Mortality due to pandemic (H1N1) 2009 influenza in England: a comparison of the first and second waves

Deaths in England attributable to pandemic (H1N1) 2009 deaths were investigated through a mandatory reporting system. The pandemic came in two waves. The second caused greater population mortality than the first (5·4 vs. 1·6 deaths per million, P<0·001). Mortality was particularly high in those with chronic neurological disease, chronic heart disease and immune suppression (450, 100, and 94 deaths per million, respectively); significantly higher than in those with chronic respiratory disease (39 per million) and those with no risk factors (2·4 per million). Greater mortality in the second wave has been observed in all previous influenza pandemics. This time, the explanation appears to be behavioural. This emphasizes the importance of maintaining public and clinical awareness of risks associated with pandemic influenza beyond the initial high-profile period.     

Using Surveillance Data to Identify Risk Factors for Severe H1N1 in First Nations

Objective

We sought to measure from surveillance data the effect of proximity to an urban centre (rurality) and other risk factors, (e.g., age, residency on a FN reservation, and pandemic wave) on hospitalization and intensive care unit admission for severe influenza.

Introduction

Research has shown that Canadian First Nation (FN) populations were disproportionately affected by the 2009 H1N1 influenza pandemic. However, the mechanisms for the disproportionate outcomes are not well understood. Possibilities such as healthcare access, infrastructure and housing issues, and pre-existing comorbidities have been suggested. We estimated the odds of hospitalization and intensive care unit admission for cases of H1N1 influenza among FN living in Manitoba, Canada, to determine the effect of location of residency and other factors on disease outcomes during the 2009 H1N1 pandemic.

Methods

We obtained surveillance data on laboratory confirmed cases of pandemic H1N1 influenza from the province of Manitoba. These data described demographic characteristics, residence location, and dates of hospital and ICU admission. We measured the rurality of each case using a pre-exiting scale (Rambeau & Todd, 2000). We tabulated the number of hospitalizations (and ICU admissions) stratified first by reservation residency and second by rurality and calculated unadjusted odds ratios. We then used logistic regression to calculate the odds of hospitalization given infection (and the odds of ICU admission given hospitalization), adjusting for age, reservation residency, rurality, and pandemic wave. We also investigated the effect of rurality and reserve residency on time to hospitalization from infection.

Results

FN individuals diagnosed with influenza and living on-reserve were more likely to be hospitalized than those living off-reserve, even after controlling for the effects of rurality (OR: 2.16, 95% CI: 1.15, 4.05). FN living in rural areas were hospitalized more frequently and experienced longer delays between infection and hospitalization than FN residing in more urban areas. Rurality and reserve residency had less effect on ICU admissions once an individual was hospitalized.

Conclusions

While it is established that FN individuals had disproportionately high rates of severe outcomes from H1N1, the causal mechanisms at work are not well understood. Reasonable possibilities include barriers to healthcare access, lack of proper housing and infrastructure, and pre-existing comorbidities. This research using surveillance data suggests that geographic location has an effect on healthcare access, including both on vs. off reserve residency as well as rurality.     

Estimate of 2009 H1N1 influenza cases in Shenzhen--the biggest migratory city in China

The 2009 novel H1N1 influenza pandemic had a significant impact on Shenzhen's population with 2063 laboratory-confirmed human H1N1 cases and five deaths being reported. We used parameters from two population-based surveys and the Shenzhen Influenza Surveillance System to estimate the total number of H1N1 influenza infections in Shenzhen in the 2009 pandemic. The attack rate of influenza-like illness (ILI) in family households was 11·2% (95% CI 9·4-13·0), with 80·2% (95% CI 77·8-82·5) seeking medical care. The ILI attack rate in workers was 38·1% (95% CI 34·3-41·7) with 72·5% (95% CI 66·9-78·0) seeking medical care. The average H1N1 positive rate in individuals reporting ILI and testing by polymerase chain reaction was 22·7%. A total of 611 000-768 000 people, or 4·7-5·9% of the Shenzhen population, are estimated to have experienced H1N1 influenza. The estimated total number of cases of H1N1 is likely to be 330 times greater than the number of laboratory-confirmed cases.     

Viral respiratory infections during the 2009 influenza A(H1N1) outbreak in the West Midlands Region, UK

In spring 2009 a new strain of influenza A(H1N1) emerged and caused a worldwide pandemic. This study utilized a large collection of respiratory specimens from suspected cases of influenza A(H1N1) in the UK West Midlands during the pandemic in order to investigate which other respiratory viruses were circulating and whether they played any role in the increased hospitalization rates seen during that period. Study specimens were selected from community and hospitalized patients positive and negative for influenza A(H1N1) and tested by PCR for other respiratory viruses. A number of infections diagnosed as influenza during the summer influenza outbreak were found to be due to other virus infections (most commonly rhinovirus). No statistically significant difference was found between the rates of respiratory virus co-infection with H1N1 in patients from community or hospital locations suggesting underlying factors were likely to be more significant than viral co-infections in determining severity of influenza A(H1N1) disease.     

Increased extent of and risk factors for pandemic (H1N1) 2009 and seasonal influenza among children, Israel

During the pandemic (H1N1) 2009 outbreak in Israel, incidence rates among children were 2× higher than that of the previous 4 influenza seasons; hospitalization rates were 5× higher. Children hospitalized for pandemic (H1N1) 2009 were older and had more underlying chronic diseases than those hospitalized for seasonal influenza.     

Comparison of Pandemic (H1N1) 2009 and Seasonal Influenza, Western Australia, 2009

We compared confirmed pandemic (H1N1) 2009 influenza and seasonal influenza diagnosed in Western Australia during the 2009 influenza season. From 3,178 eligible reports, 984 pandemic and 356 seasonal influenza patients were selected; 871 (88.5%) and 288 (80.9%) were interviewed, respectively. Patients in both groups reported a median of 6 of 11 symptoms; the difference between groups in the proportion reporting any given symptom was <10%. Fewer than half the patients in both groups had >1 underlying condition, and only diabetes was associated with pandemic (H1N1) 2009 influenza (odds ratio [OR] 1.9, 95% confidence interval [CI] 1.1–3.5). A total of 129 (14.8%) persons with pandemic (H1N1) 2009 and 36 (12.5%) persons with seasonal influenza were hospitalized (p = 0.22). After controlling for age, we found that patient hospitalization was associated with pandemic (H1N1) 2009 influenza (OR 1.5; 95% CI 1.1–2.1). Contemporaneous pandemic and seasonal influenza infections were substantially similar in terms of patients’ symptoms, risk factors, and proportion hospitalized.     

Risk factors of influenza (H1N1) 2009 hospitalization and effectiveness of pharmaceutical and nonpharmaceutical interventions in its prevention: a case-control study

Potentially useful pharmaceutical measures to limit the impact of pandemic influenza in the community include antiviral drugs (neuraminidase inhibitors) and the influenza and pneumococcal vaccines, as influenza predisposes to bacterial pneumonia caused by Streptococcus pneumoniae. Non-pharmaceutical measures include hand washing and respiratory hygiene. Due to the lack of knowledge of the effectiveness of these measures in a pandemic situation, in September 2009, CIBER de Epidemiología y Salud Pública presented a multicenter case-control study, with controls matched for age, hospital and date of hospitalization, to investigate these aspects in 37 hospitals in 7 Spanish autonomous communities, in response to the call for research projects by the Ministry of Science and Innovation Research Program on Influenza A (H1N1) in Spain. For each confirmed hospitalized case of pandemic influenza, 1 confirmed outpatient case and 3 controls (2 hospitalized and 1 outpatient) were selected. Demographic variables, underlying medical conditions, use of antiviral agents, vaccines received and hygiene habits were collected for all cases and controls. In hospitalized cases, information on antiviral therapy and disease progression was collected. A total of 3750 patients were recruited by October 2010. Data cleansing and the recovery of variables is now underway. The involvement of the Public Health Directorate has been instrumental in adapting the project to the evolution of the pandemic.     

Vaccine effectiveness in preventing influenza hospitalizations in Navarre, Spain, 2010-2011: cohort and case-control study

We evaluated the 2010-2011 seasonal influenza vaccine effectiveness in preventing hospitalizations. Using healthcare databases we defined the target population for vaccination in Navarre, Spain, consisting of 217,320 people with major chronic conditions or aged 60 years and older. All hospitalized patients with influenza-like illness (ILI) were swabbed for influenza testing. A total of 269 patients with ILI were hospitalized and 61 of them were found positive for influenza virus: 58 for A(H1N1)2009 and 3 for B virus. The incidence rates of hospitalization with laboratory-confirmed influenza were compared by vaccination status. In the Cox regression model adjusted for sex, age, children in the household, urban/rural residence, comorbidity, pandemic vaccination, pneumococcal vaccination, outpatient visits and hospitalization in the previous year, the seasonal vaccine effectiveness was 58% (95% CI: 16-79%). The nested test-negative case-control analysis gave an adjusted estimate of 59% (95% CI: 4-83%). These results suggest a moderate effect of the 2010-2011 seasonal influenza vaccine in preventing hospitalization in a risk population. The close estimates obtained in the cohort and the test-negative case-control analyses suggest good control of biases.     

Adult intensive-care patients with 2009 pandemic influenza A(H1N1) infection

In France, the surveillance of hospitalized cases of pandemic influenza was implemented in July 2009 and restricted to intensive-care unit (ICU) patients in November. We described the characteristics of the 1065 adult patients admitted to ICUs and analysed risk factors for severe outcome (mechanical ventilation or death). Eighty-seven percent of cases were aged 15-64 years. The case-fatality ratio was 20%. The risk for severe outcome increased with age and obesity while this association was negative for chronic respiratory disease. Late antiviral therapy was associated with a severe outcome in ICU patients with risk factors (adjusted OR 2·0, 95% CI 1·4-3·0). This study confirms the considerable contribution of young adults to A(H1N1) 2009 mortality. It shows the role of obesity as an independent risk factor for severe disease, and of early antiviral therapy as a protective factor, at least in patients with risk factors.     

Influenza epidemiology among hospitalized children in Stockholm,Sweden 1998–2014

BackgroundInfluenza remains a common reason for the hospitalization of children. There is a need for long term studies that are also population based. We describe the epidemiology of severe influenza in a defined population 1998–2014.MethodRetrospective study of annually collected data of virologically confirmed influenza in hospitalized children 0–17 years living in the catchment area (230,000 children). We gathered information about comorbidity and complications from case records, and compared Influenza A, B and A(H1N1)pdm09 with respect to these factors.ResultsA total of 922 children with influenza were hospitalized. The mean rate remained unchanged at 22.5–24.2 per 100,000 children per year. There were two major outbreaks: influenza A(H3N2) in 2003–2004 and the A(H1N1) pandemic in 2009–2010. The proportion of children with influenza B increased from 8% during the first half of the study period to 28% during the second half. The highest admission rate was found in children <3 months of age, 169 per 100,000. Children with influenza B were older than those with influenza A. Comorbidity was found in 34%, complications in 41%, and 11% needed intensive care management. The mortality rate was 0.17/100,000 children.ConclusionInfluenza remains an important reason for the hospitalization of children, especially during the first years of life. The increasing proportion of influenza B may have to be considered when recommending influenza vaccines.     

Vaccination against pandemic influenza A/H1N1 among healthcare workers and reasons for refusing vaccination in Istanbul in last pandemic alert phase

Coverage of the HCWs as target population is one of the important determinants for the impact of vaccination. To determine the vaccination against the pandemic influenza A/H1N1 among HCWs, we conducted a cross-sectional questionnaire survey in a public hospital in Istanbul from December 7 to December 22, 2009. Out of total 941 HCWs 718 (76.3%) completed the questionnaires. Nearly one-fourth (23.1%) of the participants were vaccinated against pandemic influenza A/H1N1. Occupation (being a doctor), receiving seasonal influenza vaccine in 2009, agreement with safety of pandemic influenza A/H1N1 vaccine and being comprehend that HCWs have a professional responsibility for getting vaccinated was the strongest independent predictive factor for accepting the pandemic influenza A/H1N1 vaccine (p < .0001). The most frequent reasons for refusing pandemic vaccine were fear of side effects and doubts about vaccine efficacy. Among HCWs 59.6% were recommending pandemic influenza vaccination to a patient even if indicated. In conclusion vaccination against pandemic influenza A/H1N1 is insufficient among HCWs. Misinformed or inadequately informed HCWs are important barrier to pandemic influenza vaccine coverage of the general public also. Educational campaigns concerning HCWs should include evidence based and comprehensible information about possible adverse effects and their incidence besides the advantages of vaccine.     

职业暴露人群A(H5N1)和甲型H1N1流感血清抗体分析

目的:了解人禽流感A(H5N1)和甲型H1N1流感职业暴露人群中的感染状况。方法:对职业暴露人群进行个案调查,采用血凝抑制法(HI)检测职业暴露人群血清中人禽流感A(H5N1)和甲型H1N1流感抗体。结果:2009年-2010年采集的624份职业暴露人群血清中未检测出人禽流感A(H5N1)抗体,而在2009年采集的血清中有5份检测出甲型H1N1流感抗体,抗体阳性率为1.55%,2010年采集的血清中抗体阳性率为11.96%,其中<29岁阳性率为17.19%,30岁～59岁阳性率为10.87%。结论:职业暴露人群中未检测出A(H5N1)流感抗体,但仍需加强职业暴露人群监测。同时甲型H1N1流感抗体水平较低,缺乏相应的抗体水平保护。     

Central European Vaccination Advisory Group (CEVAG) guidance statement on recommendations for 2009 pandemic influenza A(H1N1) vaccination

The 2009 influenza A(H1N1) pandemic is markedly different from seasonal influenza with the disease affecting the younger population and a larger than expected number of severe or fatal cases has been seen in pregnant women, obese people and in people who were otherwise healthy. In Europe, influenza activity caused by the 2009 influenza A(H1N1) virus has passed the winter peak with nearly all countries now reporting lower influenza activity. However, although the rate of 2009 pandemic influenza A(H1N1) is declining, fatal cases continue to be reported and the future is hard to predict. The most effective protection against influenza is vaccination and increasing vaccine coverage is the only way to eliminate uncertainties regarding possible future waves of 2009 pandemic influenza A(H1N1). Recommendations have been developed for several central European countries but there is no clear or uniform definition with respect to priority groups or age groups who should receive vaccination. This paper contains the Central European Vaccination Advisory Group (CEVAG) guidance statement on recommendations for the vaccination of adults and children against 2009 pandemic influenza A(H1N1). CEVAG recommends vaccination of all health-care workers, pregnant women, children ≥6 months and <2 years of age and people with chronic medical conditions as a first priority.     

北京市人群甲型H1N1流感血清流行病学调查

目的 了解和掌握北京市人群对甲型H1N1流感的免疫水平.方法 在2009年11月27日至12月23日从医院患者(排除感染科和呼吸科)、血液中心志愿者和体检中心健康体检者中随机选取调查对象进行问卷调查,并采集血清标本进行甲型H1N1流感病毒血凝抑制(HI)抗体检测.结果 共选取调查对象856名,其中127名(14.8%)调查对象体内甲型H1N1流感病毒HI抗体为阳性.0～5岁、6～17岁、18～55岁、≥56岁年龄组HI抗体阳性率分别为14.5%、19.4%、17.4℅和8.0%(P=0.009).不同性别HI抗体阳性率差异无统计学意义(P=0.693).人群血清HI抗体年龄加权阳性率为15.8%.多因素logistic回归分析显示,年龄、出现过急性呼吸道症状以及接种甲型H1N1流感疫苗与HI抗体阳性呈显著性相关.结论 北京市已经有超过15%的人群具有甲型H1N1流感保护性抗体,普通人群中已经建立一定的免疫屏障.     

The impact of influenza on the Canadian First Nations

In March and April 2009, pandemic H1N1 2009 influenza A virus (pH1N1 2009) emerged among residents of and travelers to Mexico, the United States and Canada. During the 2009 pandemic, cases of pH1N1 2009 infection were reported from over 214 countries, with at least 18,449 recorded deaths. In Canada, over 8,500 cases were hospitalized, 16.8% of which required intensive care. A particularly concerning occurrence was the spread of pH1N1 2009 into First Nations communities in Canada. Although Aboriginal peoples constitute only 3.8% of Canada's population, members of the First Nations were 6.5 times more likely to be admitted to an ICU with pH1N1 2009 influenza than non-First Nations, and had rates of hospitalization nearly triple that of the national cumulative crude rate for all Canadians. We herein provide a succinct review of our current understanding of the risk of influenza among First Nations populations in Canada.     

Maternal and infant outcomes among severely ill pregnant and postpartum women with 2009 pandemic influenza A (H1N1)--United States, April 2009-August 2010

Pregnant women with influenza are at increased risk for hospitalization and death. Since 2004, the Advisory Committee on Immunization Practices (ACIP) has recommended inactivated influenza vaccine for all women who are pregnant during influenza season, regardless of trimester. Nonetheless, after the 2004 recommendation, estimated annual influenza vaccination coverage among pregnant women was approximately 15%, before increasing to nearly 50% during the 2009 influenza A (H1N1) pandemic. Since April 2009, CDC has collaborated with state and local health departments to conduct enhanced surveillance for severe influenza among pregnant and postpartum women. To assess maternal and infant outcomes among severely ill pregnant and postpartum women with 2009 H1N1 during the 2009 H1N1 pandemic, CDC analyzed data for the period April 15, 2009 to August 10, 2010. This report summarizes the results of that analysis, which found that, among 347 severely ill pregnant women, 75 died from 2009 H1N1, and 272 were admitted to an intensive-care unit (ICU) and survived. Women who survived received antiviral treatment sooner after symptom onset than women who died. Pregnant women with severe influenza who delivered during their influenza hospitalization were more likely to deliver preterm and low birth weight infants than those in the general U.S. population; infants born after their mother's influenza hospitalization discharge were more likely to be small for gestational age. These data document the severe effects of 2009 H1N1 on pregnant women and their infants, emphasize the importance of vaccinating pregnant women against influenza, and demonstrate the value of prompt administration of antivirals to pregnant women with suspected or confirmed influenza.     

Outbreaks of pandemic (H1N1) 2009 and seasonal influenza A (H3N2) on cruise ship

To determine the extent and pattern of influenza transmission and effectiveness of containment measures, we investigated dual outbreaks of pandemic (H1N1) 2009 and influenza A (H3N2) that had occurred on a cruise ship in May 2009. Of 1,970 passengers and 734 crew members, 82 (3.0%) were infected with pandemic (H1N1) 2009 virus, 98 (3.6%) with influenza A (H3N2) virus, and 2 (0.1%) with both. Among 45 children who visited the ship's childcare center, infection rate for pandemic (H1N1) 2009 was higher than that for influenza A (H3N2) viruses. Disembarked passengers reported a high level of compliance with isolation and quarantine recommendations. We found 4 subsequent cases epidemiologically linked to passengers but no evidence of sustained transmission to the community or passengers on the next cruise. Among this population of generally healthy passengers, children seemed more susceptible to pandemic (H1N1) 2009 than to influenza (H3N2) viruses. Intensive disease control measures successfully contained these outbreaks.     

Pandemic A(H1N1) 2009 influenza: review of the Southern Hemisphere experience

We sought to systematically review the published literature describing the epidemiological aspects of the first wave of pandemic A(H1N1) 2009 influenza in the Southern Hemisphere. Fifteen studies were included in this review, originating from South America, Australia or New Zealand, and Africa. Across the different studies, 16·8-45·3% of the laboratory-confirmed cases were admitted to hospital, and 7·5-26·0% of these cases were admitted to intensive care units (ICUs). The fatality rate was 0·5-1·5% for laboratory-confirmed cases in 6/8 studies reporting specific relevant data, and 14·3-22·2% for cases admitted to ICUs in 5/7 studies, respectively. In 4/5 studies the majority of laboratory-confirmed cases were observed in young and middle-aged adults, the percentage of older adults increased the higher the level of healthcare the cases received (e.g. laboratory confirmation, hospitalization or ICU admission) or for fatal cases. Many of the cases had no prior comorbidity, including conditions identified as risk factors for seasonal influenza. Pregnant women represented 7·4-9·1% and 7·1-9·1% of unselected laboratory-confirmed cases and of those admitted to ICUs, respectively. Obesity and morbid obesity were more commonly reported as the level of healthcare increased.     

北京市2009年甲型H 1N 1流感防控效果定量评价

目的 定量评价北京市甲型H1N1流感的防控措施效果,为制定和调整传染病防控策略提供依据.方法 利用北京市2009年甲型H1N1流感流行病学数据,基于传染病传播动力学机制,考虑了甲型H1N1流感的季节性,并引入疫苗接种量,建立定量评价甲型H1N1流感防控效果的数学模型.结果 2009年北京市甲型H1N1流感的平均潜伏期约为1.82 d,平均感染期约为2.08 d, 前中后三期有效再生数分别为1.13、1.65 和 0.96;北京市采取了一系列甲型H1N1 流感防控措施使2009年甲型H1N1流感报告的实际病例数远远小于其自然状态下的累计例数;接种甲型H1N1流感疫苗使2009年累计病例数减少24.08%,且使发病高峰时间推后.结论 北京市采取的一系甲型H1N1流感防控措施整体上显著有效,接种甲型H1N1流感疫苗不仅降低了疫情规模, 还能延迟疫情达到高峰的时间 .