Seasonal trends of viral respiratory tract infections in the tropics

Modeling and predicting seasonal influenza transmission in warm regions using climatological parameters

Background

Influenza transmission is often associated with climatic factors. As the epidemic pattern varies geographically, the roles of climatic factors may not be unique. Previous in vivo studies revealed the direct effect of winter-like humidity on air-borne influenza transmission that dominates in regions with temperate climate, while influenza in the tropics is more effectively transmitted through direct contact.

Methodology/Principal Findings

Using time series model, we analyzed the role of climatic factors on the epidemiology of influenza transmission in two regions characterized by warm climate: Hong Kong (China) and Maricopa County (Arizona, USA). These two regions have comparable temperature but distinctly different rainfall. Specifically we employed Autoregressive Integrated Moving Average (ARIMA) model along with climatic parameters as measured from ground stations and NASA satellites. Our studies showed that including the climatic variables as input series result in models with better performance than the univariate model where the influenza cases depend only on its past values and error signal. The best model for Hong Kong influenza was obtained when Land Surface Temperature (LST), rainfall and relative humidity were included as input series. Meanwhile for Maricopa County we found that including either maximum atmospheric pressure or mean air temperature gave the most improvement in the model performances.

Conclusions/Significance

Our results showed that including the environmental variables generally increases the prediction capability. Therefore, for countries without advanced influenza surveillance systems, environmental variables can be used for estimating influenza transmission at present and in the near future.

Pandemic (H1N1) 2009 surveillance and prevalence of seasonal influenza, Singapore

On April 25, 2009, Singapore implemented strict containment measures for pandemic (H1N1) 2009 with enhanced surveillance and hospital isolation. In the first month, seasonal influenza, predominantly virus subtype H3N2, was diagnosed for 32% of patients with acute febrile respiratory illness. Our findings underscore the high prevalence of seasonal influenza in Singapore.

Using satellite images of environmental changes to predict infectious disease outbreaks

A strong global satellite imaging system is essential for predicting outbreaks.

Recent events clearly illustrate a continued vulnerability of large populations to infectious diseases, which is related to our changing human-constructed and natural environments. A single person with multidrug-resistant tuberculosis in 2007 provided a wake-up call to the United States and global public health infrastructure, as the health professionals and the public realized that today’s ease of airline travel can potentially expose hundreds of persons to an untreatable disease associated with an infectious agent. Ease of travel, population increase, population displacement, pollution, agricultural activity, changing socioeconomic structures, and international conflicts worldwide have each contributed to infectious disease events. Today, however, nothing is larger in scale, has more potential for long-term effects, and is more uncertain than the effects of climate change on infectious disease outbreaks, epidemics, and pandemics. We discuss advances in our ability to predict these events and, in particular, the critical role that satellite imaging could play in mounting an effective response.

Pandemic Influenza: Potential Contribution to Disease Burden

Records of disease outbreaks resembling influenza date to the writings of Hippocrates (fifth century BPE). Since then, influenza has afflicted humans around the globe. The most severe (“Spanish Flu” 10.1007/978-0-387-78665-0_6287) of three major outbreaks of the twentieth century killed approximately 20–50 million people worldwide. More recently, the global spread of highly pathogenic bird-adapted strain H5N1 is considered a significant pandemic threat. Since 2003, a total of 379 cases and 239 deaths have been reported. This chapter provides an overview of the genetic characteristics of the virus that elucidate its ability to continuously evade a host’s immune system; it describes some of the approaches used to quantify the burden of influenza and discusses their implications for the prevention and containment of future pandemics. The preliminary findings of the studies discussed here suggest that influenza-related burden is highly underestimated in tropical and subtropical regions of the world. This implicates that proper assessment of influenza-related morbidity and mortality worldwide is essential in planning and allocating resources to protect against what could be one of mankind’s most devastating challenges. A summary of learned lessons from past influenza pandemics are described and new intervention strategies aim at curtailing a future pandemic are discussed. More importantly, however, is the discussion of today’s challenges such as antiviral resistance, limited resources in a world that is globally connected and the imminent gap between the capacity (resources available) of developed and developing parts of the world to respond to a pandemic.

Influenza excess mortality from 1950-2000 in tropical Singapore

Introduction

Tropical regions have been shown to exhibit different influenza seasonal patterns compared to their temperate counterparts. However, there is little information about the burden of annual tropical influenza epidemics across time, and the relationship between tropical influenza epidemics compared with other regions.

Methods

Data on monthly national mortality and population was obtained from 1947 to 2003 in Singapore. To determine excess mortality for each month, we used a moving average analysis for each month from 1950 to 2000. From 1972, influenza viral surveillance data was available. Before 1972, information was obtained from serial annual government reports, peer-reviewed journal articles and press articles.

Results

The influenza pandemics of 1957 and 1968 resulted in substantial mortality. In addition, there were 20 other time points with significant excess mortality. Of the 12 periods with significant excess mortality post-1972, only one point (1988) did not correspond to a recorded influenza activity. For the 8 periods with significant excess mortality periods before 1972 excluding the pandemic years, 2 years (1951 and 1953) had newspaper reports of increased pneumonia deaths. Excess mortality could be observed in almost all periods with recorded influenza outbreaks but did not always exceed the 95% confidence limits of the baseline mortality rate.

Conclusion

Influenza epidemics were the likely cause of most excess mortality periods in post-war tropical Singapore, although not every epidemic resulted in high mortality. It is therefore important to have good influenza surveillance systems in place to detect influenza activity.

Norovirus seasonality and the potential impact of climate change

Seasonal variation in norovirus infection is a recognized but poorly understood phenomenon. It is likely to be based on biological, environmental and behavioural factors that regulate transmission, virulence and persistence of the virions in host populations. Understanding the seasonal dependency of norovirus infection is an important step towards understanding its epidemiology, with subsequent implementation of efficient measures of surveillance and control. Whether or not climate change could influence the seasonal patterns of norovirus infection, by impacting on its transmission, geographic distribution and prevalence, has not yet been considered. This review addresses the question.

Using satellite images of environmental changes to predict infectious disease outbreaks

Recent events clearly illustrate a continued vulnerability of large populations to infectious diseases, which is related to our changing human-constructed and natural environments. A single person with multidrug-resistant tuberculosis in 2007 provided a wake-up call to the United States and global public health infrastructure, as the health professionals and the public realized that today's ease of airline travel can potentially expose hundreds of persons to an untreatable disease associated with an infectious agent. Ease of travel, population increase, population displacement, pollution, agricultural activity, changing socioeconomic structures, and international conflicts worldwide have each contributed to infectious disease events. Today, however, nothing is larger in scale, has more potential for long-term effects, and is more uncertain than the effects of climate change on infectious disease outbreaks, epidemics, and pandemics. We discuss advances in our ability to predict these events and, in particular, the critical role that satellite imaging could play in mounting an effective response.

Comparative evaluation of real-time PCR and conventional RT-PCR during a 2 year surveillance for influenza and respiratory syncytial virus among children with acute respiratory infections in Kolkata, India, reveals a distinct seasonality of infection

Acute respiratory tract infections (ARTIs) are one of the most common causes of morbidity and mortality in young children worldwide. Influenza virus and respiratory syncytial virus (RSV) are the predominant aetiological agents during seasonal epidemics, and thus rapid and sensitive molecular tests for screening for such agents and timely identification of epidemics are required. This study compared real-time quantitative PCR (qPCR) with conventional RT-PCR for parallel identification of influenza A virus (IAV) or influenza B virus (IBV) and RSV. A total of 1091 respiratory samples was examined from children with suspected ARTIs between January 2007 and December 2008. Of these, 275 (25.21 %) were positive for either influenza or RSV by qPCR compared with 262 (24 .01%) positive by RT-PCR. Overall, IAV, IBV and RSV were detected in 121 (11.09 %), 59 (5.41 %) and 95 (8.71 %) samples, respectively. In spite of overlapping clinical symptoms, RSV and influenza virus showed distinct seasonal peaks. IAV correlated positively and RSV negatively with rainfall and temperature. No distinct seasonality was observed in IBV infections. This is, to the best of our knowledge, the first report of a systemic surveillance of respiratory viruses with seasonal correlation and prevalence rates from eastern India. This 2 year comparative analysis also confirmed the feasibility of using qPCR in developing countries, which will not only improve the scope for prevention of epidemics, but will also provide crucial epidemiological data from tropical regions.

Influenza epidemiology and characterization of influenza viruses in patients seeking treatment for acute fever in Cambodia

The epidemiology, symptomology, and viral aetiology of endemic influenza remain largely uncharacterized in Cambodia. In December 2006, we established passive hospital-based surveillance to identify the causes of acute undifferentiated fever in patients seeking healthcare. Fever was defined as tympanic membrane temperature >38°C. From December 2006 to December 2008, 4233 patients were screened for influenza virus by real-time reverse-transcriptase polymerase chain reaction (rRT–PCR). Of these patients, 1151 (27·2%) were positive for influenza. Cough (68·8%vs. 50·5%,P<0·0001) and sore throat (55·0%vs. 41·9%,P<0·0001) were more often associated with laboratory-confirmed influenza-infected patients compared to influenza-negative enrollees. A clear influenza season was evident between July and December with a peak during the rainy season. Influenza A and B viruses were identified in 768 (66·3%) and 388 (33·7%) of the influenza-positive population (n=1153), respectively. In December 2008, passive surveillance identified infection of the avian influenza virus H5N1 in a 19-year-old farmer from Kandal province who subsequently recovered. From a subset of diagnostic samples submitted in 2007, 15 A(H1N1), seven A(H3N2) and seven B viruses were isolated. The predominant subtype tested was influenza A(H1N1), with the majority antigenically related to the A/Solomon Island/03/2006 vaccine strain. The influenza A(H3N2) isolates and influenza B viruses analysed were closely related to A/Brisbane/10/2007 or B/Ohio/01/2005 (B/Victoria/2/87-lineage) vaccine strains, respectively. Phylogenetic analysis of the HA1 region of the HA gene of influenza A(H1N1) viruses demonstrated that the Cambodian isolates belonged to clade 2C along with representative H1N1 viruses circulating in SE Asia at the time. These viruses remained sensitive to oseltamivir. In total, our data suggest that viral influenza infections contribute to nearly one-fifth of acute febrile illnesses and demonstrate the importance of influenza surveillance in Cambodia.

Incidence of common respiratory viral infections related to climate factors in hospitalized children in Hong Kong

Hong Kong has a subtropical climate and an influenza seasonality lying approximately mid-way (March–June) between those of the Northern (November–March) and Southern (June–September) hemispheres. Respiratory syncytial virus (RSV) shares a similar seasonality to that of influenza in Hong Kong and is another important respiratory infection of childhood. Daily virus incidence data from public hospitals in Hong Kong's New Territory East Cluster, together with Hong Kong climate data were obtained for 2000–2007. Statistical time-series analysis using monthly time windows showed that influenza A and RSV incidence increased with higher environmental relative humidity, whereas influenza B incidence decreased with higher environmental temperatures. The other climate variables (including vapour pressure as a measure of absolute humidity) were not significantly related to the incidence of these respiratory viruses. Data from this study further reinforces the concept that the relationship between climate factors and respiratory virus incidence differ between subtropical/tropical and temperate countries.

RNA viruses in community-acquired childhood pneumonia in semi-urban Nepal; a cross-sectional study

BACKGROUND

Pneumonia is among the main causes of illness and death in children <5 years of age. There is a need to better describe the epidemiology of viral community-acquired pneumonia (CAP) in developing countries.

METHODS

From July 2004 to June 2007, we examined nasopharyngeal aspirates (NPA) from 2,230 cases of pneumonia (World Health Organization criteria) in children 2 to 35 months old recruited in a randomized trial of zinc supplementation at a field clinic in Bhaktapur, Nepal. The specimens were examined for respiratory syncytial virus (RSV), influenza virus type A (InfA) and B (InfB), parainfluenza virus types 1, 2 and 3 (PIV1, PIV2, and PIV3), and human metapneumovirus (hMPV) using a multiplex reverse transcriptase polymerase chain reaction (PCR) assay.

RESULTS

We identified 919 virus isolates in 887 (40.0%) of the 2,219 NPA specimens with a valid PCR result, of which 334 (15.1%) yielded RSV, 164 (7.4%) InfA, 129 (5.8%) PIV3, 98 (4.4%) PIV1, 93 (4.2%) hMPV, 84 (3.8%) InfB, and 17 (0.8%) PIV2. CAP occurred in an epidemic pattern with substantial temporal variation during the three years of study. The largest peaks of pneumonia occurrence coincided with peaks of RSV infection, which occurred in epidemics during the rainy season and in winter. The monthly number of RSV infections was positively correlated with relative humidity (rs = 0.40, P = 0.01), but not with temperature or rainfall. An hMPV epidemic occurred during one of the three winter seasons and the monthly number of hMPV cases was also associated with relative humidity (rs = 0.55, P = 0.0005).

CONCLUSION

Respiratory RNA viruses were detected from NPA in 40% of CAP cases in our study. The most commonly isolated viruses were RSV, InfA, and PIV3. RSV infections contributed substantially to the observed CAP epidemics. The occurrence of viral CAP in this community seemed to reflect more or less overlapping micro-epidemics with several respiratory viruses, highlighting the challenges of developing and implementing effective public health control measures.

Prevalence and seasonality of influenza-like illness in children, Nicaragua, 2005-2007

Case rates were high and had marked seasonal peaks.

Although information about seasonality and prevalence of influenza is crucial for development of effective prevention and control strategies, limited data exist on the epidemiology of influenza in tropical countries. To better understand influenza in Nicaragua, we performed a prospective 2-year cohort study of influenza-like illness (ILI) involving 4,276 children, 2–11 years of age, in Managua, during April 2005–April 2007. One peak of ILI activity occurred during 2005, in June–July; 2 peaks occurred during 2006, in June–July and November–December. The rate of ILI was 34.8/100 person-years. A household risk factor survey administered to a subset (61%) of participants identified the following risk factors: young age, asthma, and increasing person density in the household. Influenza virus circulation was confirmed during each ILI peak by laboratory testing of a subset of samples. Our findings demonstrate a high rate of ILI, with seasonal peaks, in children in Nicaragua.

Effect of environmental factors on the spatio-temporal patterns of influenza spread

Although spatio-temporal patterns of influenza spread often suggest that environmental factors play a role, their effect on the geographical variation in the timing of annual epidemics has not been assessed. We examined the effect of solar radiation, dew point, temperature and geographical position on the city-specific timing of epidemics in the USA. Using paediatric in-patient data from hospitals in 35 cities for each influenza season in the study period 2000-2005, we determined 'epidemic timing' by identifying the week of peak influenza activity. For each city we calculated averages of daily climate measurements for 1 October to 31 December. Bayesian hierarchical models were used to assess the strength of association between each variable and epidemic timing. Of the climate variables only solar radiation was significantly related to epidemic timing (95% CI -0.027 to -0.0032). Future studies may elucidate biological mechanisms intrinsically linked to solar radiation that contribute to epidemic timing in temperate regions.

Influenza vaccine strain selection and recent studies on the global migration of seasonal influenza viruses

Annual influenza epidemics in humans affect 5-15% of the population, causing an estimated half million deaths worldwide per year [Stohr K. Influenza-WHO cares. Lancet Infectious Diseases 2002;2(9):517]. The virus can infect this proportion of people year after year because the virus has an extensive capacity to evolve and thus evade the immune response. For example, since the influenza A(H3N2) subtype entered the human population in 1968 the A(H3N2) component of the influenza vaccine has had to be updated almost 30 times to track the evolution of the viruses and remain effective. The World Health Organization Global Influenza Surveillance Network (WHO GISN) tracks and analyzes the evolution and epidemiology of influenza viruses for the primary purpose of vaccine strain selection and to improve the strain selection process through studies aimed at better understanding virus evolution and epidemiology. Here we give an overview of the strain selection process and outline recent investigations into the global migration of seasonal influenza viruses.

Severe parainfluenza virus type 2 supraglottitis in an immunocompetent adult host: an unusual cause of a paramyxoviridae viral infection

Parainfluenza virus is a major cause of respiratory illness in humans, manifesting from mild upper respiratory tract infection to bronchiolitis and pneumonia, especially in children. We report - to our knowledge - the first case of a nonimmunocompromised adult patient with human parainfluenza type 2 supraglottitis immediately after returning from China.

Epidemiology

The common cold is the result of an upper respiratory tract infection causing an acute syndrome characterised by a combination of non-specific symptoms, including sore throat, cough, fever, rhinorrhoea, malaise, headache, and myalgia. Respiratory viruses, alone or in combination, are the most common cause. The course f illness can be complicated by bacterial agents, causing pharyngitis or sinusitis, but the are a rare cause of cold and flu-like illnesses (CFLIs). Our understanding of CFLI epidemiology has been enhanced by molecular detection methods, particularly polymerase chain reaction (PCR) testing. PCR has not only improved detection of previously known viruses, but within the last decade has resulted in the detection of many divergent novel respiratory virus species. Human rhinovirus (HRV) infections cause nearly all CFLIs and they can be responsible for asthma and chronic obstructive pulmonary disease exacerbations. HRVs are co-detected with other respiratory viruses in statistically significant patterns, with HRVs occurring in the lowest proportion of co-detections, compared to most other respiratory viruses. Some recently identified rhinoviruses may populate an entirely new putative HRV species; HRV C. Further work is required to confirm a causal role for these newly identified viruses in CFLIs. The burden of illness associated with CFLIs is poorly documented, but where data are available, the impact of CFLIs is considerable. Individual infections, although they do not commonly result in more severe respiratory tract illness, are associated with substantial direct and indirect resource use. The product of frequency and burden for CFLIs is likely to be greater in magnitude than for any other respiratory syndrome, but further work is required to document this. Our understanding of the viral causes of CLFIs, although incomplete, has improved in recent years. Documenting burden is also an important step in progress towards improved control and management of these illnesses.

Influenza-associated morbidity in subtropical Taiwan

OBJECTIVES

The purpose of this study was to assess the characteristics of influenza-associated morbidity in subtropical Taiwan, corresponding to the seasonal patterns, weather, and co-circulation of influenza (sub)types, and other respiratory viruses, where the burden of influenza is poorly quantified.

METHODS

This study applied the virus variation-guided Poisson seasonal regression models to evaluate the impact of epidemic influenza on morbidity in Taiwan for 1999-2006. The models allow for the adjusting of influenza-associated morbidity for factors such as annual trend, seasonality, temperature, relative humidity, influenza A (H1N1), A (H3N2), B, and respiratory syncytial virus.

RESULTS

Influenza-associated morbidity was associated more strongly with temperature than relative humidity. Influenza A (H3N2) was more coordinated with other virus (sub)types than A (H1N1). Type B dominated simultaneously with A (H3N2) at times, whereas A (H3N2) and A (H1N1) rarely dominated simultaneously with each other. Epidemiologically, A (H3N2) appeared to be the dominant subtype (51%), followed by type B (39%) and then A (H1N1) (10%) for influenza-associated morbidity.

CONCLUSIONS

This study suggests that seasonality and influenza (sub)types contribute significantly to influenza morbidity in subtropical Taiwan. This is important for influenza control managers who are involved actively in using epidemic and climate information to achieve influenza-reduction targets in subtropical regions.

Association of respiratory virus activity and environmental factors with the incidence of invasive pneumococcal disease

OBJECTIVES

To correlate the incidence rate of invasive pneumococcal disease (IPD) with fluctuations in respiratory virus activity and environmental factors in Christchurch, New Zealand.

METHODS

Ecological study comparing incidence rates of IPD with incidence rates of respiratory virus detection, meteorologic and air pollution data during 1995-2006. The relationship between annualized monthly rates of IPD and annualized monthly rates of respiratory virus detection and monthly meteorologic recordings and air pollution data was assessed using Spearman's rank correlation coefficient and negative binomial regression analysis.

RESULTS

Incidence rates of IPD were statistically significantly correlated with increasing detection rates of influenza viruses, respiratory syncytial virus (RSV), adenovirus and parainfluenza virus 3. Furthermore, rates of IPD were statistically significantly correlated with decreasing daily temperature, sunshine hours and wind speed, and with increasing air pollution levels and humidity. After regression analysis, the only statistically significant associations in the total population were between influenza virus activity, parainfluenza virus 3 activity and air pollution levels and increased rates of IPD, although RSV activity was associated with increased rates of IPD in children <5 years old.

CONCLUSIONS

Incidence rates of IPD are associated with the increased activity of some respiratory viruses and with air pollution in Christchurch.

Inactivation of influenza A viruses in the environment and modes of transmission: a critical review

OBJECTIVES

The relative importance of airborne, droplet and contact transmission of influenza A virus and the efficiency of control measures depends among other factors on the inactivation of viruses in different environmental media.

METHODS

We systematically review available information on the environmental inactivation of influenza A viruses and employ information on infectious dose and results from mathematical models to assess transmission modes.

RESULTS

Daily inactivation rate constants differ by several orders of magnitude: on inanimate surfaces and in aerosols daily inactivation rates are in the order of 1-10(2), on hands in the order of 10(3). Influenza virus can survive in aerosols for several hours, on hands for a few minutes. Nasal infectious dose of influenza A is several orders of magnitude larger than airborne infectious dose.

CONCLUSIONS

The airborne route is a potentially important transmission pathway for influenza in indoor environments. The importance of droplet transmission has to be reassessed. Contact transmission can be limited by fast inactivation of influenza virus on hands and is more so than airborne transmission dependent on behavioral parameters. However, the potentially large inocula deposited in the environment through sneezing and the protective effect of nasal mucus on virus survival could make contact transmission a key transmission mode.

Human bocavirus infection in a neonatal intensive care unit

Human bocavirus (HBoV) plays a non-insignificant role as a pathogen in respiratory tract diseases in the pediatric population, especially in infants younger than 2 years of age. In this paper, we have described two cases of a possible nosocomial infection in a neonatal intensive care unit being HBoV the sole detected respiratory virus in clinical samples.

Twentieth Century Influenza Pandemics in Singapore

Introduction: Singapore was substantially affected by three 20th Century pandemics. This study describes the course of the pandemics, and the preventive measures adopted. Materials and Methods: We reviewed and researched a wide range of material including peer-reviewed journal articles, Ministry of Health reports, Straits Settlements reports and newspaper articles. Monthly mortality data were obtained from various official sources in Singapore. Results: The 1918 epidemic in Singapore occurred in 2 waves – June to July, and October to November – resulting in up to 3500 deaths. The 1957 epidemic occurred in May, and resulted in widespread morbidity, with 77,000 outpatient attendances in government clinics alone. The 1968 epidemic occurred in August and lasted a few weeks, with outpatient attendances increasing by more than 65%. The preventive measures instituted by the Singapore government during the pandemics included the closure of schools, promulgation of public health messages, setting up of influenza treatment centres, and screening at ports. Students, businessmen and healthcare workers were all severely affected by the pandemics. Conclusions: Tropical cities should be prepared in case of a future pandemic. Some of the preventive measures used in previous pandemics may be applicable during the next pandemic.

Palivizumab for the prophylaxis of respiratory syncytial virus infection

Palivizumab (Synagis®, MedImmune, Inc., USA) is a humanized monoclonal antibody that provides immunoprophylaxis against respiratory syncytial virus (RSV). RSV causes seasonal epidemics (winter or wet-season) of serious lower respiratory tract infections in young infants with subsequent increased frequency of recurrent wheezing during early childhood. Two large, double-blind, placebo-controlled trials including infants at high risk for severe RSV infection showed significant reduction of RSV-related hospitalizations: a 55% reduction in 1502 infants with prematurity and/or bronchopulmonary dysplasia and a 45% reduction in 1287 infants with hemodynamically significant congenital heart disease. Palivizumab proved to be as safe as an intramuscular injection of 15 mg/kg every 30 days for 5 months according to local epidemiology. Recent data suggest further benefits for palivizumab prophylaxis by reduction of recurrent post-RSV wheezing.

Incidence of respiratory viruses among travelers with a febrile syndrome returning from tropical and subtropical areas

Fifty million people are estimated to travel from industrial countries to the tropics annually. In spite of exhaustive studies and widely different diagnosis among returned patients, some cases of febrile illnesses remain without an etiological diagnosis, suggesting that these cases could be due to viral respiratory tract infections. From August 2005 to October 2006, 118 febrile patients without a specific diagnosis in their first visit at the Center for International Health of the Hospital Clínic of Barcelona were included. In all of them, in order to study respiratory viruses, a nasopharyngeal swab was collected. Clinical and radiological features and epidemiological data, as well as other samples for microbiologic studies, were also collected during consultation. Based on the physician's judgment at the time of consultation, patients were classified into four groups: respiratory symptoms (62%), febrile syndrome with nonspecific symptoms (24%), digestive symptoms (10%), and patients presenting both respiratory and digestive symptoms (4%). A pathogen microorganism was detected in 61 patients (52%). Respiratory viruses were detected in 44 out of 118 (37%) travelers included in the study, representing 56% of the patients with respiratory symptoms. The most frequently viruses detected were influenza virus (38%), rhinovirus (23%), adenovirus (9%), and respiratory syncytial virus (9%). Respiratory viruses have been shown to play an important role in imported fever. In light of the fact that international tourism is an increasing phenomenon, new strategies to prevent the spread of respiratory viruses should be considered, specially for influenza when a vaccine is available. J. Med. Virol. 80:711–715, 2008. © 2008 Wiley‐Liss, Inc.

High temperature (30 degrees C) blocks aerosol but not contact transmission of influenza virus

Influenza causes significant morbidity in tropical regions; however, unlike in temperate zones, influenza in the tropics is not strongly associated with a given season. We have recently shown that influenza virus transmission in the guinea pig model is most efficient under cold, dry conditions, which are rare in the tropics. Herein, we report the lack of aerosol transmission at 30 degrees C and at all humidities tested. Conversely, transmission via the contact route was equally efficient at 30 degrees C and 20 degrees C. Our data imply that contact or short-range spread predominates in the tropics and offer an explanation for the lack of a well-defined, recurrent influenza season affecting tropical and subtropical regions of the world.

Effect of meteorological variables on the incidence of respiratory tract infections

OBJECTIVE

The possible effect of the various meteorological variables on the incidence of upper and lower respiratory tract infections (RTIs) has intrigued the scientific community for decades.

METHODS

We performed a retrospective analysis regarding the association between meteorological variables and clinical data for upper and lower RTIs in the area of Attica, Greece.

RESULTS

There was a statistically significant (P<0.001) negative correlation between weekly average temperature with the proportion of weekly house call visits resulting in a diagnosis of upper or lower RTIs 4 days later (R=-0.56 and -0.71 for upper and lower RTIs, respectively) as well as 7 days later (R=-0.57 and -0.71 for upper and lower RTIs, respectively) and during the same day (R=-0.55 and -0.68 for upper and lower RTIs, respectively). In addition, there was a negative correlation between weekly wind chill average (and minimum) temperature as well as a positive correlation of relative humidity with upper and lower RTIs. In contrast, there was no significant correlation between wind speed and upper or lower RTIs.

CONCLUSIONS

The findings suggest that house call visits due to upper and lower RTIs increased as the average temperature in the area of Attica decreased.

Climatic, temporal, and geographic characteristics of respiratory syncytial virus disease in a tropical island population

Respiratory syncytial virus (RSV) is an important cause of morbidity in children worldwide, although data from equatorial regions are limited. We analysed climatic, spatial, and temporal data for children presenting to hospitals in Lombok island, Indonesia with clinical pneumonia. During the study period, 2878 children presented and 741 RSV cases were identified. In multivariate analysis with an 8-day lag, occurrence of rain was associated with 64% higher incidence of RSV disease [incidence rate ratio (IRR) 1.64, 95% confidence interval (CI) 1.13-2.38]. A 1% rise in mean relative humidity and 1 degree C increase in mean air temperature was associated with a 6% (IRR 1.06, 95% CI 1.03-1.10) and 44% (IRR 1.44, 95% CI 1.24-1.66) increase in RSV cases, respectively. Four statistically significant local clusters of RSV pneumonia were identified within the annual island-wide epidemics. This study demonstrates statistical association of monsoon-associated weather in equatorial Indonesia with RSV. Moreover, within the island-wide epidemics, localized RSV outbreaks suggest local factors influence RSV disease.

Climate change and infectious diseases

The worldwide upturn in the occurrence of both new (emerging) and reemerging or spreading infectious diseases highlights the importance of underlying environmental and social conditions as determinants of the generation, spread, and impact of infectious diseases in human populations. Human ecology is undergoing rapid transition. This encompasses urbanization, rising consumerism, changes in working conditions, population aging, marked increases in mobility, changes in culture and behavior, evolving health-care technologies, and other factors. Global climate change is becoming a further, and major, large-scale influence on the pattern of infectious disease transmission. It is likely to become increasingly important over at least the next halfcentury, as the massive, highinertial, and somewhat unpredictable process of climate change continues. The many ways in which climate change does and will influence infectious diseases are subject to a plethora of modifying influences by other factors and processes: constitutional characteristics of hosts, vectors and pathogens; the prevailing ambient conditions; and coexistent changes in other social, economic, behavioral, and environmental factors. This global anthropogenic process, climate change, along with other unprecedented global environmental changes, is beginning to destabilize and weaken the planet's life-support systems. Infectious diseases, unlike other diseases, depend on the biology and behavior—each often climate-sensitive—of two or more parties. Hence, these diseases will be particularly susceptible to changes as the world's climate and its climate-sensitive geochemical and ecological systems undergo change over the coming decades.

Severe bronchiolitis and respiratory syncytial virus among young children in Hawaii

BACKGROUND

Lower respiratory tract infections are a leading cause of hospitalization and mortality among children worldwide. Our objective was to describe the incidence and epidemiology of severe bronchiolitis, respiratory syncytial virus (RSV), and pneumonia among children in Hawaii.

METHODS

Retrospective analysis of the patient-linked hospital discharge data associated with bronchiolitis, RSV, and pneumonia among Hawaii residents younger than 5 years of age during 1997 through 2004 using the Hawaii State Inpatient Database.

RESULTS

During 1997 through 2004, the average annual incidence rates for bronchiolitis, RSV, and pneumonia were 3.8, 2.7, and 6.8 per 1000 children younger than 5 years, respectively. The incidence of each condition was higher for infants younger than 1 year (15.1, 9.8, and 15.9 per 1000 infants, respectively) than the incidence for children 1-4 years of age, and higher for boys compared with girls. The incidence of each condition was highest among Native Hawaiian and other Pacific Islander children compared with children of other race groups living in Hawaii. Most hospitalizations occurred during the months of October through February. Estimated median hospital charges were $4806 (bronchiolitis), $5465 (RSV) and $5240 (pneumonia), with overall average annual charges of $11.5 million.

CONCLUSION

The incidence and hospitalization rates for bronchiolitis, RSV, and pneumonia among children younger than 5 years of age in Hawaii were low; the corresponding hospitalization rates were lower than those for the general U.S. population. However, the hospitalization rates for each condition among Hawaiian and other Pacific Islander children were much higher than those for other race groups or for the U.S. population.

Temperature, humidity, and ultraviolet B radiation predict community respiratory syncytial virus activity

To obtain knowledge of how meteorological conditions affect community epidemics of respiratory syncytial virus (RSV) infection, RSV activity was recorded year-round in 9 cities that differ markedly in geographic location and climate. Local weather conditions were correlated with weekly or monthly RSV cases. Similar reports from other areas varying in climate were also reviewed. Results demonstrated that for all sites combined, weekly RSV activity was related to temperature in a bimodal fashion, with peaks of activity at temperatures more than 24-30 degrees C and at 2-6 degrees C. RSV activity also was greatest at 45-65% relative humidity. RSV activity was inversely related to ultraviolet B (UVB) radiance at 3 sites where this could be analyzed; the fourth site had minimal amounts of annual UVB radiance. At sites with persistently warm temperatures and high humidity, RSV activity was continuous throughout the year, peaking in summer and early autumn. In temperate climates, RSV activity was maximal during winter, correlating with lower temperatures. In areas where temperatures remained cold throughout the year, RSV activity again became nearly continuous. These data led us to conclude that community activity of RSV is substantial when both ambient temperatures and absolute humidity are very high, perhaps reflecting greater stability of RSV in aerosols; transmission of RSV in cooler climates is inversely related to temperature, possibly as a result of increased stability of the virus in secretions in the colder environment; and UVB radiation may inactivate the virus in the environment or influence susceptibility to RSV by altering host resistance.

The relationship of meteorological conditions to the epidemic activity of respiratory syncytial virus

Our aim was to obtain knowledge of how meteorological conditions affect community epidemics of respiratory syncytial virus (RSV) infection. To this end we recorded year-round RSV activity in nine cities that differ markedly in geographic location and climate. We correlated local weather conditions with weekly or monthly RSV cases. We reviewed similar reports from other areas varying in climate. Weekly RSV activity was related to temperature in a bimodal fashion, with peaks of activity at temperatures above 24-30 degrees C and at 2-6 degrees C. RSV activity was also greatest at 45-65% relative humidity. RSV activity was inversely related to UVB radiance at three sites where this could be tested. At sites with persistently warm temperatures and high humidity, RSV activity was continuous throughout the year, peaking in summer and early autumn. In temperate climates, RSV activity was maximal during winter, correlating with lower temperatures. In areas where temperatures remained colder throughout the year, RSV activity again became nearly continuous. Community activity of RSV is substantial when both ambient temperatures and absolute humidity are very high, perhaps reflecting greater stability of RSV in aerosols. Transmission of RSV in cooler climates is inversely related to temperature possibly as a result of increased stability of the virus in secretions in the colder environment. UVB radiation may inactivate virus in the environment, or influence susceptibility to RSV by altering host resistance.

[Human bocavirus infections in Spanish 0-14 year-old: clinical and epidemiological characteristics of an emerging respiratory virus]

INTRODUCTION

In 2005 a new respiratory virus, called human bocavirus (HBoV), was cloned from respiratory samples from Swedish infants and children with lower respiratory tract infections.

OBJECTIVES

To determine whether HBoV has circulated in Spain, estimate the frequency of HBoV infections in patients hospitalized for respiratory infection and describe the clinical and epidemiological characteristics of these patients.

PATIENTS AND METHODS

We performed a descriptive prospective study of confirmed HBoV infections in patients aged < 14 years old, hospitalized for respiratory infections between October 2004 and June 2005. Virologic diagnosis was based on multiple RT-PCR for respiratory syncytial virus (RSV) A and B, influenza A,B, and C, parainfluenza 1-4, adenovirus and rhinovirus; PCR was used for human metapneumovirus (hMPV) and PCR in nasopharyngeal aspirates was used for HBoV. The clinical and epidemiological characteristics of patients were analyzed.

RESULTS

Fifty-two cases of HBoV infection were detected, representing 17.1% (95% CI: 13% a 21%) of patients hospitalized for respiratory infections. HBoV was the third most frequent viral agent after RSV (30%) and rhinovirus (25%). In 39 patients (71.1%) coinfection with another respiratory virus was detected. Fifty percent of the patients were aged less than 13.6 months and 75% were aged less than 2 years. The most frequent diagnoses were recurrent wheezing (55.8%), bronchiolitis (21.2%) and pneumonia (15.4%). Clinical sepsis with petechial exanthema was found in two patients. Fever > 38 degrees C was found in 72.1% and radiological infiltrate in 44%. Hypoxia was present in 55.8 % of the patients. HBoV was isolated in distinct episodes in two patients. Coinfections were similar to simple infections except that hypoxia was more frequent in the former (p = 0.038).

CONCLUSIONS

HBoV is one of the most frequent viruses in severe respiratory infections in patients aged less than 14 years old. Only RSV and rhinovirus are more frequent. Coinfections are highly frequent. Most patients are infants with recurrent wheezing and bronchiolitis.

Understanding the transmission dynamics of respiratory syncytial virus using multiple time series and nested models

The nature and role of re-infection and partial immunity are likely to be important determinants of the transmission dynamics of human respiratory syncytial virus (hRSV). We propose a single model structure that captures four possible host responses to infection and subsequent reinfection: partial susceptibility, altered infection duration, reduced infectiousness and temporary immunity (which might be partial). The magnitude of these responses is determined by four homotopy parameters, and by setting some of these parameters to extreme values we generate a set of eight nested, deterministic transmission models. In order to investigate hRSV transmission dynamics, we applied these models to incidence data from eight international locations. Seasonality is included as cyclic variation in transmission. Parameters associated with the natural history of the infection were assumed to be independent of geographic location, while others, such as those associated with seasonality, were assumed location specific. Models incorporating either of the two extreme assumptions for immunity (none or solid and lifelong) were unable to reproduce the observed dynamics. Model fits with either waning or partial immunity to disease or both were visually comparable. The best fitting structure was a lifelong partial immunity to both disease and infection. Observed patterns were reproduced by stochastic simulations using the parameter values estimated from the deterministic models.

Dynamic patterns of avian and human influenza in east and southeast Asia

The seasonal patterns of human influenza in temperate regions have been well documented; however, much less attention has been paid to patterns of infection in the tropical and subtropical areas of east and southeast Asia. During the period 1997-2006, this region experienced several outbreaks of highly pathogenic avian influenza A (H5N1) in hosts including wild and domestic poultry, human beings, and other mammals. H5N1 is thought to be a likely source of a pandemic strain of human influenza. Incidence of both human influenza and avian influenza in human beings shows evidence of seasonality throughout east and southeast Asia, although the seasonal patterns in tropical and subtropical areas are not as simple or as pronounced as those in temperate regions around the world. The possibility of a human being becoming co-infected with both human and avian strains of influenza is not restricted to a short season, although the risks do appear to be greatest during the winter months.

Travel Recommendations for Older Adults

Older age is an important factor in preparing travelers owing not only to physiologic changes and the increased probability of underlying medical conditions and prescription medications but also to immune status with regard to naturally acquired immunity versus immunization for vaccine-preventable diseases. Cardiovascular events (including myocardial infarctions and cerebrovascular accidents) account for most deaths abroad, followed by injuries. To plan for healthy travel, international travelers should be advised to seek care at least 4 to 6 weeks before departure. Travel medicine is a dynamic field because conditions worldwide are subject to rapid change. Clinicians must maintain a current base of knowledge if they will be regularly advising travelers or must set a threshold for referral to a travel medicine specialist.

The effect of ventilation strategies of child care centers on indoor air quality and respiratory health of children in Singapore

This paper reports the effects of ventilation strategies on indoor air quality (IAQ) and respiratory health of children within 104 child care centers (CCCs) in a hot and humid climate. The CCCs were categorized by ventilation strategies: natural (NV), air-conditioned and mechanically ventilated (ACMV), air-conditioned using split units (AC), and hybrid (NV and AC operated intermittently). The concentration levels of IAQ parameters in NV CCCs are characterized by the influence of the outdoors and good dilution of indoor pollutants. The lower ventilation rates in air-conditioned CCCs result in higher concentrations of occupant-related pollutants but lower outdoor pollutant ingress. This study also revealed lower prevalence for most asthma and allergy, and respiratory symptoms in children attending NV CCCs. In multivariate analyses controlled for the effects of confounders, the risk of current rhinitis among children is significantly higher if they attend mechanically ventilated CCCs compared to NV CCCs. Air-conditioned CCCs were also associated with higher adjusted prevalence ratio of severe phlegm and cough symptoms and lower respiratory illness. Finally, children attending CCCs with hybrid ventilation are at high risk for almost all the respiratory symptoms studied.

PRACTICAL IMPLICATIONS

This large field study indicates that different ventilation strategies employed by child care centers can cause significant variations in the indoor air quality and prevalence of asthma, allergies and respiratory symptoms of attending children. The higher prevalence rates of allergic and respiratory symptoms among young children, whose immune system is still under-developed, in child care centers, whether fully or partially air-conditioned, suggest that ventilation and plausible growth and propagation mechanisms of allergens and infectious agents be further investigated.

Influenza pandemics in Singapore, a tropical, globally connected city

Tropical cities such as Singapore do not have well-defined influenza seasons but have not been spared from influenza pandemics. The 1918 epidemic in Singapore, which was then already a major global trading hub, occurred in 2 waves, June-July, and October-November, and resulted in > or = 2,870 deaths. The excess mortality rate was higher than that for industrialized nations in the Northern Hemisphere but lower than that for less industrialized countries in Asia and Africa. The 1957 epidemic occurred in May and resulted in widespread illness. The 1968 epidemic occurred in August and lasted a few weeks, again with widespread illness. Tropical cities may be affected early in a pandemic and have higher mortality rates. With the increase in travel and trade, a future pandemic may reach a globally connected city early and spread worldwide. Preparedness and surveillance plans must be developed to include the megacities of the tropical world.

Community acquired pneumonia in the tropics

PURPOSE OF REVIEW

Due to the exponential growth of international exchange, millions of travelers are exposed to respiratory pathogens in the tropics and may return ill. Community-acquired pneumonia is one of the more prevalent infections.

RECENT FINDINGS

The acquisition of infections in the tropics, including community-acquired pneumonias, has been described for several centuries. During recent decades some microorganisms have been disclosed as causative of the disease (Legionella pneumophila in 1976 and hantavirus in 1990); other microorganisms are real new pathogens that were not previously demonstrated to have a pathogenic role in humans (e.g. severe acute respiratory syndrome coronavirus producing an outbreak in 2003 and H5N1 avian influenza virus producing an increasing number of human cases over the last few years).

SUMMARY

A number of microorganisms may produce pneumonia in people who live or have traveled to tropical zones. History, including geography and epidemiology, physical exam and complementary workout are precious tools for the diagnosis, therapy and prevention. Exposure to microorganisms in tropical areas may show different patterns. A high index of suspicion, detailed investigation of travel, exposure history of the patient, and a basic understanding of the incubation periods and distribution of the various potential pathogens are imperative for the diagnosis.

Epidemiology, clinical characteristics and antimicrobial resistance patterns of community-acquired pneumonia in 1702 hospitalized children in Singapore

OBJECTIVE AND BACKGROUND

Childhood community-acquired pneumonia (CAP) remains a leading cause of morbidity and mortality worldwide. The features of childhood CAP vary between countries. The aim of this study was to delineate the clinical characteristics, complications, spectrum of pathogens and patterns of antimicrobial resistance associated with hospitalized cases of childhood CAP in Singapore.

METHODS

A retrospective study was conducted of patients discharged from Singapore's only children's hospital over a 3-year period with a principal diagnosis of CAP.

RESULTS

A total of 1702 children, with a median age of 4.2 years (range: 1 month-16.3 years) were enrolled. A pathogen was identifiable in 38.4% of cases, including Mycoplasma pneumoniae in 20.3%, typical respiratory bacteria in 10.3% (64.6%Streptococcus pneumoniae; 21.7% non-typeable Haemophilus influenzae), viruses in 5.5% and mixed bacterial/viral infections in 2%. The majority of M. pneumoniae infections were in school-aged children (>5 years). Severity of infection was greater in CAP caused by typical bacteria, as reflected by length of hospital stay, CRP level, white cell and absolute neutrophil counts. Mortality from typical bacterial infections (8.9%) exceeded that from M. pneumoniae (0.3%) and viral pneumonias (0%) (P < 0.001). Aminopenicillins were often prescribed empirically for suspected S. pneumoniae and H. influenzae infections; however, resistance to these agents was frequently documented among S. pneumoniae (58.5%) and H. influenzae isolates (51%).

CONCLUSION

In Singaporean children hospitalized with CAP, M. pneumoniae is the most commonly identified causative organism, followed by common respiratory viruses, S. pneumoniae and H. influenzae. Streptococcus pneumoniae and H. influenzae are associated with greater severity of infection than other organisms, and have high levels of resistance to commonly prescribed antibiotics.

The management of acute bronchitis in children

Acute bronchitis is one of the most common infections reported in children under 5 years of age, and is a leading cause of hospitalisation. In general practice, confusion surrounds the clinical diagnosis of acute bronchitis, especially when distinguishing it from asthma. The microbiological causes are mostly known, but the contribution of each is much less clear, and they are non-specific in their clinical expression in individual cases. Viral pathogens, particularly respiratory syncytial virus and rhinoviruses are cited as the leading agents in the development of serious episodes, but other pathogens may also be important. This article covers a range of issues surrounding acute bronchitis, including epidemiology and pathogenesis, as well as the management, prevention and treatment of disease in children.

Seasonal infectious disease epidemiology

Seasonal change in the incidence of infectious diseases is a common phenomenon in both temperate and tropical climates. However, the mechanisms responsible for seasonal disease incidence, and the epidemiological consequences of seasonality, are poorly understood with rare exception. Standard epidemiological theory and concepts such as the basic reproductive number R0 no longer apply, and the implications for interventions that themselves may be periodic, such as pulse vaccination, have not been formally examined. This paper examines the causes and consequences of seasonality, and in so doing derives several new results concerning vaccination strategy and the interpretation of disease outbreak data. It begins with a brief review of published scientific studies in support of different causes of seasonality in infectious diseases of humans, identifying four principal mechanisms and their association with different routes of transmission. It then describes the consequences of seasonality for R0, disease outbreaks, endemic dynamics and persistence. Finally, a mathematical analysis of routine and pulse vaccination programmes for seasonal infections is presented. The synthesis of seasonal infectious disease epidemiology attempted by this paper highlights the need for further empirical and theoretical work.

Epidemiology and clinical characteristics of respiratory syncytial virus infections in Jordan

This study was carried out to determine the prevalence, seasonal distribution of RSV, the signs and symptoms associated with it in Jordan. A total of 200 nasopharyngeal aspirates were obtained from hospitalized children (below 2 years old). RSV was detected in 12.5% of patients using direct immunofluorescence technique. Most infections were associated with bronchilolitis, and higher rates of hypoxemia, retractions, tachypnea, hyperinflation and interstitial infiltrates in 1 to 3 months old children. RSV showed a clear temporal periodicity. The epidemic began in December and disappeared in March with a peak of incidence during February 2003 and January 2004. The seasonal distribution showed a significant correlation with temperature, rainfall and relative humidity. This study provides further information on RSV epidemiology which could help in planning of prevention and control programs in Jordan, distinguishing RSV infections on the basis of the clinical picture and considering RSV between December and March each year.

Influenza-related deaths and hospitalizations in Hong Kong: a subtropical area

BACKGROUND

While influenza vaccination has been widely used in developed countries to reduce mortality and morbidity in high-risk populations, the lack of regional data on the health burden of influenza and the uncertainty of the applicability of data from temperate areas have been major impediments to establishing an evidence-based policy on the wider use of influenza vaccine in tropical and subtropical regions of the world.

OBJECTIVES

The aim of this study was to estimate the annual excess deaths and hospitalizations related to influenza in the Hong Kong Special Administrative Region (HKSAR) for the years 1999 and 2000.

STUDY DESIGN AND METHODS

Correlation and regression models were used to estimate the excess deaths and hospitalizations related to influenza in the general population of HKSAR for the years 1999 and 2000, using routinely collected mortality and hospitalization data, and virological laboratory data collected by the HKSAR Influenza Surveillance System.

RESULTS

The annual mean excess numbers of deaths related to influenza in Hong Kong were estimated to be 613 for pneumonia and influenza, and 2302 for respiratory and circulatory diseases. The mean excess numbers of hospitalizations attributable to influenza were 4051 for pneumonia and influenza, and 15,873 for respiratory and circulatory diseases. The crude influenza-related mortality and hospitalization rates in Hong Kong, a subtropical area, exceeded those documented in temperate regions.

CONCLUSIONS

The finding of significant mortality and morbidity related to influenza in a subtropical area is in accordance with the results of previous studies in tropical and subtropical regions. This simple methodology can be used for the development of influenza immunization policy in many developing countries in tropical and subtropical regions. The enormous potential of influenza vaccination in saving lives and reducing suffering warrants serious consideration of the expanded use of influenza vaccine in tropical and subtropical regions.

Influenza-associated deaths in tropical Singapore

Surveillance and annual vaccination are needed for at-risk populations in tropical countries.

We used a regression model to examine the impact of influenza on death rates in tropical Singapore for the period 1996–2003. Influenza A (H3N2) was the predominant circulating influenza virus subtype, with consistently significant and robust effect on mortality rates. Influenza was associated with an annual death rate from all causes, from underlying pneumonia and influenza, and from underlying circulatory and respiratory conditions of 14.8 (95% confidence interval 9.8–19.8), 2.9 (1.0–5.0), and 11.9 (8.3–15.7) per 100,000 person-years, respectively. These results are comparable with observations in the United States and subtropical Hong Kong. An estimated 6.5% of underlying pneumonia and influenza deaths were attributable to influenza. The proportion of influenza-associated deaths was 11.3 times higher in persons age >65 years than in the general population. Our findings support the need for influenza surveillance and annual influenza vaccination for at-risk populations in tropical countries.

Economics of neuraminidase inhibitor stock piling for pandemic influenza, Singapore

We compared strategies for stock piling neuraminidase inhibitors to treat and prevent influenza in Singapore. Cost-benefit and cost-effectiveness analyses, with Monte Carlo simulations, were used to determine economic outcomes. A pandemic in a population of 4.2 million would result in an estimated 525-1,775 deaths, 10,700-38,600 hospitalization days, and economic costs of 0.7 dollars to 2.2 billion Singapore dollars. The treatment-only strategy had optimal economic benefits: stock piles of antiviral agents for 40% of the population would save an estimated 418 lives and 414 million dollars, at a cost of 52.6 million dollars per shelf-life cycle of the stock pile. Prophylaxis was economically beneficial in high-risk subpopulations, which account for 78% of deaths, and in pandemics in which the death rate was >0.6%. Prophylaxis for pandemics with a 5% case-fatality rate would save 50,000 lives and 81 billion dollars. These models can help policymakers weigh the options for pandemic planning.

[Influenza and travelling]

There is a risk for the traveler to acquire an exotic disease when traveling and to introduce it in non-endemic areas after returning. Influenza is a good example of such a disease. The incidence of flu in travelers is unknown. However, numerous outbreaks of flu have been reported in groups of travelers: package tours, pilgrims, elderly people, and travel by plane or cruise ships. Nowadays vaccination against flu is not recommended in travelers unless they belong to groups at risk for flu. Nonetheless vaccination against flu is difficult to apply to travelers due to problems in vaccine availability and inadequacy between vaccine strains and strains responsible for ongoing outbreaks in the opposite hemisphere. This vaccination seems important to travelers because flu may impair their vacation. In addition, it is also interesting for the community if it limits the spread of flu worldwide.

The SIRC model and influenza A

We develop a simple ordinary differential equation model to study the epidemiological consequences of the drift mechanism for influenza A viruses. Improving over the classical SIR approach, we introduce a fourth class (C) for the cross-immune individuals in the population, i.e., those that recovered after being infected by different strains of the same viral subtype in the past years. The SIRC model predicts that the prevalence of a virus is maximum for an intermediate value of R(0), the basic reproduction number. Via a bifurcation analysis of the model, we discuss the effect of seasonality on the epidemiological regimes. For realistic parameter values, the model exhibits a rich variety of behaviors, including chaos and multi-stable periodic outbreaks. Comparison with empirical evidence shows that the simulated regimes are qualitatively and quantitatively consistent with reality, both for tropical and temperate countries. We find that the basins of attraction of coexisting cycles can be fractal sets, thus predictability can in some cases become problematic even theoretically. In accordance with previous studies, we find that increasing cross-immunity tends to complicate the dynamics of the system.

Kawasaki disease: what is the epidemiology telling us about the etiology?

Kawasaki disease (KD) is an important and common inflammatory vasculitis of early childhood with a striking predilection for the coronary arteries. It is the predominant cause of paediatric acquired heart disease in developed countries. Despite 40 years of research, the aetiology of KD remains unknown and consequently there is no diagnostic test and treatment is non-specific and sub-optimal. The consensus is that KD is due to one or more widely distributed infectious agent(s), which evoke an abnormal immunological response in genetically susceptible individuals. The epidemiology of KD has been extensively investigated in many populations and provides much of the supporting evidence for the consensus regarding etiology. These epidemiological data are reviewed here, in the context of the etiopathogenesis. It is suggested that these data provide additional clues regarding the cause of KD and may account for some of the continuing controversies in the field.