Risk factors for human infection with avian influenza A H5N1, Vietnam, 2004

Zoonotic transmission of avian influenza virus (H5N1), Egypt, 2006-2009

During March 2006-March 2009, a total of 6,355 suspected cases of avian influenza (H5N1) were reported to the Ministry of Health in Egypt. Sixty-three (1%) patients had confirmed infections; 24 (38%) died. Risk factors for death included female sex, age > or = 15 years, and receiving the first dose of oseltamivir >2 days after illness onset. All but 2 case-patients reported exposure to domestic poultry probably infected with avian influenza virus (H5N1). No cases of human-to-human transmission were found. Greatest risks for infection and death were reported among women > or = 15 years of age, who accounted for 38% of infections and 83% of deaths. The lower case-fatality rate in Egypt could be caused by a less virulent virus clade. However, the lower mortality rate seems to be caused by the large number of infected children who were identified early, received prompt treatment, and had less severe clinical disease.

Pathogenicity of highly pathogenic avian H5N1 influenza A viruses isolated from humans between 2003 and 2008 in northern Vietnam

Vietnam is one of the countries most affected by highly pathogenic H5N1 influenza A viruses. To evaluate the potential pathogenicity in mammals of H5N1 viruses isolated from humans in Vietnam, we determined the sequences of all eight genes of 22 human isolates collected between 2003 and 2008 and compared their virulence in mice. The isolates were classified into clade 1 and clade 2.3.4 and differed in pathogenicity for mice. Whilst lysine at position 627 of PB2 (PB2-627K) is a critical virulence determinant for clade 2.3.4 viruses, asparagine at position 701 of PB2 and other unknown virulence determinants appear to be involved in the high pathogenicity of clade 1 viruses, warranting further studies to determine the factors responsible for the high virulence of H5N1 viruses in mammals.

Avian influenza A H5N1 virus

Although influenza A viruses of avian origin have long been responsible for influenza pandemics, including the "Spanish flu" pandemic of 1918, human infections caused by avian subtypes of influenza A virus, most notably H5N1, have emerged since the 1990s (H5N1 in 1997; H9N2 in 1999; and H7N7 in 2003). The wide geographic distribution of influenza A H5N1 in avian species, and the number and severity of human infections are unprecedented. Together with the ongoing genetic evolution of this virus, these features make influenza A H5N1 a likely candidate for a future influenza pandemic. This article discusses the epidemiology, pathogenesis, and diagnosis of human infections caused by influenza A H5N1 virus.

Risk factors of poultry outbreaks and human cases of H5N1 avian influenza virus infection in West Java Province, Indonesia

BACKGROUND

The purpose of this study was to determine the association of potential risk factors to the spread and maintenance of the highly pathogenic avian influenza (HPAI) H5N1 virus in poultry and humans at the district level in West Java Province, Indonesia.

METHODS

The association of demography and environmental risk factors including poultry density, human density, road density, percentage of paddy field, and percentage of swamp, dyke and pond with both HPAI human cases and HPAI outbreaks in poultry were assessed using a descriptive epidemiological design. We also assessed the association of HPAI outbreaks in poultry with HPAI human cases. Poisson regression (generalized linear modeling and generalized estimating equations) was used to analyze the data corrected for over-dispersion.

RESULTS

There were 794 HPAI outbreaks in poultry covering 24 of the 25 districts in our study during 2003-2008 and 34 HPAI human cases involving 12 districts during 2005-2008. We found that two risk factors--poultry density and road density--had a statistically significant correlation with the number of HPAI outbreaks in poultry. The number of poultry outbreaks had a negative association with poultry density (29% effect) and a positive association with road density (67% effect). The number of human cases was significantly associated with the number of poultry outbreaks (34% effect), but with none of the other risk factors considered.

CONCLUSIONS

We conclude that the most effective way to prevent human HPAI cases is to intervene directly in the poultry sector. Our study further suggests that implementing preventive measures in backyard chicken farming and limiting transport of live poultry and their products are promising options to this end.

What is the evidence of a role for host genetics in susceptibility to influenza A/H5N1?

The apparent family clustering of avian influenza A/H5N1 has led several groups to postulate the existence of a host genetic influence on susceptibility to A/H5N1, yet the role of host factors on the risk of A/H5N1 disease has received remarkably little attention compared to the efforts focused on viral factors. We examined the epidemiological patterns of human A/H5N1 cases, their possible explanations, and the plausibility of a host genetic effect on susceptibility to A/H5N1 infection. The preponderance of familial clustering of cases and the relative lack of non-familial clusters, the occurrence of related cases separated by time and place, and the paucity of cases in some highly exposed groups such as poultry cullers, are consistent with a host genetic effect. Animal models support the biological plausibility of genetic susceptibility to A/H5N1. Although the evidence is circumstantial, host genetic factors are a parsimonious explanation for the unusual epidemiology of human A/H5N1 cases and warrant further investigation.

Knowledge and anticipated attitudes of the community about bird flu outbreak in Turkey, 2007-2008: a survey-based descriptive study

OBJECTIVE

To determine factors associated with knowledge and anticipated attitudes to a foreseen avian influenza outbreak in a high-risk population from a Turkish remote region.

METHODS

A random, cross-sectional face-to-face survey of 1,046 Turkish adults.

RESULTS

The proportion of participants concerned about contracting the virus was significantly lower amongst the less educated and rural located respondents. Significantly more rural than urban located participants declared not complying with quarantine policies and not handing out their poultry in case of an influenza outbreak. Factors associated with protective behaviours were higher level of education, urban location, not performing backyard farming of poultry, and preferring ready-to-eat products.

CONCLUSIONS

Preparedness against bird flu endemic in remote regions could be hindered by factors, such as low levels of education and economic dependence on small-scale backyard farming. The baseline data collected in this survey will be useful in monitoring changes over time in the population's perceptions of threat, and its attitude towards compliance with specific public health recommendations.

Knowledge, attitudes and practices (KAP) relating to avian influenza in urban and rural areas of China

BACKGROUND

Studies have revealed that visiting poultry markets and direct contact with sick or dead poultry are significant risk factors for H5N1 infection, the practices of which could possibly be influenced by people's knowledge, attitudes and practices (KAPs) associated with avian influenza (AI). To determine the KAPs associated with AI among the Chinese general population, a cross-sectional survey was conducted in China.

METHODS

We used standardized, structured questionnaires distributed in both an urban area (Shenzhen, Guangdong Province; n = 1,826) and a rural area (Xiuning, Anhui Province; n = 2,572) using the probability proportional to size (PPS) sampling technique.

RESULTS

Approximately three-quarters of participants in both groups requested more information about AI. The preferred source of information for both groups was television. Almost three-quarters of all participants were aware of AI as an infectious disease; the urban group was more aware that it could be transmitted through poultry, that it could be prevented, and was more familiar with the relationship between AI and human infection. The villagers in Xiuning were more concerned than Shenzhen residents about human AI viral infection. Regarding preventative measures, a higher percentage of the urban group used soap for hand washing whereas the rural group preferred water only. Almost half of the participants in both groups had continued to eat poultry after being informed about the disease.

CONCLUSIONS

Our study shows a high degree of awareness of human AI in both urban and rural populations, and could provide scientific support to assist the Chinese government in developing strategies and health-education campaigns to prevent AI infection among the general population.

[Avian influenza in children]

The emerging A (H5N1) influenza virus is a clear pandemic threat. This avian virus is responsible for the largest epizootic event described so far. To date, 423 humans have been infected. In humans, this virus is responsible for a rapidly developing pneumonia, with an acute respiratory failure leading to death in 60% of the infected cases. The multi-organ failure seems to result from the cytokine storm. A (H5N1) infections are mainly reported in children and young adults. Different hypotheses have been proposed to explain this specific feature, including the lack of control of cytokine release during infection, or the presence of alternative cellular receptors. The specific susceptibility of children is more likely to be related with exposure to infected birds than to specific immune or physiological factors. The proper and efficient management of A (H5N1) infection is possible nowadays. Today, the pandemic threat is real and may be imminent because of the circulation of new A (H1N1). However, an active surveillance of A (H5N1) virus remains very important to monitor the genetic evolution of this changing and virulent virus.

Influenza A: From highly pathogenic H5N1 to pandemic 2009 H1N1. Epidemiology and clinical features

The last decade has seen the emergence of two new influenza A subtypes and they have become a cause of concern for the global community. These are the highly pathogenic H5N1 influenza A virus (H5N1) and the Pandemic 2009 influenza H1N1 virus. Since 2003 the H5N1 virus has caused widespread disease and death in poultry, mainly in south East Asia and Africa. In humans the number of cases infected with this virus is few but the mortality has been about 60%. Most patients have presented with severe pneumonia and acute respiratory distress syndrome. The second influenza virus, the pandemic H1N1 2009, emerged in Mexico in March this year. This virus acquired the ability for sustained human to human spread and within a few months spread throughout the world and infected over 4 lakh individuals. The symptoms of infection with this virus are similar to seasonal influenza but it currently affecting younger individuals more often. Fortunately the mortality has been low. Both these new influenza viruses are currently circulating and have different clinical and epidemiological characteristics.

Vaccination of poultry workers: delivery and uptake of seasonal influenza immunization

Avian influenza is a highly infectious disease in poultry and although the risk of human infection is low, concerns exist that it could evolve into a new human strain of pandemic potential if reassortment with a human influenza virus occurs. In January 2007, the UK government introduced a programme to vaccinate poultry workers to reduce the potential of such an event. This study evaluates the delivery, uptake and costs of the programme in three counties of England. A questionnaire survey was completed by consultants in public health in all the Primary Care Trusts in Norfolk, Suffolk and Cambridgeshire in May 2007. The delivery of the programme varied between Primary Care Trusts, including being delivered in some cases by clinics in primary care, by general practitioners and occupational health services in others. The uptake of vaccination was low ranging from 7% to 29% at a cost of £29 to £132 per person vaccinated. Vaccination of poultry workers as a public health measure to prevent an influenza pandemic is likely to be ineffective with the level of coverage found in this evaluation in our region.

Avian influenza--a review for doctors in travel medicine

First identified in humans in Hong Kong, influenza A/H5N1, known commonly as avian influenza, has caused human disease in 15 countries around the world. Although the current number of confirmed patients is tiny compared to seasonal and the recently emerged H1N1 'swine' influenza, H5N1 remains a candidate for the next highly pathogenic influenza pandemic. Currently, H5N1 has very limited ability to spread from person-to-person but this may change because of mutation or reassortment with other influenza viruses leading to an influenza pandemic with high mortality. If this occurs travellers are likely to be affected and travel medicine doctors will need to consider avian influenza in returning febrile travellers. The early clinical features may be dismissed easily as 'the flu' resulting in delayed treatment. Treatment options are limited. Oral oseltamivir alone has been the most commonly used drug but mortality remains substantial, up to 80% in Indonesia. Intravenous peramivir has been filed for registration and IV zanamivir is being developed. This review will focus on the epidemiological and clinical features of influenza A/H5N1 avian influenza and will highlight aspects relevant to travel medicine doctors.

Influenza in outpatient ILI case-patients in national hospital-based surveillance, Bangladesh, 2007-2008

BACKGROUND

Recent population-based estimates in a Dhaka low-income community suggest that influenza was prevalent among children. To explore the epidemiology and seasonality of influenza throughout the country and among all age groups, we established nationally representative hospital-based surveillance necessary to guide influenza prevention and control efforts.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted influenza-like illness and severe acute respiratory illness sentinel surveillance in 12 hospitals across Bangladesh during May 2007-December 2008. We collected specimens from 3,699 patients, 385 (10%) which were influenza positive by real time RT-PCR. Among the sample-positive patients, 192 (51%) were type A and 188 (49%) were type B. Hemagglutinin subtyping of type A viruses detected 137 (71%) A/H1 and 55 (29%) A/H3, but no A/H5 or other novel influenza strains. The frequency of influenza cases was highest among children aged under 5 years (44%), while the proportions of laboratory confirmed cases was highest among participants aged 11-15 (18%). We applied kriging, a geo-statistical technique, to explore the spatial and temporal spread of influenza and found that, during 2008, influenza was first identified in large port cities and then gradually spread to other parts of the country. We identified a distinct influenza peak during the rainy season (May-September).

CONCLUSIONS/SIGNIFICANCE

Our surveillance data confirms that influenza is prevalent throughout Bangladesh, affecting a wide range of ages and causing considerable morbidity and hospital care. A unimodal influenza seasonality may allow Bangladesh to time annual influenza prevention messages and vaccination campaigns to reduce the national influenza burden. To scale-up such national interventions, we need to quantify the national rates of influenza and the economic burden associated with this disease through further studies.

Effectiveness and cost-effectiveness of expanded antiviral prophylaxis and adjuvanted vaccination strategies for an influenza A (H5N1) pandemic

BACKGROUND

The pandemic potential of influenza A (H5N1) virus is a prominent public health concern of the 21st century.

OBJECTIVE

To estimate the effectiveness and cost-effectiveness of alternative pandemic (H5N1) mitigation and response strategies.

DESIGN

Compartmental epidemic model in conjunction with a Markov model of disease progression.

DATA SOURCES

Literature and expert opinion.

TARGET POPULATION

Residents of a U.S. metropolitan city with a population of 8.3 million.

TIME HORIZON

Lifetime.

PERSPECTIVE

Societal.

INTERVENTIONS

3 scenarios: 1) vaccination and antiviral pharmacotherapy in quantities similar to those currently available in the U.S. stockpile (stockpiled strategy), 2) stockpiled strategy but with expanded distribution of antiviral agents (expanded prophylaxis strategy), and 3) stockpiled strategy but with adjuvanted vaccine (expanded vaccination strategy). All scenarios assumed standard nonpharmaceutical interventions.

OUTCOME MEASURES

Infections and deaths averted, costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness.

RESULTS OF BASE-CASE ANALYSIS

Expanded vaccination was the most effective and cost-effective of the 3 strategies, averting 68% of infections and deaths and gaining 404 030 QALYs at $10 844 per QALY gained relative to the stockpiled strategy.

RESULTS OF SENSITIVITY ANALYSIS

Expanded vaccination remained incrementally cost-effective over a wide range of assumptions.

LIMITATIONS

The model assumed homogenous mixing of cases and contacts; heterogeneous mixing would result in faster initial spread, followed by slower spread. We did not model interventions for children or older adults; the model is not designed to target interventions to specific groups.

CONCLUSION

Expanded adjuvanted vaccination is an effective and cost-effective mitigation strategy for an influenza A (H5N1) pandemic. Expanded antiviral prophylaxis can help delay the pandemic while additional strategies are implemented.

PRIMARY FUNDING SOURCE

National Institutes of Health and Agency for Healthcare Research and Quality.

Effectiveness and cost-effectiveness of vaccination against pandemic influenza (H1N1) 2009

BACKGROUND

Decisions on the timing and extent of vaccination against pandemic (H1N1) 2009 virus are complex.

OBJECTIVE

To estimate the effectiveness and cost-effectiveness of pandemic influenza (H1N1) vaccination under different scenarios in October or November 2009.

DESIGN

Compartmental epidemic model in conjunction with a Markov model of disease progression.

DATA SOURCES

Literature and expert opinion.

TARGET POPULATION

Residents of a major U.S. metropolitan city with a population of 8.3 million.

TIME HORIZON

Lifetime.

PERSPECTIVE

Societal.

INTERVENTIONS

Vaccination in mid-October or mid-November 2009.

OUTCOME MEASURES

Infections and deaths averted, costs, quality-adjusted life-years (QALYs), and incremental cost-effectiveness.

RESULTS OF BASE-CASE ANALYSIS

Assuming each primary infection causes 1.5 secondary infections, vaccinating 40% of the population in October or November would be cost-saving. Vaccination in October would avert 2051 deaths, gain 69 679 QALYs, and save $469 million compared with no vaccination; vaccination in November would avert 1468 deaths, gain 49 422 QALYs, and save $302 million.

RESULTS OF SENSITIVITY ANALYSIS

Vaccination is even more cost-saving if longer incubation periods, lower rates of infectiousness, or increased implementation of nonpharmaceutical interventions delay time to the peak of the pandemic. Vaccination saves fewer lives and is less cost-effective if the epidemic peaks earlier than mid-October.

LIMITATIONS

The model assumed homogenous mixing of case-patients and contacts; heterogeneous mixing would result in faster initial spread, followed by slower spread. Additional costs and savings not included in the model would make vaccination more cost-saving.

CONCLUSION

Earlier vaccination against pandemic (H1N1) 2009 prevents more deaths and is more cost-saving. Complete population coverage is not necessary to reduce the viral reproductive rate sufficiently to help shorten the pandemic.

PRIMARY FUNDING SOURCE

Agency for Healthcare Research and Quality and National Institute on Drug Abuse.

Live poultry exposure, Guangzhou, China, 2006

BACKGROUND

Live poultry in wet markets and backyard husbandry comprise potentially major exposure sources for human cases of H5N1 avian influenza. In China the magnitude of risk from this exposure is unknown. We estimated exposure based on self-reported behavior.

METHODS

In January-March 2006, 1550 face-to-face interviews derived from stratified cluster and randomized within-household sampling provided data on live poultry exposure in Guangzhou, China based on self-reported buying and touching patterns. Standardized exposures were calculated and after adjustment extrapolated to the urban population.

RESULTS

The results, adjusted for gender, showed that 1,248/1,550 (80%, 95% Confidence Limits 78-82%) respondents reported an average of 20.5 live chicken purchases/household annually. Of those buying poultry 33% touched poultry before buying while 20% of households raised live poultry. Total exposures from wet market and backyard husbandry in Guangzhou greatly exceed those of adjacent Hong Kong (15,280,000 e/year vs. 1,110,900 e/year). Backyard exposure frequency likely exceeds that from live poultry retail, but purchases were more prevalent and hence comprise a significant risk source.

CONCLUSION

The Guangzhou population faces risks from the high prevalence of exposures during purchase and poultry rearing. Better management for raising and selling poultry in Guangzhou is needed.

A primer on strategies for prevention and control of seasonal and pandemic influenza

The United States has made considerable progress in pandemic preparedness. Limited attention, however, has been given to the challenges faced by populations that will be at increased risk of the consequences of the pandemic, including challenges caused by societal, economic, and health-related factors. This supplement to the American Journal of Public Health focuses on the challenges faced by at-risk and vulnerable populations in preparing for and responding to an influenza pandemic. Here, we provide background information for subsequent articles throughout the supplement. We summarize (1) seasonal influenza epidemiology, transmission, clinical illness, diagnosis, vaccines, and antiviral medications; (2) H5N1 avian influenza; and (3) pandemic influenza vaccines, antiviral medications, and nonpharmaceutical interventions.

Pseudoparticle neutralization is a reliable assay to measure immunity and cross-reactivity to H5N1 influenza viruses

The standard serological methods present limitations for the measurement of immunity against H5N1 influenza strains. The hemagglutination inhibition (HI) assay lacks sensitivity and requires standardization, while the viral micro-neutralization (MN) assay needs handling of live virus. We produced pseudoparticles expressing hemagglutinin from clades 1 or 2 H5N1 in order to measure neutralizing antibodies in human sera after prime-boost vaccination with plain or MF59-adjuvanted H5N1 clade 1 subunit vaccines. Titers measured by pseudoparticle neutralization (PPN) assay significantly correlated with those measured by HI, single radial haemolysis or MN, with a PPN titer of 1:357 corresponding to an MN titer of 1:80. Notably, results from the PPN assay, confirm that MF59-H5N1 vaccine induces potent and long-lasting neutralizing antibody responses not only against the vaccine strain, but also against several heterologous clade 2 strains. Overall, the PPN assay represents a valid alternative to conventional serological methods for the evaluation of H5N1 vaccine immunogenicity.

Seroprevalence of antibodies to avian influenza virus A (H5N1) among residents of villages with human cases, Thailand, 2005

No evidence of influenza virus A (H5N1) neutralizing antibodies was found in residents of 4 villages where human cases had occurred the previous year.

In 2005, we assessed the seroprevalence of neutralizing antibodies to avian influenza virus A (H5N1) among 901 residents of 4 villages in Thailand where at least 1 confirmed human case of influenza (H5N1) had occurred during 2004. Although 68.1% of survey participants (median age 40 years) were exposed to backyard poultry and 25.7% were exposed to sick or dead chickens, all participants were seronegative for influenza virus (H5N1).

Association between human cases and poultry outbreaks of highly pathogenic avian influenza in Vietnam from 2003 to 2007: a nationwide study

This study quantifies the spatio-temporal association between outbreaks of highly pathogenic avian influenza H5N1 in domestic poultry (n = 3050) and human cases (n = 99) in Vietnam during 2003-2007, using rare events logistic regression. After adjusting for the effect of known confounders, the odds of a human case being reported to authorities increased by a factor of 6.17 [95% confidence interval (CI) 3.33-11.38] and 2.48 (95% CI 1.20 - 5.13) if poultry outbreaks were reported in the same district 1 week and 4 weeks later respectively. When jointly considering poultry outbreaks in the same and neighbouring districts, occurrence of poultry outbreaks in the same week, 1-week later, and 4 weeks later increased the odds of a human case by a factor of 2.75 (95% CI 1.43-5.30), 2.56 (95% CI 1.31-5.00) and 2.70 (95% CI 1.56-4.66) respectively. Our study found evidence of different levels of association between human cases and poultry outbreaks in the North and the South of the country. When considering the 9-week interval extending from 4 weeks before to 4 weeks after the week of reporting a human case, in the South poultry outbreaks were recorded in 58% of cases in the same district and 83% of cases in either the same or neighbouring districts, whereas in the North the equivalent results were only 23% and 42%. The strength of the association between human and poultry cases declined over the study period. We conclude that owner reporting of clinical disease in poultry needs to be enhanced by targeted agent-specific surveillance integrated with preventive and other measures, if human exposure is to be minimized.

Risk factors for human illness with avian influenza A (H5N1) virus infection in China

BACKGROUND

In China, 30 human cases of avian influenza A (H5N1) virus infection were identified through July 2008. We conducted a retrospective case-control study to identify risk factors for influenza H5N1 disease in China.

METHODS

A questionnaire about potential influenza H5N1 exposures was administered to 28 patients with influenza H5N1 and to 134 randomly selected control subjects matched by age, sex, and location or to proxies. Conditional logistic regression analyses were performed.

RESULTS

Before their illness, patients living in urban areas had visited wet poultry markets, and patients living in rural areas had exposure to sick or dead backyard poultry. In multivariable analyses, independent risk factors for influenza H5N1 were direct contact with sick or dead poultry (odds ratio [OR], 506.6 [95% confidence interval {CI}, 15.7-16319.6]; P<.001), indirect exposure to sick or dead poultry (OR, 56.9 [95% CI, 4.3-745.6]; P=.002), and visiting a wet poultry market (OR, 15.4 [95% CI, 3.0-80.2]; P=.001).

CONCLUSIONS

To prevent human influenza H5N1 in China, the level of education about avoiding direct or close exposures to sick or dead poultry should be increased, and interventions to prevent the spread of influenza H5N1 at live poultry markets should be implemented.

Human avian influenza A (H5N1) virus infection in China

Highly pathogenic influenza A (H5N1) virus causes a widespread poultry deaths worldwide. The first human H5N1 infected case was reported in Hong Kong Special Administrative Region of China in 1997. Since then, the virus re-emerged in 2003 and continues to infect people worldwide. Currently, over 400 human infections have been reported in more than 15 countries and mortality rate is greater than 60%. H5N1 viruses still pose a potential pandemic threat in the future because of the continuing global spread and evolution. Here, we summarize the epidemiological, clinical and virological characteristics of human H5N1 infection in China monitored and identified by our national surveillance systems.

Highly pathogenic H5N1 avian influenza virus: cause of the next pandemic?

Since 1997, when human infections with a highly pathogenic (HP) avian influenza A virus (AIV) subtype H5N1 - previously infecting only birds - were identified in a Hong Kong outbreak, global attention has focused on the potential for this virus to cause the next pandemic. From December 2003, an unprecedented H5N1 epizootic in poultry and migrating wild birds has spread across Asia and into Europe, the Middle East, and Africa. Humans in close contact with sick poultry and on rare occasion with other infected humans, have become infected. As of early March 2007, 12 countries have reported 167 deaths among 277 laboratory-confirmed human infections to WHO. WHO has declared the world to be in Phase 3 of a Pandemic Alert Period. This paper reviews the evolution of HP AIV H5N1, molecular changes that enable AIVs to infect and replicate in human cells and spread efficiently from person-to-person, and strategies to prevent the emergence of a pandemic virus.

Emerging influenza virus: a global threat

Since 1918, influenza virus has been one of the major causes of morbidity and mortality, especially among young children. Though the commonly circulating strain of the virus is not virulent enough to cause mortality, the ability of the virus genome to mutate at a very high rate may lead to the emergence of a highly virulent strain that may become the cause of the next pandemic. Apart from the influenza virus strain circulating in humans (H1N1 and H3N2), the avian influenza H5N1 H7 and H9 virus strains have also been reported to have caused human infections, H5N1 H7 and H9 have shown their ability to cross the species barrier from birds to humans and further replicate in humans. This review addresses the biological and epidemiological aspects of influenza virus and efforts to have a control on the virus globally.

Evidence of previous avian influenza infection among US turkey workers

The threat of an influenza pandemic is looming, with new cases of sporadic avian influenza infections in man frequently reported. Exposure to diseased poultry is a leading risk factor for these infections. In this study, we used logistic regression to investigate serological evidence of previous infection with avian influenza subtypes H4, H5, H6, H7, H8, H9, H10, and H11 among 95 adults occupationally exposed to turkeys in the US Midwest and 82 unexposed controls. Our results indicate that farmers practising backyard, organic or free-ranging turkey production methods are at an increased risk of infection with avian influenza. Among these farmers, the adjusted odds ratios (ORs) for elevated microneutralization assay titres against avian H4, H5, H6, H9, and H10 influenza strains ranged between 3.9 (95% CI 1.2-12.8) and 15.3 (95% CI 2.0-115.2) when compared to non-exposed controls. The measured ORs were adjusted for antibody titres against human influenza viruses and other exposure variables. These data suggest that sometime in their lives, the workers had been exposed to low pathogenicity avian influenza viruses. These findings support calls for inclusion of agricultural workers in priority groups in pandemic influenza preparedness efforts. These data further support increasing surveillance and other preparedness efforts to include not only confinement poultry facilities, but more importantly, also small scale farms.

Avian influenza risk perception and live poultry purchase in Guangzhou, China, 2006

Human H5N1 highly pathogenic avian influenza (HPAI) infection is associated with intimate exposure to live poultry. Perceptions of risk can modify behaviors, influencing actual exposure. However, greater hazard is not necessarily followed by perception of greater risk and more precautionary behavior because self-serving cognitive biases modulate precautionary and hazardous behaviors. We examined risk perception associated with avian influenza. A total of 1,550 face-to-face within-household interviews and 1,760 telephone interviews were derived to study avian influenza risk perception and live poultry use in Guangzhou and Hong Kong, respectively. Chi-square and Mann-Whitney tests assessed bivariate associations and risk distributions, respectively, and fully adjusted multivariate logistic models determined independent risk associations. Relative to Hong Kong, perceived "generalized" risk from buying live poultry (GZ, 58%, 95% confidence interval 55-60% vs. HK, 41%, 39-43%; chi(2)= 86.95, df = 1, p < 0.001) and perceived self/family risk from buying (z =-2.092, p = 0.036) were higher in Guangzhou. Higher perceived "generalized" risk was associated with not buying live poultry (OR = 0.65, 0.49-0.85), consistent with the pattern seen in Hong Kong, while perceived higher self/family risk was associated with buying ("likely/very likely/certain" OR = 1.74, 1.18-2.59); no such association was seen in Hong Kong. Multivariate adjustment indicated older age was associated with buying live poultry in Guangzhou (OR = 2.91, 1.36-6.25). Guangzhou respondents perceived greater risk relative to Hong Kong. Buying live poultry was associated with perceptions of less "generalized" risk but more self/family risk. Higher generalized risk was associated with fewer live poultry purchases, suggesting generalized risk may be a useful indicator of precautionary HPAI risk behavior.

Avian influenza outbreaks in chickens, Bangladesh

To determine the epidemiology of outbreaks of avian influenza A virus (subtypes H5N1, H9N2) in chickens in Bangladesh, we conducted surveys and examined virus isolates. The outbreak began in backyard chickens. Probable sources of infection included egg trays and vehicles from local live bird markets and larger live bird markets.

Knowledge, attitudes, and practices regarding avian influenza (H5N1), Afghanistan

From February through April 2007, avian influenza (H5N1) was confirmed in poultry in 4 of 34 Afghan provinces. A survey conducted in 2 affected and 3 unaffected provinces found that greater knowledge about reducing exposure was associated with higher socioeconomic status, residence in affected provinces, and not owning backyard poultry.

Influenza A H5N1 clade 2.3.4 virus with a different antiviral susceptibility profile replaced clade 1 virus in humans in northern Vietnam

Background

Prior to 2007, highly pathogenic avian influenza (HPAI) H5N1 viruses isolated from poultry and humans in Vietnam were consistently reported to be clade 1 viruses, susceptible to oseltamivir but resistant to amantadine. Here we describe the re-emergence of human HPAI H5N1 virus infections in Vietnam in 2007 and the characteristics of the isolated viruses.

Methods and Findings

Respiratory specimens from patients suspected to be infected with avian influenza in 2007 were screened by influenza and H5 subtype specific polymerase chain reaction. Isolated H5N1 strains were further characterized by genome sequencing and drug susceptibility testing. Eleven poultry outbreak isolates from 2007 were included in the sequence analysis. Eight patients, all of them from northern Vietnam, were diagnosed with H5N1 in 2007 and five of them died. Phylogenetic analysis of H5N1 viruses isolated from humans and poultry in 2007 showed that clade 2.3.4 H5N1 viruses replaced clade 1 viruses in northern Vietnam. Four human H5N1 strains had eight-fold reduced in-vitro susceptibility to oseltamivir as compared to clade 1 viruses. In two poultry isolates the I117V mutation was found in the neuraminidase gene, which is associated with reduced susceptibility to oseltamivir. No mutations in the M2 gene conferring amantadine resistance were found.

Conclusion

In 2007, H5N1 clade 2.3.4 viruses replaced clade 1 viruses in northern Vietnam and were susceptible to amantadine but showed reduced susceptibility to oseltamivir. Combination antiviral therapy with oseltamivir and amantadine for human cases in Vietnam is recommended.

Avian influenza: the tip of the iceberg

For some years now, we have been living with the fear of an impending pandemic of avian influenza (AI). Despite the recognition, in 1996, of the global threat posed by the highly pathogenic H5N1 influenza virus found in farmed geese in Guangdong Province, China, planning for the anticipated epidemic remains woefully inadequate; this is especially true in developing countries such as Saudi Arabia. These deficiencies became obvious in 1997, with the outbreak of AI in the live animal markets in Hong Kong that led to the transmission of infection to 18 humans with close contact with diseased birds; there were six reported deaths. In 2003, with the reemergence of H5N1 (considered the most likely AI virus) in the Republic of Korea and its subsequent spread to Thailand, Vietnam, Hong Kong and China. Many countries started aggressively making preparations to meet the threat. The pressure for real action from governments has increased. Most developed countries have requested increased funding for the search for a more effective vaccine, for stockpiling possibly helpful antiviral drugs, and for intensifying domestic and global surveillance. Most countries, however, continue to be inadequately prepared for such an epidemic, especially with regard to animal surveillance in the farm market and surveillance among migratory birds. Even now, most countries do not have the ability to detect disease among humans in the early stages of an outbreak nor do most hospitals comply with effective infection control measures that could curtail the spread of the virus in the early stages of an epidemic. In Saudi Arabia we are rapidly implementing many of these measures.

Frequency and patterns of contact with domestic poultry and potential risk of H5N1 transmission to humans living in rural Cambodia

BACKGROUND

Since 2004, H5N1 outbreaks have been recurrent in domestic poultry and humans in Cambodia. To date, seven human cases (100% CFR) and 22 outbreaks in poultry have been confirmed. Household ownership of backyard poultry (FAO Sector 4 poultry production) in rural Cambodia is high. An understanding of the extent and frequency of poultry handing behaviors in these settings is necessary to assess the risk associated with different practices and to formulate sensible recommendations to mitigate this risk. We collected new data from six geographic regions to examine patterns of human contact with poultry among rural farmers in Cambodia and identify populations with the highest potential exposure to H5N1.

METHODS AND FINDINGS

A cross-sectional survey was undertaken in which 3,600 backyard poultry owners from 115 randomly selected villages in six provinces throughout Cambodia were interviewed. Using risk assessment methods, patterns of contact with poultry as surrogate measures of exposure to H5N1 were used to generate risk indices of potential H5N1 transmission to different populations in contact with poultry. Estimates of human exposure risk for each study participant (n = 3600) were obtained by multiplying each reported practice with a transmission risk-weighting factor and summing these over all practices reported by each individual. Exposure risk estimates were then examined stratified by age and gender. Subjects reported high contact with domestic poultry (chickens and ducks) through the daily care and food preparation practices, however contact patterns varied by gender and age. Males between the ages of 26-40 reported practices of contact with poultry that give rise to the highest H5N1 transmission risk potential, followed closely by males between the ages of 16-25. Overall, males had a higher exposure risk potential than females across all age groups (p < 0.001).

CONCLUSIONS

Our results demonstrate that most of the population in rural Cambodia is in frequent contact with domestic poultry. About half of the population in this study carried out on a regular basis at least one of the practices considered to be high risk for the effective transmission if the bird is infected. There was however substantial variation in the frequency of different practices and thus the potential risk of transmission of H5N1 from poultry to humans is not uniform across age and gender even amongst populations living in close proximity to poultry.

Factors associated with case fatality of human H5N1 virus infections in Indonesia: a case series

BACKGROUND

Indonesia has had the most human cases of highly pathogenic avian influenza A (H5N1) and one of the highest case-fatality rates worldwide. We described the factors associated with H5N1 case-fatality in Indonesia.

METHODS

Between June, 2005, and February, 2008, there were 127 confirmed H5N1 infections. Investigation teams were deployed to investigate and manage each confirmed case; they obtained epidemiological and clinical data from case-investigation reports when possible and through interviews with patients, family members, and key individuals.

FINDINGS

Of the 127 patients with confirmed H5N1 infections, 103 (81%) died. Median time to hospitalisation was 6 days (range 1-16). Of the 122 hospitalised patients for whom data were available, 121 (99%) had fever, 107 (88%) cough, and 103 (84%) dyspnoea on reaching hospital. However, for the first 2 days after onset, most had non-specific symptoms; only 31 had both fever and cough, and nine had fever and dyspnoea. Median time from onset to oseltamivir treatment was 7 days (range 0-21 days); treatment started within 2 days for one patient who survived, four (36.4%) of 11 receiving treatment within 2-4 days survived, six (37.5%) of 16 receiving treatment within 5-6 days survived, and ten (18.5%) of 44 receiving treatment at 7 days or later survived (p=0.03). Initiation of treatment within 2 days was associated with significantly lower mortality than was initiation at 5-6 days or later than 7 days (p<0.0001). Mortality was lower in clustered than unclustered cases (odds ratio 33.3, 95% CI 3.13-273). Treatment started at a median of 5 days (range 0-13 days) from onset in secondary cases in clusters compared with 8 days (range 4-16) for primary cases (p=0.04).

INTERPRETATION

Development of better diagnostic methods and improved case management might improve identification of patients with H5N1 influenza, which could decrease mortality by allowing for earlier treatment with oseltamivir.

Genetic susceptibility and resistance to influenza infection and disease in humans and mice

Although genetic risk factors for influenza infection have not yet been defined in people, differences in genetic background and related variation in the response to infection, as well as viral virulence, are all likely to influence both the likelihood of infection and disease severity. However, apart from characterization of viral binding sites in avian and mammalian hosts, relatively little investigation has focused on host genetic determinants of susceptibility or resistance to infection, or the severity of the associated disease in humans or other species. Similarly, the role of genetic background in the generation of an efficacious immune response to either infection or vaccination has not been extensively evaluated. However, genetic influences on susceptibility and resistance to numerous infectious agents and on the resultant host inflammatory and immune responses are well established in both humans and other animals. Mouse-adapted strains of human influenza viruses and the use of inbred strains of laboratory mice have supported extensive characterization of the pathogenesis and immunology of influenza virus infections. Like individual humans, inbred strains of mice vary in their reactions to influenza infection, particularly with regard to the inflammatory response and disease severity, supporting the potential use of these mice as a valuable surrogate for human genetic variation. Relying heavily on what we have learned from mice, this overview summarizes existing animal, human and epidemiologic data suggestive of host genetic influences on influenza infection.

A nationally coordinated laboratory system for human avian influenza A (H5N1) in Thailand: program design, analysis, and evaluation

BACKGROUND

The first phase of national surveillance for avian influenza (H5N1) human disease in Thailand occurred over a 4-month period that began on 1 December 2003. Subsequently, a nationally coordinated laboratory system (NCLS) for avian influenza (H5N1) was created to assess population-based surveillance, specimen procurement, case detection, and reporting at the national level.

METHODS

We conducted a pre- and postintervention study to evaluate the NCLS designed during the 6-week interval from 1 April through 15 May 2004. During the pre-NCLS period (1 December 2003 through 31 March 2004), 12 cases of human avian influenza (H5N1) were confirmed. During the post-NCLS period (16 May 2004 through 31 December 2006), interventions were implemented for human avian influenza (H5N1) surveillance, case detection, and expedited, computer-based reporting.

RESULTS

During the pre- and post-NCLS periods, 777 (85%) of 915 and 10,434 (95%) of 11,042 clinical respiratory specimens, respectively, were adequate for confirmatory testing (P<.001), the median time from procurement to results decreased from 17 days (range, 14-24 days) to 1.8 days (range, 0.25-4 days; P<.001), and the duration of specimen shipment decreased from 46.5 h to 21.1 h (P<.001). Thirteen cases of avian influenza (H5N1) were detected during the 31-month postintervention period. H5N1 reverse-transcriptase polymerase chain reaction and real-time reverse-transcriptase polymerase chain reaction sensitivity was 100% and specificity was 99.8%.

CONCLUSIONS

The NCLS exemplifies a systematic approach to national surveillance for avian influenza A (H5N1). This NCLS program in Thailand serves as a model for human avian influenza (H5N1) preparedness that can be adopted or modified for use in other countries.

Review of clinical symptoms and spectrum in humans with influenza A/H5N1 infection

Influenza A/H5N1 infection has become the major emerging infectious disease of global concern again since late 2003. A history of exposure to dead or sick poultry or wild birds occurs in over 60% of cases of human H5N1 infection. The incubation period of avian-to-human transmission is generally between 2 and 5 days and the median duration of symptoms before hospitalization is about 4.5 days. The clinical spectrum has ranged from asymptomatic infection or mild influenza-like illness to severe pneumonia and multi-organ failure. Fever > 38 degrees C, cough and dyspnoea are the major symptoms on presentation, whereas gastrointestinal symptoms such as watery diarrhoea, vomiting and abdominal pain are common early in the course of the disease. In contrast, upper respiratory tract symptoms are less prominent in human H5N1 infection when compared to seasonal influenza. Laboratory features of human H5N1 infection include leucopoenia, especially lymphopenia, elevated amino-transaminases, thrombocytopenia, prolonged prothrombin time and activated partial thromboplastin time, increased D-Dimer, increased serum lactate dehydrogenase and creatinine phospho-kinase, and hypoalbuminemia. A low absolute lymphocyte count on admission is associated with more severe disease and death. Radiographic abnormalities include multi-focal airspace consolidation, interstitial infiltrates, patchy or lobar involvement, with rapid progression to bilateral and diffuse ground-glass opacities consistent with ARDS. However, none of the clinical, laboratory and radiographic features are specific to H5N1 infection. A detailed exposure history needs to be elicited, including any close contact with sick or dead poultry, wild birds, other severely ill persons, travel to an area with A/H5N1 activity or work in laboratory handling samples possibly containing A/H5N1 virus.

Estimation of the basic reproductive number (R0) for epidemic, highly pathogenic avian influenza subtype H5N1 spread

Three different methods were used for estimating the basic reproductive number (R0) from data on 110 outbreaks of highly pathogenic avian influenza (HPAI) subtype H5N1 that occurred in village poultry in Romania, 12 May to 6 June 2006. We assumed a village-level infectious period of 7 days. The methods applied were GIS-based identification of nearest infectious neighbour (based on either Euclidean or road distance), the method of epidemic doubling time, and a susceptible–infectious (SI) modelling approach. In general, the estimated basic reproductive numbers were consistent: 2·14, 1·95, 2·68 and 2·21, respectively. Although the true basic reproductive number in this epidemic is unknown, results suggest that the use of a range of methods might be useful for characterizing epidemics of infectious diseases. Once the basic reproductive number has been estimated, better control strategies and targeted surveillance programmes can be designed.

Virtual epidemic in a virtual city: simulating the spread of influenza in a US metropolitan area

A wide variety of biologic, physiologic, social, economic, and geographic factors may affect the transmission, spread, and impact of influenza. Recent concerns about an impending influenza epidemic have generated a need for predictive computer simulation models to forecast the spread of influenza and the effectiveness of prevention and control strategies. We designed an agent-based computer simulation of a theoretical influenza epidemic in Norfolk, Va, that included extensive city-level details and computer representations of every Norfolk citizen, including their expected behavior and social interactions. The simulation introduced 200 infected cases on November 27, 2002 (day 87), and tracked the progress of the epidemic. On average, the prevalence peaked on day 178 (12.2% of the population). Our model showed a cyclical variation in influenza cases by day of the week with fewer people being exposed on weekends, differences in emergency room and clinic visits by day of the week, an earlier peak in influenza cases, and persistent high prevalence among people age 65 or older and the daily prevalence of infection among health-care workers. The level of detail included in our simulation model made these findings possible. Compared with other existing models, our model has a very extensive and detailed social network, which may be important because individuals with more social interactions and extensive social networks may be more likely to spread influenza. Our simulation may serve as a virtual laboratory to better understand the way different factors and interventions affect the spread of influenza.

Lack of piped water and sewage services is associated with pediatric lower respiratory tract infection in Alaska

OBJECTIVES

To determine the association between the high incidence of lower respiratory tract infection (LRI) documented among young Alaskan children and the absence of modern water service (in-home piped water/septic system or water delivered by closed haul truck) found commonly in rural Alaskan communities.

STUDY DESIGN

A community-level analysis was performed of all 108 Alaskan communities with at least 15 children <2 years of age enrolled in Medicaid during 1998-2003. Community LRI incidence rates were determined from a Medicaid database with standard LRI billing codes. Potentially confounding community-level demographic variables were obtained, as was availability of water service.

RESULTS

During linear regression analysis, the percentage of households with modern water service in a community predicted community-level outpatient (beta = -0.53; P < .001) and inpatient (beta = -0.15; P = .088) LRI incidence rates when controlling for the degree of household crowding, unemployment, adult education, tobacco cigarette use, wood stove use, and poverty. Modest improvements in water service delivery were not shown to be associated with changes in LRI burden.

CONCLUSIONS

Lack of modern water service in Alaska is associated with high pediatric LRI incidence. These communities should receive modern water service, but this intervention alone may not dramatically reduce LRI burden.

Epidemiology of H5N1 avian influenza

High pathogenic (HP) H5N1 avian influenza (AI) infection has been reported in domestic poultry, wildlife, and human populations since 1996. Risk of infection is associated with direct contact with infected birds. The mode of H5N1 spread from Asia to Europe, Africa and the Far East is unclear; risk factors such as legal and illegal domestic poultry and exotic bird trade, and migratory bird movements have been documented. Measures used to control disease such as culling, stamping out, cleaning and disinfection, and vaccination have not been successful in eradicating H5N1 in Asia, but have been effective in Europe.

Evidence for a heritable predisposition to death due to influenza

Animal model studies and human epidemiological studies have shown that some infectious diseases develop primarily in individuals with an inherited predisposition. A heritable contribution to the development of severe influenza virus infection (i.e., that which results in death) has not previously been hypothesized or tested. Evidence for a heritable contribution to death due to influenza was examined using a resource consisting of a genealogy of the Utah population linked to death certificates in Utah over a period of 100 years. The relative risks of death due to influenza were estimated for the relatives of 4,855 individuals who died of influenza. Both close and distant relatives of individuals who died of influenza were shown to have a significantly increased risk of dying of influenza, consistent with a combination of shared exposure and genetic effects. These data provide strong support for a heritable contribution to predisposition to death due to influenza.

Low frequency of infection with avian influenza virus (H5N1) among poultry farmers, Thailand, 2004

In Thai provinces where avian influenza outbreaks in poultry had been confirmed in the preceding 6 months, serum from 322 poultry farmers was tested for antibodies to avian influenza virus subtype H5N1 by microneutralization assay. No study participant met the World Health Organization serologic criteria for confirmed infection.

Human influenza A (H5N1) cases, urban areas of People's Republic of China, 2005-2006

We investigated potential sources of infection for 6 confirmed influenza A (H5N1) patients who resided in urban areas of People’s Republic of China. None had known exposure to sick poultry or poultry that died from illness, but all had visited wet poultry markets before illness.