Performance of rapid-test kits for the detection of the pandemic influenza A/H1N1 virus

The early detection of pandemic influenza strains is a key factor for clinicians in treatment decisions and infection control practices. The aims of this study were to determine the analytical sensitivity and clinical performance of the commercially available influenza rapid tests in Taiwan. Four rapid tests for influenza virus (BinaxNow test, QuickVue test, TRU test, and Formosa Rapid test) were evaluated for their detection limit against four influenza viruses (the 2009 pandemic influenza A virus H1N1, seasonal influenza virus H1N1, H3N2, and influenza B virus) circulating in Taiwan. The viral load of these isolates were quantified by rtRT-PCR and then diluted 2-fold serially for the comparison. The lowest detectable viral load of the pandemic influenza A virus H1N1 by the Formosa Rapid test, QuickVue test, TRU test, and Binax Now test was 5.3 × 10⁴, 1.0 × 10⁵, 1.0 × 10⁵, and 4.2 × 10⁵ copies/μL, respectively. Of these four tests, the two most sensitive tests (the QuickVue test and the Formosa Rapid test) were chosen to evaluate 62 nasopharyngeal specimens from patients who were suspected of infection with pandemic influenza A virus H1N1. The positive rate for the Formosa Rapid test and the QuickVue test were 53.2% (33/62) and 45.2% (28/62) (McNemar's test, P = 0.125), respectively. In conclusion, the Formosa Rapid test was the most sensitive test in the present study for the detection of influenza antigens and its clinical performance was similar to that of the QuickVue test (Kappa = 0.776). This suggests that the Formosa Rapid test could be used to aid clinical decision making in primary health care settings during outbreaks of influenza.     

A novel H1N1 virus causes the first pandemic of the 21st century

A novel H1N1 virus of swine origin (H1N1v ) is currently spreading in humans, giving rise to the first pandemic in 40 years. The disease is of moderate severity but has notable differences from seasonal influenza. In contrast to seasonal influenza, those over 60 years are relatively spared, a likely consequence of the presence of H1N1v cross‐neutralizing antibody in this age group. Most patients appear to have mild influenza‐like illness and many of the complications leading to hospitalization and mortality occur in those with underlying disease conditions or pregnancy. Studies in animal models suggest that the novel H1N1v pandemic virus causes a more severe illness and appears to have a greater predilection for the alveolar epithelium than seasonal influenza viruses. As there are as yet little data on the pathogenesis and immunology of H1N1v infection in humans, we have reviewed relevant data from past pandemics, from seasonal influenza and avian influenza H5N1 to highlight key issues pertaining to pathogenesis and immunology.     

Viral genetic sequence variations in pandemic H1N1/2009 and seasonal H3N2 influenza viruses within an individual, a household and a community

Background

There are few data in the literature on viral sequence variation between host generations/successive transmission events. Relatively little is known about the sequence heterogeneity of the influenza viruses transmitted within families.

Objectives

To study the molecular epidemiology of influenza virus and to determine the sequence variation within an individual, a household and a community during the first wave of influenza pandemic in 2009.

Study design

A prospective study of household transmission of influenza A in Hong Kong was conducted during the pandemic in 2009. The HA and NA sequences of pandemic and seasonal influenza A viral isolates identified in this household transmission study were sequences and analyzed.

Results

Our results indicated that there were multiple introductions of influenza viruses into Hong Kong. Sequence analysis of these isolates suggested that members of these family clusters acquired the infection by household transmissions. Interestingly, unlike those concluded from previous household transmission studies, we observed sequence variations between sequential samples from the same person and also within the same household.

Conclusions

Family clusters of influenza A viral infection are predominantly the result of secondary transmission within a household. Our results also suggested that the intra-host viral sequence variation might be more common that than previously thought.     

Characteristics of hospitalized children with 2009 pandemic influenza A (H1N1): a multicenter study in Korea

The majority of Korean patients with pandemic influenza A (H1N1) during the 2009 epidemic were under 20 yr of age. The limited data on the clinical characteristics of these children led us to conduct a case note-based investigation of children admitted to 6 university hospitals with 2009 H1N1 influenza. A total of 804 children was enrolled. The median age was 5 yr; 63.8% were males; and 22.4% had at least one chronic underlying disease. Ninety-five of the patients (11.8%) were critically ill and they suffered more from shortness of breath, dyspnea and lymphopenia than the other patients. Among all the patients, 98.8% were treated with antivirals and 73% received treatment within 48 hr of illness onset. All the enrolled patients are alive and appear to have had good outcomes, probably due to the early intervention and antiviral treatment. This study deals with hospitalized children whose diagnoses of influenza A (H1N1) were confirmed, and therefore provides important new information about the clinical patterns of children with influenza A (H1N1) in Korea.     

Fatal cases of 2009 pandemic influenza A (H1N1) in Korea

The aim of this study was to describe the features of deaths associated with the 2009 pandemic influenza A (H1N1) by 26 November 2009 in Korea. We collected standardized case reports on 115 confirmed deaths through a nationwide enhanced influenza surveillance system. The median age was 61 yr (interquartile range [IQR], 0.2-97 yr) and 58 (50.4%) were females. The case fatality rate was estimated as 16 per 100,000 cases. The age-related mortality rate had a J-shaped curve. Eighty-three patients (72.2%) had at least 1 underlying medical disease. Bacterial co-infections were detected in the blood or sputum specimens from 34 patients. Of the 63 patients who were hospitalized in the intensive care unit (ICU), the median time from symptom onset to hospital admission was 2 days (IQR, 0-22 days), and the median time from hospitalization to ICU admission was 1 day (IQR, 0-17 days). Neuraminidase inhibitors were administered to 100 patients (87.0%), 36% of whom began treatment within 2 days. In conclusion, fatal cases from the 2009 influenza A (H1N1) infection in Korea are mainly aged individuals with underlying disease, and associated with pneumonia, bacterial co-infections, and multi-organ failure.     

2009-2011年广东省甲型H1N1流感病毒血凝素基因的进化特征

目的 了解2009-2011年广东甲型H1N1流感病毒血凝素基因的HA1进化特征。方法 选取广东甲型H1N1流感病毒83株,提取病毒RNA,经RT-PCR反应扩增HA1并测序,测定的序列用生物信息软件分析,与GenBank中相关序列比较,并对推导的编码氨基酸序列进行进化分析。结果 2009-2011年广东甲型H1N1流感病毒HA1基因的进化速率是5.2× 10-3,高于人季节性H1N1病毒;变异氨基酸多数位于HA蛋白表面,其中部分位于抗原决定簇;在两例死亡病例分离株HA1的第222位氨基酸发生D222G/D222N变异。结论 遗传进化分析表明,甲型H1N1流感病毒发生了一定程度的变异,造成2011年初在广东的再次流行。HA1的第222位氨基酸变异可能与疾病的严重程度有关。     

北京市中小学生甲型H1N1流感感染影响因素的病例对照研究

目的 探讨北京市中、小学生甲型H1N1流感感染的相关影响因素.方法采用1∶2病例-对照研究方法,通过问卷调查,在6个区县收集304对病例和对照的个人卫生习惯、疫苗接种史、搭乘交通工具等信息.结果多因素logistic回归结果显示,教室内学生密度,教室通风情况,课间活动范围,打喷嚏后是否洗手,睡眠时间,上学交通方式,接种...     

北京市中小学生甲型H1N1流感感染影响因素的病例对照研究

目的 探讨北京市中、小学生甲型H1N1流感感染的相关影响因素.方法采用1∶2病例-对照研究方法,通过问卷调查,在6个区县收集304对病例和对照的个人卫生习惯、疫苗接种史、搭乘交通工具等信息.结果多因素logistic回归结果显示,教室内学生密度,教室通风情况,课间活动范围,打喷嚏后是否洗手,睡眠时间,上学交通方式,接种甲流疫苗和不带病上课与甲型H1N1流感感染有关.结论参加户外活动、加强教室通风、注意手卫生、保证睡眠允足、不乘坐密闭的交通工具、接种甲型H1N1流感疫苗是预防中小学生甲型H1N1流感感染的重要手段.     

Characteristics of outpatients with pandemic H1N1/09 influenza in a tertiary care university hospital in Korea

The pandemic H1N1/09 emerged rapidly in Korea. Here, we describe the clinical characteristics of outpatients in Seoul, Korea who were infected in the 2009 H1N1 pandemic. We reviewed the cases of outpatients with pandemic H1N1/09 who visited a tertiary care teaching hospital between September 1 and December 31, 2009. Infection with pandemic H1N1/09 was confirmed by molecular tests. Of a total of 7,182 tests, 3,020 (42.0%) were positive. Compared with 473 cases of influenza- like illness (ILI), the 586 confirmed cases of pandemic H1N1/09 differed in age [odds ratio (OR) 0.975] and fulfilling at least one of the following factors: age < 5 or ≥ 65 years, history of contact with other pandemic H1N1/09-infected individuals (OR 0.611), fever ≥ 37.8°C (OR 3.567), cough (OR 2.290), and myalgia (OR 1.559). The sensitivity of the best criteria, "fever (≥ 37.8°C) plus cough" (41.03%) in this study was lower than that of the Korea Centers for Disease Control and Prevention (KCDC) criteria (47.95%), whereas the positive likelihood ratio (3.55) and positive predictive value (81.6) of this criteria was higher than those of the KCDC criteria (2.98 and 78.7, respectively). The clinical characteristics of pandemic H1N1/09 are, in many regards, indistinguishable from those of ILI. Moreover, the accuracy and predictability of criteria which include only symptoms or signs were not sufficient to diagnose pandemic H1N1/09 infection. Therefore, use of a combination of symptoms with confirmatory laboratory testing is necessary for accurate diagnosis of pandemic H1N1/09.     

Both influenza hemagglutinin and polymerase acidic genes are important for delayed pandemic 2009 H1N1 virus clearance in the ferret model

We previously showed that a pandemic virus, A/Tennessee/560/09(H1N1), had the potential to adapt to human bronchial epithelial cells by the acquisition of hemagglutinin (HA) K154Q and polymerase acidic (PA) protein L295P mutations that conferred a more virulent phenotype. To better elucidate the role of each mutations, we generated recombinant viruses carrying single mutations or both mutations concurrently. The replication of all mutant viruses was significantly higher than that of the wild-type A/Tennessee/560/09 virus in human cells. The HA K154Q mutation reduced the receptor binding affinity of A/Tennessee/560/09 virus to 6-Su-6′SLN and biantennary 6′SLN receptors. In ferrets, H1N1 virus with HA K154Q and PA L295P mutations exhibited significantly higher titers in the upper respiratory tract compared to all other viruses 6 days post-infection. Our results suggest that both single mutations HA K154Q and PA L295P are necessary for delayed virus clearance of A/Tennessee/560/09(H1N1) influenza virus in a ferret animal model.     

Evaluation of direct immunofluorescence test with PCR for detection of novel influenza A (H1N1) virus during 2009 pandemic

During the 2009 novel influenza (H1N1) pandemic, the sensitivity of direct immunofluorescence assay (DFA) for H1N1 infection was 62% (266/429) of that of the polymerase chain reaction (PCR) test. The sensitivity of the DFA differed significantly with the age of patients: the sensitivity was the highest (71.8%) for patients aged <10 years and the lowest for patients aged ≥30 years. The sensitivity of DFA in patients aged ≥30 years was 40.7%. Furthermore, the sensitivity (67.3%, 171/254) of DFA was higher for patients who had a high temperature at admission. An increase in the incidence of H1N1 infection did not influence the sensitivity of DFA (62.1% vs. 62%; p=0.984) test, but resulted in a decrease in the negative predictive value, from 92.4% (700/757) to 69.6% (247/355). PCR may be useful as the initial test for diagnosing H1N1 infection in patients aged ≥30 years with a normal temperature at presentation.     

A pandemic H1N1 influenza virus-like particle vaccine induces cross-protection in mice

Influenza virus-like particles (VLPs) represent promising alternative vaccines. However, it is necessary to demonstrate that influenza VLPs confer cross-protection against antigenically distinct viruses. In this study, a VLP vaccine comprising hemagglutinin (HA) and M1 from the A/California/04/2009 (H1N1) were used and its ability to induce cross-protective efficacy against heterologous viruses A/PR/8/34 (H1N1) and A/New Caledonia/20/99 (H1N1) in mice was assessed. Vaccination with 2009 H1 VLPs induced significantly higher levels of IgG cross-reactive with these heterologous viruses after the second boost compared to after the prime or first boost. Lung virus titers also decreased significantly and the lung cross-reactive IgG response after lethal virus challenge was significantly greater in immunized mice compared to naïve mice. Vaccinated mice showed 100% protection against A/PR/8/34 and A/Caledonia/20/99 viruses with only moderate body weight loss and induction of cross-reactive recall, IgG antibody-secreting cell responses. The variations in HA amino acid sequences and antigenic sites were determined and correlated with induction of cross-protective immunity. These results indicate that VLPs can be used as an effective vaccine that confers cross-protection against antigenically distinct viruses.