Delayed clearance of viral load and marked cytokine activation in severe cases of pandemic H1N1 2009 influenza virus infection

Swine, human or avian influenza viruses differentially activates porcine dendritic cells cytokine profile

Swine influenza virus (SwIV) is considered a zoonosis and the fact that swine may act as an intermediate reservoir for avian influenza virus, potentially infectious for humans, highlights its relevance and the need to understand the interaction of different influenza viruses with the porcine immune system. Thus, in vitro porcine bone marrow-derived dendritic cell (poBMDCs) were infected with a circulating SwIV A/Swine/Spain/SF32071/2007(H3N2), 2009 human pandemic influenza virus A/Catalonia/63/2009(H1N1), low pathogenic avian influenza virus (LPAIV) A/Anas plathyrhynchos/Spain/1877/2009(aH7N2) or high pathogenic avian influenza virus (HPAIV) A/Chicken/Italy/5093/1999(aH7N1). Swine influenza virus H3N2 infection induced an increase of SLA-I and CD80/86 at 16 and 24h post infection (hpi), whereas the other viruses did not. All viruses induced gene expression of NF-κB, TGF-β, IFN-β and IL-10 at the mRNA level in swine poBMDCs to different extents and in a time-dependent manner. All viruses induced the secretion of IL-12 mostly at 24hpi whereas IL-18 was detected at all tested times. Only swH3N2 induced IFN-α in a time-dependent manner. Swine H3N2, aH7N2 and aH7N1 induced secretion of TNF-α also in a time-dependent manner. Inhibition of NF-κB resulted in a decrease of IFN-α and IL-12 secretion by swH3N2-infected poBMDC at 24hpi, suggesting a role of this transcription factor in the synthesis of these cytokines. Altogether, these data might help in understanding the relationship between influenza viruses and porcine dendritic cells in the innate immune response in swine controlled through soluble mediators and transcription factors.

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.

Adjunctive therapies and immunomodulatory agents in the management of severe influenza

In addition to neuraminidase inhibitors and other drugs that directly target viral replication, a number of adjunctive and immunomodulatory therapies are currently under evaluation for the treatment of influenza. These novel treatments, which focus either on pathophysiological aspects of influenza virus infection or the neutralization of virus with antibodies, are the subject of this review. Cytokine dysregulation has been observed in patients with severe influenza, such as avian influenza A (H5N1) and pandemic 2009 influenza A (H1N1pdm09) virus infections, but the role of immunomodulatory therapy is unclear, due to lack of data from randomized controlled trials (RCTs). Convalescent plasma appears to be useful as an adjunctive therapy for the treatment of H5N1 and H1N1pdm09 infections. Until lately, data interpretation was limited to case reports and studies of non-randomized design, but a recent RCT found that patients with severe influenza A (H1N1pdm09) who were treated with hyperimmune immunoglobulin from persons who had survived the same disease had a lower peak viral load and lower mortality than controls, providing treatment was begun within 5 days of symptom onset. The efficacy of agents with potential immunomodulating effects, including intravenous immunoglobulin, N-acetylcysteine, acute use of statins, macrolides, peroxisome proliferator-activated receptors agonists, celecoxib and mesalazine, and the role of plasmapheresis and hemoperfusion as rescue therapy, deserve more investigation and where feasible, studies by RCTs. Prospective observational studies have shown that systemic corticosteroids increase morbidity (e.g., secondary infections) and mortality in H1N1pdm09 influenza. This article forms part of a symposium in Antiviral Research on "Treatment of influenza: targeting the virus or the host."

CD4+ T cells recognize unique and conserved 2009 H1N1 influenza hemagglutinin epitopes after natural infection and vaccination

Influenza A/California/4/2009 (H1N1/09) is a recently emerged influenza virus capable of causing serious illness or death in otherwise healthy individuals. Serious outcomes were most common in young adults and children, suggesting that pre-existing heterologous immunity may influence the severity of infection. Using tetramers, we identified CD4(+) T-cell epitopes within H1N1/09 hemagglutinin (HA) that share extensive homology with seasonal influenza and epitopes that are unique to H1N1/09 HA. Ex vivo tetramer staining revealed that T cells specific for conserved epitopes were detectable within the memory compartment, whereas T cells specific for unique epitopes were naive and infrequent prior to infection or vaccination. Following infection, the frequencies of T cells specific for unique epitopes were 11-fold higher, reaching levels comparable to those of T cells specific for immunodominant epitopes. In contrast, the frequencies of T cells specific for conserved epitopes were only 2- to 3-fold higher following infection. In general, H1HA-reactive T cells exhibited a memory phenotype, expressed CXCR3 and secreted IFN-γ, indicating a predominantly Th1-polarized response. A similar Th1 response was seen in vaccinated subjects, but the expansion of T cells specific for HA epitopes was comparatively modest after vaccination. Our findings indicate that CD4(+) T cells recognize both strain-specific and conserved epitopes within the influenza HA protein and suggest that naive T cells specific for HA epitopes undergo significant expansion, whereas memory T cells specific for the conserved epitopes undergo more restrained expansion.

The cardiovascular manifestations of influenza: a systematic review

Influenza accounts for 3 to 5 million cases of severe illness and up to 300,000 deaths annually, presenting a considerable burden to healthcare services. A spectrum of cardiovascular complications has been reported in association with influenza infection. This can occur through direct effects of the virus on the myocardium or through exacerbation of existing cardiovascular disease. Direct myocardial involvement presenting as myocarditis is not uncommon during influenza infection. Clinical presentation may vary from asymptomatic to fulminant myocarditis resulting in cardiogenic shock and death. Cardiovascular mortality is also increased during influenza epidemics in patients with pre-existing coronary artery disease. Rates of myocardial infarction have been shown to increase following influenza outbreaks, whilst decreases in cardiovascular mortality have been demonstrated following influenza vaccination in high risk patients. The purpose of this review is to provide an overview of cardiovascular complications, their presentation, clinical course and the management options available following influenza infection.

Innate immune function and mortality in critically ill children with influenza: a multicenter study

OBJECTIVE

To prospectively evaluate relationships among serum cytokine levels, innate immune responsiveness, and mortality in a multicenter cohort of critically ill children with influenza infection.

DESIGN

Prospective, multicenter, observational study.

SETTING

Fifteen pediatric ICUs among members of the Pediatric Acute Lung Injury and Sepsis Investigators network.

PATIENTS

Patients ≤18 yrs old admitted to a PICU with community-acquired influenza infection. A control group of outpatient children was also evaluated.

INTERVENTIONS

ICU patients underwent sampling within 72 hrs of ICU admission for measurement of a panel of 31 serum cytokine levels and quantification of whole blood ex vivo lipopolysaccharide-stimulated tumor necrosis factor-α production capacity using a standardized stimulation protocol. Outpatient control subjects also underwent measurement of tumor necrosis factor-α production capacity.

MEASUREMENTS AND MAIN RESULTS

Fifty-two patients (44 survivors, eight deaths) were sampled. High levels of serum cytokines (granulocyte macrophage colony-stimulating factor, interleukin-6, interleukin-8, interferon-inducible protein-10, monocyte chemotactic protein-1, and macrophage inflammatory protein-1α) were associated with mortality (p < 0.0016 for each comparison) as was the presence of secondary infection with Staphylococcus aureus (p = 0.007), particularly methicillin-resistant S. aureus (p < 0.0001). Nonsurvivors were immunosuppressed with leukopenia and markedly reduced tumor necrosis factor-α production capacity compared with outpatient control subjects (n = 21, p < 0.0001) and to ICU survivors (p < 0.0001). This association remained after controlling for multiple covariables. A tumor necrosis factor-α response <250 pg/mL was highly predictive of death and longer duration of ICU stay (p < 0.0001). Patients with S. aureus coinfection demonstrated the greatest degree of immunosuppression (p < 0.0001).

CONCLUSIONS

High serum levels of cytokines can coexist with marked innate immune suppression in children with critical influenza. Severe, early innate immune suppression is highly associated with both S. aureus coinfection and mortality in this population. Multicenter innate immune function testing is feasible and can identify these high-risk children.

Assessing mathematical models of influenza infections using features of the immune response

The role of the host immune response in determining the severity and duration of an influenza infection is still unclear. In order to identify severity factors and more accurately predict the course of an influenza infection within a human host, an understanding of the impact of host factors on the infection process is required. Despite the lack of sufficiently diverse experimental data describing the time course of the various immune response components, published mathematical models were constructed from limited human or animal data using various strategies and simplifying assumptions. To assess the validity of these models, we assemble previously published experimental data of the dynamics and role of cytotoxic T lymphocytes, antibodies, and interferon and determined qualitative key features of their effect that should be captured by mathematical models. We test these existing models by confronting them with experimental data and find that no single model agrees completely with the variety of influenza viral kinetics responses observed experimentally when various immune response components are suppressed. Our analysis highlights the strong and weak points of each mathematical model and highlights areas where additional experimental data could elucidate specific mechanisms, constrain model design, and complete our understanding of the immune response to influenza.

Modeling host genetic regulation of influenza pathogenesis in the collaborative cross

Genetic variation contributes to host responses and outcomes following infection by influenza A virus or other viral infections. Yet narrow windows of disease symptoms and confounding environmental factors have made it difficult to identify polymorphic genes that contribute to differential disease outcomes in human populations. Therefore, to control for these confounding environmental variables in a system that models the levels of genetic diversity found in outbred populations such as humans, we used incipient lines of the highly genetically diverse Collaborative Cross (CC) recombinant inbred (RI) panel (the pre-CC population) to study how genetic variation impacts influenza associated disease across a genetically diverse population. A wide range of variation in influenza disease related phenotypes including virus replication, virus-induced inflammation, and weight loss was observed. Many of the disease associated phenotypes were correlated, with viral replication and virus-induced inflammation being predictors of virus-induced weight loss. Despite these correlations, pre-CC mice with unique and novel disease phenotype combinations were observed. We also identified sets of transcripts (modules) that were correlated with aspects of disease. In order to identify how host genetic polymorphisms contribute to the observed variation in disease, we conducted quantitative trait loci (QTL) mapping. We identified several QTL contributing to specific aspects of the host response including virus-induced weight loss, titer, pulmonary edema, neutrophil recruitment to the airways, and transcriptional expression. Existing whole-genome sequence data was applied to identify high priority candidate genes within QTL regions. A key host response QTL was located at the site of the known anti-influenza Mx1 gene. We sequenced the coding regions of Mx1 in the eight CC founder strains, and identified a novel Mx1 allele that showed reduced ability to inhibit viral replication, while maintaining protection from weight loss.

Host responses to an infectious agent are highly variable across the human population, however, it is not entirely clear how various factors such as pathogen dose, demography, environment and host genetic polymorphisms contribute to variable host responses and infectious outcomes. In this study, a new in vivo experimental model was used that recapitulates many of the genetic characteristics of an outbred population, such as humans. By controlling viral dose, environment and demographic variables, we were able to focus on the role that host genetic variation plays in influenza virus infection. Both the range of disease phenotypes and the combinations of sets of disease phenotypes at 4 days post infection across this population exhibited a large amount of diversity, reminiscent of the variation seen across the human population. Multiple host genome regions were identified that contributed to different aspects of the host response to influenza infection. Taken together, these results emphasize the critical role of host genetics in the response to infectious diseases. Given the breadth of host responses seen within this population, several new models for unique host responses to infection were identified.

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.

Use of nasopharyngeal aspirate for diagnosis of pneumocystis pneumonia

Quantitative PCR on nasopharyngeal aspirate (NPA) can achieve high sensitivity and specificity in diagnosing Pneumocystis pneumonia (PCP) compared to microscopic examination of bronchoscopic specimens in a population with low HIV prevalence. Since NPA is a minimally invasive procedure, it is ideal as a screening test for PCP.

Viral pneumonitis is increased in obese patients during the first wave of pandemic A(H1N1) 2009 virus

Introduction

There is conflicting data as to whether obesity is an independent risk factor for mortality in severe pandemic (H1N1) 2009 influenza (A(H1N1)pdm09). It is postulated that excess inflammation and cytokine production in obese patients following severe influenza infection leads to viral pneumonitis and/or acute respiratory distress syndrome.

Methods

Demographic, laboratory and clinical data prospectively collected from obese and non-obese patients admitted to nine adult Australian intensive care units (ICU) during the first A(H1N1)pdm09 wave, supplemented with retrospectively collected data, were compared.

Results

Of 173 patients, 100 (57.8%), 73 (42.2%) and 23 (13.3%) had body mass index (BMI) <30 kg/m², ≥30 kg/m² (obese) and ≥40 kg/m² (morbidly obese) respectively. Compared to non-obese patients, obese patients were younger (mean age 43.4 vs. 48.4 years, p = 0.035) and more likely to develop pneumonitis (61% vs. 44%, p = 0.029). Extracorporeal membrane oxygenation use was greater in morbidly obese compared to non-obese patients (17.4% vs. 4.7%, p = 0.04). Higher mortality rates were observed in non-obese compared to obese patients, but not after adjusting for severity of disease. C-reactive protein (CRP) levels and hospital length of stay (LOS) were similar. Amongst ICU survivors, obese patients had longer ICU LOS (median 11.9 vs. 6.8 days, p = 0.017). Similar trends were observed when only patients infected with A(H1N1)pdm09 were examined.

Conclusions

Among patients admitted to ICU during the first wave of A(H1N1)pdm09, obese and morbidly obese patients with severe infection were more likely to develop pneumonitis compared to non-obese patients, but mortality rates were not increased. CRP is not an accurate marker of pneumonitis.

The first, second and third wave of pandemic influenza A (H1N1)pdm09 in North Denmark Region 2009-2011: a population-based study of hospitalizations

Background and objectives

Denmark experienced three waves of the new pandemic influenza A (H1N1)pdm09 from July 2009 to February 2011. The aim of the study was to describe the epidemiology and clinical characteristics of hospitalized patients in a defined population of North Denmark Region with a mixed urban and rural community of 579 000 inhabitants.

Methods

Review of medical records of all hospitalized patients with confirmed influenza A from July 2009 to February 2011.

Results

Two hundred and seventy‐three patients were admitted to hospital. The age‐related population incidences of hospitalization were as follows: 0–14 years: 111/100 000, 15–64 years: 39/100 000, and ≥65 years: 17/100 000. During the first wave (July 2009–August 2009), three patients were admitted – none received treatment in intensive care units (ICUs), during the second wave (October 2009–January 2010), 158 patients were admitted – nine received treatment in ICUs, and during the third wave (December 2010–February 2011), 112 patients were admitted – 25 received treatment in ICUs. Fourteen patients (5%) died within 30 days of diagnosis (median 55 years; range 14–76 years) and additional seven patients (2·6%) died within 365 days (median 25 years; range 1–86 years).

Conclusions

Patients hospitalized with pandemic influenza A (H1N1)pdm09 were predominantly children and younger adults, and only a few patients were >65 years. The third wave was the most severe taking the number and percentage of patients admitted to ICUs and 30‐day mortality into consideration. We observed that the incidence of hospitalizations as well as clinical severity among younger adults did not decline from the second to the third wave.

Pandemic H1N1 influenza-associated myocarditis in a patient with Castleman’s disease

We report on a patient with longstanding multicentric Castleman’s disease, hyaline-vascular type, who presented with nearly-fatal myocarditis associated with a 2009 pandemic H1N1 influenza virus infection. This is the first case of such an association described in the literature.

A (H1N1) pdm09 HA D222 variants associated with severity and mortality in patients during a second wave in Mexico

Background

Pandemic type A (H1N1) influenza arose in early 2009, probably in Mexico and the United States, and reappeared in North America in September for seven more months. An amino acid substitution in the hemagglutinin (HA), D222G, has been reported in a significant proportion of patients with a severe and fatal outcome. We studied the prevalence of HA222 substitutions in patients in Mexico during the second wave and its association with clinical outcome and pathogenicity in a mouse model.

Methods

The nucleotide sequences of hemagglutinin (HA) from viruses collected from 77 patients were determined including 50 severe and fatal cases and 27 ambulatory cases. Deep sequencing was done on 5 samples from severe or fatal cases in order to determine the quasispecies proportion. Weight loss and mortality due to infection with cultured influenza viruses were analyzed in a mouse model.

Results

Viruses from 14 out of 50 hospitalized patients (28%) had a non aspartic acid residue at the HA 222 position (nD222), while all 27 ambulatory patients had D222 (p = 0.0014). G222 was detected as sole species or in coexistence with N222 and D222 in 12 patients with severe disease including 8 who died. N222 in coexistence with D222 was detected in 1 patient who died and co-occurrence of A222 and V222, together with D222, was detected in another patient who died. The patients with a nD222 residue had higher mortality (71.4%), compared to the group with only D222 (22.2%, p = 0.0008). Four of the 14 viruses from hospitalized patients were cultured and intranasally infected into mice. Two viruses with G222 were lethal while a third virus, with G222, caused only mild illness in mice similar to the fourth virus that contained D222.

Conclusions

We confirm the elevated incidence of HA222 (H1N1)pdm09 variants in severe disease and mortality. Both clinical and mouse infection data support the idea that nD222 mutations contribute to increased severity of disease but additional determinants in disease outcome may be present.

Macrolide-based regimens in absence of bacterial co-infection in critically ill H1N1 patients with primary viral pneumonia

PURPOSE

To determine whether macrolide-based treatment is associated with mortality in critically ill H1N1 patients with primary viral pneumonia.

METHODS

Secondary analysis of a prospective, observational, multicenter study conducted across 148 Intensive Care Units (ICU) in Spain.

RESULTS

Primary viral pneumonia was present in 733 ICU patients with pandemic influenza A (H1N1) virus infection with severe respiratory failure. Macrolide-based treatment was administered to 190 (25.9 %) patients. Patients who received macrolides had chronic obstructive pulmonary disease more often, lower severity on admission (APACHE II score on ICU admission (13.1 ± 6.8 vs. 14.4 ± 7.4 points, p < 0.05), and multiple organ dysfunction syndrome less often (23.4 vs. 30.1 %, p < 0.05). Length of ICU stay in survivors was not significantly different in patients who received macrolides compared to patients who did not (10 (IQR 4-20) vs. 10 (IQR 5-20), p = 0.9). ICU mortality was 24.1 % (n = 177). Patients with macrolide-based treatment had lower ICU mortality in the univariate analysis (19.2 vs. 28.1 %, p = 0.02); however, a propensity score analysis showed no effect of macrolide-based treatment on ICU mortality (OR = 0.87; 95 % CI 0.55-1.37, p = 0.5). Moreover, the sensitivity analysis revealed very similar results (OR = 0.91; 95 % CI 0.58-1.44, p = 0.7). A separate analysis of patients under mechanical ventilation yielded similar results (OR = 0.77; 95 % CI 0.44-1.35, p = 0.4).

CONCLUSION

Our results suggest that macrolide-based treatment was not associated with improved survival in critically ill H1N1 patients with primary viral pneumonia.

Leptin mediates the pathogenesis of severe 2009 pandemic influenza A(H1N1) infection associated with cytokine dysregulation in mice with diet-induced obesity

BACKGROUND

Obesity is associated with a high circulating leptin level and severe 2009 pandemic influenza A virus subtype H1N1 (A[H1N1]pdm09) infection. The mechanism for severe lung injury in obese patients and the specific treatment strategy remain elusive.

METHOD

We studied the pathogenesis of A(H1N1)pdm09 infection in a mouse model of diet-induced obesity.

RESULTS

Obese mice had significantly higher initial pulmonary viral titer and mortality after challenge with A(H1N1)pdm09, compared with age-matched lean mice. Compared with lean mice, obese mice had heightened proinflammatory cytokine and chemokine levels and more severe pulmonary inflammatory damage. Furthermore, obese mice had a higher preexisting serum leptin level but a lower preexisting adiponectin level. Recombinant mouse leptin increased the interleukin 6 (IL-6) messenger RNA expression in mouse single-lung-cell preparations, mouse macrophages, and mouse lung epithelial cell lines infected with A(H1N1)pdm09. Administration of anti-leptin antibody improved the survival of infected obese mice, with associated reductions in pulmonary levels of the proinflammatory cytokines IL-6 and interleukin 1β but not the pulmonary viral titer.

CONCLUSIONS

Our findings suggest that preexisting high levels of circulating leptin contribute to the development of severe lung injury by A(H1N1)pdm09 in mice with diet-induced obesity. The therapeutic strategy of leptin neutralization for the reduction of proinflammatory responses and pulmonary damage in obese patients warrants further investigations.

Characterization in vitro and in vivo of a pandemic H1N1 influenza virus from a fatal case

Pandemic 2009 H1N1 (pH1N1) influenza viruses caused mild symptoms in most infected patients. However, a greater rate of severe disease was observed in healthy young adults and children without co-morbid conditions. Here we tested whether influenza strains displaying differential virulence could be present among circulating pH1N1 viruses. The biological properties and the genotype of viruses isolated from a patient showing mild disease (M) or from a fatal case (F), both without known co-morbid conditions were compared in vitro and in vivo. The F virus presented faster growth kinetics and stronger induction of cytokines than M virus in human alveolar lung epithelial cells. In the murine model in vivo, the F virus showed a stronger morbidity and mortality than M virus. Remarkably, a higher proportion of mice presenting infectious virus in the hearts, was found in F virus-infected animals. Altogether, the data indicate that strains of pH1N1 virus with enhanced pathogenicity circulated during the 2009 pandemic. In addition, examination of chemokine receptor 5 (CCR5) genotype, recently reported as involved in severe influenza virus disease, revealed that the F virus-infected patient was homozygous for the deleted form of CCR5 receptor (CCR5Δ32).

Performance of multiplex commercial kits to quantify cytokine and chemokine responses in culture supernatants from Plasmodium falciparum stimulations

Background

Cytokines and chemokines are relevant biomarkers of pathology and immunity to infectious diseases such as malaria. Several commercially available kits based on quantitative suspension array technologies allow the profiling of multiple cytokines and chemokines in small volumes of sample. However, kits are being continuously improved and information on their performance is lacking.

Methodology/Principal Findings

Different cytokine/chemokine kits, two flow cytometry-based (eBioscience® FlowCytomix™ and BD™ Cytometric Bead Array Human Enhanced Sensitivity) and four Luminex®-based (Invitrogen™ Human Cytokine 25-Plex Panel, Invitrogen™ Human Cytokine Magnetic 30-Plex Panel, Bio-Rad® Bio-Plex Pro™ Human Cytokine Plex Assay and Millipore™ MILLIPLEX® MAP Plex Kit) were compared. Samples tested were supernatants of peripheral blood mononuclear cells of malaria-exposed children stimulated with Plasmodium falciparum parasite lysates. Number of responses in range that could be detected was determined and reproducibility of duplicates was evaluated by the Bland-Altman test. Luminex® kits performed better than flow cytometry kits in number of responses in range and reproducibility. Luminex® kits were more reproducible when magnetic beads were used. However, within each methodology overall performance depended on the analyte tested in each kit. Within the Luminex® kits, the Invitrogen™ with polystyrene beads had the poorer performance, whereas Invitrogen™ with magnetic beads had the higher percentage of cytokines/chemokines with both readings in range (40%), followed by Bio-Rad® with magnetic beads (35%). Regarding reproducibility, the Millipore™ kit had the highest percentage (60%) of cytokines/chemokines with acceptable limits of agreement (<30%), followed by the Invitrogen™ with magnetic beads (40%) that had tighter limits of agreement.

Conclusions/Significance

Currently available kits for cytokine and chemokine quantification differ in reproducibility and concentration range of accurate detection. Luminex®-based kits with magnetic beads perform the best. Data highlights the importance of testing different kits before each study to choose the most appropriate, depending on the priority of the cytokines assessed.

Oseltamivir pharmacokinetics, dosing, and resistance among children aged <2 years with influenza

BACKGROUND

Children <2 years of age are at high risk of influenza-related mortality and morbidity. However, the appropriate dose of oseltamivir for children <2 years of age is unknown.

METHODS

The National Institute of Allergy and Infectious Diseases Collaborative Antiviral Study Group evaluated oseltamivir in infants aged <2 years in an age-de-escalation, adaptive design with a targeted systemic exposure.

RESULTS

From 2006 to 2010, 87 subjects enrolled. An oseltamivir dose of 3.0 mg/kg produced drug exposures within the target range in subjects 0-8 months of age, although there was a greater degree of variability in infants <3 months of age. In subjects 9-11 months of age, a dose of 3.5 mg/kg produced drug exposures within the target range. Six of 10 subjects aged 12-23 months receiving the Food and Drug Administration-approved unit dose for this age group (ie, 30 mg) had oseltamivir carboxylate exposures below the target range. Virus from 3 subjects developed oseltamivir resistance during antiviral treatment.

CONCLUSIONS

The appropriate twice-daily oral oseltamivir dose for infants ≤8 months of age is 3.0 mg/kg, while the dose for infants 9-11 months old is 3.5 mg/kg.

Influenza A virus protein PB1-F2 from different strains shows distinct structural signatures

The proapoptotic influenza A virus PB1-F2 protein contributes to viral pathogenicity and is present in most human and avian influenza isolates. The structures of full-length PB1-F2 of the influenza strains Pandemic flu 2009 H1N1, 1918 Spanish flu H1N1, Bird flu H5N1 and H1N1 PR8, have been characterized by NMR and CD spectroscopy. The study was conducted using chemically synthesized full-length PB1-F2 protein and fragments thereof. The amino acid residues 30-70 of PR8 PB1-F2 were found to be responsible for amyloid formation of the protein, which could be assigned to formation of β-sheet structures, although α-helices were the only structural features detected under conditions that mimic a membranous environment. At membranous conditions, in which the proteins are found in their most structured state, significant differences become apparent between the PB1-F2 variants investigated. In contrast to Pandemic flu 2009 H1N1 and PR8 PB1-F2, which exhibit a continuous extensive C-terminal α-helix, both Spanish flu H1N1 and Bird flu H5N1 PB1-F2 contain a loop region with residues 66-71 that divides the C-terminus into two shorter helices. The observed structural differences are located to the C-terminal ends of the proteins to which most of the known functions of these proteins have been assigned. A C-terminal helix-loop-helix motif might be a structural signature for PB1-F2 of the highly pathogenic influenza viruses as observed for 1918 Spanish flu H1N1 and Bird flu H5N1 PB1-F2. This signature could indicate the pathological nature of viruses emerging in the future and thus aid in the recognition of these viruses.

Pandemic influenza A/H1N1 virus infection and TNF, LTA, IL1B, IL6, IL8, and CCL polymorphisms in Mexican population: a case-control study

Background

Some patients have a greater response to viral infection than do others having a similar level of viral replication. Hypercytokinemia is the principal immunopathological mechanism that contributes to a severer clinical course in cases of influenza A/H1N1. The benefit produced, or damage caused, by these cytokines in severe disease is not known. The genes that code for these molecules are polymorphic and certain alleles have been associated with susceptibility to various diseases. The objective of the present study was to determine whether there was an association between polymorphisms of TNF, LTA, IL1B, IL6, IL8, and CCL1 and the infection and severity of the illness caused by the pandemic A/H1N1 in Mexico in 2009.

Methods

Case–control study. The cases were patients confirmed with real time PCR with infection by the A/H1N1 pandemic virus. The controls were patients with infection like to influenza and non-familial healthy contacts of the patients with influenza. Medical history and outcome of the disease was registered. The DNA samples were genotyped for polymorphisms TNF rs361525, rs1800629, and rs1800750; LTA rs909253; IL1B rs16944; IL6 rs1818879; IL8 rs4073; and CCL1 rs2282691. Odds ratio (OR) and the 95% confidence interval (95% CI) were calculated. The logistic regression model was adjusted by age and severity of the illness in cases.

Results

Infection with the pandemic A/H1N1 virus was associated with the following genotypes: TNF rs361525 AA, OR = 27.00; 95% CI = 3.07–1248.77); LTA rs909253 AG (OR = 4.33, 95% CI = 1.82–10.32); TNF rs1800750 AA (OR = 4.33, 95% CI = 1.48–12.64); additionally, LTA rs909253 AG showed a limited statistically significant association with mortality (p = 0.06, OR = 3.13). Carriers of the TNF rs1800629 GA genotype were associated with high levels of blood urea nitrogen (p = 0.05); those of the TNF rs1800750 AA genotype, with high levels of creatine phosphokinase (p=0.05). The IL1B rs16944 AA genotype was associated with an elevated number of leukocytes (p <0.001) and the IL8 rs4073 AA genotype, with a higher value for P_aO₂ mm Hg.

Conclusion

The polymorphisms of genes involved in the inflammatory process contributed to the severity of the clinical behavior of infection by the pandemic influenza A/H1N1 virus.

Avian influenza A H5N1 virus: a continuous threat to humans

We report the first case of severe pneumonia due to co-infection with the emerging avian influenza A (H5N1) virus subclade 2.3.2.1 and Mycoplasma pneumoniae. The patient was a returning traveller who had visited a poultry market in South China. We then review the epidemiology, virology, interspecies barrier limiting poultry-to-human transmission, clinical manifestation, laboratory diagnosis, treatment and control measures of H5N1 clades that can be transmitted to humans. The recent controversy regarding the experiments involving aerosol transmission of recombinant H5N1 virus between ferrets is discussed. We also review the relative contribution of the poor response to antiviral treatment and the virus-induced hyperinflammatory damage to the pathogenesis and the high mortality of this infection. The factors related to the host, virus or medical intervention leading to the difference in disease mortality of different countries remain unknown. Because most developing countries have difficulty in instituting effective biosecurity measures, poultry vaccination becomes an important control measure. The rapid evolution of the virus would adversely affect the efficacy of poultry vaccination unless a correctly matched vaccine was chosen, manufactured and administered in a timely manner. Vigilant surveillance must continue to allow better preparedness for another poultry or human pandemic due to new viral mutants.

Functional status of older nursing home residents can affect the efficacy of influenza vaccination

BACKGROUND

The efficacy of influenza vaccination in older nursing home residents is frequently overestimated due to frailty selection bias. Limited data exist to examine this issue.

METHODS

We conducted a prospective cohort study from December 2009 to November 2010 to evaluate the efficacy of influenza vaccination in old nursing home residents with respect to their functional status. Participants were stratified according to the Barthel Index (BI) into good functioning (GF; BI > 60), intermediate functioning (IF; BI = 5-60), and poor functioning (PF; BI = 0). Participants were vaccinated by monovalent H1N1 2009 and trivalent seasonal influenza vaccinations (H1N1-TIV), TIV alone, or remained unvaccinated by choice. The associations between all-cause mortality, vaccination efficacy, and functional status were examined.

RESULTS

A total of 711 older nursing home residents were enrolled (GF group: N = 230; IF group: N = 246; PF group: N = 235). At 12 months, H1N1-TIV recipients had the lowest all-cause mortality, whereas unvaccinated residents had the highest all-cause mortality in all three functional status groups. In the comparison between H1N1-TIV recipients and TIV alone recipients, the hazard ratios (HRs) of all-cause mortality were lower in the GF group and higher in the PF group (GF group: HR 0.30 [0.07-0.95], p < .05; IF group: HR 0.40 [0.18-0.86], p < .05; PF group: HR 0.53 [0.28-0.99], p < .05). The same observation was found in comparison between other vaccination statuses (H1N1-TIV vs unvaccinated and TIV alone vs unvaccinated).

CONCLUSIONS

Influenza vaccination was associated with reduced all-cause mortality in older nursing home residents with different functional statuses. Vaccine efficacy in reducing mortality declined with increasingly impaired functional status.

Oligomeric recombinant H5 HA1 vaccine produced in bacteria protects ferrets from homologous and heterologous wild-type H5N1 influenza challenge and controls viral loads better than subunit H5N1 vaccine by eliciting high-affinity antibodies

Recombinant hemagglutinin from influenza viruses with pandemic potential can be produced rapidly in various cell substrates. In this study, we compared the functionality and immunogenicity of bacterially produced oligomeric or monomeric HA1 proteins from H5N1 (A/Vietnam/1203/04) with those of the egg-based licensed subunit H5N1 (SU-H5N1) vaccine in ferrets challenged with homologous or heterologous H5N1 highly pathogenic influenza strains. Ferrets were vaccinated twice with the oligomeric or monomeric rHA1 or with SU-H5N1 (Sanofi Pasteur) emulsified with Titermax adjuvant and were challenged with wild-type homologous (A/Vietnam/1203/04; clade 1) or heterologous (A/Whooperswan/Mongolia/244/2005; clade 2.2) virus. Only the oligomeric rHA1 (not the monomeric rHA1) immunogen and the SU-H5N1 vaccine provided protection against the lethality and morbidity of homologous and heterologous highly pathogenic H5N1. Oligomeric rHA1 generated more cross-neutralizing antibodies and higher levels of serum antibody binding to HA1, with stronger avidity and a better IgG/IgM ratio, than monomeric HA1 and SU-H5N1 vaccines, as determined by surface plasmon resonance (SPR). Importantly, viral loads after heterologous H5N1 challenge were more efficiently controlled in ferrets vaccinated with the oligomeric rHA1 immunogen than in SU-H5N1-vaccinated ferrets. The reduction of viral loads in the nasal washes correlated strongly with higher-avidity antibodies to oligomeric rHA1 derived from H5N1 clade 1 and clade 2.2 viruses, as measured by SPR. This is the first study to show the role of antibody avidity for the HA1 globular head domain in reduction of viral loads in the upper respiratory tract, which could significantly reduce viral transmission.

Corticosteroid treatment ameliorates acute lung injury induced by 2009 swine origin influenza A (H1N1) virus in mice

BACKGROUND

The 2009 influenza pandemic affected people in almost all countries in the world, especially in younger age groups. During this time, the debate over whether to use corticosteroid treatment in severe influenza H1N1 infections patients resurfaced and was disputed by clinicians. There is an urgent need for a susceptible animal model of 2009 H1N1 infection that can be used to evaluate the pathogenesis and the therapeutic effect of corticosteroid treatment during infection.

METHODOLOGY/PRINCIPAL FINDINGS

We intranasally inoculated two groups of C57BL/6 and BALB/c mice (using 4- or 6-to 8-week-old mice) to compare the pathogenesis of several different H1N1 strains in mice of different ages. Based on the results, a very susceptible 4-week-old C57BL/6 mouse model of Beijing 501 strain of 2009 H1N1 virus infection was established, showing significantly elevated lung edema and cytokine levels compared to controls. Using our established animal model, the cytokine production profile and lung histology were assessed at different times post-infection, revealing increased lung lesions in a time-dependent manner. In additional,the mice were also treated with dexamethasone, which significantly improved survival rate and lung lesions in infected mice compared to those in control mice. Our data showed that corticosteroid treatment ameliorated acute lung injury induced by the 2009 A/H1N1 virus in mice and suggested that corticosteroids are valid drugs for treating 2009 A/H1N1 infection.

CONCLUSIONS/SIGNIFICANCE

Using the established, very susceptible 2009 Pandemic Influenza A (H1N1) mouse model, our studies indicate that corticosteroids are a potential therapeutic remedy that may address the increasing concerns over future 2009 A/H1N1 pandemics.

Dose sparing intradermal trivalent influenza (2010/2011) vaccination overcomes reduced immunogenicity of the 2009 H1N1 strain

BACKGROUND

We hypothesized that low dose intradermal vaccination of the trivalent influenza vaccine (TIV) delivered by the MicronJet600™ (NanoPass Technologies, Israel) would be non-inferior to the full dose intramuscular and mid dose Intanza(®) vaccination in the elderly and the chronically ill adults.

METHODS

We performed a prospective randomized trial on elderly and chronically ill adults. Subjects were randomly assigned into 4 groups. Groups ID3 and ID9 received reduced dose ID TIV (3 μg and 9 μg of hemagglutinin (HA) per strain respectively) delivered by MicronJet600™ (NanoPass Technologies, Israel). Group INT9 received reduced dose ID TIV (9 μg) delivered by Becton Dickinson's Soluvia™ device (Intanza(®)9, Sanofi-Pasteur, France). Control group IM15 received a full dose IM TIV (15 μg). We measured antibody titers by hemagglutination inhibition (HAI) and microneutralization (MN) assays at baseline and day 21.

RESULTS

Baseline characteristics for all groups were similar (group and sample sizes: ID3=63; ID9=68; INT9=65; and IM15=66). At day 21 post vaccination, the GMT ratio and the seroconversion rates difference for all three strains of the ID vaccine groups were non-inferior to the IM vaccine group. The seroconversion rate, seroprotection rate, and the GMT of the H1N1 strains by HAI and MN assays were significantly higher in the ID groups compared with the full dose IM vaccine group. The seroconversion rates of the H3N2 strain by HAI assay were also significantly higher in the ID groups when compared with the full dose IM group. Direct comparison among the three ID groups showed no significant differences. No serious adverse events related to vaccination were reported.

CONCLUSION

Dose-sparing ID TIV can overcome reduced immunogenicity of the H1N1 strain, and according to some measures, for the H3N2 strain. At risk subjects indicated for the TIV should be considered for intradermal immunization to compensate for reduced immunogenicity.

Protection from inflammatory organ damage in a murine model of hemophagocytic lymphohistiocytosis using treatment with IL-18 binding protein

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening condition due to the association of an infectious agent with lymphocyte cytotoxicity defects, either of congenital genetic origin in children or presumably acquired in adults. In HLH patients, an excess of lymphocyte or macrophage cytokines, such as IFN-γ and TNFα is present in serum. In animal models of the disease, IFN-γ and TNF-α have been shown to play a central pathogenic role. In humans, unusually high concentrations of IL-18, an inducer of IFN-γ, and TNF-α have been reported, and are associated with an imbalance between IL-18 and its natural inhibitor IL-18 binding protein (IL-18BP) resulting in an excess of free IL-18. Here we studied whether IL-18BP could reduce disease severity in an animal model of HLH. Mouse cytomegalovirus infection in perforin-1 knock-out mice induced a lethal condition similar to human HLH characterized by cytopenia with marked inflammatory lesions in the liver and spleen as well as the presence of hemophagocytosis in bone marrow. IL-18BP treatment decreased hemophagocytosis and reversed liver as well as spleen damage. IL-18BP treatment also reduced both IFN-γ and TNF-α production by CD8(+) T and NK cells, as well as Fas ligand expression on NK cell surface. These data suggest that IL-18BP is beneficial in an animal model of HLH and in combination with anti-infectious therapy may be a promising strategy to treat HLH patients.

Mouse-adapted H9N2 influenza A virus PB2 protein M147L and E627K mutations are critical for high virulence

H9N2 influenza viruses have been circulating worldwide in multiple avian species and have repeatedly infected humans to cause typical disease. The continued avian-to-human interspecies transmission of H9N2 viruses raises concerns about the possibility of viral adaption with increased virulence for humans. To investigate the genetic basis of H9N2 influenza virus host range and pathogenicity in mammals, we generated a mouse-adapted H9N2 virus (SD16-MA) that possessed significantly higher virulence than wide-type virus (SD16). Increased virulence was detectable after 8 sequential lung passages in mice. Five amino acid substitutions were found in the genome of SD16-MA compared with SD16 virus: PB2 (M147L, V250G and E627K), HA (L226Q) and M1 (R210K). Assessments of replication in mice showed that all of the SD16-MA PB2, HA and M1 genome segments increased virus replication; however, only the mouse-adapted PB2 significantly increased virulence. Although the PB2 E627K amino acid substitution enhanced viral polymerase activity and replication, none of the single mutations of mouse adapted PB2 could confer increased virulence on the SD16 backbone. The combination of M147L and E627K significantly enhanced viral replication ability and virulence in mice. Thus, our results show that the combination of PB2 amino acids at position 147 and 627 is critical for the increased pathogenicity of H9N2 influenza virus in mammalian host.

Outbreak of pandemic 2009 influenza A/H1N1 infection in the hematology ward: fatal clinical outcome of hematopoietic stem cell transplant recipients and emergence of the H275Y neuraminidase mutation

We report an outbreak of pandemic 2009 influenza A/H1N1 virus (2009 H1N1) infection that occurred in the hematology ward of our institution during the 2010–2011 influenza season. A total of seven hospitalized patients with hematologic tumors, including five recipients of hematopoietic stem cell transplantation (HSCT), successively developed rapid influenza detection test (RIDT)-positive influenza A; four patients had laboratory-confirmed 2009 H1N1 infection. Three HSCT recipients required mechanical ventilation support and two were admitted to the intensive care unit; they died of progressive respiratory failure despite receiving available anti-viral drugs. We implemented outbreak-control measures including transferal of RIDT-positive patients to a single-patient room and chemoprophylaxis with oseltamivir. We note that the H275Y neuraminidase mutation was detected in respiratory specimens from three patients, who were administered therapeutic or prophylactic dosages of oseltamivir. The present report demonstrates that the nosocomial 2009 H1N1 outbreak in the hematology ward led to fatal clinical outcomes and the emergence of a resistant virus at a markedly high rate.

Viruses associated with pneumonia in adults

Viral pneumonia, which is typically associated with disease in childhood, is increasingly recognized as causing problems in adults. Certain viruses, such as influenza virus, can attack fully immunocompetent adults, but many viruses take advantage of more-vulnerable patients. The latter include patients receiving immunosuppressive therapy and elderly subjects, particularly those residing in long-term care facilities. The range of viruses producing pneumonia in adults includes common agents, such as varicella-zoster virus and influenza virus, as well as respiratory syncytial virus, human metapneumovirus, adenoviruses, picornaviruses, and coronaviruses. The roles played by other agents, such as rhinoviruses and human bocaviruses, in pneumonia are still under study. While therapy for most of theses agents, at least in adults, has not yet been fully clarified, it is reasonable to assume antivirals may work in certain situations if they are introduced early enough in the course of infection.

Prevention of novel influenza infection in newborns in hospital settings: considerations and strategies during the 2009 H1N1 pandemic

During the 2009 influenza A (H1N1) pandemic, many pregnant women experienced severe illness and some gave birth while ill with suspected or confirmed pandemic (H1N1) 2009 influenza. Because of concerns about possible transmission of this novel virus to immunologically naïve newborns, and the absence of definitive studies regarding this risk, the Centers for Disease Control and Prevention (CDC) reviewed relevant literature to understand the potential burden of disease and routes of transmission affecting newborns. This report describes the issues considered during the 2009 H1N1 pandemic as CDC developed guidance to protect newborns in hospital settings. Also presented is a framework of protection efforts to prevent novel influenza infection in fetuses/newborns before birth and in hospital settings. Although developed specifically for the pandemic, the framework may be useful during future novel influenza outbreaks.

Case report: Increased viral receptor expression associated with high viral load and severe pneumonia in a young patient infected with 2009 H1N1 influenza a with no pre-existing conditions

A case of unusually high severity of influenza pneumonia leading to acute respiratory distress syndrome and death was investigated. This was a previously a healthy 28-year-old man with no underlying conditions, admitted to a hospital during the first wave of influenza pandemic in Thailand in July 2009. He had experienced high fever and influenza-like illness for 5 days before coming to the hospital. He developed acute respiratory distress syndrome and expired on day 7 after admission. In comparison to three other cases of influenza pneumonia in the same outbreak with known risk factors for severe influenza, such as pregnancy and diabetes mellitus, a much higher viral load was detected in the lungs of this patient despite antiviral treatment. In agreement with the high viral load, the lung specimens from this patient, but not the other three patients, showed a high expression of α-2,6-linked sialic acid by lectin staining. The gene responsible for the synthesis of this sialic acid was also found to be upregulated. The data indicated overexpression of the viral receptor as a potential mechanism for severe disease in some patients.

A functional variation in CD55 increases the severity of 2009 pandemic H1N1 influenza A virus infection

Infection due to 2009 pandemic H1N1 influenza A virus (A[H1N1]pdm09) is commonly manifested as mild infection but occasionally as severe pneumonia. We hypothesized that host genetic variations may contribute to disease severity. An initially small-scale genome-wide association study guided the selection of CD55 single-nucleotide polymorphisms in 425 Chinese patients with severe (n = 177) or mild (n = 248) disease. Carriers of rs2564978 genotype T/T were significantly associated with severe infection (odds ratio, 1.75; P = .011) under a recessive model, after adjustment for clinical confounders. An allele-specific effect on CD55 expression was revealed and ascribed to a promoter indel variation, which was in complete linkage disequilibrium with rs2564978. The promoter variant with deletion exhibited significantly lower transcriptional activity. We further demonstrated that CD55 can protect respiratory epithelial cells from complement attack. Additionally, A(H1N1)pdm09 infection promoted CD55 expression. In conclusion, CD55 polymorphisms are associated with severe A(H1N1)pdm09 infection. CD55 may exert a substantial impact on the disease severity of A(H1N1)pdm09 infection.

Heterogeneous virulence of pandemic 2009 influenza H1N1 virus in mice

BACKGROUND

Understanding the pathogenesis of influenza infection is a key factor leading to the prevention and control of future outbreaks. Pandemic 2009 Influenza H1N1 infection, although frequently mild, led to a severe and fatal form of disease in certain cases that make its virulence nature debatable. Much effort has been made toward explaining the determinants of disease severity; however, no absolute reason has been established.

RESULTS

This study presents the heterogeneous virulence of clinically similar strains of pandemic 2009 influenza virus in human alveolar adenocarcinoma cells and mice. The viruses were obtained from patients who were admitted in a local hospital in China with a similar course of infection and recovered. The A/Nanchang/8002/2009 and A/Nanchang/8011/2009 viruses showed efficient replication and high lethality in mice while infection with A/Nanchang/8008/2009 was not lethal with impaired viral replication, minimal pathology and modest proinflammatory activity in lungs. Sequence analysis displayed prominent differences between polymerase subunits (PB2 and PA) of viral genomes that might correlate with their different phenotypic behavior.

CONCLUSIONS

The study confirms that biological heterogeneity, linked with the extent of viral replication, exists among pandemic H1N1 strains that may serve as a benchmark for future investigations on influenza pathogenesis.

Viral load at diagnosis and influenza A H1N1 (2009) disease severity in children

To assess viral load at diagnosis (VLAD) as a biomarker of novel influenza disease severity, epidemiologic and clinical data of admitted patients <18 years old with Influenza A H1N1 (2009) infection and respiratory symptoms were prospectively collected in a single pediatric tertiary hospital, from weeks 30-51 of 2009. Seventy patients were included. VLAD in children who had symptoms for ≥ 5 days was an accurate parameter distinguishing the patients who required mechanical ventilation (MV) from those who did not required it (area under the ROC curve: 0.73; P=0.03). Having <4.5 log10 copies/ml with ≥ 5 days of symptoms was associated with a lower risk of requiring MV.

High titer and avidity of nonneutralizing antibodies against influenza vaccine antigen are associated with severe influenza

The importance of neutralizing antibody in protection against influenza virus is well established, but the role of the early antibody response during the initial stage of infection in affecting the severity of disease is unknown. The 2009 influenza pandemic provided a unique opportunity for study because most patients lacked preexisting neutralizing antibody. In this study, we compared the antibody responses of 52 patients with severe or mild disease, using sera collected at admission. A microneutralization (MN) assay was used to detect neutralizing antibody. We also developed an enzyme-linked immunosorbent assay (ELISA) which detects both neutralizing and nonneutralizing antibodies against viral antigens from a split-virion inactivated monovalent influenza virus vaccine. While the MN titers were not significantly different between the two groups (P = 0.764), the ELISA titer and ELISA/MN titer ratio were significantly higher for patients with severe disease than for those with mild disease (P = 0.004 and P = 0.011, respectively). This finding suggested that in patients with severe disease, a larger proportion of serum antibodies were antibodies with no detectable neutralizing activity. The antibody avidity was also significantly higher in patients with severe disease than in those with mild disease (P < 0.05). Among patients with severe disease, those who required positive pressure ventilation (PPV) had significantly higher ELISA titers than those who did not require PPV (P < 0.05). Multivariate analysis showed that the ELISA titer and antibody avidity were independently associated with severe disease. Higher titers of nonneutralizing antibody with higher avidity at the early stage of influenza virus infection may be associated with worse clinical severity and poorer outcomes.

2009 H1N1 fatalities: the New Mexico experience

Histopathologic features of New Mexico 2009 H1N1 fatalities have not been representative of those reported nationwide. We retrospectively reviewed medical records of all New Mexico 2009 pandemic influenza A (pH1N1) fatalities (n = 50). In cases in which autopsy was performed (n = 12), histologic sections and culture results were examined. In contrast to previously published studies, the majority of our fatalities did not have diffuse alveolar damage (DAD) (2/12; 16.7%). Common findings included pulmonary interstitial inflammation and edema, tracheobronchitis, and pneumonia. Two cases had significant extra-pulmonary manifestations: myocarditis and cerebral edema with herniation. The majority had a rapid disease course: range from 1 to 12 days (median, 2 days), and Native Americans were disproportionately represented among fatalities. These findings suggest that New Mexico H1N1 fatalities generally did not survive long enough to develop the classic picture of DAD. Pathologists should be aware that H1N1 may cause extra-pulmonary pathology and perform postmortem cultures and histologic sampling accordingly.

An influenza reassortant with polymerase of pH1N1 and NS gene of H3N2 influenza A virus is attenuated in vivo

Influenza viruses readily mutate by accumulating point mutations and also by reassortment in which they acquire whole gene segments from another virus in a co-infected host. The NS1 gene is a major virulence factor of influenza A virus. The effects of changes in NS1 sequence depend on the influenza polymerase constellation. Here, we investigated the consequences of a virus with the polymerase of pandemic H1N1 2009 acquiring an NS gene segment derived from a seasonal influenza A H3N2 virus, a combination that might arise during natural reassortment of viruses that currently circulate in humans. We generated recombinant influenza viruses with surface HA and NA genes and matrix M gene segment from A/PR/8/34 virus, but different combinations of polymerase and NS genes. Thus, any changes in phenotype were not due to differences in receptor use, entry, uncoating or virus release. In Madin-Darby canine kidney (MDCK) cells, the virus with the NS gene from the H3N2 parent showed enhanced replication, probably a result of increased control of the interferon response. However, in mice the same virus was attenuated in comparison with the virus containing homologous pH1N1 polymerase and NS genes. Levels of viral RNA during single-cycles of replication were lower for the virus with H3N2 NS, and this virus reached lower titres in the lungs of infected mice. Thus, virus with pH1N1 polymerase genes did not increase its virulence by acquiring the H3N2 NS gene segment, and MDCK cells were a poor predictor of the outcome of infection in vivo.

Two years after pandemic influenza A/2009/H1N1: what have we learned?

The world had been anticipating another influenza pandemic since the last one in 1968. The pandemic influenza A H1N1 2009 virus (A/2009/H1N1) finally arrived, causing the first pandemic influenza of the new millennium, which has affected over 214 countries and caused over 18,449 deaths. Because of the persistent threat from the A/H5N1 virus since 1997 and the outbreak of the severe acute respiratory syndrome (SARS) coronavirus in 2003, medical and scientific communities have been more prepared in mindset and infrastructure. This preparedness has allowed for rapid and effective research on the epidemiological, clinical, pathological, immunological, virological, and other basic scientific aspects of the disease, with impacts on its control. A PubMed search using the keywords "pandemic influenza virus H1N1 2009" yielded over 2,500 publications, which markedly exceeded the number published on previous pandemics. Only representative works with relevance to clinical microbiology and infectious diseases are reviewed in this article. A significant increase in the understanding of this virus and the disease within such a short amount of time has allowed for the timely development of diagnostic tests, treatments, and preventive measures. These findings could prove useful for future randomized controlled clinical trials and the epidemiological control of future pandemics.

George K, Hewlett IK, Linnen JM, Norris PJ. Sensitive detection assays for influenza RNA do not reveal viremia in US blood donors

BACKGROUND

There have been anecdotal reports of influenza viremia since the 1960s. We present an assessment of the prevalence of seasonal and 2009 H1N1 influenza viremia (via RNA testing) in blood donor populations using multiple sensitive detection assays.

METHODS

Several influenza RNA amplification assays, including transcription-mediated amplification (TMA) and 2 reverse-transcription polymerase chain reaction (RT-PCR) assays, were evaluated and used to test donor samples. Retrospective samples from 478 subjects drawn at sites with high influenza activity were tested. Prospective samples were collected from 1004 blood donors who called their donation center within 3 days of donation complaining of influenza-like illness (ILI). The plasma collected on the day of donation for these subjects was tested.

RESULTS

Of the repository samples, 2 of 478 plasma samples were initially reactive but not repeat reactive by influenza TMA. Of blood donors reporting ILI symptoms postdonation, 1 of 1004 samples was TMA initially reactive but not repeat reactive; all samples were nonreactive by RT-PCR testing.

CONCLUSIONS

Targeting blood donor populations most likely to have influenza infection, we failed to detect influenza RNA in 1482 donor samples, with most tested by 3 different RNA assays. Seasonal influenza does not appear to pose a significant contamination threat to the blood supply.

Pandemic (H1N1) 2009 influenza in Canadian pediatric cancer and hematopoietic stem cell transplant patients

BACKGROUND

The impact of pandemic H1N1 influenza (pH1N1) virus in pediatric cancer is uncertain. The objectives of this study were to characterize the clinical course of pH1N1 and identify factors associated with severe outcomes.

METHODS

We conducted a Canadian multicenter retrospective review of children with cancer and stem cell transplant (SCT) recipients who were diagnosed with laboratory-confirmed pH1N1 infection between May 1, 2009 and January 31, 2010.

RESULTS

We identified 100 (19 in wave 1 and 81 in wave 2) cases of pH1N1 infection. Median age was 8.7 years. 71% had a hematologic malignancy, and 20% received SCT. Median duration of fever and illness was 2 and 12.5 days, respectively. 51 (51.5%) were hospitalized for a median of 5 days, with no deaths and only 1 requiring admission to the intensive care unit. Radiologically confirmed pneumonia was diagnosed in 10 (10%). Interruption of chemotherapy or conditioning occurred in 43 patients. In multivariable analyses, age <5 years (relative to ≥ 10 years) and neutropenia were associated with hospitalization while neutropenia was associated with pneumonia. Despite oseltamivir use in 89%, viral shedding was prolonged (median, 46 days) and often persisted after symptom resolution. However, an extended treatment course (>5 days) correlated with shortened duration of viral shedding (P=0.041).

CONCLUSIONS

pH1N1 infection in pediatric cancer and SCT patients infrequently caused complications but commonly interrupted cancer treatment. Persistent shedding of virus after illness resolution was common. Further research is needed to verify this finding as it could have implications for treatment guidelines and infection control practices.

Course of pandemic influenza A(H1N1) 2009 virus infection in Dutch patients

The clinical dynamics of influenza A(H1N1) 2009 infections in 61 laboratory-confirmed Dutch cases were examined. An episode lasted a median of 7·5 days of which 2 days included fever. Respiratory symptoms resolved slowly, while systemic symptoms peaked early in the episode and disappeared quickly. Severity of each symptom was rated highest in the first few days. Furthermore, diarrhoea was negatively associated with viral load, but not with faecal excretion of influenza virus. Cases with comorbidities appeared to have higher viral loads than the cases without, suggesting a less effective immune response. These results complement information obtained through traditional surveillance.

Severe pandemic H1N1 2009 infection is associated with transient NK and T deficiency and aberrant CD8 responses

Background

It is unclear why the severity of influenza varies in healthy adults or why the burden of severe influenza shifts to young adults when pandemic strains emerge. One possibility is that cross-protective T cell responses wane in this age group in the absence of recent infection. We therefore compared the acute cellular immune response in previously healthy adults with severe versus mild pandemic H1N1 infection.

Methods and Principal Findings

49 previously healthy adults admitted to the National Hospital of Tropical Diseases, Viet Nam with RT-PCR-confirmed 2009 H1N1 infection were prospectively enrolled. 39 recovered quickly whereas 10 developed severe symptoms requiring supplemental oxygen and prolonged hospitalization. Peripheral blood lymphocyte subset counts and activation (HLADR, CD38) and differentiation (CD27, CD28) marker expression were determined on days 0, 2, 5, 10, 14 and 28 by flow cytometry. NK, CD4 and CD8 lymphopenia developed in 100%, 90% and 60% of severe cases versus 13% (p<0.001), 28%, (p = 0.001) and 18% (p = 0.014) of mild cases. CD4 and NK counts normalized following recovery. B cell counts were not significantly associated with severity. CD8 activation peaked 6–8 days after mild influenza onset, when 13% (6–22%) were HLADR+CD38+, and was accompanied by a significant loss of resting/CD27+CD28+ cells without accumulation of CD27+CD28− or CD27−CD28− cells. In severe influenza CD8 activation peaked more than 9 days post-onset, and/or was excessive (30–90% HLADR+CD38+) in association with accumulation of CD27+CD28− cells and maintenance of CD8 counts.

Conclusion

Severe influenza is associated with transient T and NK cell deficiency. CD8 phenotype changes during mild influenza are consistent with a rapidly resolving memory response whereas in severe influenza activation is either delayed or excessive, and partially differentiated cells accumulate within blood indicating that recruitment of effector cells to the lung could be impaired.