2009 pandemic influenza A (H1N1): pathology and pathogenesis of 100 fatal cases in the United States

Long-term survival of influenza virus infected club cells drives immunopathology

Respiratory infection of influenza A virus (IAV) is frequently characterized by extensive immunopathology and proinflammatory signaling that can persist after virus clearance. In this report, we identify cells that become infected, but survive, acute influenza virus infection. We demonstrate that these cells, known as club cells, elicit a robust transcriptional response to virus infection, show increased interferon stimulation, and induce high levels of proinflammatory cytokines after successful viral clearance. Specific depletion of these surviving cells leads to a reduction in lung tissue damage associated with IAV infection. We propose a model in which infected, surviving club cells establish a proinflammatory environment aimed at controlling virus levels, but at the same time contribute to lung pathology.

Use of linked electronic health records to assess mortality and length of stay associated with pandemic influenza A(H1N1)pdm09 at a UK teaching hospital

Effective use of data linkage is becoming an increasingly important focus in the new healthcare system in England. We linked data from the results of a multiplex PCR assay for respiratory viruses for a population of 230 inpatients at a UK teaching hospital with their patient administrative system records in order to compare the mortality and length of stay of patients who tested positive for influenza A(H1N1)pdm09 with those positive for another influenza A virus. The results indicated a reduced risk of death among influenza A(H1N1)pdm09 patients compared to other influenza A strains, with an adjusted risk ratio of 0·25 (95% confidence interval 0·08-0·75, P = 0·01), while no significant differences were found between the lengths of stay in the hospital for these two groups. Further development of such methods to link hospital data in a routine fashion could provide a rapid means of gaining epidemiological insights into emerging infectious diseases.

Pathogenic influenza B virus in the ferret model establishes lower respiratory tract infection

Influenza B viruses have become increasingly more prominent during influenza seasons. Influenza B infection is typically considered a mild disease and receives less attention than influenza A, but has been causing 20 to 50 % of the total influenza incidence in several regions around the world. Although there is increasing evidence of mid to lower respiratory tract diseases such as bronchitis and pneumonia in influenza B patients, little is known about the pathogenesis of recent influenza B viruses. Here we investigated the clinical and pathological profiles of infection with strains representing the two current co-circulating B lineages (B/Yamagata and B/Victoria) in the ferret model. Specifically, we studied two B/Victoria (B/Brisbane/60/2008 and B/Bolivia/1526/2010) and two B/Yamagata (B/Florida/04/2006 and B/Wisconsin/01/2010) strain infections in ferrets and observed strain-specific but not lineage-specific pathogenicity. We found B/Brisbane/60/2008 caused the most severe clinical illness and B/Brisbane/60/2008 and the B/Yamagata strains instigated pathology in the middle to lower respiratory tract. Importantly, B/Brisbane/60/2008 established efficient lower respiratory tract infection with high viral burden. Our phylogenetic analyses demonstrate profound reassortment among recent influenza B viruses, which indicates the genetic make-up of B/Brisbane/60/2008 differs from the other strains. This may explain the pathogenicity difference post-infection in ferrets.

HIV-1 and its gp120 inhibits the influenza A(H1N1)pdm09 life cycle in an IFITM3-dependent fashion

HIV-1-infected patients co-infected with A(H1N1)pdm09 surprisingly presented benign clinical outcome. The knowledge that HIV-1 changes the host homeostatic equilibrium, which may favor the patient resistance to some co-pathogens, prompted us to investigate whether HIV-1 infection could influence A(H1N1)pdm09 life cycle in vitro. We show here that exposure of A(H1N1)pdm09-infected epithelial cells to HIV-1 viral particles or its gp120 enhanced by 25% the IFITM3 content, resulting in a decrease in influenza replication. This event was dependent on toll-like receptor 2 and 4. Moreover, knockdown of IFITM3 prevented HIV-1 ability to inhibit A(H1N1)pdm09 replication. HIV-1 infection also increased IFITM3 levels in human primary macrophages by almost 100%. Consequently, the arrival of influenza ribonucleoproteins (RNPs) to nucleus of macrophages was inhibited, as evaluated by different approaches. Reduction of influenza RNPs entry into the nucleus tolled A(H1N1)pdm09 life cycle in macrophages earlier than usual, limiting influenza's ability to induce TNF-α. As judged by analysis of the influenza hemagglutin (HA) gene from in vitro experiments and from samples of HIV-1/A(H1N1)pdm09 co-infected individuals, the HIV-1-induced reduction of influenza replication resulted in delayed viral evolution. Our results may provide insights on the mechanisms that may have attenuated the clinical course of Influenza in HIV-1/A(H1N1)pdm09 co-infected patients during the recent influenza form 2009/2010.

Encephalitis related to a H1N1 vaccination: case report and review of the literature

OBJECTIVES

To illustrate that acute, even dramatic, demyelination of the central nervous system and encephalitis can occur after viral, i.e., influenza A/H1N1 vaccination or infection.

PATIENTS AND METHODS

We describe a case of encephalitis/acute disseminated encephalomyelitis associated with vaccination against influenza A/H1N1 and review the available literature.

RESULTS

We report a case of a 26-year-old female who developed symptoms of acute encephalitis 5 days after vaccination against the pandemic 2009 A/H1N1 influenza. MRI of the brain showed confluent T2-hyperintense signal intensity changes in the deep white matter which further confirmed the diagnosis of encephalitis/acute disseminated encephalomyelitis. Despite therapy with immunoglobulins and corticosteroids, her persistent vegetative state continued. In light of the dramatic cause of this case, we reviewed all 21 other previously reported cases of central nervous system demyelination related to H1N1 vaccination and/or infection.

CONCLUSIONS

The available data suggest that even severe central nervous system demyelination i.e. acute encephalitis/disseminated encephalomyelitis and transverse myelitis may very rarely be associated with vaccination against novel influenza A/H1N1 or with A/H1N1 infection itself.

Influenza and endemic viral pneumonia

Viruses are a common and important cause of severe community-acquired pneumonia, and may lead to severe respiratory disease and admission to the intensive care unit. Influenza is the most common virus associated with severe viral pneumonia, although other important causes include respiratory syncytial virus, adenovirus, metapneumonia virus, and coronaviruses. Viral pneumonias tend to have a seasonal predilection and are often preceded by a typical viral prodrome. This article focuses on severe influenza pneumonia, including the 2009 H1N1 pandemic, and briefly discusses other causes of severe respiratory disease of viral etiology.

Molecular basis of a pandemic of avian-type influenza virus

Despite heroic efforts to prevent the emergence of an influenza pandemic, avian influenza A virus has prevailed by crossing the species barriers to infect humans worldwide, occasionally with morbidity and mortality at unprecedented levels, and the virus later usually continues circulation in humans as a seasonal influenza virus, resulting in health-social-economic problems each year. Here, we review current knowledge of influenza viruses, their life cycle, interspecies transmission, and past pandemics and discuss the molecular basis of pandemic acquisition, notably of hemagglutinin (lectin) acting as a key contributor to change in host specificity in viral infection.

Viral-bacterial interactions-therapeutic implications

Viral and bacterial respiratory tract infections are a leading cause of morbidity and mortality worldwide, despite the development of vaccines and potent antibiotics. Frequently, viruses and bacteria can co‐infect the same host, resulting in heightened pathology and severity of illness compared to single infections. Bacterial superinfections have been a significant cause of death during every influenza pandemic, including the 2009 H1N1 pandemic. This review will analyze the epidemiology and global impact of viral and bacterial co‐infections of the respiratory tract, with an emphasis on bacterial infections following influenza. We will next examine the mechanisms by which viral infections enhance the acquisition and severity of bacterial infections. Finally, we will discuss current management strategies for diagnosing and treating patients with suspected or confirmed viral‐bacterial infections of the respiratory tract. Further investigation into the interactions between viral and bacterial infections is necessary for developing new therapeutic approaches aimed at mitigating the severity of co‐infections.

Bacterial and viral infections associated with influenza

Influenza‐associated bacterial and viral infections are responsible for high levels of morbidity and death during pandemic and seasonal influenza episodes. A review was undertaken to assess and evaluate the incidence, epidemiology, aetiology, clinical importance and impact of bacterial and viral co‐infection and secondary infection associated with influenza. A review was carried out of published articles covering bacterial and viral infections associated with pandemic and seasonal influenza between 1918 and 2009 (and published through December 2011) to include both pulmonary and extra‐pulmonary infections. While pneumococcal infection remains the predominant cause of bacterial pneumonia, the review highlights the importance of other co‐ and secondary bacterial and viral infections associated with influenza, and the emergence of newly identified dual infections associated with the 2009 H1N1 pandemic strain. Severe influenza‐associated pneumonia is often bacterial and will necessitate antibiotic treatment. In addition to the well‐known bacterial causes, less common bacteria such as Legionella pneumophila may also be associated with influenza when new influenza strains emerge. This review should provide clinicians with an overview of the range of bacterial and viral co‐ or secondary infections that could present with influenza illness.

Impact of preceding flu-like illness on the serotype distribution of pneumococcal pneumonia

BACKGROUND

Even though the pathogenicity and invasiveness of pneumococcus largely depend on capsular types, the impact of serotypes on post-viral pneumococcal pneumonia is unknown.

METHODS AND FINDINGS

This study was performed to evaluate the impact of capsular serotypes on the development of pneumococcal pneumonia after preceding respiratory viral infections. Patients with a diagnosis of pneumococcal pneumonia were identified. Pneumonia patients were divided into two groups (post-viral pneumococcal pneumonia versus primary pneumococcal pneumonia), and then their pneumococcal serotypes were compared. Nine hundred and nineteen patients with pneumococcal pneumonia were identified during the study period, including 327 (35.6%) cases with post-viral pneumococcal pneumonia and 592 (64.4%) cases with primary pneumococcal pneumonia. Overall, serotypes 3 and 19A were the most prevalent, followed by serotypes 19F, 6A, and 11A/11E. Although relatively uncommon (33 cases, 3.6%), infrequently colonizing invasive serotypes (4, 5, 7F/7A, 8, 9V/9A, 12F, and 18C) were significantly associated with preceding respiratory viral infections (69.7%, P<0.01). Multivariate analysis revealed several statistically significant risk factors for post-viral pneumococcal pneumonia: immunodeficiency (OR 1.66; 95% CI, 1.10-2.53), chronic lung diseases (OR 1.43; 95% CI, 1.09-1.93) and ICI serotypes (OR 4.66; 95% CI, 2.07-10.47).

CONCLUSIONS

Infrequently colonizing invasive serotypes would be more likely to cause pneumococcal pneumonia after preceding respiratory viral illness, particularly in patients with immunodeficiency or chronic lung diseases.

Protection of ferrets from pulmonary injury due to H1N1 2009 influenza virus infection: immunopathology tractable by sphingosine-1-phosphate 1 receptor agonist therapy

Influenza infection of humans remains an important public health problem. Vaccine strategies result in a significant but only partial control (65-85%) of infection. Thus, chemotherapeutic approaches are needed to provide a solution both for vaccine failures and to limit infection in the unvaccinated population. Previously (Walsh et al., 2011; Teijaro et al., 2011) documented that sphingosine-1-phosphate 1 receptor (S1P1R) agonists significantly protected mice against pathogenic H1N1 influenza virus by limiting immunopathologic damage while allowing host control of the infection. Here we extend that observation by documenting S1P1R agonist can control pathogenic H1N1 influenza infection in ferrets. S1P1R agonist was more effective in reducing pulmonary injury than the antiviral drug oseltamivir but, importantly, combined therapy was significantly more effective than either therapy alone.

The pathology and pathogenesis of experimental severe acute respiratory syndrome and influenza in animal models

Respiratory viruses that emerge in the human population may cause high morbidity and mortality, as well as concern about pandemic spread. Examples are severe acute respiratory syndrome coronavirus (SARS-CoV) and novel variants of influenza A virus, such as H5N1 and pandemic H1N1. Different animal models are used to develop therapeutic and preventive measures against such viruses, but it is not clear which are most suitable. Therefore, this review compares animal models of SARS and influenza, with an emphasis on non-human primates, ferrets and cats. Firstly, the pathology and pathogenesis of SARS and influenza are compared. Both diseases are similar in that they affect mainly the respiratory tract and cause inflammation and necrosis centred on the pulmonary alveoli and bronchioles. Important differences are the presence of multinucleated giant cells and intra-alveolar fibrosis in SARS and more fulminant necrotizing and haemorrhagic pneumonia in H5N1 influenza. Secondly, the pathology and pathogenesis of SARS and influenza in man and experimental animals are compared. Host species, host age, route of inoculation, location of sampling and timing of sampling are important to design an animal model that most closely mimics human disease. The design of appropriate animal models requires an accurate pathological description of human cases, as well as a good understanding of the effect of experimental variables on disease outcome.

The hemagglutinin: a determinant of pathogenicity

The hemagglutinin (HA) is a prime determinant of the pathogenicity of influenza A viruses. It initiates infection by binding to cell surface receptors and by inducing membrane fusion. The fusion capacity of HA depends on cleavage activation by host proteases, and it has long been known that highly pathogenic avian influenza viruses displaying a multibasic cleavage site differ in protease sensitivity from low pathogenic avian and mammalian influenza viruses with a monobasic cleavage site. Evidence is increasing that there are also variations in proteolytic activation among the viruses with a monobasic cleavage site, and several proteases have been identified recently that activate these viruses in a natural setting. Differences in protease sensitivity of HA and in tissue specificity of the enzymes are important determinants for virus tropism in the respiratory tract and for systemic spread of infection. Protease inhibitors that interfere with cleavage activation have the potential to be used for antiviral therapy and attenuated viruses have been generated by mutation of the cleavage site that can be used for the development of inactivated and live vaccines. It has long been known that human and avian influenza viruses differ in their specificity for sialic acid-containing cell receptors, and it is now clear that human tissues contain also receptors for avian viruses. Differences in receptor-binding specificity of seasonal and zoonotic viruses and differential expression of receptors for these viruses in the human respiratory tract account, at least partially, for the severity of disease. Receptor binding and fusion activation are modulated by HA glycosylation, and interaction of the glycans of HA with cellular lectins also affects virus infectivity. Interestingly, some of the mechanisms underlying pathogenicity are determinants of host range and transmissibility, as well.

Influenza A(H1N1)pdm09-related pneumonia and other complications

Influenza A(H1N1)pdm09 virus infection was associated with significant morbidity, mainly among children and young adults. The majority of patients had self-limited mild-to-moderate uncomplicated disease. However, some patients developed severe illness and some died. In addition to respiratory complications, several complications due to direct and indirect effects on other body systems were associated with influenza A(H1N1)pdm09 virus infection. The main complications reported in hospitalized adults with influenza A(H1N1)pdm09 were pneumonia (primary influenza pneumonia and concomitant/secondary bacterial pneumonia), exacerbations of chronic pulmonary diseases (mainly chronic obstructive pulmonary disease and asthma), the need for intensive unit care admission (including mechanical ventilation, acute respiratory distress syndrome and septic shock), nosocomial infections and acute cardiac events. In experimentally infected animals, the level of pulmonary replication of the influenza A(H1N1)pdm09 virus was higher than that of seasonal influenza viruses. Pathological studies in autopsy specimens indicated that the influenza A(H1N1)pdm09 virus mainly targeted the lower respiratory tract, resulting in diffuse alveolar damage (edema, hyaline membranes, inflammation, and fibrosis), manifested clinically by severe acute respiratory distress syndrome with refractory hypoxemia. Influenza A(H1N1)pdm09-related pneumonia and other complications were associated with increased morbidity and mortality among hospitalized patients.

Pandemic influenza A/H1N1: comparative analysis of microscopic lung histopathological findings

OBJECTIVE

To analyze the histopathological lung findings of four fatal cases of the 2009 H1N1 influenza pandemic and their correlation with clinical and epidemiological characteristics.

METHODS

Descriptive data from medical records of four patients who died in the Intensive Care Unit of a university hospital in 2009. Nasopharyngeal aspirate specimens were collected from the patients and were analyzed by real-time polymerase chain reaction. Lung biopsy was performed post mortem; a score of intensity for pathological changes was applied.

RESULTS

Three patients had positive real-time polymerase chain reaction (although all of them had a clinical diagnose of influenza H1N1). The main histopathological changes were: exudative diffuse alveolar damage with atelectasis; varying degrees of alveolar hemorrhage and edema, necrosis and sloughing of the respiratory epithelium in several bronchioli; and thrombus formation. One of the patients (the pregnant one) presented histopathological findings of cytomegalic inclusion.

CONCLUSION

The pulmonary histopathological findings in patients with fatal 2009 H1N1 influenza pandemic disclosed intense alveolar damage and hemorrhage and severe bronchiolitis. A co-infection with cytomegalovirus was described in the pregnant patient.

Characterization of innate responses to influenza virus infection in a novel lung type I epithelial cell model

Type I alveolar epithelial cells are a replicative niche for influenza in vivo, yet their response to infection is not fully understood. To better characterize their cellular responses, we have created an immortalized murine lung epithelial type I cell line (LET1). These cells support spreading influenza virus infection in the absence of exogenous protease and thus permit simultaneous analysis of viral replication dynamics and host cell responses. LET1 cells can be productively infected with human, swine and mouse-adapted strains of influenza virus and exhibit expression of an antiviral transcriptional programme and robust cytokine secretion. We characterized influenza virus replication dynamics and host responses of lung type I epithelial cells and identified the capacity of epithelial cell-derived type I IFN to regulate specific modules of antiviral effectors to establish an effective antiviral state. Together, our results indicate that the type I epithelial cell can play a major role in restricting influenza virus infection without contribution from the haematopoietic compartment.

Early host responses of seasonal and pandemic influenza A viruses in primary well-differentiated human lung epithelial cells

Replication, cell tropism and the magnitude of the host's antiviral immune response each contribute to the resulting pathogenicity of influenza A viruses (IAV) in humans. In contrast to seasonal IAV in human cases, the 2009 H1N1 pandemic IAV (H1N1pdm) shows a greater tropism for infection of the lung similar to H5N1. We hypothesized that host responses during infection of well-differentiated, primary human bronchial epithelial cells (wd-NHBE) may differ between seasonal (H1N1 A/BN/59/07) and H1N1pdm isolates from a fatal (A/KY/180/10) and nonfatal (A/KY/136/09) case. For each virus, the level of infectious virus and host response to infection (gene expression and apical/basal cytokine/chemokine profiles) were measured in wd-NHBE at 8, 24, 36, 48 and 72 hours post-infection (hpi). At 24 and 36 hpi, KY/180 showed a significant, ten-fold higher titer as compared to the other two isolates. Apical cytokine/chemokine levels of IL-6, IL-8 and GRO were similar in wd-NHBE cells infected by each of these viruses. At 24 and 36 hpi, NHBE cells had greater levels of pro-inflammatory cytokines including IFN-α, CCL2, TNF-α, and CCL5, when infected by pandemic viruses as compared with seasonal. Polarization of IL-6 in wd-NHBE cells was greatest at 36 hpi for all isolates. Differential polarized secretion was suggested for CCL5 across isolates. Despite differences in viral titer across isolates, no significant differences were observed in KY/180 and KY/136 gene expression intensity profiles. Microarray profiles of wd-NHBE cells diverged at 36 hpi with 1647 genes commonly shared by wd-NHBE cells infected by pandemic, but not seasonal isolates. Significant differences were observed in cytokine signaling, apoptosis, and cytoskeletal arrangement pathways. Our studies revealed differences in temporal dynamics and basal levels of cytokine/chemokine responses of wd-NHBE cells infected with each isolate; however, wd-NHBE cell gene intensity profiles were not significantly different between the two pandemic isolates suggesting post-transcriptional or later differences in viral-host interactions.

Pathogenesis of influenza-induced acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a fatal complication of influenza infection. In this Review we provide an integrated model for its pathogenesis. ARDS involves damage to the epithelial-endothelial barrier, fluid leakage into the alveolar lumen, and respiratory insufficiency. The most important part of the epithelial-endothelial barrier is the alveolar epithelium, strengthened by tight junctions. Influenza virus targets these epithelial cells, reducing sodium pump activity, damaging tight junctions, and killing infected cells. Infected epithelial cells produce cytokines that attract leucocytes--neutrophils and macrophages--and activate adjacent endothelial cells. Activated endothelial cells and infiltrated leucocytes stimulate further infiltration, and leucocytes induce production of reactive oxygen species and nitric oxide that damage the barrier. Activated macrophages also cause direct apoptosis of epithelial cells. This model for influenza-induced ARDS differs from the classic model, which is centred on endothelial damage, and provides a rationale for therapeutic intervention to moderate host response in influenza-induced ARDS.

The value of radiographic findings for the progression of pandemic 2009 influenza A/H1N1 virus infection

Background

Most illnesses caused by pandemic influenza A (H1N1) pdm09 virus (A/H1N1) infection are acute and self-limiting among children. However, in some children, disease progression is rapid and may require hospitalization and transfer to a pediatric intensive care unit (PICU). We investigated factors associated with rapid disease progression among children admitted to hospital for A/H1N1 infection, particularly findings on initial chest radiographs.

Methods

In this retrospective study, we investigated the records of children who had received a laboratory or clinical diagnosis of A/H1N1 infection and were admitted to the largest children’s hospital in Japan between May 2009 and March 2010. The medical records were reviewed for age, underlying diseases, vital signs on admission, initial chest radiographic findings, and clinical outcomes. According to chest radiographic findings, patients were classified into 4 groups, as follows: [1] normal (n = 46), [2] hilar and/or peribronchial markings alone (n = 64), [3] consolidation (n = 64), and [4] other findings (n = 29). Factors associated with clinical outcomes were analyzed using logistic regression.

Results

Two hundreds and three patients (median 6.8 years) were enrolled in this study. Fifteen percent (31/203) of patients were admitted to PICU. Among 31 patients, 39% (12/31) of patients required mechanical ventilation (MV). When the initial chest radiographic findings were compared between patients with consolidation (n = 64) and those without consolidation (n = 139), a higher percentage of patients with consolidation were admitted to PICU (29.7% vs.8.6%, P < 0.001) and required MV (17.2% vs. 0.7%, P < 0.001). These findings remain significant when the data were analyzed with the logistic regression (P < 0.001, P < 0.001, respectively).

Conclusions

Consolidation on initial chest radiographs was the most significant factor to predict clinical course of hospitalized children with the 2009 A/H1N1 infection.

Pandemic H1N1 influenza A directly induces a robust and acute inflammatory gene signature in primary human bronchial epithelial cells downstream of membrane fusion

Pandemic H1N1 influenza A (H1N1pdm) elicits stronger pulmonary inflammation than previously circulating seasonal H1N1 influenza A (sH1N1), yet mechanisms of inflammatory activation in respiratory epithelial cells during H1N1pdm infection are unclear. We investigated host responses to H1N1pdm/sH1N1 infection and virus entry mechanisms in primary human bronchial epithelial cells in vitro. H1N1pdm infection rapidly initiated a robust inflammatory gene signature (3 h post-infection) not elicited by sH1N1 infection. Protein secretion inhibition had no effect on gene induction. Infection with membrane fusion deficient H1N1pdm failed to induce robust inflammatory gene expression which was rescued with restoration of fusion ability, suggesting H1N1pdm directly triggered the inflammatory signature downstream of membrane fusion. Investigation of intra-virion components revealed H1N1pdm viral RNA (vRNA) triggered a stronger inflammatory phenotype than sH1N1 vRNA. Thus, our study is first to report H1N1pdm induces greater inflammatory gene expression than sH1N1 in vitro due to direct virus-epithelial cell interaction.

Computed tomography findings in patients with H1N1 influenza A infection

The present study aimed to review high resolution computed tomography findings in patients with H1N1 influenza A infection. The most common tomographic findings include ground-glass opacities, areas of consolidation or a combination of both patterns. Some patients may also present bronchial wall thickening, airspace nodules, crazy-paving pattern, perilobular opacity, air trapping and findings related to organizing pneumonia. These abnormalities are frequently bilateral, with subpleural distribution. Despite their nonspecificity, it is important to recognize the main tomographic findings in patients affected by H1N1 virus in order to include this possibility in the differential diagnosis, characterize complications and contribute in the follow-up, particularly in cases of severe disease.

Molecular characterization of Staphylococcus aureus and influenza virus coinfections in patients with fatal Pneumonia

Molecular techniques were used to characterize genetic features of Staphylococcus aureus in 66 fatal cases of pneumonia caused by S. aureus and influenza A or B viruses. Nucleic acids were extracted from formalin-fixed, paraffin-embedded tissues. The majority of cases revealed genetic markers for Panton-Valentine leukocidin, mecA, and spa type t008.

Cytokine and chemokine profiles in lung tissues from fatal cases of 2009 pandemic influenza A (H1N1): role of the host immune response in pathogenesis

Pathological studies on fatal cases caused by 2009 pandemic influenza H1N1 virus (2009 pH1N1) reported extensive diffuse alveolar damage and virus infection predominantly in the lung parenchyma. However, the host immune response after severe 2009 pH1N1 infection is poorly understood. Herein, we investigated viral load, the immune response, and apoptosis in lung tissues from 50 fatal cases with 2009 pH1N1 virus infection. The results suggested that 7 of the 27 cytokines/chemokines showed remarkably high expression, including IL-1 receptor antagonist protein, IL-6, tumor necrosis factor-α, IL-8, monocyte chemoattractant protein-1, macrophage inflammatory protein 1-β, and interferon-inducible protein-10 in lung tissues of 2009 pH1N1 fatal cases. Viral load, which showed the highest level on day 7 of illness onset and persisted until day 17 of illness, was positively correlated with mRNA levels of IL-1 receptor antagonist protein, monocyte chemoattractant protein-1, macrophage inflammatory protein 1-β, interferon-inducible protein-10, and regulated on activation normal T-cell expressed and secreted. Apoptosis was evident in lung tissues stained by the TUNEL assay. Decreased Fas and elevated FasL mRNA levels were present in lung tissues, and cleaved caspase-3 was frequently seen in pneumocytes, submucosal glands, and lymphoid tissues. The pathogenesis of the 2009 pH1N1 virus infection is associated with viral replication and production of proinflammatory mediators. FasL and caspase-3 are involved in the pathway of 2009 pH1N1 virus-induced apoptosis in lung tissues, and the disequilibrium between the Fas and FasL level in lung tissues could contribute to delayed clearance of the virus and subsequent pathological damages.

Neutrophilic bacterial meningitis: pathology and etiologic diagnosis of fatal cases

The frequency of fatalities due to acute bacterial meningitis has decreased significantly due to vaccinations, early diagnoses, and treatments. We studied brain tissues of patients with fatal neutrophilic meningitis referred to the Centers for Disease Control for etiologic diagnosis from 2000-2009 to highlight aspects of the disease that may be preventable or treatable. Demographic, clinical, and laboratory data were extracted from records. Of 117 cases in the database with a diagnosis of meningitis or meningoencephalitis, 39 had neutrophilic inflammation in the meninges. Inflammatory cells infiltrated the superficial cortex in 16 of 39 (41%) cases. Bacteria were found using Gram and bacterial silver stains in 72% of cases, immunohistochemistry in 69% (including two cases where the meningococcus was found outside the meninges), and PCR in 74%. Streptococcus pneumoniae was the cause of the meningitis in 14 patients and Neisseria meningitidis in 9. In addition, Streptococcus spp. were found to be the cause in six cases, while Staphylococcus aureus, Staphylococcus spp., Enterococcus spp., and Fusobacterium were the cause of one case each. There were six cases in which no specific etiological agent could be determined. The mean age of the patients with S. pneumoniae was 39 years (range 0-65), with N. meningitidis was 19 years (range 7-51), whereas that for all others was 31 years (range 0-68). In summary, our study shows that S. pneumoniae continues to be the most frequent cause of fatal neutrophilic bacterial meningitis followed by N. meningitidis, both vaccine preventable diseases.

Influenza and respiratory syncytial virus are the major respiratory viruses detected from prospective testing of pediatric and adult coronial autopsies

BACKGROUND

To ascertain the full mortality of influenza and other respiratory viruses, the testing of community autopsy specimens is essential.

METHODS

Respiratory virus PCR and culture were performed on 2418 fresh unfrozen respiratory samples collected from 1611 coronial cases where the death was either unknown or infection was suspected, from July 2007 to June 2011, to detect the common respiratory viruses in children and adults, using standardized microbiological testing.

RESULTS

The respiratory virus positive rate was 8·3% (134 cases) with a peak of 28% (42 of 151 cases) in children under 10 years of age. Influenza virus was the commonest respiratory virus (50 cases, 3%), followed by respiratory syncytial virus (RSV) (30 cases, 2%). All tested respiratory viruses were found in children, most commonly adenovirus, enterovirus and RSV, and influenza A and RSV predominated in those over 60 years, but coinfection was uncommon. Almost all influenza cases occurred when influenza was widely circulating in the community but few were diagnosed pre-mortem. Influenza and RSV detection was associated with bronchitis or bronchiolitis in 7 (9%) of the 80 cases and caused pneumonia in 14 (0·8%) deaths overall.

CONCLUSIONS

Our prospective review of respiratory viruses using standardized testing found a single lower respiratory tract autopsy specimen for respiratory virus PCR would detect most community infections at the time of death.

Identifying the interaction between influenza and pneumococcal pneumonia using incidence data

The association between influenza virus and the bacterium Streptococcus pneumoniae (pneumococcus) has been proposed as a polymicrobial system, whereby transmission and pathogenicity of one pathogen (the bacterium) are affected by interactions with the other (the virus). However, studies focusing on different scales of resolution have painted an inconsistent picture: Individual-scale animal experiments have unequivocally demonstrated an association, whereas epidemiological support in human populations is, at best, inconclusive. We integrate weekly incidence reports and a mechanistic transmission model within a likelihood-based inference framework to characterize the nature, timing, and magnitude of this interaction. We find support for a strong but short-lived interaction, with influenza infection increasing susceptibility to pneumococcal pneumonia ~100-fold. We infer modest population-level impacts arising from strong processes at the level of an individual, thereby resolving the dichotomy in seemingly inconsistent observations across scales. An accurate characterization of the influenza-pneumococcal interaction can form a basis for more effective clinical care and public health measures for pneumococcal pneumonia.

Use of ex vivo and in vitro cultures of the human respiratory tract to study the tropism and host responses of highly pathogenic avian influenza A (H5N1) and other influenza viruses

The tropism of influenza viruses for the human respiratory tract is a key determinant of host-range, and consequently, of pathogenesis and transmission. Insights can be obtained from clinical and autopsy studies of human disease and relevant animal models. Ex vivo cultures of the human respiratory tract and in vitro cultures of primary human cells can provide complementary information provided they are physiologically comparable in relevant characteristics to human tissues in vivo, e.g. virus receptor distribution, state of differentiation. We review different experimental models for their physiological relevance and summarize available data using these cultures in relation to highly pathogenic avian influenza H5N1, in comparison where relevant, with other influenza viruses. Transformed continuous cell-lines often differ in important ways to the corresponding tissues in vivo. The state of differentiation of primary human cells (respiratory epithelium, macrophages) can markedly affect virus tropism and host responses. Ex vivo cultures of human respiratory tissues provide a close resemblance to tissues in vivo and may be used to risk assess animal viruses for pandemic threat. Physiological factors (age, inflammation) can markedly affect virus receptor expression and virus tropism. Taken together with data from clinical studies on infected humans and relevant animal models, data from ex vivo and in vitro cultures of human tissues and cells can provide insights into virus transmission and pathogenesis and may provide understanding that leads to novel therapeutic interventions.

Differentiated phenotypes of primary murine alveolar epithelial cells and their susceptibility to infection by respiratory viruses

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Alveolar epithelial cells are important targets in severe respiratory viral infection.

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Murine ATI and ATII cultures are an in vitro model for viral pathogenesis.

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ATI cells are infected by IAV and MHV-1, not mouse-adapted SARS-CoV.

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ATII cells are infected by IAV, MHV-1, and mouse-adapted SARS-CoV.

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ATI and ATII cells express cytokines upon infection by respiratory viruses.

Severe respiratory viral infections are associated with spread to the alveoli of the lungs. There are multiple murine models of severe respiratory viral infections that have been used to identify viral and host factors that contribute to disease severity. Primary cultures of murine alveolar epithelial cells provide a robust in vitro model to perform mechanistic studies that can be correlated with in vivo studies to identify cell type-specific factors that contribute to pathology within the alveoli of the lung during viral infection. In this study, we established an in vitro model to compare the responses of type I (ATI) and type II (ATII) alveolar epithelial cells to infection by respiratory viruses used in murine models: mouse-adapted severe acute respiratory syndrome-associated coronavirus (SARS-CoV, v2163), murine coronavirus MHV-1, and influenza A (H1N1) virus, strain PR8. Murine alveolar cells cultured to maintain an ATII cell phenotype, determined by expression of LBP180, were susceptible to infection by all three viruses. In contrast, ATII cells that were cultured to trans-differentiate into an ATI-like cell phenotype were susceptible to MHV-1 and PR8, but not mouse-adapted SARS-CoV. Epithelial cells produce cytokines in response to viral infections, thereby activating immune responses. Thus, virus-induced cytokine expression was quantified in ATI and ATII cells. Both cell types had increased expression of IL-1β mRNA upon viral infection, though at different levels. While MHV-1 and PR8 induced expression of a number of shared cytokines in ATI cells, there were several cytokines whose expression was induced uniquely by MHV-1 infection. In summary, ATI and ATII cells exhibited differential susceptibilities and cytokine responses to infection by respiratory viruses. This in vitro model will be critical for future studies to determine the roles of these specialized cell types in the pathogenesis of respiratory viral infection.

Altered response to A(H1N1)pnd09 vaccination in pregnant women: a single blinded randomized controlled trial

Background

Pregnant women were suspected to be at particular risk when H1N1pnd09 influenza became pandemic in 2009. Our primary objective was to compare the immune responses conferred by MF59®-adjuvanted vaccine (Focetria®) in H1N1pnd09-naïve pregnant and non-pregnant women. The secondary aims were to compare influences of dose and adjuvant on the immune response.

Methods

The study was nested in the Copenhagen Prospective Studies on Asthma in Childhood (COPSAC₂₀₁₀) pregnancy cohort in 2009-2010 and conducted as a single-blinded block-randomised [1∶1∶1] controlled clinical trial in pregnant women after gestational week 20: (1) 7.5 µg H1N1pnd09 antigen with MF59-adjuvant (Pa7.5 µg); (2) 3.75 µg antigen half MF59-adjuvanted (Pa3.75 µg); (3) 15 µg antigen unadjuvanted (P15 µg); and in non-pregnant women receiving (4) 7.5 µg antigen full adjuvanted (NPa7.5 µg). Blood samples were collected at baseline, 3 weeks, 3 and 10 months after vaccination, adverse events were recorded prospectively.

Results

58 pregnant women were allocated to Pa7.5 µg and 149 non-pregnant women were recruited to NPa7.5 µg. The sero-conversion rate was significantly increased in non-pregnant (NPa7.5 µg) compared with pregnant (Pa7.5 µg) women (OR = 2.48 [1.03–5.95], p = 0.04) and geometric mean titers trended towards being higher, but this difference was not statistically significant (ratio 1.27 [0.85–1.93], p = 0.23). The significant titer increase rate showed no difference between pregnant (Pa7.5 µg) and non-pregnant (NPa7.5 µg) groups (OR = 0.49 [0.13–1.85], p = 0.29).

Conclusion

Our study suggests the immune response to the 7.5 µg MF59-adjuvanted Focetria® H1N1pnd09 vaccine in pregnant women may be diminished compared with non-pregnant women.

Trial Registration

ClinicalTrials.gov NCT01012557.

Clinical characteristics and outcomes in hospitalized patients with respiratory viral co-infection during the 2009 H1N1 influenza pandemic

Background

The clinical consequences of co-infection with two or more respiratory viruses are poorly understood. We sought to determine if co-infection with pandemic 2009–2010 influenza A H1N1 (pH1N1) and another respiratory virus was associated with worse clinical outcomes.

Methods

A retrospective cohort study was performed of all hospitalized patients with a positive respiratory viral panel (RVP) for two or more viruses within 72 hours of admission at our institution from October 2009 to December 2009. We compared patients infected with one respiratory virus to those with respiratory viral co-infection.

Results

We identified 617 inpatients with a positive RVP sample with a single virus and 49 inpatients with a positive RVP sample for two viruses (i.e. co-infection). Co-infected patients were significantly younger, more often had fever/chills, tachypnea, and they more often demonstrated interstitial opacities suggestive of viral pneumonia on the presenting chest radiograph (OR 7.5, 95% CI 3.4–16.5). The likelihood of death, length of stay, and requirement for intensive care unit level of care were similar in both groups, but patients with any respiratory virus co-infection were more likely to experience complications, particularly treatment for a secondary bacterial pneumonia (OR 6.8, 95% CI 3.3–14.2). Patients co-infected with pH1N1 and another respiratory virus were more likely to present with chest radiograph changes suggestive of a viral pneumonia, compared to mono-infection with pH1N1 (OR 16.9, 95% CI 4.5–62.7). By logistic regression using mono-infection with non-PH1N1 viruses as the reference group, co-infection with pH1N1 was the strongest independent predictor of treatment for a secondary bacterial pneumonia (OR 17.8, 95% CI 6.7–47.1).

Conclusion

Patients with viral co-infection, particularly with pH1N1, were more likely to have chest radiograph features compatible with a viral pneumonia and complications during their hospital course, particularly treatment for secondary bacterial pneumonia. Despite this, co-infection was not associated with ICU admission.

Benefit of conjugate pneumococcal vaccination in preventing influenza hospitalization in children: a case-control study

BACKGROUND

The pneumococcal conjugate vaccine (PCV) might prevent hospitalizations in children because of the role of Streptococcus pneumoniae in the complications of influenza infection. We investigated the benefit of PCV vaccination in preventing influenza hospitalization in children <5 years of age during the 2009 to 2010 pandemic wave and the 2010 to 2011 influenza epidemic in Spain.

METHODS

A multicenter matched case-control study was undertaken in 27 hospitals from 7 Spanish regions between July 2009 and April 2011. A case was defined as a hospitalized patient between 6 months and 5 years of age with influenza virus infection confirmed by real-time reverse-transcription polymerase chain reaction. We selected 2 matched controls for each case from patients with unplanned hospital admission for reasons other than acute respiratory infection or influenza-like illness. Cases and controls were matched according to age, date of hospitalization and province of residence. Crude and adjusted odds ratios were calculated for associations between influenza hospitalization and PCV vaccination.

RESULTS

One hundred ninety-four cases and 342 controls were included in the study. In the 2009 to 2010 pandemic wave, the adjusted benefit in preventing hospitalization was 48% (95% confidence interval: 1 to 76) in fully vaccinated children compared with -79% (95% confidence interval: -341 to 27) in the 2010 to 2011 influenza season.

CONCLUSIONS

The results obtained suggest that, in children <5 years of age, PCV vaccination reduced hospitalization during the 2009 to 2010 pandemic wave. By contrast, there was no observed benefit of vaccination in the 2010 to 2011 influenza season.

Effectiveness of vaccination with 23-valent pneumococcal polysaccharide vaccine in preventing hospitalization with laboratory confirmed influenza during the 2009-2010 and 2010-2011 seasons

BACKGROUND

Since influenza predisposes to bacterial pneumonia caused by Streptococcus pneumoniae, studies have suggested that pneumococcal vaccination might reduce its occurrence during pandemics. We assessed the effectiveness of pneumococcal polysaccharide vaccination alone and in combination with influenza vaccination in preventing influenza hospitalization during the 2009-2010 pandemic wave and 2010-2011 influenza epidemic.

RESULTS

1187 cases and 2328 controls were included. The adjusted estimate of effectiveness of pneumococcal vaccination in preventing influenza hospitalization was 41% (95% CI 8-62) in all patients and 43% (95% CI 2-78) in patients aged ≥ 65 y. The adjusted effectiveness of dual PPV23 and influenza vaccination was 81% (95% CI 65-90) in all patients and 76% (95% CI 46-90) in patients aged ≥ 65 y. The adjusted effectiveness of influenza vaccination alone was 58% (95% CI 38-72).

METHODS

We conducted a multicenter case-control study in 36 Spanish hospitals. We selected patients aged ≥ 18 y hospitalized with confirmed influenza and two hospitalized controls per case, matched according to age, date of hospitalization and province of residence. Multivariate analysis was performed using conditional logistic regression. Subjects were considered vaccinated if they had received the pneumococcal or seasonal influenza vaccine>14 d (or>7 d for pandemic influenza vaccine) before the onset of symptoms (cases) or the onset of symptoms in matched cases (controls).

CONCLUSIONS

In elderly people and adults with chronic illness, pneumococcal vaccination may reduce hospitalizations during the influenza season. In people vaccinated with both the influenza and pneumococcal vaccines, the benefit in hospitalizations avoided was greater than in those vaccinated only against influenza.

The battle between influenza and the innate immune response in the human respiratory tract

Influenza is a viral infection of the respiratory tract. Infection is normally confined to the upper respiratory tract but certain viral strains have evolved the ability to infect the lower respiratory tract, including the alveoli, leading to inflammation and a disease pattern of diffuse alveolar damage. Factors leading to this sequence of events are novel influenza strains, or strains that have viral proteins, in particular the NS1 protein that allow it to escape the innate immune system. There are three main barriers that prevent infection of pneumocytes - mucin, host defence lectins and cells such as macrophages. Viruses have developed strategies such as neuraminidase and glycosylation patterns that allow this evasion. Though there has been much investment in antiviral drugs, it is proposed that more attention should be directed towards developing or utilizing compounds that enhance the ability of the innate immune system to combat viral infection.

Management of influenza infection in solid-organ transplant recipients: consensus statement of the Group for the Study of Infection in Transplant Recipients (GESITRA) of the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC) and the Spanish Network for Research in Infectious Diseases (REIPI)

BACKGROUND

Solid organ transplant (SOT) recipients are at greater risk than the general population for complications and mortality from influenza infection.

METHODS

Researchers and clinicians with experience in SOT infections have developed this consensus document in collaboration with several Spanish scientific societies and study networks related to transplant management. We conducted a systematic review to assess the management and prevention of influenza infection in SOT recipients. Evidence levels based on the available literature are given for each recommendation. This article was written in accordance with international recommendations on consensus statements and the recommendations of the Appraisal of Guidelines for Research and Evaluation II (AGREE II).

RESULTS

Recommendations are provided on the procurement of organs from donors with suspected or confirmed influenza infection. We highlight the importance of the possibility of influenza infection in any SOT recipient presenting upper or lower respiratory symptoms, including pneumonia. The importance of early antiviral treatment of SOT recipients with suspected or confirmed influenza infection and the necessity of annual influenza vaccination are emphasized. The microbiological techniques for diagnosis of influenza infection are reviewed. Guidelines for the use of antiviral prophylaxis in inpatients and outpatients are provided. Recommendations for household contacts of SOT recipients with influenza infection and health care workers in close contact with transplant patients are also included. Finally antiviral dose adjustment guidelines are presented for cases of impaired renal function and for pediatric populations.

CONCLUSIONS

The latest scientific information available regarding influenza infection in the context of SOT is incorporated into this document.

Glycomic analysis of human respiratory tract tissues and correlation with influenza virus infection

The first step in influenza infection of the human respiratory tract is binding of the virus to sialic (Sia) acid terminated receptors. The binding of different strains of virus for the receptor is determined by the α linkage of the sialic acid to galactose and the adjacent glycan structure. In this study the N- and O-glycan composition of the human lung, bronchus and nasopharynx was characterized by mass spectrometry. Analysis showed that there was a wide spectrum of both Sia α2-3 and α2-6 glycans in the lung and bronchus. This glycan structural data was then utilized in combination with binding data from 4 of the published glycan arrays to assess whether these current glycan arrays were able to predict replication of human, avian and swine viruses in human ex vivo respiratory tract tissues. The most comprehensive array from the Consortium for Functional Glycomics contained the greatest diversity of sialylated glycans, but was not predictive of productive replication in the bronchus and lung. Our findings indicate that more comprehensive but focused arrays need to be developed to investigate influenza virus binding in an assessment of newly emerging influenza viruses.

This study was performed to determine what possible glycan receptors for influenza were present in the human respiratory tract. We compared the glycans present on existing published glycan arrays with the actual glycans identified in the human respiratory tract by mass spectrometric analysis to determine how representative these arrays would be for potential binding. The most comprehensive array to date only contained approximately half the range of the actual glycans present. Over the past 5 years we have performed ex-vivo infection of 113 bronchial and 185 lung samples with seasonal, avian and swine influenza viruses, and have demonstrated that the lung is able to be infected by all types of influenza viruses but that the bronchus can also be infected by a limited range of avian, swine and seasonal viruses. The key findings are that there is wide spectrum of glycans present in the respiratory tract which can be used by influenza viruses for infection, and the currently available arrays are not predictive of successful infection. Our findings will be of use for researchers in developing more comprehensive and focused arrays for the screening of emerging influenza viruses and bacteria in order to determine their potential threat to humans.

Pathological study of archival lung tissues from five fatal cases of avian H5N1 influenza in Vietnam

Highly pathogenic avian H5N1 influenza virus (H5N1) infection in humans causes acute respiratory distress syndrome, leading to multiple organ failure. Five fatal cases of H5N1 infection in Vietnam were analyzed pathologically to reveal virus distribution, and local proinflammatory cytokine and chemokine expression profiles in formalin-fixed, paraffin-embedded lung tissues. Our main histopathological findings showed diffuse alveolar damage in the lungs. The infiltration of myeloperoxidase-positive and/or CD68 (clone KP-1)-positive neutrophils and monocytes/macrophages was remarkable in the alveolar septa and alveolar spaces. Immunohistochemistry revealed that H5N1 mainly infected alveolar epithelial cells and monocytes/macrophages in lungs. H5N1 replication was confirmed by detecting H5N1 mRNA in epithelial cells using in situ hybridization. Quantitation of H5N1 RNA using quantitative reverse transcription PCR assays revealed that the level of H5N1 RNA was increased in cases during early phases of the disease. We quantified the expression of tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, IL-8, regulated on activation normal T-cell expressed and secreted (commonly known as RANTES), and interferon-gamma-inducible protein of 10 kDa (IP-10) in formalin-fixed, paraffin-embedded lung sections. Their expression levels correlated with H5N1 RNA copy numbers detected in the same lung region. Double immunofluorescence staining revealed that TNF-α, IL-6, IL-8 and IP-10 were expressed in epithelial cells and/or monocytes/macrophages. In particular, IL-6 was also expressed in endothelial cells. The dissemination of H5N1 beyond respiratory organs was not confirmed in two cases examined in this study.

Predictive factors of severe multilobar pneumonia and shock in patients with influenza

Purpose

To identify risk factors present at admission in adult patients hospitalised due to influenza virus infection during the 2009/10 and 2010/11 seasons—including whether infection was from pandemic or seasonal influenza A infections—that were associated with the likelihood of developing severe pneumonia with multilobar involvement and shock.

Methods

Prospective cohort study. Patients hospitalised due to influenza virus infection were recruited. We collected information on sociodemographic characteristics, pre-existing medical conditions, vaccinations, toxic habits, previous medications, exposure to social environments, and EuroQoL-5D (EQ-5D). Severe pneumonia with multilobar involvement and/or shock (SPAS) was the primary outcome of interest. We constructed two multivariate logistic regression models to explain the likelihood of developing SPAS and to create a clinical prediction rule for developing SPAS that includes clinically relevant variables.

Results

Laboratory-confirmed A(H1N1)pdm09, EQ-5D utility score 7 days before admission, more than one comorbidity, altered mental status, dyspnoea on arrival, days from onset of symptoms, and influenza season were associated with SPAS. In addition, not being vaccinated against seasonal influenza in the previous year, anaemia, altered mental status, fever and dyspnoea on arrival at hospital, difficulties in performing activities of daily living in the previous 7 days, and days from onset of symptoms to arrival at hospital were related to the likelihood of SPAS (area under the curve value of 0.75; Hosmer–Lemeshow p value of 0.84).

Conclusions

These variables should be taken into account by physicians evaluating a patient affected by influenza as additional information to that provided by the usual risk scores.

Phenotypic differences in virulence and immune response in closely related clinical isolates of influenza A 2009 H1N1 pandemic viruses in mice

To capture the possible genotypic and phenotypic differences of the 2009 influenza A virus H1N1 pandemic (H1N1pdm) strains circulating in adult hospitalized patients, we isolated and sequenced nine H1N1pdm viruses from patients hospitalized during 2009–2010 with severe influenza pneumonia in Kentucky. Each viral isolate was characterized in mice along with two additional H1N1 pandemic strains and one seasonal strain to assess replication and virulence. All isolates showed similar levels of replication in nasal turbinates and lung, but varied in their ability to cause morbidity. Further differences were identified in cytokine and chemokine responses. IL-6 and KC were expressed early in mice infected with strains associated with higher virulence. Strains that showed lower pathogenicity in mice had greater IFNγ, MIG, and IL-10 responses. A principal component analysis (PCA) of the cytokine and chemokine profiles revealed 4 immune response phenotypes that correlated with the severity of disease. A/KY/180/10, which showed the greatest virulence with a rapid onset of disease progression, was compared in additional studies with A/KY/136/09, which showed low virulence in mice. Analyses comparing a low (KY/136) versus a high (KY/180) virulent isolate showed a significant difference in the kinetics of infection within the lower respiratory tract and immune responses. Notably by 4 DPI, virus titers within the lung, bronchoalveolar lavage fluid (BALf), and cells within the BAL (BALc) revealed that the KY/136 replicated in BALc, while KY/180 replication persisted in lungs and BALc. In summary, our studies suggest four phenotypic groups based on immune responses that result in different virulence outcomes in H1N1pdm isolates with a high degree of genetic similarity. In vitro studies with two of these isolates suggested that the more virulent isolate, KY/180, replicates productively in macrophages and this may be a key determinant in tipping the response toward a more severe disease progression.

Respiratory viral and pneumococcal coinfection of the respiratory tract: implications of pneumococcal vaccination

The interactions between Streptococcus pneumoniae and other respiratory pathogens have been studied in vitro, in animal models and in humans - including epidemiologic and vaccine probe studies. Interactions of pneumococcus with respiratory viruses are common, and many mechanisms have been suggested to explain this phenomenon. The aim of this review is to explore pneumococcal interactions with respiratory viruses and consider the potential role that the pneumococcal polysaccharide-protein conjugate vaccine may play in modifying pneumococcal-respiratory viral interactions.

Infection of the upper respiratory tract with seasonal influenza A(H3N2) virus induces protective immunity in ferrets against infection with A(H1N1)pdm09 virus after intranasal, but not intratracheal, inoculation

The clinical symptoms caused by infection with influenza A virus vary widely and depend on the strain causing the infection, the dose and route of inoculation, and the presence of preexisting immunity. In most cases, seasonal influenza A viruses cause relatively mild upper respiratory tract disease, while sometimes patients develop an acute severe pneumonia. Heterosubtypic immunity induced by previous infections with influenza A viruses may dampen the development of clinical symptoms caused by infection with influenza A viruses of another subtype, as is the case during influenza pandemics. Here we show that ferrets acquire protective immunity after infection of the upper respiratory tract with a seasonal influenza A(H3N2) virus against subsequent infection with influenza A(H1N1)pdm09 virus inoculated by the intranasal route. However, protective heterosubtypic immunity was afforded locally, since the prior infection with the A(H3N2) virus did not provide protection against the development of pneumonia induced after intratracheal inoculation with the A(H1N1)pdm09 virus. Interestingly, some of these animals developed more severe disease than that observed in naïve control animals. These findings are of interest in light of the development of so-called universal influenza vaccines that aim at the induction of cross-reactive T cell responses.

In situ molecular identification of the influenza A (H1N1) 2009 Neuraminidase in patients with severe and fatal infections during a pandemic in Mexico City

Background

In April 2009, public health surveillance detected an increased number of influenza-like illnesses in Mexico City’s hospitals. The etiological agent was subsequently determined to be a spread of a worldwide novel influenza A (H1N1) triple reassortant. The purpose of the present study was to demonstrate that molecular detection of pandemic influenza A (H1N1) 2009 strains is possible in archival material such as paraffin-embedded lung samples.

Methods

In order to detect A (H1N1) virus sequences in archived biological samples, eight paraffin-embedded lung samples from patients who died of pneumonia and respiratory failure were tested for influenza A (H1N1) Neuraminidase (NA) RNA using in situ RT-PCR.

Results

We detected NA transcripts in 100% of the previously diagnosed A (H1N1)-positive samples as a cytoplasmic signal. No expression was detected by in situ RT-PCR in two Influenza-like Illness A (H1N1)-negative patients using standard protocols nor in a non-related cervical cell line. In situ relative transcription levels correlated with those obtained when in vitro RT-PCR assays were performed. Partial sequences of the NA gene from A (H1N1)-positive patients were obtained by the in situ RT-PCR-sequencing method. Sequence analysis showed 98% similarity with influenza viruses reported previously in other places.

Conclusions

We have successfully amplified specific influenza A (H1N1) NA sequences using stored clinical material; results suggest that this strategy could be useful when clinical RNA samples are quantity limited, or when poor quality is obtained. Here, we provide a very sensitive method that specifically detects the neuraminidase viral RNA in lung samples from patients who died from pneumonia caused by Influenza A (H1N1) outbreak in Mexico City.

Lower respiratory tract hemorrhage associated with 2009 pandemic influenza A (H1N1) virus infection

Please cite this paper as: Kennedy et al. for the 2009 Pandemic H1N1 Influenza‐Associated Lower Respiratory Tract Hemorrhage Working Group. (2012) Lower respiratory tract hemorrhage associated with 2009 pandemic influenza A (H1N1) virus infection. Influenza and Other Respiratory Viruses DOI: 10.1111/irv.12022.

Background  Influenza‐associated lower respiratory tract hemorrhage (LRTH) has been reported in previous pandemics and is a rare complication of seasonal influenza virus infection. We describe patients with LRTH associated with 2009 pandemic influenza A (H1N1) (pH1N1) virus infection identified from April 2009 to April 2010 in the United States.

Methods  We ascertained patients with pH1N1‐associated LRTH through state and local surveillance, the Emerging Infections Program, and CDCs Infectious Diseases Pathology Branch. All patients had influenza A, evidence of pneumonia, and evidence of LRTH.

Results  We identified 44 cases; the median number of days from illness onset to clinical signs of LRTH was one. Hemoptysis or respiratory tract bleeding was documented in 40% of pH1N1‐associated LRTH cases, often present early during the course of illness. Twenty‐one (48%) patients with LRTH had no other hemorrhagic diatheses. Seven (23%) patients with LRTH received antiviral treatment within two days of illness onset.

Conclusions  During influenza season, clinicians should consider influenza infection in the differential diagnosis for patients presenting with hemoptysis or other signs or symptoms of LRTH. While the impact of timing of antiviral therapy on this complication has not been studied, the rapid progression of LRTH may support use of early empiric therapy. Continued investigation is necessary to betterdefine the clinical spectrum of both seasonal influenza‐ and pH1N1‐associated LRTH.