An outbreak of primary dengue infection among migrant Chinese workers in Singapore characterized by prominent gastrointestinal symptoms and a high proportion of symptomatic cases

The epidemiologic and economic burden of dengue in Singapore: A systematic review

BACKGROUND

Despite its well-regarded vector control program, Singapore remains susceptible to dengue epidemics. To assist evaluation of dengue interventions, we aimed to synthesize current data on the epidemiologic and economic burden of dengue in Singapore.

METHODOLOGY

We used multiple databases (PubMed, Embase, Cochrane, international/national repositories, surveillance) to search for published and gray literature (2000-2022). We included observational and cost studies, and two interventional studies, reporting Singapore-specific data on our co-primary outcomes, dengue incidence and dengue-related costs. Quality was assessed using the Newcastle-Ottawa Scale and an adapted cost-of-illness evaluation checklist. We performed a narrative synthesis and grouped studies according to reported outcomes and available stratified analyses.

FINDINGS

In total, 333 reports (330 epidemiological, 3 economic) were included. Most published epidemiological studies (89%) and all economic studies were of good quality. All gray literature reports were from the Ministry of Health or National Environment Agency. Based predominantly on surveillance data, Singapore experienced multiple outbreaks in 2000-2021, attaining peak incidence rate in 2020 (621.1 cases/100,000 person-years). Stratified analyses revealed the highest incidence rates in DENV-2 and DENV-3 serotypes and the 15-44 age group. Among dengue cases, the risk of hospitalization has been highest in the ≥45-year-old age groups while the risks of dengue hemorrhagic fever and death have generally been low (both <1%) for the last decade. Our search yielded limited data on deaths by age, severity, and infection type (primary, secondary, post-secondary). Seroprevalence (dengue immunoglobulin G) increases with age but has remained <50% in the general population. Comprising 21-63% indirect costs, dengue-related total costs were higher in 2010-2020 (SGD 148 million) versus the preceding decade (SGD 58-110 million).

CONCLUSION

Despite abundant passive surveillance data, more stratified and up-to-date data on the epidemiologic and economic burden of dengue are warranted in Singapore to continuously assess prevention and management strategies.

Occupational exposure to malaria, leishmaniasis and arbovirus vectors in endemic regions: A systematic review

Vector-borne diseases, including dengue, leishmaniasis and malaria, may be more common among individuals whose occupations or behaviours bring them into frequent contact with these disease vectors outside of their homes. A systematic review was conducted to ascertain at-risk occupations and situations that put individuals at increased risk of exposure to these disease vectors in endemic regions and identify the most suitable interventions for each exposure. The review was conducted in accordance with PRISMA guidelines on articles published between 1945 and October 2021, searched in 16 online databases. The primary outcome was incidence or prevalence of dengue, leishmaniasis or malaria. The review excluded ecological and qualitative studies, abstracts only, letters, commentaries, reviews, and studies of laboratory-acquired infections. Studies were appraised, data extracted, and a descriptive analysis conducted. Bite interventions for each risk group were assessed. A total of 1170 articles were screened and 99 included. Malaria, leishmaniasis and dengue were presented in 47, 41 and 24 articles, respectively; some articles presented multiple conditions. The most represented populations were soldiers, 38% (43 of 112 studies); refugees and travellers, 15% (17) each; migrant workers, 12.5% (14); miners, 9% (10); farmers, 5% (6); rubber tappers and missionaries, 1.8% (2) each; and forest workers, 0.9% (1). Risk of exposure was categorised into round-the-clock or specific times of day/night dependent on occupation. Exposure to these vectors presents a critical and understudied concern for outdoor workers and mobile populations. When devising interventions to provide round-the-clock vector bite protection, two populations are considered. First, mobile populations, characterized by their high mobility, may find potential benefits in insecticide-treated clothing, though more research and optimization are essential. Treated clothing offers personal vector protection and holds promise for economically disadvantaged individuals, especially when enabling them to self-treat their clothing to repel vectors. Secondly, semi-permanent and permanent settlement populations can receive a combination of interventions that offer both personal and community protection, including spatial repellents, suitable for extended stays. Existing research is heavily biased towards tourism and the military, diverting attention and resources from vulnerable populations where these interventions are most required like refugee populations as well as those residing in sub-Saharan Africa.

A review of knowledge, attitudes and practices regarding mosquitoes and mosquito-borne infectious diseases in nonendemic regions

Mosquito-borne infectious diseases (MBIDs) present significant public health risks within tropical and subtropical regions. However, the rapid spread of MBIDs from these areas to temperate regions increase the risk of their emergence in nonendemic regions, i.e., regions where diseases are still sporadic and not sustained in the population. Raising awareness about preventive measures and protective behaviors is of primary importance to face the risks of vector-borne diseases. In this context, the number of studies on knowledge, attitude, and practice (KAP) about mosquitoes and MBIDs has grown rapidly in response to the need to identify knowledge and practices in nonendemic countries to fight mosquito proliferation. Building upon the recent developments in this field, we conducted the first-ever literature review to examine KAP studies conducted in nonendemic regions. Our aim was to identify the community's knowledge and attitudes that shape practices concerning the prevention of MBIDs. We used specific keywords regarding the scope of this review and then selected studies that were performed in nonendemic regions for MBIDs, including regions located in European countries, the USA or Asia. We identified 32 KAP studies, the oldest from 2003. The findings in the reviewed studies show that survey participants generally possessed a rather good understanding of mosquito breeding sites. However, there were notable variations in knowledge and perception of MBIDs, primarily linked to the geographic location of the survey and the prevalence of infectious outbreaks related to mosquito transmission. These findings highlight the significant influence of knowledge and awareness in fostering effective mosquito control practices. Moreover, socioeconomic status, particularly educational attainment, and respondents' gender emerged as key determinants in explaining the variability of appropriate practices. The survey results thus show the crucial role of knowledge, emphasizing the need for widespread awareness and information campaigns, encompassing both appropriate practices and efficient mosquito control methods. Understanding the interaction between these factors could provide good guidelines for implementing awareness plans and ultimately motivate the population to actively fight against mosquito proliferation and MBIDs development.

Kinetics of severe dengue virus infection and development of gut pathology in mice

IMPORTANCE

Dengue virus, an arbovirus, causes an estimated 100 million symptomatic infections annually and is an increasing threat as the mosquito range expands with climate change. Dengue epidemics are a substantial strain on local economies and health infrastructure, and an understanding of what drives severe disease may enable treatments to help reduce hospitalizations. Factors exacerbating dengue disease are debated, but gut-related symptoms are much more frequent in severe than mild cases. Using mouse models of dengue infection, we have shown that inflammation and damage are earlier and more severe in the gut than in other tissues. Additionally, we observed impairment of the gut mucus layer and propose that breakdown of the barrier function exacerbates inflammation and promotes severe dengue disease. This idea is supported by recent data from human patients showing elevated bacteria-derived molecules in dengue patient serum. Therapies aiming to maintain gut integrity may help to abrogate severe dengue disease.

Asymptomatic dengue infection rate: A systematic literature review

Objectives

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

Methods

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

Results

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

Conclusion

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

A Cluster of Dengue Cases in Travelers: A Clinical Series from Thailand

Dengue is an overlooked tropical disease for which billions of people are at risk. The disease, caused by a Flavivirus with four distinct serotypes, is transmitted primarily by urban Aedes mosquito species. The infection leads to a spectrum of clinical manifestations, with the majority being asymptomatic. Primary dengue fever and, to a greater extent, a subsequent infection with a different serotype is associated with increased severity. Increased global travel and recreational tourism expose individuals naïve to the dengue viruses, the most common arboviral infections among travelers. We describe a cluster of possible primary acute dengue infections in a group of 12 individuals who presented to Bangkok Hospital for Tropical Diseases in 2017. Infection was confirmed by dengue NS1 antigen and multiplex real-time RT-PCR. Nine individuals required hospitalization, and four developed dengue warning signs. Leukocytes, neutrophils, and platelets declined towards defervescence and were negatively correlated with day of illness. Six clinical isolates were identified as dengue serotype-1, with 100% nucleotide identity suggesting that these patients were infected with the same virus.

Clinical and Biochemical Characteristics of Dengue Infections in Children From Sri Lanka

Introduction:

Analyzing dengue disease patterns from different parts of the world should help us formulate more evidence based treatment guidelines and appropriately allocate limited healthcare resources. Therefore, we described the disease characteristics of hospitalised pediatric patients with dengue infections from Sri Lanka during the 2017 dengue epidemic.

Methods:

Clinical and biochemical characteristics of pediatric dengue patients treated at a secondary care hospital in Sri Lanka from 1 June 2017 to 31 August 2017 were analyzed. Our findings were compared with previous pediatric dengue studies in Asia.

Results: A total of 305

patients (number of males = 184(60%); mean age = 8.6 years) were analyzed. DF (Dengue Fever)—245 (80.3%), DHF (Dengue Hemorrhagic fever)—I:52 (17%), DHF—II:7 (2.3%), and DHF—III:1 (0.3%). Significant associations were found between DHF and abdominal symptoms/signs and overt bleeding manifestations (P < .001). Time of onset of the critical phase was variable (Day 3: 12%, Day 4-5: 78%, Day 6: 5%, and Day 7: 5%). Platelet and white-cell counts (WBC) were significantly lower in DHF than DF; liver enzyme derangement was mild and was similar in the DHF and DF subgroups. None had cardiac, renal, or neurological manifestations and all recovered uneventfully.

Conclusion:

In Sri Lankan pediatric dengue patients, we found abdominal symptoms and signs, decreased WBC and platelet counts and bleeding manifestations were to be significantly associated with DHF. Liver enzyme derangement did not predict DHF. The time of onset of the critical phase was difficult to predict due to the considerable variations noted.

Unusual clinical manifestations of dengue disease - Real or imagined?

The disease caused by each of the four serotypes of dengue virus (DENV) have plagued humans since last century. Symptoms of dengue virus (DENV) infection range from asymptomatic to dengue fever (DF) to severe dengue disease (SDD). One third of the world's population lives in regions with active urban DENV transmission, and thousands of serologically naïve travelers visit these areas annually, making a significant portion of the human population at risk of being infected. Even though lifelong immunity to the homotypic serotype is achieved after a primary DENV infection. Heterotypic DENV infections may be exacerbated by a pre-existing immune memory to the primary infection and can result in an increased probability of severe disease. Not only, age, comorbidities and presence of antibodies transferred passively from dengue-immune mother to infants are considered risk factors to dengue severe forms. Plasma leakage and multiple organ impairment are well documented in the literature, affecting liver, lung, brain, muscle, and kidney. However, unusual manifestation, severe or not, have been reported and may require medical attention. This review will summarize and discuss the increasing reports of unusual manifestations in the clinical course of dengue infection.

Impact of population displacement and forced movements on the transmission and outbreaks of Aedes-borne viral diseases: Dengue as a model

Population displacement and other forced movement patterns following natural disasters, armed conflicts or due to socioeconomic reasons contribute to the global emergence of Aedes-borne viral disease epidemics. In particular, dengue epidemiology is critically affected by situations of displacement and forced movement patterns, particularly within and across borders. In this respect, waves of human movements have been a major driver for the changing epidemiology and outbreaks of the disease on local, regional and global scales. Both emerging dengue autochthonous transmission and outbreaks in countries known to be non-endemic and co-circulation and hyperendemicity with multiple dengue virus serotypes have led to the emergence of severe disease forms such as dengue hemorrhagic fever and dengue shock syndrome. This paper reviews the emergence of dengue outbreaks driven by population displacement and forced movements following natural disasters and conflicts within the context of regional and sub-regional groupings.

Pattern of dengue virus infections in adult patients from Sri Lanka

Background

Sri Lanka experienced its largest dengue epidemic in 2017. This study describes the disease pattern of adult dengue patients from two hospitals in Sri Lanka.

Methods

Demographic, clinical and investigation findings of adult dengue patients admitted to the two hospitals from June to August 2017 were collected and analysed.

Results

A total of 1167 patients (777 males [66.2%], mean age 32.9 y) were studied. There were 775 (66.4%) patients with dengue fever (DF), 334 (28.6%) with dengue haemorrhagic fever grade I, 54 (4.6%) with DHF grade II and 4 (0.3%) with DHF grade III. DHF was significantly associated with abdominal symptoms/signs and bleeding manifestations (p<0.001). A considerable variation in time of onset of the critical phase was noted (day 3, 11.9%; day 4-5, 63.1%; day 6, 16.2%; day ≥7, 8.7%). Significantly lower platelet and white blood cell counts and elevated transaminase levels were found in DHF than DF (p<0.001). Other complications included myocarditis (two patients) and mild renal impairment (three patients). None had neurological manifestations.

Conclusions

We found abdominal symptoms/signs, low platelet and white blood cell counts and high transaminase to be associated with DHF. The onset of the critical phase was variable and difficult to predict. Compiling data from various regions would help to understand disease patterns, which in turn would help in formulating evidence-based management guidelines and the allocation of limited health care resources.

Differences in clinical features and dengue severity between local and migrant Chinese with dengue infection in Singapore

Dengue is endemic in Singapore but not China. We compared clinical features and disease severity of dengue between local and migrant Chinese, most of whom were construction workers, in Singapore. A retrospective study with all hospitalized dengue patients from 2005 to 2008 were performed, including 2609 local and 1195 migrant Chinese. Compared with local Chinese, migrant Chinese were younger. There were more males, but fewer had comorbidities. Migrant Chinese had more headache, eye pain, nausea and myalgia. They had significantly lower median leukocyte count, ALT and AST, and higher platelet count nadir. Among warning signs, migrant Chinese had significantly less persistent vomiting, clinical fluid accumulation, hepatomegaly, hematocrit rise with rapid platelet drop, and more mucosal bleeding. Adjusted for age, gender and comorbidities, migrant Chinese were significantly at higher risk of dengue hemorrhagic fever (DHF) (adjusted odds ratio [aOR]: 1.20, 95% confidence interval [CI]: 1.03–1.41) and dengue shock syndrome (aOR: 1.49, 95% CI: 1.06–2.10), and had longer hospitalization (β coefficient value: 0.27, 95%CI: 0.09–0.44, p = 0.003). There was 1 death among migrant Chinese and 2 deaths among local Chinese. We documented differences in clinical and laboratory features, and dengue severity between local and migrant Chinese in Singapore. Migrant Chinese may need more medical attention given higher risk of DHF.

Infectious diseases and migrant worker health in Singapore: a receiving country's perspective

BACKGROUND

Approximately 1.4 million migrant workers reside in Singapore, presenting unique infectious disease challenges to both migrants and Singapore.

METHODS

A Pubmed, MEDLINE (Ovid), EBSCO Host (Global Health) and Google Scholar search was performed for both peer, non-peer reviewed articles and reports relevant to migrant health in Singapore, published between 1 January 1989 and 1 September 2016. Additional studies were identified from citations within searched articles. We also reviewed published data and policy documents from the Ministries of Health and Manpower, Singapore.

RESULTS

A significant proportion of malaria, enteric fevers, hepatitis A and E and tuberculosis diagnosed in Singapore involve migrant workers. From the 1990-2000 through 2009-11, while malaria and hepatitis A cases have decreased and remain sporadic, enteric fevers and tuberculosis cases have increased, possibly due to greater influx of migrant workers. Hepatitis E numbers remain low but migrant workers account for half of diagnosed cases. In an interplay of immune naivete, work and living conditions, migrants in the construction industry are at higher risk of arboviral infections such as dengue, Zika and chikungunya. Infections such as chikungunya were likely introduced into Singapore by travellers including migrant workers from the Indian subcontinent but autochthonous transmission continued due to the presence of competent mosquito vectors. There is less data regarding sexual health, networks and infections amongst migrant workers, an area which merits further attention.

CONCLUSIONS

Migrant workers appear to be at higher risk than Singaporeans for specific infectious diseases, probably due to a complex interplay of several factors, including higher disease prevalence in their countries of origin, socio-economic factors, their living conditions in Singapore and financial, language and cultural barriers to healthcare access. Receiving countries need improved surveillance, expansion of preventive measures and decreased barriers to healthcare access for migrant workers.

Benefits and risks of the Sanofi-Pasteur dengue vaccine: Modeling optimal deployment

The first approved dengue vaccine has now been licensed in six countries. We propose that this live attenuated vaccine acts like a silent natural infection in priming or boosting host immunity. A transmission dynamic model incorporating this hypothesis fits recent clinical trial data well and predicts that vaccine effectiveness depends strongly on the age group vaccinated and local transmission intensity. Vaccination in low-transmission settings may increase the incidence of more severe "secondary-like" infection and, thus, the numbers hospitalized for dengue. In moderate transmission settings, we predict positive impacts overall but increased risks of hospitalization with dengue disease for individuals who are vaccinated when seronegative. However, in high-transmission settings, vaccination benefits both the whole population and seronegative recipients. Our analysis can help inform policy-makers evaluating this and other candidate dengue vaccines.

Public Health Responses to and Challenges for the Control of Dengue Transmission in High-Income Countries: Four Case Studies

Dengue has a negative impact in low- and lower middle-income countries, but also affects upper middle- and high-income countries. Despite the efforts at controlling this disease, it is unclear why dengue remains an issue in affluent countries. A better understanding of dengue epidemiology and its burden, and those of chikungunya virus and Zika virus which share vectors with dengue, is required to prevent the emergence of these diseases in high-income countries in the future. The purpose of this review was to assess the relative burden of dengue in four high-income countries and to appraise the similarities and differences in dengue transmission. We searched PubMed, ISI Web of Science, and Google Scholar using specific keywords for articles published up to 05 May 2016. We found that outbreaks rarely occur where only Aedes albopictus is present. The main similarities between countries uncovered by our review are the proximity to dengue-endemic countries, the presence of a competent mosquito vector, a largely nonimmune population, and a lack of citizens' engagement in control of mosquito breeding. We identified important epidemiological and environmental issues including the increase of local transmission despite control efforts, population growth, difficulty locating larval sites, and increased human mobility from neighboring endemic countries. Budget cuts in health and lack of practical vaccines contribute to an increased risk. To be successful, dengue-control programs for high-income countries must consider the epidemiology of dengue in other countries and use this information to minimize virus importation, improve the control of the cryptic larval habitat, and engage the community in reducing vector breeding. Finally, the presence of a communicable disease center is critical for managing and reducing future disease risks.

Weighing up the costs of seeking health care for dengue symptoms: a grounded theory study of backpackers' decision-making processes

Dengue fever, a mosquito-borne virus, is an ongoing public health issue in North Queensland. Importation of dengue fever by travellers visiting or returning to Australia can lead to epidemics. The mosquito can acquire the virus in the symptomatic viraemic phase, so timely recognition of cases is important to prevent epidemics. There is a gap in the literature about backpackers' knowledge of dengue fever and the decision-making process they use when considering utilising the Australian health-care system. This study uses grounded theory methods to construct a theory that explains the process backpackers use when seeking health care. Fifty semi-structured interviews with backpackers, hostel receptionists, travel agents and pharmacists were analysed, resulting in identification of a core category: 'weighing up the costs of seeking health care'. This core category has three subcategories: 'self-assessment of health status', 'wait-and-see' and 'seek direction'. Findings from this study identified key areas where health promotion material and increased access to health-care professionals could reduce the risk of backpackers spreading dengue fever.

Acute kidney injury in dengue virus infection

Background

Dengue is a growing public health problem in Pakistan and acute kidney injury (AKI) is one of the least studied complications of dengue virus infection (DVI). The aim of this study was to determine the frequency, severity and predictors of AKI in patients with DVI and to study the impact of AKI on the length of hospital stay and mortality.

Methods

We retrospectively reviewed medical records of patients aged ≥14 years hospitalized with a primary diagnosis of DVI at Aga Khan University Hospital Karachi between January 2008 and December 2010. Binary logistic regression models were constructed to identify factors associated with the development of AKI and to study the impact of AKI on hospital stays of more than 3 days.

Results

Out of 532 patients, AKI was present in 13.3% (71/532). Approximately two-thirds (64.8%) of these patients had mild AKI and a third (35.2%) had moderate to severe AKI. Independent predictors for AKI were male gender [odds ratio (OD) 4.43; 95% CI 1.92–10.23], presence of dengue hemorrhagic and dengue shock syndrome (DSS, OD 2.14; 95% CI 1.06–4.32), neurological involvement (OD 12.08; 95% CI 2.82–51.77) and prolonged activated partial thromboplastin time (aPTT, OD 1.81; 95% CI 1.003–3.26). AKI was associated with a length of stay ≥3 days when compared with those who did not have AKI (OD 2.98; 95% CI 1.66–5.34). Eight patients (11.3%) with AKI died whereas there were no mortalities in patients without AKI (P < 0.001). Only 5 patients (7%) had persistent kidney dysfunction at discharge.

Conclusions

AKI in DVI is associated with neurological involvement, prolongation of aPTT, greater length of hospital stay and increased mortality.

Trends of fluid requirement in dengue fever and dengue haemorrhagic fever: a single centre experience in Sri Lanka

BACKGROUND

Meticulous fluid management is the mainstay of treatment in dengue fever that is currently governed by consensus guidelines rather than by strong research evidence. To examine this issue we audited the fluid requirement of a cohort of adult patients with dengue fever (DF) and dengue haemorrhagic fever (DHF) in a tertiary care clinical setting.

RESULTS

This retrospective cohort study was conducted from July 2012 to January 2013 in Teaching Hospital, Peradeniya, Sri Lanka. Adult patients with confirmed dengue infection managed according to the national and WHO guidelines were included. Their fluid requirement was audited once data collection was over in both DF and DHF groups. Out of 302 patients, 209 (69%) had serological confirmation of dengue infection, comprising 62 (30%) patients gone into critical phase of DHF. Mean age of the DHF group was 30 years (range 12-63 years) and included more males (n = 42, 68%, p < 0.05). Their mean duration of fever on admission and total duration of fever were 4 days and 6 days respectively. DHF group had high incidence of vomiting, abdominal pain and flushing, lowest platelet counts and highest haematocrit values compared to DF group. In DHF group, the mean total daily requirements of fluid from 2(nd) to 7(th) day were 2123, 2733, 2846, 2981, 3139 and 3154 milliliters respectively to maintain a safe haematocrit value and the vital parameters. However, in DF group the fluid requirement was lowest on 3(rd) day (2158 milliliters). DHF group had significantly high fluid requirement on 5(th) -7(th) day compared to DF group (p < 0.05).

CONCLUSIONS

Patients in critical phase of DHF required a higher volume of fluids from the 3(rd) day of fever and again on 5(th) to 7(th) day of fever. Despite being an audit, these finding could be useful in future updates of guidelines and designing research.

Demographic and clinical features of suspected dengue and dengue haemorrhagic fever in the Northern Province of Sri Lanka, a region afflicted by an internal conflict for more than 30 years-a retrospective analysis

OBJECTIVES

The aim of this study was to determine the demographic, clinical, and notification data of suspected dengue fever (DF) and dengue hemorrhagic fever (DHF) cases admitted to Jaffna Teaching Hospital, Sri Lanka.

METHODS

The data were collected from bed head tickets of all patients presenting with clinically suspected DF/DHF from October 2009 to September 2010.

RESULTS

A total of 1085 clinically suspected DF/DHF cases were identified, with high numbers occurring during December 2009 to March 2010. The majority of the reported patients were females (n = 550, 50.7%) and approximately three-quarters of the patients (n = 797, 73.5%) were adults. All had fever, but fever spikes were noted in only 129 cases (11.9%; 95% confidence interval (CI) 10.1-13.9%). Over 50% of cases had vomiting (95% CI 47.5-53.5%). Haemorrhages were noted in 266 (24.5%), with gum bleeding in 99 patients (37.2%). Low white blood cell and platelet counts were noted in 27.1% and 85.6% of cases, respectively. Of the 1085 cases, only 24 (2.2%) were screened for dengue IgM/IgG and only 458 cases (42.2%) were notified to the Epidemiology Unit, Ministry of Health, Sri Lanka.

CONCLUSIONS

The absence of laboratory diagnosis and poor notification to the Epidemiology Unit were the major drawbacks noted.

Predictors of hospital stay and mortality in dengue virus infection-experience from Aga Khan University Hospital Pakistan

Background

Dengue virus infection (DVI) is very common infection. There is scarcity of data on factor associated with increased hospital stay and mortality in dengue virus infection (DVI). This study was done to know about factors associated with increased hospital stay and mortality in patients admitted with DVI.

Results

Out of 532 patients, two third (72.6%) had stay ≤3 days while one third (27.4%) had stay greater than 3 days. The mean length of hospital stay was 3.46 ± 3.45 days. Factors associated with increased hospital stay (>3 days) included AKI (acute kidney injury) (Odd ratio 2.98; 95% CI 1.66-5.34), prolonged prothrombin time (Odd ratio 2.03; 95% CI 1.07-3.84), prolonged activated partial thromboplastin time (aPTT) (Odd ratio 1.80; CI 95% 1.15-2.83) and increased age of > 41.10 years (Odd ratio 1.03; CI 95% 1.01-1.04).Mortality was 1.5%. High mortality was found in those with AKI (P <0.01), dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) (P <0.001), respiratory failure (P0.01), prolong PT (P 0.001), prolong aPTT (P0.01) and increased hospital stay (P0.04).

Conclusion

Increasing age, coagulopathy and acute kidney injury in patients with DVI is associated with increased hospital stay. Morality was more in patients with AKI, DHF and DSS, respiratory failure, coagulopathy and these patients had more prolonged hospitalization.

Health-seeking behaviour of male foreign migrant workers living in a dormitory in Singapore

Background

Foreign workers’ migrant status may hinder their utilisation of health services. This study describes the health-seeking behaviour and beliefs of a group of male migrant workers in Singapore and the barriers limiting their access to primary healthcare.

Methods

A cross-sectional study of 525 male migrant workers, ≥21 years old and of Indian, Bangladeshi or Myanmar nationality, was conducted at a dormitory via self-administered questionnaires covering demographics, prevalence of medical conditions and health-seeking behaviours through hypothetical scenarios and personal experience.

Results

71% (95%CI: 67 to 75%) of participants did not have or were not aware if they had healthcare insurance. 53% (95%CI: 48 to 57%) reported ever having had an illness episode while in Singapore, of whom 87% (95%CI: 82 to 91%) saw a doctor. The number of rest days was significantly associated with higher probability of having consulted a doctor for their last illness episode (p = 0.026), and higher basic monthly salary was associated with seeing a doctor within 3 days of illness (p = 0.002). Of those who saw a doctor, 84% (95%CI: 79 to 89%) responded that they did so because they felt medical care would help them to work better. While 55% (95%CI: 36 to 73%) said they did not see a doctor because the illness was not serious, those with lower salaries were significantly more likely to cite inadequate finances (55% of those earning < S$500/month). In hypothetical injury or illness scenarios, most responded that they would see the doctor, but a sizeable proportion (15% 95%CI: 12 to 18%) said they would continue to work even in a work-related injury scenario that caused severe pain and functional impairment. Those with lower salaries were significantly more likely to believe they would have to pay for their own healthcare or be uncertain about who would pay.

Conclusions

The majority of foreign workers in this study sought healthcare when they fell ill. However, knowledge about health-related insurance was poor and a sizeable minority, in particular those earning < S$500 per month, may face significant issues in accessing care.

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

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

Implications of discordance in world health organization 1997 and 2009 dengue classifications in adult dengue

BACKGROUND

Revised dengue guidelines were published by the World Health Organization (WHO) in 2009 addressing severe dengue cases not classified by dengue hemorrhagic fever (DHF) and shock syndrome (DSS).

METHODS AND PRINCIPAL FINDINGS

We conducted a retrospective cohort study to compare WHO 2009 and 1997 classifications using 1278 adult dengue cases confirmed by polymerase chain reaction assay from Singapore epidemics in 2004 and 2007 (predominantly serotype 1 and 2 respectively).DHF occurred in 14.3%, DSS 2.7% and severe dengue 16.0%. The two WHO dengue classifications were discordant in defining severe disease (p<0.001). Five DSS patients (15%) were classified as non-severe dengue without warning signs. Of severe dengue patients, 107 did not fulfil DHF criteria. Of these, 14.9% had self-resolving isolated elevated aminotransferases, 18.7% gastrointestinal bleeding without hemodynamic compromise and 56.1% plasma leakage with isolated tachycardia. We compared both guidelines against requirement for intensive care including the single death in this series: all six had severe dengue; only four had DHF as two lacked bleeding manifestations but had plasma leakage. Increasing length of hospitalization was noted among severe cases with both classifications but the trend was only statistically significant for WHO 2009. Length of hospitalization was significantly longer for severe plasma leakage compared with severe bleeding or organ impairment. Requirement for hospitalization increased using WHO 2009 from 17.0% to 51.3%.

CONCLUSIONS

While the WHO 2009 dengue classification is clinically useful, we propose retaining criteria for plasma leakage and hemodynamic compromise from WHO 1997, and refining definitions of severe bleeding and organ impairment to improve clinical relevance having found that differences in these accounted for the discordance between classifications. Findings from our retrospective study may be limited by the study site - a tertiary referral center in a hyperendemic country - and should be evaluated in a wider range of geographic settings.

Dengue fever and dengue haemorrhagic fever in adolescents and adults

Dengue fever (DF) is endemic in tropical and subtropical zones and the prevalence is increasing across South-east Asia, Africa, the Western Pacific and the Americas. In recent years, the spread of unplanned urbanisation, with associated substandard housing, overcrowding and deterioration in water, sewage and waste management systems, has created ideal conditions for increased transmission of the dengue virus in tropical urban centres. While dengue infection has traditionally been considered a paediatric disease, the age distribution of dengue has been rising and more cases have been observed in adolescents and adults. Furthermore, the development of tourism in the tropics has led to an increase in the number of tourists who become infected, most of whom are adults. Symptoms and risk factors for dengue haemorrhagic fever (DHF) and severe dengue differ between children and adults, with co-morbidities and incidence in more elderly patients associated with greater risk of mortality. Treatment options for DF and DHF in adults, as for children, centre round fluid replacement (either orally or intravenously, depending on severity) and antipyretics. Further data are needed on the optimal treatment of adult patients.

Contribution of dengue fever to the burden of acute febrile illnesses in Papua New Guinea: an age-specific prospective study

Malaria is a major contributor to the burden of febrile illnesses in Papua New Guinea (PNG). Dengue fever (DF) is likely to contribute; however, its epidemiology in PNG is poorly understood. We performed a prospective age-stratified study in outpatient clinics investigating the prevalence of DF; 578 patients were enrolled, and 317 patients with a negative rapid diagnostic test (RDT) for malaria were tested for dengue. Malaria was confirmed in 52% (301/578, 95% confidence interval [CI] = 48-56%), DF was diagnosed in 8% (46/578, 95% CI = 6-10%), and 40% (95% CI = 36-44%) had neither diagnosis. Among the 317 malaria RDT-negative patients, 14% (45/317, 95% CI = 10-18%) had DF. The seroprevalence of dengue immunoglobulin G (IgG) was 83% (204/247, 95% CI = 78-87%), and no dengue hemorrhagic fever was seen. This study provides good evidence for the first time that DF is common in PNG and is responsible for 8% of fever episodes. The common occurrence of DF in a population with presumed previous exposure to dengue is an important observation.

Contribution of dengue fever to the burden of acute febrile illnesses in Papua New Guinea: an age-specific prospective study

Malaria is a major contributor to the burden of febrile illnesses in Papua New Guinea (PNG). Dengue fever (DF) is likely to contribute; however, its epidemiology in PNG is poorly understood. We performed a prospective age-stratified study in outpatient clinics investigating the prevalence of DF; 578 patients were enrolled, and 317 patients with a negative rapid diagnostic test (RDT) for malaria were tested for dengue. Malaria was confirmed in 52% (301/578, 95% confidence interval [CI] = 48-56%), DF was diagnosed in 8% (46/578, 95% CI = 6-10%), and 40% (95% CI = 36-44%) had neither diagnosis. Among the 317 malaria RDT-negative patients, 14% (45/317, 95% CI = 10-18%) had DF. The seroprevalence of dengue immunoglobulin G (IgG) was 83% (204/247, 95% CI = 78-87%), and no dengue hemorrhagic fever was seen. This study provides good evidence for the first time that DF is common in PNG and is responsible for 8% of fever episodes. The common occurrence of DF in a population with presumed previous exposure to dengue is an important observation.

Characteristic of dengue disease in Taiwan: 2002-2007

Taiwan's dengue outbreaks have a unique type of transmission: starting by import from abroad in early summer, spreading out locally, and ending in the winter. This pattern repeats every year. Most of the dengue patients are adults, with dengue fever peaking in the 50-54 year age range, and dengue hemorrhagic fever in the 60-64 year age range. Two patterns of dengue infection were found: DENV-2 in 2002 with 74% of secondary infection in contrast to non-DENV-2 (DENV-1 or DENV-3) in 2004-2007 with approximately 70% of primary infection. Secondary dengue virus infection increases disease morbidity, but not mortality in adults. The active serological surveillance shows two-thirds of the dengue-infected adults are symptomatic post infection. The Taiwanese experience of adult dengue should be valuable for countries or areas where, although dengue is not endemic, the Aedes aegypti vector exists and dengue virus can be introduced by travelers.

Oxidative damage in dengue fever

Oxidative stress may be important in the pathogenesis of dengue infection. Using accurate markers of oxidative damage, we assessed the extent of oxidative damage in dengue patients. The levels of hydroxyeicosatetraenoic acid products (HETEs), F(2)-isoprostanes (F(2)-IsoPs), and cholesterol oxidation products (COPs) were measured in 28 adult dengue patients and 28 age-matched study controls during the febrile, defervescent, and convalescent stages of infection. We compared the absolute and the percentage change in these markers in relation to key clinical parameters and inflammatory markers. The levels of total HETEs and total HETEs/arachidonate, total F(2)-IsoPs/arachidonate, and COPs/cholesterol were higher during the febrile compared to the convalescent level. Total HETEs correlated positively with admission systolic blood pressure (r=0.52, p<0.05), whereas an inverse relationship was found between 7beta-hydroxycholesterol and systolic and diastolic blood pressure (r=-0.61 and -0.59, respectively, p<0.01). The urinary F(2)-IsoP level was higher in urine during the febrile stage compared to the convalescent level. Despite lower total cholesterol levels during the febrile stage compared to convalescent levels, a higher percentage of cholesterol was found as COPs (7beta-, 24-, and 27-hydroxycholesterol). The levels of platelet-activating factor-acetylhydrolase activity, vascular cellular adhesion molecule-1, tumor necrosis factor-alpha, and high-sensitivity C-reactive protein were higher during the febrile stage compared to their convalescent levels (p<0.01). Markers of oxidative damage are altered during the various stages of dengue infection.

Relationship between circulating vascular endothelial growth factor and its soluble receptors in adults with dengue virus infection: a case-control study

BACKGROUND

We performed a case-control study to assess the relationship between vascular endothelial growth factor (VEGF) and its soluble receptors (sVEGFR-1 and 2) in adult patients with dengue fever (DF) and dengue hemorrhagic fever (DHF).

METHODS

We recruited 60 adult patients (34 DF and 26 DHF) with serologically-confirmed dengue infections, 10 patients with non-hemorrhagic infections, and 31 community-based healthy volunteers. The levels of VEGF, sVEGFR-1, and sVEGFR-2 were measured and the differences in these markers were compared using one-way analysis of variance (ANOVA), which was adjusted for multiple comparisons.

RESULTS

We observed lower VEGF levels in DF and DHF compared to study controls (p<0.01). sVEGFR-1 was higher in DHF than DF, whilst sVEGFR-2 was lower in DF and DHF compared to study controls (all p<0.01). In DHF, lower VEGF levels were observed in older patients. The use of a single marker, sVEGFR-1>350 pg/ml, was predictive of DHF.

CONCLUSION

The changes in VEGF and its soluble receptors highlight the importance of vascular permeability cytokines in the pathogenesis of DHF.

Dengue in Southeast Asia: epidemiological characteristics and strategic challenges in disease prevention

Dengue emerged as a public health burden in Southeast Asia during and following the Second World War and has become increasingly important, with progressively longer and more frequent cyclical epidemics of dengue fever/dengue hemorrhagic fever. Despite this trend, surveillance for this vector-borne viral disease remains largely passive in most Southeast Asian countries, without adequate laboratory support. We review here the factors that may have contributed to the changing epidemiology of dengue in Southeast Asia as well as challenges of disease prevention. We also discuss a regional approach to active dengue virus surveillance, focusing on urban areas where the viruses are maintained, which may be a solution to limited financial resources since most of the countries in the region have developing economies. A regional approach would also result in a greater likelihood of success in disease prevention since the large volume of human travel is a major factor contributing to the geographical spread of dengue viruses.

Predictive value of simple clinical and laboratory variables for dengue hemorrhagic fever in adults

BACKGROUND

Singapore experienced its worst dengue outbreak in 30 years in 2004, with 9459 notified cases, of which 83% were hospitalized.

OBJECTIVES

To determine predictors of dengue hemorrhagic fever (DHF) upon first presentation to hospital to aid clinicians in determining need for admission.

STUDY DESIGN

We conducted a retrospective cohort study on dengue patients in Tan Tock Seng Hospital, Singapore in 2004, with patients categorized into dengue fever (DF) and DHF. Demographic, clinical, and laboratory variables upon first presentation were compared to determine the likelihood of developing DHF.

RESULTS

There were 1973 dengue patients-118 (6.0%) were DHF, of which 82 (4.2%) developed DHF during hospitalization. From the multivariate analysis, patients with bleeding had an odds of developing DHF 237.6 times that of DF, a unit decrease in total protein (g/L) had an odds of 1.28 times, a unit increase in blood urea (mmol/L) had an odds of 1.31 times, and a unit decrease in lymphocyte proportion had an odds of 1.08 times. The model had a sensitivity of 97.6%, specificity of 60.2%, and may reduce 1118 (56.7%) dengue admissions.

CONCLUSIONS

A few easily available clinical and laboratory results may assist clinicians in determining dengue admissions.

Dengue virus-mosquito interactions

The mosquito Aedes aegypti is more widely dispersed now than at any time in the past, placing billions of humans at risk of infection with one or more of the four dengue viruses. This review presents and discusses information on mosquito-dengue infection dynamics and describes the prominent role that temperature and rainfall play in controlling dengue viral transmission including discussions of the effect of interannual climate variations and the predicted effect of global warming. Complementary human determinants of dengue epidemiology include viremia titer, variation in viremic period, enhanced viremias, and threshold viremia. Topics covered include epidemiological phenomena such as traveling waves, the generation of genetic diversity of dengue viruses following virgin soil introductions and in hyperendemic settings, and evidence for and against viral virulence as a determinant of the severity of dengue infections. Also described is the crucial role of monotypic and heterotypic herd immunity in shaping dengue epidemic behavior.

Post-infectious fatigue syndrome in dengue infection

BACKGROUND

Although the acute manifestations of dengue are well known, few studies have assessed the long-term consequences of dengue infection. We prospectively studied the incidence and factors associated with fatigue in a cohort of patients following dengue infection.

METHODS

We included patients with serologically confirmed dengue infection admitted to the National University Hospital, Singapore, during a dengue outbreak from October-November 2005. The severity of dengue was graded as dengue fever, dengue haemorrhagic fever and dengue shock syndrome. A follow-up telephone interview was performed two months following hospital discharge, where a Fatigue Questionnaire was administered. The presence of significant fatigue was considered as the main outcome measure. Significance was assessed at P<0.05.

RESULTS

One hundred twenty-seven patients, 71 (55.9%) males and 56 (44.1%) females, of mean age 36.06 years (range, 16-70; S.D., 13.722), participated in this study. Twenty-five (19.7%) patients had dengue haemorrhagic fever and the remaining 102 (80.3%) had dengue fever. In multivariate analysis, increased age, female sex, the presence of chills, and the absence of rashes were significantly associated with the development of fatigue post-dengue infection. There was no significant association between fatigue and dengue severity.

CONCLUSIONS

This observation represents the first systematic evidence that dengue can result in clinical disease beyond the acute phases of infection. Host factors, such as age and sex may be important in the pathogenesis of this clinical entity.

Symptoms and risk factors of ocular complications following dengue infection

BACKGROUND

Dengue infection can result in severe ocular complications. We prospectively studied the range of ocular symptoms in a cohort of patients with dengue infection.

METHODS

We included adult patients with serologically confirmed dengue infection who received clinical care at the National University Hospital, Singapore. They were assessed for demographic characteristics, ocular symptoms, laboratory parameters and dengue severity. Patients with two or more ocular symptoms were referred to an ophthalmologist and underwent full ophthalmologic examination that included visual acuity, slit-lamp examination and indirect fundoscopic examination. Descriptive and logistic regression analyses were performed and statistical significance was set at p<0.05.

RESULTS

One hundred and fifty-six patients, aged (S.D.) 33.94 (12.7) years, consisting of 89 (57.1%) males and 67 (42.9%) females, participated in this study. They reported ocular symptoms, such as eye strain (30%), retro-ocular pain (20%), blurring of vision (10%), double vision (3%), foreign body sensation (3%), eye flashes (2%) and floaters (1%). Multivariate analysis identified white cell count (odds ratio, OR 0.531; 95% CI 0.292, 0.963) and serum albumin (OR 0.758; 95% confidence intervals, CI 0.618, 0.928) as significant predictors of clinically significant ocular symptoms. The triad of symptoms (eye flashes, floaters and blurring of vision) was highly predictive for the development of retinal hemorrhages (positive predictive value 100%).

CONCLUSIONS

Dengue virus results in a spectrum of ocular manifestations, ranging from non-specific symptoms to severe retinal hemorrhages. Further studies are needed to validate the triad of ocular symptoms as a screening tool for severe ocular complications following dengue infection.

Dengue prevention and 35 years of vector control in Singapore

A vector control program must be based on epidemiologic and entomologic data.

After a 15-year period of low incidence, dengue has reemerged in Singapore in the past decade. We identify potential causes of this resurgence. A combination of lowered herd immunity, virus transmission outside the home, an increase in the age of infection, and the adoption of a case-reactive approach to vector control contribute to the increased dengue incidence. Singapore's experience with dengue indicates that prevention efforts may not be sustainable. For renewed success, Singapore needs to return to a vector control program that is based on carefully collected entomologic and epidemiologic data. Singapore's taking on a leadership role in strengthening disease surveillance and control in Southeast Asia may also be useful in reducing virus importation.

Innate and adaptive cellular immunity in flavivirus-naïve human recipients of a live-attenuated dengue serotype 3 vaccine produced in Vero cells (VDV3)

VDV3, a clonal derivative of the Mahidol live-attenuated dengue 3 vaccine was prepared in Vero cells. Despite satisfactory preclinical evaluation, VDV3 was reactogenic in humans. We explored whether immunological mechanisms contributed to this outcome by monitoring innate and adaptive cellular immune responses for 28 days after vaccination. While no variations were seen in serum IL12 or TNFalpha levels, a high IFNgamma secretion was detected from Day 8, concomitant to IFNalpha, followed by IL10. Specific Th1 and CD8 responses were detected on Day 28, with high IFNgamma/TNFalpha ratios. Vaccinees exhibited very homogeneous class I HLA profiles, and a new HLA B60-restricted CD8 epitope was identified in NS3. We propose that, among other factors, adaptive immunity may have contributed to reactogenicity, even after this primary vaccination. In addition, the unexpected discordance observed between preclinical results and clinical outcome in humans led us to reconsider some of our preclinical acceptance criteria. Lessons learned from these results will help us to pursue the development of safe and immunogenic vaccines.

Acute transverse myelitis following dengue virus infection

The spinal cord is infrequently affected following dengue virus infection. We report a case of transverse myelitis that developed 2 weeks after acute dengue infection and review the literature to elucidate the pathogenesis of spinal cord involvement in dengue infection. We postulate that temporal factors may play a role in the different clinical manifestations, i.e. that acute parainfectious dengue infection presents with flaccid paralysis, whereas late-stage (postinfectious) dengue infection, presents with spastic weakness. Further studies need to be performed to elucidate the mechanisms of spinal neurological damage in dengue.