autochthonous dengue cases. These findings support the hypothesis that vector sympatry and interactions may influence the risk of a dengue outbreak.Conclusions: Our results confirm the hypothesis that the dengue virus is more transmissible in regions with warmer weather conditions (high SCI for Ae. aegypti). SCI of Ae. aegypti would be a valuable index to predict dengue transmission even in the absence of Ae. aegypti but with Ae. albopictus present. The results also support that the SCI is beneficial for evaluating dengue outbreak risk in terms of vector sympatry and interactions in the absence of entomology data in future research.

Dynamics of notified cases of dengue in Alagoas: Geospatialization and Applied Statistics

The aim of the study was to evaluate the reported cases of dengue in the State of Alagoas via applied statistics and geospatialization.Dengue data were obtained from the DATASUS system between 2000 and 2015. The time series was submitted to descriptive and exploratory statistics and the Pettitt test. In the dengue case maps, the Spline method via QGis version 3.4 was used. In descriptive statistics, only 10 municipalities were evaluated based on the largest case records. All municipalities were above the average of dengue cases in 2010, the year of the biggest recent flood in the state. The boxplot pointed out that all 10 municipalities were positive asymmetric in a few months for dengue cases, the exception was Delmiro Gouveia. The Pettitt test identified biannual cycles (2006/2007 and 2009/2010) associated with the phases of ENSO (El Niño and La Niña) in the moderate category, followed by the months of January, February, April and December, corresponding to the performance of some systems synoptics. In the mapping of annual cases of dengue, the highest records occurred in the Agreste and East Alagoas. Geospatialization and applied statistics are efficient in the spatiotemporal evaluation of dengue cases in Alagoas.

Timely surveillance and temporal calibration of disease response against human infectious diseases

Background Disease surveillance and response are critical components of epidemic preparedness. The disease response, in most cases, is a set of reactive measures that follow the outcomes of the disease surveillance. Hence, timely surveillance is a prerequisite for an effective response. Methodology/principal findings We apply epidemiological soundness criteria in combination with the Latent Influence Point Process and time-to-event models to construct a disease spread network. The network implicitly quantifies the fertility (whether a case leads to secondary cases) and reproduction (number of secondary cases per infectious case) of the cases as well as the size and generations (of the infection chain) of the outbreaks. We test our approach by applying it to historic dengue case data from Australia. Using the data, we empirically confirm that high morbidity relates positively with delay in disease response. Moreover, we identify what constitutes timely surveillance by applying various thresholds of disease response delay to the network and report their impact on case fertility, reproduction, number of generations and ultimately, outbreak size. We observe that enforcing a response delay threshold of 5 days leads to a large average reduction across all parameters (occurrence 87%, reproduction 83%, outbreak size 80% and outbreak generations 47%), whereas extending the threshold to 10 days, in comparison, significantly limits the effectiveness of the response actions. Lastly, we identify the components of the disease surveillance system that can be calibrated to achieve the identified thresholds. Conclusion We identify practically achievable, timely surveillance thresholds (on temporal scale) that lead to an effective response and identify how they can be satisfied. Our approach can be utilized to provide guidelines on spatially and demographically targeted resource allocation for public awareness campaigns as well as to improve diagnostic abilities and turn-around times for the doctors and laboratories involved.

Estimating the annual dengue force of infection from the age of reporting primary infections across urban centres in endemic countries

Background Stratifying dengue risk within endemic countries is crucial for allocating limited control interventions. Current methods of monitoring dengue transmission intensity rely on potentially inaccurate incidence estimates. We investigated whether incidence or alternate metrics obtained from standard, or laboratory, surveillance operations represent accurate surrogate indicators of the burden of dengue and can be used to monitor the force of infection (FOI) across urban centres. Methods Among those who reported and resided in 13 cities across the Philippines, we collected epidemiological data from all dengue case reports between 2014 and 2017 (N 80,043) and additional laboratory data from a cross-section of sampled case reports (N 11,906) between 2014 and 2018. At the city level, we estimated the aggregated annual FOI from age-accumulated IgG among the non-dengue reporting population using catalytic modelling. We compared city-aggregated FOI estimates to aggregated incidence and the mean age of clinically and laboratory diagnosed dengue cases using Pearson’s Correlation coefficient and generated predicted FOI estimates using regression modelling. Results We observed spatial heterogeneity in the dengue average annual FOI across sampled cities, ranging from 0.054 [0.036–0.081] to 0.249 [0.223–0.279]. Compared to FOI estimates, the mean age of primary dengue infections had the strongest association (ρ −0.848, p value<0.001) followed by the mean age of those reporting with warning signs (ρ −0.642, p value 0.018). Using regression modelling, we estimated the predicted annual dengue FOI across urban centres from the age of those reporting with primary infections and revealed prominent spatio-temporal heterogeneity in transmission intensity. Conclusions We show the mean age of those reporting with their first dengue infection or those reporting with warning signs of dengue represent superior indicators of the dengue FOI compared to crude incidence across urban centres. Our work provides a framework for national dengue surveillance to routinely monitor transmission and target control interventions to populations most in need.

Entomological Risk Assessment for Dengue Virus Transmission during 2016–2020 in Kamphaeng Phet, Thailand

Individual houses with high risks of dengue virus (DENV) transmission might be a source of virus transmission within the neighborhood. We conducted an entomological risk assessment for DENV transmission at the household level, comprising family cohort members residing in the same location, to assess the risk for dengue virus transmitted by mosquito vectors. The studies were conducted in Kamphaeng Phet Province, Thailand, during 2016–2020. Entomological investigations were performed in 35 cohort families on day 1 and day 14 after receiving dengue case reports. DENV was found in 22 Aedes samples (4.9%) out of 451 tested samples. A significantly higher DENV infection rate was detected in vectors collected on day 1 (6.64%) compared to those collected on day 14 (1.82%). Annual vector surveillance was carried out in 732 houses, with 1002 traps catching 3653 Aedes females. The majority of the 13,228 water containers examined were made from plastic and clay, with used tires serving as a primary container, with 59.55% larval abundance. Larval indices, as indicators of dengue epidemics and to evaluate disease and vector control approaches, were calculated. As a result, high values of larval indices indicated the considerably high risk of dengue transmission in these communities.

Development of Smartphone-Based Early Alerts and Mosquito Monitoring System and Geographic Instrument System Applications

BACKGROUND: At present, dengue fever is a threat to society and causes rapid death. Aedes aegypti mosquito bites can transmit disease to the public. Environmental factors in society are the primary role that can transmit Dengue hemorrhagic fever (DHF). AIM: Creating a survey system using a smartphone for early alertness to larva monitoring in the Darul Imarah sub-district, Aceh Besar district. METHODS: This study used a descriptive quantitative approach which was carried out by the survey method. The research location is located in Darul Imarah District, Aceh Besar District. Primary data contain the value of the Container index (CI), House index (HI), and Breteau index (BI). This study’s population was all cadres of Juru Jentik (jumantik) in the area of Darul Imarah District, AcehBesar District. The sample in this study was taken from a cadre of larva monitoring officers (jumantik) in the district of Darul Imarah, Aceh Besar. The data collection stage includes data collection of DHF cases from the Puskesmas and data entry. Then proceed with taking the coordinates of the research location and entering the HI and CI, and News Index (BI) data. Data collection begins with data buffering, grouping, and kernel density to be processed into Geographics Instrument System (GIS)-based data. then Analyze descriptive data to describe Smartphone Link. Next, Analytical Analysis of GIS Research Instruments is carried out followed by a checklist of CI, HI, BI data. RESULTS: The results of research on larvae monitoring in Darul Imarah sub-district, it is known that of the 120 houses that were inspected for larvae, 74 houses were cheerful 46 houses were negative for larvae. The number of containers inspected from 120 houses was 502, with the results that 309 houses were found to be larvae and 193 houses were not found. The HI value obtained was 62%, the CI value was 61%, the BI value was 103%, the larva-free number value obtained was 38.3%. Based on these results, it is known that the density figure level is at the larva density level, which is included in the high-density category. In 2018, there were 16 cases of DHF in Darul Imarah District; in 2019, it increased to 60 cases, and in 2020 to 13 cases. The results of buffer analysis in the zone 50 m from the dengue case sufferer’s house showed that mosquitoes originating from the house of the dengue case sufferers were a risk factor that resulted in the transmission of dengue. CONCLUSION: From the survey results, it is known that the density figure is in the high larva density category. The smartphone method is better used for larva density surveys by cadres than manual. Regular larva monitoring will increase this alert system to anticipate cases.

Effectiveness of Wolbachia-infected mosquito deployments in reducing the incidence of dengue and other Aedes-borne diseases in Niterói, Brazil: A quasi-experimental study

Background The introduction of the bacterium Wolbachia (wMel strain) into Aedes aegypti mosquitoes reduces their capacity to transmit dengue and other arboviruses. Evidence of a reduction in dengue case incidence following field releases of wMel-infected Ae. aegypti has been reported previously from a cluster randomised controlled trial in Indonesia, and quasi-experimental studies in Indonesia and northern Australia. Methodology/Principal findings Following pilot releases in 2015–2016 and a period of intensive community engagement, deployments of adult wMel-infected Ae. aegypti mosquitoes were conducted in Niterói, Brazil during 2017–2019. Deployments were phased across four release zones, with a total area of 83 km2 and a residential population of approximately 373,000. A quasi-experimental design was used to evaluate the effectiveness of wMel deployments in reducing dengue, chikungunya and Zika incidence. An untreated control zone was pre-defined, which was comparable to the intervention area in historical dengue trends. The wMel intervention effect was estimated by controlled interrupted time series analysis of monthly dengue, chikungunya and Zika case notifications to the public health surveillance system before, during and after releases, from release zones and the control zone. Three years after commencement of releases, wMel introgression into local Ae. aegypti populations was heterogeneous throughout Niterói, reaching a high prevalence (>80%) in the earliest release zone, and more moderate levels (prevalence 40–70%) elsewhere. Despite this spatial heterogeneity in entomological outcomes, the wMel intervention was associated with a 69% reduction in dengue incidence (95% confidence interval 54%, 79%), a 56% reduction in chikungunya incidence (95%CI 16%, 77%) and a 37% reduction in Zika incidence (95%CI 1%, 60%), in the aggregate release area compared with the pre-defined control area. This significant intervention effect on dengue was replicated across all four release zones, and in three of four zones for chikungunya, though not in individual release zones for Zika. Conclusions/Significance We demonstrate that wMel Wolbachia can be successfully introgressed into Ae. aegypti populations in a large and complex urban setting, and that a significant public health benefit from reduced incidence of Aedes-borne disease accrues even where the prevalence of wMel in local mosquito populations is moderate and spatially heterogeneous. These findings are consistent with the results of randomised and non-randomised field trials in Indonesia and northern Australia, and are supportive of the Wolbachia biocontrol method as a multivalent intervention against dengue, chikungunya and Zika.

Short Report: Adult Aedes abundance and risk of dengue transmission

Dengue is transmitted mainly by the adult female Aedes aegypti mosquito. However, little is known about the impact of adult Aedes abundance on the risk of dengue transmission. Here we analysed nationally representative dengue case and vector surveillance data collected from Singapore, to determine the effect of adult Aedes abundance on the risk of dengue transmission. A case was an area with active dengue transmission as indicated by the presence of dengue cluster. A control was an area where no dengue cluster was reported. Using multivariate logistic regression, we analysed 88 cases and 602 controls and estimated the odds of dengue cluster formation at various adult Aedes abundance levels, estimated by the mean number of adult female Aedes per Gravitrap per week and categorised into Low, Moderate, High and Very High abundance level. We found that the risk of dengue cluster formation was positively associated with adult Ae. aegypti abundance. We observed a three to four-fold increase in the odds of dengue clusters forming in areas with High (AOR: 3.40, 95% CI: 2.09, 5.52) and Very High (AOR: 3.99, 95% CI: 2.46, 6.46) adult Aedes aegypti abundance level compared to those with low Ae. aegypti abundance level. Our study strengthens the evidence for the use of adult Aedes indices for dengue risk assessment and early warning for dengue outbreaks. Entomological indicators of adult Ae. aegypti could be used to anticipate and prioritize areas for dengue control.