Impact of human mobility on the emergence of dengue epidemics in Pakistan

The recent emergence of dengue viruses into new susceptible human populations throughout Asia and the Middle East, driven in part by human travel on both local and global scales, represents a significant global health risk, particularly in areas with changing climatic suitability for the mosquito vector. In Pakistan, dengue has been endemic for decades in the southern port city of Karachi, but large epidemics in the northeast have emerged only since 2011. Pakistan is therefore representative of many countries on the verge of countrywide endemic dengue transmission, where prevention, surveillance, and preparedness are key priorities in previously dengue-free regions. We analyze spatially explicit dengue case data from a large outbreak in Pakistan in 2013 and compare the dynamics of the epidemic to an epidemiological model of dengue virus transmission based on climate and mobility data from ∼40 million mobile phone subscribers. We find that mobile phone-based mobility estimates predict the geographic spread and timing of epidemics in both recently epidemic and emerging locations. We combine transmission suitability maps with estimates of seasonal dengue virus importation to generate fine-scale dynamic risk maps with direct application to dengue containment and epidemic preparedness.Dengue is the most rapidly spreading mosquito-borne disease worldwide (1, 2). Half the global population now lives in at-risk regions for dengue virus transmission, due to the wide distribution of the mosquito vector, Aedes aegypti, which thrives in peri-urban areas and transmits the virus between humans (3). Dengue virus can cause acute febrile illness and carries the risk of severe disease, hospitalization, and shock syndrome, especially in clinical settings with little experience treating dengue patients. There is currently no specific therapeutic protocol for, or vaccine against, infection (1). Current control measures focus on vector control, although these measures are often logistically difficult and have shown varying efficacy in controlling epidemics (4). In the absence of effective prevention and treatment, public health system preparedness remains the single most important tool for minimizing morbidity and mortality as dengue epidemics spread beyond endemic areas (5, 6).The introduction of dengue into new populations is mediated by travel of infected individuals to areas that can support transmission, because mosquito vectors move only short distances during their lifespans (3, 7–12). International travel to endemic countries has resulted in imported cases and outbreaks in Europe and the Americas (2, 8, 10, 13). Local variation in transmission, within a single city for example, is also driven by mobility patterns of individuals on short timescales (7). Forecasting methods are needed to spatially target interventions and epidemic preparedness measures that reflect both the changing temporal risks of importation and environmental suitability that go beyond solely climate-based methods (14).Dengue has long been endemic in most Southeast Asian countries (1), but has more recently emerged in parts of the Middle East and South Asia, including Pakistan (15, 16). In Pakistan, the transmission of dengue viruses was largely confined to the southern city of Karachi until 2011 when a large dengue epidemic with over 20,000 cases occurred in the northeastern city of Lahore (16), causing significant morbidity and mortality. In 2013, a second large epidemic occurred in northeastern Pakistan in Punjab and Khyber-Pakhtunkhwa (KP) provinces, establishing the region as an emerging focus of seasonal dengue epidemics. It has been hypothesized that the recent geographic expansion of A. aegypti mosquito vectors, changing environmental suitability, and human importation of dengue from endemic regions all contributed to the emergence of dengue in northern areas (17). Pakistan is therefore representative of many countries that are on the verge of countrywide endemic dengue transmission and are struggling to contain its emergence into previously dengue-free regions.Measuring changing risks of importation events that spark epidemics has been extremely challenging on the refined temporal and spatial scales necessary to inform local policies (18). Being able to predict when to prepare surveillance systems and health facilities for dengue outbreaks could dramatically reduce the morbidity and mortality associated with epidemics and would allow policy makers to pinpoint regions that are particularly vulnerable to imported cases, for vector control. Mobile phone data offer direct measures of human aggregation and movement and represent a unique source of information on the human determinants of the geographic expansion of emerging epidemic diseases like dengue. Here, we conduct a retrospective epidemiological analysis of large dengue outbreaks in Pakistan in 2013, to examine the predictive ability of an epidemiological model that integrates human mobility from the largest mobile phone dataset analyzed to date with climate information. We show that within-country human mobility predicts emerging epidemics in Pakistan, and epidemiological models incorporating this type of data can predict the spatial extent and timing of outbreaks, providing a new approach to forecasting.     

Necrotizing fasciitis involving the chest and abdominal wall caused by Raoultella planticola

Background

Dengue is considered one of the most common mosquito borne illnesses in the world. Although its clinical course is usually uneventful, complications have rarely been known to arise. These include neurological manifestations such as neuropathies.

Case presentation

We report a middle aged patient from urban Sri Lanka who developed diaphragmatic paralysis secondary to phrenic neuropathy a month after recovering from dengue fever. He was managed conservatively and made a full recovery subsequently.

Conclusion

Isolated phrenic nerve palsy causing diaphragmatic paralysis should be considered a recognized complication of Dengue fever. A patient usually gains full recovery with conservative management.     

Dengue Hemorrhagic Fever: A State-of-the-Art Review Focused in Pulmonary Involvement

Dengue fever is an arboviral disease transmitted to humans through the bites of infected female Aedes mosquitoes. Dengue virus is a member of the Flaviviridae family, and human infection can be caused by any of the four antigenically distinct serotypes (DENV 1–4). The infection has become recognized as the most important and prevalent arboviral disease in humans, endemic in almost 100 countries worldwide. Nearly 3 billion people live in areas with transmission risk. Autochthonous transmission of the virus in previously disease-free areas, increased incidence in endemic areas, and epidemic resurgence in controlled regions could increase the risk of contracting more severe forms of the disease, such as dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS). Symptomatic dengue virus infection can present with a wide range of clinical manifestations, from mild fever to life-threatening DSS. Thoracic complications may manifest as pleural effusion, pneumonitis, non-cardiogenic pulmonary edema, and hemorrhage/hemoptysis. No vaccine is currently available and no specific treatment for dengue fever exists, but prevention and prompt management of complications in patients with DHF can help reduce mortality. This review describes the main clinical, pathological, and imaging findings of thoracic involvement in DHF.     

Recall of intestinal helminthiasis by HIV-infected South Africans and avoidance of possible misinterpretation of egg excretion in worm/HIV co-infection analyses

Background

The reproducibilty of dengue IgM and IgG ELISA was studied in serum and filter paper blood spots from Vietnamese febrile patients.

Methods

781 pairs of acute (t0) and convalescent sera, obtained after three weeks (t3) and 161 corresponding pairs of filter paper blood spots were tested with ELISA for dengue IgG and IgM. 74 serum pairs were tested again in another laboratory with similar methods, after a mean of 252 days.

Results

Cases were classified as no dengue (10 %), past dengue (55%) acute primary (7%) or secondary (28%) dengue. Significant differences between the two laboratories' results were found leading to different diagnostic classification (kappa 0.46, p < 0.001). Filter paper results correlated poorly to serum values, being more variable and lower with a mean (95% CI) difference of 0.82 (0.36 to 1.28) for IgMt3, 0.94 (0.51 to 1.37) for IgGt0 and 0.26 (-0.20 to 0.71) for IgGt3. This also led to differences in diagnostic classification (kappa value 0.44, p < 0.001) The duration of storage of frozen serum and dried filter papers, sealed in nylon bags in an air-conditioned room, had no significant effect on the ELISA results.

Conclusion

Dengue virus IgG antibodies in serum and filter papers was not affected by duration of storage, but was subject to inter-laboratory variability. Dengue virus IgM antibodies measured in serum reconstituted from blood spots on filter papers were lower than in serum, in particular in the acute phase of disease. Therefore this method limits its value for diagnostic confirmation of individual patients with dengue virus infections. However the detection of dengue virus IgG antibodies eluted from filter paper can be used for sero-prevalence cross sectional studies.     

Risk of Dengue in Travelers: Implications for Dengue Vaccination

Purpose of Review

Dengue is found in tropics and subtropics that are considered to be popular travel destinations. We set out to review the burden of dengue on international travelers.

Recent Findings

GeoSentinel, a global network of travel medicine providers, has seen an increasing trend of dengue in returning travelers over the past decades. In Southeast Asia, annual proportionate morbidity increased from 50 dengue cases per 1000 ill-returned travelers in non-epidemic years to an average of 159 cases per 1000 travelers during epidemic years. Dengue is the leading cause of fever in returning travelers, having overtaken malaria for travelers to Southeast Asia. Most dengue seroconversion studies in travelers report an attack rate of around 5% depending on duration of travel and destination.

Summary

Dengue vaccination would be justified for travelers. The first licensed dengue vaccine CYD-TDV is only recommended in seropositive individuals. This review considers preventive measures including how best to use the first licensed dengue vaccine CYD-TDV.

     

Improving Dengue Diagnostics and Management Through Innovative Technology

Purpose of Review

Dengue continues to be a major global public health threat. Symptomatic infections can cause a spectrum of disease ranging from a mild febrile illness to severe and potentially life-threatening manifestations. Management relies on supportive treatment with careful fluid replacement. The purpose of this review is to define the unmet needs and challenges in current dengue diagnostics and patient monitoring and outline potential novel technologies to address these needs.

Recent Findings

There have been recent advances in molecular and point-of-care (POC) diagnostics as well as technologies including wireless communication, low-power microelectronics, and wearable sensors that have opened up new possibilities for management, clinical monitoring, and real-time surveillance of dengue.

Summary

Novel platforms utilizing innovative technologies for POC dengue diagnostics and wearable patient monitors have the potential to revolutionize dengue surveillance, outbreak response, and management at population and individual levels. Validation studies of these technologies are urgently required in dengue-endemic areas.

     

Region-wide synchrony and traveling waves of dengue across eight countries in Southeast Asia

Dengue is a mosquito-transmitted virus infection that causes epidemics of febrile illness and hemorrhagic fever across the tropics and subtropics worldwide. Annual epidemics are commonly observed, but there is substantial spatiotemporal heterogeneity in intensity. A better understanding of this heterogeneity in dengue transmission could lead to improved epidemic prediction and disease control. Time series decomposition methods enable the isolation and study of temporal epidemic dynamics with a specific periodicity (e.g., annual cycles related to climatic drivers and multiannual cycles caused by dynamics in population immunity). We collected and analyzed up to 18 y of monthly dengue surveillance reports on a total of 3.5 million reported dengue cases from 273 provinces in eight countries in Southeast Asia, covering ∼10⁷ km². We detected strong patterns of synchronous dengue transmission across the entire region, most markedly during a period of high incidence in 1997–1998, which was followed by a period of extremely low incidence in 2001–2002. This synchrony in dengue incidence coincided with elevated temperatures throughout the region in 1997–1998 and the strongest El Niño episode of the century. Multiannual dengue cycles (2–5 y) were highly coherent with the Oceanic Niño Index, and synchrony of these cycles increased with temperature. We also detected localized traveling waves of multiannual dengue epidemic cycles in Thailand, Laos, and the Philippines that were dependent on temperature. This study reveals forcing mechanisms that drive synchronization of dengue epidemics on a continental scale across Southeast Asia.Dengue virus (DENV) is an arbovirus transmitted by Aedes mosquitos in the tropics and subtropics of the world. The virus causes an estimated 390 million infections per year, resulting in 96 million clinically symptomatic cases (1). DENV has four serotypes (DENV-1, DENV-2, DENV-3, and DENV-4) that each circulate worldwide. The spatial propagation of dengue transmission at short distances by the mosquito vector is well-understood, but the mechanism of long-distance spread has remained unclear. Disease transmission over large geographical distances is difficult to measure directly, but epidemiological coupling of locations revealed by synchrony in population-level disease patterns has been used successfully in the past to infer mechanisms of spread (2–4). For example, synchrony and its spatial hierarchies indicated that measles in the United Kingdom spread from urban centers to rural areas through a mechanism of fadeout and reintroduction (2). Other studies have suggested that influenza in the United States spreads through workforce commuting (3) and that dengue spreads along a major road in Cambodia (5). Studying epidemic synchrony requires data at high spatiotemporal resolution for a large sample of locations. Data limitations have restricted previous studies on disease spread and synchrony to small geographical areas within country boundaries. Given the increased (cross-border) mobility of populations, strong evidence of global warming, and potential for rapid, global spread of highly pathogenic infectious diseases, a better understanding of the mechanisms of long-distance disease spread and spatial synchrony is becoming essential for global health security.Some infectious diseases in endemic settings, such as dengue or influenza, occur annually in well-defined cycles that depend on climate factors, such as precipitation. In addition to an annual cycle, significant variability at multiannual periodicities has been observed for dengue (6, 7). This multiannual periodicity is thought to be driven by cycling of immunity in the host population and has been observed to vary over time (6). To better understand the spatiotemporal dynamics of large epidemics, previous studies used various time series decomposition methods to isolate multiannual oscillations from background annual cycles and higher frequency noise. For example, previous work on disease spread focused on the 1.5–3 y cycle for measles (2), the 3.5–4.5 and 5–6 y cycles for pertussis (8), and the 2–3 y (9, 10) and 3–4 y cycles (6) for dengue.Whereas mechanisms that cause spatial patterns of multiannual cycles of diseases, such as measles and pertussis, are known (2, 4, 11), these mechanisms remain unclear for dengue. Previous studies have suggested that immunity-driven extinction–reintroduction dynamics of DENV serotypes can play a role, particularly around urban centers (6, 12). The role of multiyear climate variation has also been studied but without consistent results (13).We studied the synchrony of multiannual dengue cycles across a large geographical area of eight countries in Southeast Asia that span 3,500 km east to west by 2,500 km north to south, with a combined population of 320 million in 2010. We used monthly dengue surveillance data that represent ∼3.5 million reported cases at the provincial level. High dengue transmission rates across all countries combined with extensive diversity in population density, climate, and geology make this region ideal to investigate the long-distance spread of major dengue epidemics that occurred in this region during the past decades.     

Seasonal dynamics of influenza in Brazil: the latitude effect

Background

Influenza is a global transmissible disease. Its dynamics is far better understood in temperate climates than in the tropics. We aim to close this knowledge gap between tropical and temperate regions by showing how the influenza seasonality evolves in Brazil, a tropical country that encompasses a wide range of latitudes and six climatic sub-types.

Methods

We analyzed a state-level, weekly Syndrome of Acute Respiratory Disease (SARI) incidence data ranging from 2010 to 2016. We combined two techniques hierarchically: first the wavelet decomposition technique to detect annual periodicity and then circular statistics to describe seasonal measures of the periodic states.

Results

We found significant annual periodicity in 44% of the states. For these, we calculated several seasonal measures such as the center of gravity or mean timing of activity. The relationship between the seasonal signatures and latitude was clear and statistically significant. States with seasonal signature are clustered along the coast. Most Amazonian and Central West states exhibit no seasonal behavior. Among the seasonal states, influenza starts in Northeast region, spreading southbound.

Conclusions

Our study advances the comprehension of influenza seasonality in tropical areas and could be used to design more effective prevention and control strategies.

     

Left pancreatectomy for primary hydatid cyst of the body of pancreas

Background

Hydatid disease is a considerable health problem worldwide. Primary hydatid disease of the pancreas is very rare.

Case report

We report the case of a 30-year-old woman who presented with abdominal pain and an epigastric mass. A diagnosis of hydatid cyst of the pancreas was established by ultrasonography before surgery. The treatment consisted of a distal pancreatectomy. The postoperative evolution was simple.

Conclusion

Hydatid disease should be considered in the differential diagnosis of all cystic masses in the pancreas, especially in the geographical regions where the disease is endemic. Surgical removal remains the main form of definitive treatment. Sometimes only one conservative procedure can be performed.     

8th international congress “sepsis and multiorgan dysfunction”

Purpose

Dengue virus is the most frequent arthropod-borne viral infection worldwide. Simultaneously to the growth of its incidence, cases of bacterial coinfection in dengue have been increasingly reported. The clinical course of dual infections may worsen for reciprocal interactions and delays in the diagnosis, so that clinicians should be aware of this eventuality. Therefore, we reviewed literature to provide an overview of the epidemiological, clinical, and physiopathological issues related to bacterial coinfections and bacteremia in dengue.

Methods

Clinical studies and case reports regarding bacteremia and bacterial coinfections in dengue and the interactions between the pathogens published on PubMed were reviewed.

Results

We found 26 case reports, only 3 studies on concurrent bacteremia and 12 studies reporting data on bacterial coinfections in dengue. According to the three available studies, the 0.18–7 % of dengue infections are accompanied by concurrent bacteremia, while the 14.3–44.4 % of dengue-related deaths seem associated to bacterial coinfections. Comorbidities, advanced age, and more severe dengue manifestations could be risk factors for dual infections. A longer duration of fever and alterations in laboratory parameters such as procalcitonin, hyponatremia, leukocyte count, and renal function tests can raise the suspicion.

Conclusions

Despite the real burden and consequences of this emerging concern is still not computable accurately due to the lack of a significant number of studies on large cohorts, clinicians need a greater awareness about it to early recognize warning signs, to properly use available diagnostic tools and to readily start antibiotic treatment able to prevent worsening in mortality and morbidity.

     

Compliance with antimalarial chemoprophylaxis in German soldiers: a 6-year survey

Purpose

Since 1992, German soldiers have been deployed in areas where malaria is endemic. Antimalarial chemoprophylaxis (CP) is directed according to the assessed risk and is provided free of charge. Compliance is crucial if its effect is to be reliable. This study analysed compliance with directed CP in German soldiers as well as its determinants.

Methods

Between 2003 and 2009, standardized questionnaire-based interviews were performed with 2,149 out of approximately 100,000 German soldiers who were deployed during this period in areas where malaria is endemic. The questionnaires dealt with information that the soldiers had received about malaria prior to their missions, with their adherence to mosquito-protective and antimalarial chemoprophylactic procedures, and their estimations of their individual level of exposure.

Results

About 1,308 out of 2,149 interviewed soldiers had been ordered to take CP, allowing for an assessment of the outcome parameter “CP-compliance”. About 76.9 % out of 1,308 soldiers to whom regular CP was directed took it regularly. The exposure variables “age”, “satisfaction with malaria counselling”, “perceived threat due to insects or mosquitoes” and “use of insect repellents” were positively associated with compliance with directed antimalarial CP.

Conclusions

The study confirms the findings of the French and US armies that even free-of-charge access to antimalarial medication will not lead to 100 % acceptance. The compliance problem is aggravated by the generally low age of deployed soldiers. Adequate counselling is crucial to increase adherence to antimalarial CP.     

Regional-scale climate-variability synchrony of cholera epidemics in West Africa

Background

The relationship between cholera and climate was explored in Africa, the continent with the most reported cases, by analyzing monthly 20-year cholera time series for five coastal adjoining West African countries: Côte d'Ivoire, Ghana, Togo, Benin and Nigeria.

Methods

We used wavelet analyses and derived methods because these are useful mathematical tools to provide information on the evolution of the periodic component over time and allow quantification of non-stationary associations between time series.

Results

The temporal variability of cholera incidence exhibits an interannual component, and a significant synchrony in cholera epidemics is highlighted at the end of the 1980's. This observed synchrony across countries, even if transient through time, is also coherent with both the local variability of rainfall and the global climate variability quantified by the Indian Oscillation Index.

Conclusion

Results of this study suggest that large and regional scale climate variability influence both the temporal dynamics and the spatial synchrony of cholera epidemics in human populations in the Gulf of Guinea, as has been described for two other tropical regions of the world, western South America and Bangladesh.

     

Progressive disseminated histoplasmosis in the HIV population in Europe in the HAART era. Case report and literature review

Introduction

In highly endemic areas, up to 20 % of human immunodeficiency virus (HIV)-infected persons will develop progressive disseminated histoplasmosis (PDH). Europe is not endemic to histoplasmosis, and the disease is mainly found in immigrants often co-infected with HIV.

Methods

We present a case of a patient with HIV and PDH highlighting the possible diagnostic difficulties that may arise in a non-endemic area and review the literature of histoplasmosis in the context of HIV infection with special focus on Europe.

Discussion

When cellular immunity wanes (usually at CD4 T-lymphocyte counts <150 cells/μL) histoplasma infection, acquired earlier, can reactivate and disseminate. PDH is an acquired immune deficiency syndrome(AIDS)-defining disease and a life-threatening infection, with a clinical spectrum ranging from an acute, fatal course with lung infiltrates and respiratory failure, shock, coagulopathy and multi-organ failure, to a more subacute disease with focal organ involvement, pancytopenia and hepatosplenomegaly. Mortality rates remain high for untreated patients, but early diagnosis, proper antifungal treatment and early initiation of antiretroviral therapy have improved the prognosis.

Conclusion

European infectious diseases physicians, microbiologists and pathologists must be aware of histoplasmosis, particularly when facing HIV-infected immigrants from endemic areas. This is increasingly important due to migration and travel activities from these areas.     

Une localisation exceptionnelle du kyste hydatique: à propos de deux cas

Introduction

The hydatid cyst is a cosmopolitan parasitic infection that constitutes a problem of public health in developing countries’ areas of breeding.

Material and methods

The aim of this work is to report on the condition of extraordinary location. We report two cases of hydatid cyst of the right buttock. The diagnosis was confirmed by ultrasound scan of the soft parts. The treatment was surgical.

Discussion

The muscle hydatic cyst is a rare disease and achievement of the buttock is exceptional, so you must always think of it in subjects living in high endemic countries. The eradication of this disease is based on prophylaxis.

Conclusion

The hydatid cyst of soft parts is a rare tumor that grows slow, with local extension. You have to think of this diagnosis, especially in subjects from high endemic countries and seek explorations needed to make the diagnosis in time and avoid therapeutic errors.     

Age- and region-specific hepatitis B prevalence in Turkey estimated using generalized linear mixed models: a systematic review

Background

In view of the long term discussion on the appropriateness of the dengue classification into dengue fever (DF), dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS), the World Health Organization (WHO) has outlined in its new global dengue guidelines a revised classification into levels of severity: dengue fever with an intermediary group of "dengue fever with warning sings", and severe dengue. The objective of this paper was to compare the two classification systems regarding applicability in clinical practice and surveillance, as well as user-friendliness and acceptance by health staff.

Methods

A mix of quantitative (prospective and retrospective review of medical charts by expert reviewers, formal staff interviews), semi-quantitative (open questions in staff interviews) and qualitative methods (focus group discussions) were used in 18 countries. Quality control of data collected was undertaken by external monitors.

Results

The applicability of the DF/DHF/DSS classification was limited, even when strict DHF criteria were not applied (13.7% of dengue cases could not be classified using the DF/DHF/DSS classification by experienced reviewers, compared to only 1.6% with the revised classification). The fact that some severe dengue cases could not be classified in the DF/DHF/DSS system was of particular concern. Both acceptance and perceived user-friendliness of the revised system were high, particularly in relation to triage and case management. The applicability of the revised classification to retrospective data sets (of importance for dengue surveillance) was also favourable. However, the need for training, dissemination and further research on the warning signs was highlighted.

Conclusions

The revised dengue classification has a high potential for facilitating dengue case management and surveillance.     

How often should we perform surveillance colonoscopy after surgery for colorectal cancer?

Purpose

Surveillance colonoscopy is undertaken after resection of colorectal cancer to detect and treat local recurrence and metachronous lesions, with the aim of improving survival. This study aimed to clarify the current timing of surveillance colonoscopies and evaluate the rates of local recurrence and metachronous tumors.

Methods

We retrospectively analyzed data from 459 patients who underwent surveillance colonoscopy at our institution after curative resection of colorectal cancer. The number and timing of surveillance colonoscopies, incidence of local recurrence and metachronous lesions, pathological findings of lesions, treatment of lesions, and outcomes were recorded.

Results

The first surveillance colonoscopy was undertaken at 6–18 months after surgery in 73 % of patients. Local recurrence was detected in three cases (0.7 %), all during the first surveillance colonoscopy, which was performed >1 year after surgery. These three patients all underwent additional surgery and were alive 5 years later. Invasive metachronous cancers were detected in six patients (1.3 %) at 18–57 months after surgery, and advanced adenomas were detected in 30 patients.

Conclusion

Considering the low incidence of postoperative lesions and the timing of lesion detection, reducing the number of surveillance colonoscopies after surgery for colorectal cancer may be appropriate.     

Timing of influenza epidemics and vaccines in the American tropics, 2002–2008, 2011–2014

Background

Influenza‐associated illness results in increased morbidity and mortality in the Americas. These effects can be mitigated with an appropriately chosen and timed influenza vaccination campaign. To provide guidance in choosing the most suitable vaccine formulation and timing of administration, it is necessary to understand the timing of influenza seasonal epidemics.

Objectives

Our main objective was to determine whether influenza occurs in seasonal patterns in the American tropics and when these patterns occurred.

Methods

Publicly available, monthly seasonal influenza data from the Pan American Health Organization and WHO, from countries in the American tropics, were obtained during 2002–2008 and 2011–2014 (excluding unseasonal pandemic activity during 2009–2010). For each country, we calculated the monthly proportion of samples that tested positive for influenza. We applied the monthly proportion data to a logistic regression model for each country.

Results

We analyzed 2002–2008 and 2011–2014 influenza surveillance data from the American tropics and identified 13 (81%) of 16 countries with influenza epidemics that, on average, started during May and lasted 4 months.

Conclusions

The majority of countries in the American tropics have seasonal epidemics that start in May. Officials in these countries should consider the impact of vaccinating persons during April with the Southern Hemisphere formulation.     

Reconstructing the 2003/2004 H3N2 influenza epidemic in Switzerland with a spatially explicit, individual-based model

Background

Simulation models of influenza spread play an important role for pandemic preparedness. However, as the world has not faced a severe pandemic for decades, except the rather mild H1N1 one in 2009, pandemic influenza models are inherently hypothetical and validation is, thus, difficult. We aim at reconstructing a recent seasonal influenza epidemic that occurred in Switzerland and deem this to be a promising validation strategy for models of influenza spread.

Methods

We present a spatially explicit, individual-based simulation model of influenza spread. The simulation model bases upon (i) simulated human travel data, (ii) data on human contact patterns and (iii) empirical knowledge on the epidemiology of influenza. For model validation we compare the simulation outcomes with empirical knowledge regarding (i) the shape of the epidemic curve, overall infection rate and reproduction number, (ii) age-dependent infection rates and time of infection, (iii) spatial patterns.

Results

The simulation model is capable of reproducing the shape of the 2003/2004 H3N2 epidemic curve of Switzerland and generates an overall infection rate (14.9 percent) and reproduction numbers (between 1.2 and 1.3), which are realistic for seasonal influenza epidemics. Age and spatial patterns observed in empirical data are also reflected by the model: Highest infection rates are in children between 5 and 14 and the disease spreads along the main transport axes from west to east.

Conclusions

We show that finding evidence for the validity of simulation models of influenza spread by challenging them with seasonal influenza outbreak data is possible and promising. Simulation models for pandemic spread gain more credibility if they are able to reproduce seasonal influenza outbreaks. For more robust modelling of seasonal influenza, serological data complementing sentinel information would be beneficial.     

Dengue as a cause of acute undifferentiated fever in Vietnam

Background  

Dengue is a common cause of fever in the tropics but its contribution to the total burden of febrile illnesses that is presented to primary health facilities in endemic regions such as Vietnam, is largely unknown. We aimed to report the frequency of dengue as a cause of fever in Binh Thuan Province, to describe the characteristics of dengue patients, and analyze the diagnostic accuracy of the health care workers and the determinants of the diagnostic process.     

The incidence of type 1 diabetes is increasing in both children and young adults in Northern Italy: 1984–2004 temporal trends

Aims/hypothesis

A shift towards younger age at onset of diabetes in susceptible people has been suggested as a possible explanation for the increasing temporal trend in incidence of type 1 diabetes. We aimed to test this hypothesis by assessing trends in incidence rates in the period 1984–2004 in children and young adults in Northern Italy.

Methods

The study bases were: (1) children resident in the Province of Turin in the period 1984–2004 and in the remaining areas of the Piedmont Region in the period 1990–2004; and (2) young adults (15–29 years) resident in the Province of Turin in the period 1984–2003. Temporal trends in rates were analysed using Poisson regression models.

Results

A total of 1,773 incident cases were identified. Overall incidence rates/100,000 person-years in the age groups 0–14 and 15–29 years were 11.3 (95% CI 10.7–12.0) and 7.1 (95% CI 6.6–7.7), respectively, with sex differences among young adults only (incidence rate ratio [IRR] in males vs females 1.41 [95% CI 1.20–1.64]). Average annual increases in incidence rates were similar in children and young adults at 3.3% (95% CI 2.5–4.1). Compared with the period 1984–89, in 2000–2004 a 60% higher risk was found in both age 0–14 years (IRR 1.60, 95% CI 1.31–1.95) and 15–29 years (IRR 1.57, 95% CI 1.26–1.96) groups. The Poisson modelling showed no interaction between calendar period and age at onset.

Conclusions/interpretation

Incidence of type 1 diabetes in Northern Italy is increasing over time in both children and young adults, not supporting the hypothesis of a shift towards younger age as the main explanation for the increasing temporal trend in children.