New look at an old problem: bacterial superinfection after influenza

Faecalibacterium duncaniae as a novel next generation probiotic against influenza

The gut-lung axis is critical during viral respiratory infections such as influenza. Gut dysbiosis during infection translates into a massive drop of microbially produced short-chain fatty acids (SCFAs). Among them, butyrate is important during influenza suggesting that microbiome-based therapeutics targeting butyrate might hold promises. The butyrate-producing bacterium Faecalibacterium duncaniae (formerly referred to as F. prausnitzii) is an emerging probiotic with several health-promoting characteristics. To investigate the potential effects of F. duncaniae on influenza outcomes, mice were gavaged with live F. duncaniae (A2-165 or I-4574 strains) five days before infection. Supplementation of F. duncaniae was associated with less severe disease, a lower pulmonary viral load, and lower levels of lung inflammation. F. duncaniae supplementation impacted on gut dysbiosis induced by infection, as assessed by 16S rRNA sequencing. Interestingly, F. duncaniae administration was associated with a recovery in levels of SCFAs (including butyrate) in infected animals. The live form of F. duncaniae was more potent that the pasteurized form in improving influenza outcomes. Lastly, F. duncaniae partially protected against secondary (systemic) bacterial infection. We conclude that F. duncaniae might serve as a novel next generation probiotic against acute viral respiratory diseases.

CT findings of 144 in-hospital patients with influenza pneumonia: A retrospective analysis

BACKGROUND/PURPOSE

Patients with influenza infection during their period of admission may have worse computed tomography (CT) manifestation according to the clinical status. This study aimed to evaluate the CT findings of in-hospital patients due to clinically significant influenza pneumonia with correlation of clinical presentations.

METHODS

In this retrospective, single center case series, 144 patients were included. All in-hospital patients were confirmed influenza infection and underwent CT scan. These patients were divided into three groups according to the clinical status of the most significant management: (1) without endotracheal tube and mechanical ventilator (ETTMV) or extracorporeal membrane oxygenation (ECMO); (2) with ETTMV; (3) with ETTMV and ECMO. Pulmonary opacities were scored according to extent. Spearman rank correlation analysis was used to evaluate the correlation between clinical parameters and CT scores.

RESULTS

The predominant CT manifestation of influenza infection was mixed ground-glass opacity (GGO) and consolidation with both lung involvement. The CT scores were all reach significant difference among all three groups (8.73 ± 6.29 vs 12.49 ± 6.69 vs 18.94 ± 4.57, p < 0.05). The chest CT score was correlated with age, mortality, and intensive care unit (ICU) days (all p values were less than 0.05). In addition, the CT score was correlated with peak lactate dehydrogenase (LDH) level and peak C-reactive protein (CRP) level (all p values were less than 0.05). Concomitant bacterial infection had higher CT score than primary influenza pneumonia (13.02 ± 7.27 vs 8.95 ± 5.99, p < 0.05).

CONCLUSION

Thin-section chest CT scores correlated with clinical and laboratory parameters in in-hospital patients with influenza pneumonia.

Neutrophil extracellular traps mediate severe lung injury induced by influenza A virus H1N1 in mice coinfected with Staphylococcus aureus

Influenza virus and bacterial infection contributed to massive morbidity and mortality. However, the underlying mechanisms were poorly understood. A coinfected model was generating by using sublethal doses of influenza A virus H1N1 A/FM/1/47(H1N1) and methicillin-resistant Staphylococcus aureus (MRSA). Further, the model was optimized to achieve the highest peak of mortality initiated by intranasal infection with 0.2LD₅₀ H1N1 and 0.16LD₅₀ MRSA at 3 days interval. Excessive neutrophil recruitment, accompanied by high levels of inflammatory cytokines and chemokines, and increased bacterial and viral load were observed in coinfected mice. Under the inflammatory environments triggered by H1N1 and MRSA, the excessive neutrophil recruitment led to the formation of neutrophil extracellular traps (NETs), associated with severe inflammation and vascular endothelial injury. Importantly, the severity of lung injury could be alleviated by treatment with DNase I or a selective neutrophil elastase inhibitor (NEi). Therefore, our data suggested that excessive neutrophil recruitment and NETs formation contributed to severe inflammation and acute lung injury in coinfected animals.

Factors Associated With 30 Day Survival in Adults With Influenza Infection Receiving Extracorporeal Membrane Oxygenation

Acute respiratory distress syndrome (ARDS) secondary to influenza in adults is associated with a high rate of morbidity and mortality. Extracorporeal membrane oxygenation (ECMO) is a supportive alternative for severe and refractory cases. This study aimed to perform a hospital-based case-control study between February 2018 and February 2020 for determining the factors associated with 30 day survival in adults with severe ARDS caused by influenza infection who are provided ECMO support. A total of 17 adults received ECMO support, mostly veno-venous for hypoxemic respiratory failure, with a 30 day survival rate of 65%. The cohort of patients who did not survive at 30 days compared with the cohort of those who did survive had higher body mass index (34 vs. 31), higher Sequential Organ Failure Assessment score (9.5 vs. 7) and lower Respiratory ECMO Survival Prediction score (2 vs. 4). This study shows the importance of evaluating the severity scores of patients before ECMO support initiation, which offers an acceptable survival in patients with severe ARDS, making it a feasible alternative in critical patients who are refractory to conventional management.

Antibody Treatment against Angiopoietin-Like 4 Reduces Pulmonary Edema and Injury in Secondary Pneumococcal Pneumonia

Secondary bacterial lung infection by Streptococcus pneumoniae (S. pneumoniae) poses a serious health concern, especially in developing countries. We posit that the emergence of multiantibiotic-resistant strains will jeopardize current treatments in these regions. Deaths arising from secondary infections are more often associated with acute lung injury, a common consequence of hypercytokinemia, than with the infection per se Given that secondary bacterial pneumonia often has a poor prognosis, newer approaches to improve treatment outcomes are urgently needed to reduce the high levels of morbidity and mortality. Using a sequential dual-infection mouse model of secondary bacterial lung infection, we show that host-directed therapy via immunoneutralization of the angiopoietin-like 4 c-isoform (cANGPTL4) reduced pulmonary edema and damage in infected mice. RNA sequencing analysis revealed that anti-cANGPTL4 treatment improved immune and coagulation functions and reduced internal bleeding and edema. Importantly, anti-cANGPTL4 antibody, when used concurrently with either conventional antibiotics or antipneumolysin antibody, prolonged the median survival of mice compared to monotherapy. Anti-cANGPTL4 treatment enhanced immune cell phagocytosis of bacteria while restricting excessive inflammation. This modification of immune responses improved the disease outcomes of secondary pneumococcal pneumonia. Taken together, our study emphasizes that host-directed therapeutic strategies are viable adjuncts to standard antimicrobial treatments.IMPORTANCE Despite extensive global efforts, secondary bacterial pneumonia still represents a major cause of death in developing countries and is an important cause of long-term functional disability arising from lung tissue damage. Newer approaches to improving treatment outcomes are needed to reduce the significant morbidity and mortality caused by infectious diseases. Our study, using an experimental mouse model of secondary S. pneumoniae infection, shows that a multimodal treatment that concurrently targets host and pathogen factors improved lung tissue integrity and extended the median survival time of infected mice. The immunoneutralization of host protein cANGPTL4 reduced the severity of pulmonary edema and damage. We show that host-directed therapeutic strategies as well as neutralizing antibodies against pathogen virulence factors are viable adjuncts to standard antimicrobial treatments such as antibiotics. In view of their different modes of action compared to antibiotics, concurrent immunotherapies using antibodies are potentially efficacious against secondary pneumococcal pneumonia caused by antibiotic-resistant pathogens.

A Rare Case of Aortoatrial Fistula from Streptococcal Endocarditis

We represent an unfortunate case of postinfluenza streptococcal endocarditis in a 34-year-old healthy male. He presented with hypoxic respiratory failure and was found to have mitral and aortic valve vegetation. Hospital course was complicated by the presence of an aortoatrial fistula from an aortic root abscess, persistent septic shock, and multiorgan failure.

Influenza virus infections in patients with malignancies -- characteristics and outcome of the season 2014/15. A survey conducted by the Infectious Diseases Working Party (AGIHO) of the German Society of Haematology and Medical Oncology (DGHO)

Influenza virus infections (IVI) may pose a vital threat to immunocompromised patients such as those suffering from malignancies, but specific data on epidemiology and outcome in these patients are scarce. In this study, we collected data on patients with active cancer or with a history of cancer, presenting with documented IVI in eight centres in Germany. Two hundred and three patients were identified, suffering from haematological malignancies or solid tumours; 109 (54 %) patients had active malignant disease. Influenza A was detected in 155 (77 %) and Influenza B in 46 (23 %) of patients (genera not determined in two patients). Clinical symptoms were consistent with upper respiratory tract infection in 55/203 (27 %), influenza-like illness in 82/203 (40 %), and pneumonia in 67/203 (33 %). Anti-viral treatment with oseltamivir was received by 116/195 (59 %). Superinfections occurred in 37/203 (18 %), and admission on an intensive care unit was required in 26/203 (13 %). Seventeen patients (9 %) died. Independent risk factors for death were delayed diagnosis of IVI and bacterial or fungal superinfection, but not underlying malignancy or ongoing immunosuppression. In conclusion, patients with IVI show high rates of pneumonia and mortality. Early and rapid diagnosis is essential. The high rate of pneumonia and superinfections should be taken into account when managing IVI in these patients.

Exogenous Activation of Invariant Natural Killer T Cells by α-Galactosylceramide Reduces Pneumococcal Outgrowth and Dissemination Postinfluenza

Influenza A virus infection can predispose to potentially devastating secondary bacterial infections. Invariant natural killer T (iNKT) cells are unconventional, lipid-reactive T lymphocytes that exert potent immunostimulatory functions. Using a mouse model of postinfluenza invasive secondary pneumococcal infection, we sought to establish whether α-galactosylceramide (α-GalCer [a potent iNKT cell agonist that is currently in clinical development]) could limit bacterial superinfection. Our results highlighted the presence of a critical time window during which α-GalCer treatment can trigger iNKT cell activation and influence resistance to postinfluenza secondary pneumococcal infection. Intranasal treatment with α-GalCer during the acute phase (on day 7) of influenza virus H3N2 and H1N1 infection failed to activate (gamma interferon [IFN-γ] and interleukin-17A [IL-17A]) iNKT cells; this effect was associated with a strongly reduced number of conventional CD103⁺ dendritic cells in the respiratory tract. In contrast, α-GalCer treatment during the early phase (on day 4) or during the resolution phase (day 14) of influenza was associated with lower pneumococcal outgrowth and dissemination. Less intense viral-bacterial pneumonia and a lower morbidity rate were observed in superinfected mice treated with both α-GalCer (day 14) and the corticosteroid dexamethasone. Our results open the way to alternative (nonantiviral/nonantibiotic) iNKT-cell-based approaches for limiting postinfluenza secondary bacterial infections.

IMPORTANCE

Despite the application of vaccination programs and antiviral drugs, influenza A virus (IAV) infection is responsible for widespread morbidity and mortality (500,000 deaths/year). Influenza infections can also result in sporadic pandemics that can be devastating: the 1918 pandemic led to the death of 50 million people. Severe bacterial infections are commonly associated with influenza and are significant contributors to the excess morbidity and mortality of influenza. Today's treatments of secondary bacterial (pneumococcal) infections are still not effective enough, and antibiotic resistance is a major issue. Hence, there is an urgent need for novel therapies. In the present study, we set out to evaluate the efficacy of α-galactosylceramide (α-GalCer)-a potent agonist of invariant NKT cells that is currently in clinical development-in a mouse model of postinfluenza, highly invasive pneumococcal pneumonia. Our data indicate that treatment with α-GalCer reduces susceptibility to superinfections and, when combined with the corticosteroid dexamethasone, reduces viral-bacterial pneumonia.

The Role of Antimicrobial Peptides in Influenza Virus Infection and Their Potential as Antiviral and Immunomodulatory Therapy

Influenza A virus (IAV) remains a major threat that can cause severe morbidity and mortality due to rapid genomic variation. Resistance of IAVs to current anti-IAV drugs has been emerging, and antimicrobial peptides (AMPs) have been considered to be potential candidates for novel treatment against IAV infection. AMPs are endogenous proteins playing important roles in host defense through direct antimicrobial and antiviral activities and through immunomodulatory effects. In this review, we will discuss the anti-IAV and immunomodulatory effects of classical AMPs (defensins and cathelicidins), and proteins more recently discovered to have AMP-like activity (histones and Alzheimer's associated β-amyloid). We will discuss the interactions between AMPs and other host defense proteins. Major emphasis will be placed on novel synthetic AMPs derived from modification of natural proteins, and on potential methods of increasing expression of endogenous AMPs, since these approaches may lead to novel antiviral therapeutics.

Canine influenza virus coinfection with Staphylococcus pseudintermedius enhances bacterial colonization, virus load and clinical presentation in mice

Background

Canine influenza virus (CIV) and Staphylococcus pseudintermedius (Sp) are pathogens that cause respiratory disease in dogs. Considering bacterial infections following influenza are a leading cause of illness and death, it is of particular meaning to investigate the interaction between these two pathogens. In this study, BALB/c mice were used as a mouse model to assess whether inoculation with CIV H3N2 followed by S. pseudintermedius 72 h later resulted in exacerbation of disease. Disease was characterized by assessment of body weight loss, titration of virus and bacteria, histopathology, and cytokine production.

Results

There was a significantly greater decrease in body weight in the co-infected group compared with the CIV-only and SP-only groups. CIV inoculation increased bacterial colonization, whereas secondary infection with S. pseudintermedius elevated the viral RNA load of CIV in tissues. The histological lesions in the brain, spleen and lung were more severe in the CIV/Sp group than in the singly treated groups. Infection with CIV alone, Sp alone or coinfection stimulated a significantly higher release of cytokines, such as interferon-gamma (IFN)-γ, interleukin 6 (IL)-6, tumor necrosis factor (TNF-α) and lymphotactin (Lptn), than was observed in the mock-infected group (PBS). Moreover, the levels of IFN-γ in the spleen and lung were higher in the CIV/Sp group compared with the CIV-only and Sp-only groups.

Conclusion

Our findings provide the first demonstration that the secondary infection of mice with Sp leads to increased clinical signs and lesions during canine influenza.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0708-6) contains supplementary material, which is available to authorized users.

Aetiological role of common respiratory viruses in acute lower respiratory infections in children under five years: A systematic review and meta-analysis

Background

Acute lower respiratory infection (ALRI) remains a major cause of childhood hospitalization and mortality in young children and the causal attribution of respiratory viruses in the aetiology of ALRI is unclear. We aimed to quantify the absolute effects of these viral exposures.

Methods

We conducted a systematic literature review (across 7 databases) of case–control studies published from 1990 to 2014 which investigated the viral profile of 18592 children under 5 years with and without ALRI. We then computed a pooled odds ratio and virus–specific attributable fraction among the exposed of 8 common viruses – respiratory syncytial virus (RSV), influenza (IFV), parainfluenza (PIV), human metapneumovirus (MPV), adenovirus (AdV), rhinovirus (RV), bocavirus (BoV), and coronavirus (CoV).

Findings

From the 23 studies included, there was strong evidence for causal attribution of RSV (OR 9.79; AFE 90%), IFV (OR 5.10; AFE 80%), PIV (OR 3.37; AFE 70%) and MPV (OR 3.76; AFE 73%), and less strong evidence for RV (OR 1.43; AFE 30%) in young children presenting with ALRI compared to those without respiratory symptoms (asymptomatic) or healthy children. However, there was no significant difference in the detection of AdV, BoV, or CoV in cases and controls.

Conclusions

This review supports RSV, IFV, PIV, MPV and RV as important causes of ALRI in young children, and provides quantitative estimates of the absolute proportion of virus–associated ALRI cases to which a viral cause can be attributed.

Mutations flanking the carbohydrate binding site of surfactant protein D confer antiviral activity for pandemic influenza A viruses

We recently reported that a trimeric neck and carbohydrate recognition domain (NCRD) fragment of human surfactant protein D (SP-D), a host defense lectin, with combinatorial substitutions at the 325 and 343 positions (D325A+R343V) exhibits markedly increased antiviral activity for seasonal strains of influenza A virus (IAV). The NCRD binds to glycan-rich viral envelope proteins including hemagglutinin (HA). We now show that replacement of D325 with serine to create D325S+R343V provided equal or increased neutralizing activity compared with D325A+R343V. The activity of the double mutants was significantly greater than that of either single mutant (D325A/S or R343V). D325A+R343V and D325S+R343V also strongly inhibited HA activity, and markedly aggregated, the 1968 pandemic H3N2 strain, Aichi68. D325S+R343V significantly reduced viral loads and mortality of mice infected with Aichi68, whereas wild-type SP-D NCRD did not. The pandemic H1N1 strains of 1918 and 2009 have only one N-linked glycan side on the head region of the HA and are fully resistant to inhibition by native SP-D. Importantly, we now show that D325A+R343V and D325S+R343V inhibited Cal09 H1N1 and related strains, and reduced uptake of Cal09 by epithelial cells. Inhibition of Cal09 was mediated by the lectin activity of the NCRDs. All known human pandemic strains have at least one glycan attachment on the top or side of the HA head, and our results indicate that they may be susceptible to inhibition by modified host defense lectins.

The amazing innate immune response to influenza A virus infection

Influenza A viruses (IAVs) remain a major health threat and a prime example of the significance of innate immunity. Our understanding of innate immunity to IAV has grown dramatically, yielding new concepts that change the way we view innate immunity as a whole. Examples include the role of p53, autophagy, microRNA, innate lymphocytes, endothelial cells and gut commensal bacteria in pulmonary innate immunity. Although the innate response is largely beneficial, it also contributes to major complications of IAV, including lung injury, bacterial super-infection and exacerbation of reactive airways disease. Research is beginning to dissect out which components of the innate response are helpful or harmful. IAV uses its limited genetic complement to maximum effect. Several viral proteins are dedicated to combating innate responses, while other viral structural or replication proteins multitask as host immune modulators. Many host innate immune proteins also multitask, having roles in cell cycle, signaling or normal lung biology. We summarize the plethora of new findings and attempt to integrate them into the larger picture of how humans have adapted to the threat posed by this remarkable virus. We explore how our expanded knowledge suggests ways to modulate helpful and harmful inflammatory responses, and develop novel treatments.

Role of type 1 natural killer T cells in pulmonary immunity

Mucosal sites are populated by a multitude of innate lymphoid cells and "innate-like" T lymphocytes expressing semiconserved T-cell receptors. Among the latter group, interest in type I natural killer T (NKT) cells has gained considerable momentum over the last decade. Exposure to NKT cell antigens is likely to occur continuously at mucosal sites. For this reason, and as they rapidly respond to stress-induced environmental cytokines, NKT cells are important contributors to immune and inflammatory responses. Here, we review the dual role of mucosal NKT cells during immune responses and pathologies with a particular focus on the lungs. Their role during pulmonary acute and chronic inflammation and respiratory infections is outlined. Whether NKT cells might provide a future attractive therapeutic target for treating human respiratory diseases is discussed.

Interleukin-22 reduces lung inflammation during influenza A virus infection and protects against secondary bacterial infection

Interleukin-22 (IL-22) has redundant, protective, or pathogenic functions during autoimmune, inflammatory, and infectious diseases. Here, we addressed the potential role of IL-22 in host defense and pathogenesis during lethal and sublethal respiratory H3N2 influenza A virus (IAV) infection. We show that IL-22, as well as factors associated with its production, are expressed in the lung tissue during the early phases of IAV infection. Our data indicate that retinoic acid receptor-related orphan receptor-γt (RORγt)-positive αβ and γδ T cells, as well as innate lymphoid cells, expressed enhanced Il22 transcripts as early as 2 days postinfection. During lethal or sublethal IAV infections, endogenous IL-22 played no role in the control of IAV replication and in the development of the IAV-specific CD8(+) T cell response. During lethal infection, where wild-type (WT) mice succumbed to severe pneumonia, the lack of IL-22 did not accelerate or delay IAV-associated pathogenesis and animal death. In stark contrast, during sublethal IAV infection, IL-22-deficient animals had enhanced lung injuries and showed a lower airway epithelial integrity relative to WT littermates. Of importance, the protective effect of endogenous IL-22 in pulmonary damages was associated with a more controlled secondary bacterial infection. Indeed, after challenge with Streptococcus pneumoniae, IAV-experienced Il22(-/-) animals were more susceptible than WT controls in terms of survival rate and bacterial burden in the lungs. Together, IL-22 plays no major role during lethal influenza but is beneficial during sublethal H3N2 IAV infection, where it limits lung inflammation and subsequent bacterial superinfections.

Endothelial cell death and intimal foam cell accumulation in the coronary artery of infected hypercholesterolemic minipigs

Apoptosis of endothelial cells (ECs) has been suggested to play a role in atherosclerosis. We studied the synergism of hypercholesterolemia with Chlamydia pneumoniae and influenza virus infections on EC morphology and intimal changes in a minipig model. The coronary artery was excised at euthanasia (19 weeks of age) and serial sections were processed for the detection of EC apoptosis, histology, and transmission electron microscopy (TEM) studies. There was a significantly higher number of TUNEL-positive ECs in infected compared to noninfected groups [0.2942 % (interquartile ranges (IR), 0.2941; n = 26) versus 0 % (IR, 0; n = 12), p < 0.01]. Caspase-3 staining was negative. Cholesterol diet together with infections induced widening of the subendothelial space and appearance of increased numbers of foam cells. TEM revealed degenerative changes in cytoplasmic organelles and signs of EC necrosis. In conclusion, infection leads to an increase in coronary EC death and seems to exacerbate cholesterol-induced intimal thickening and foam cell accumulation.

[A case of descending necrotizing mediastinitis caused by infection with Streptococcus agalactiae in a patient with diabetes mellitus]

We report a case with an atypical presentation of descending necrotizing mediastinitis (DNM). A 47-year-old woman with a medical history of untreated type 2 diabetes mellitus and influenza type A virus infection 2 weeks prior to admission was referred to our hospital complaining of right cervical pain and right upper limb swelling. A chest enhanced computed tomographic (CT) scan showed a ring-enhanced mass-like shadow extending from the right sternomastoid muscle down to the right upper mediastinum, compressing the right subclavicular vein. We diagnosed the patient as having DNM based on a physical examination and the CT findings. Because the abscess extended from deep in the neck to the upper mediastinum and right upper pleural space, emergent abscess debridement and drainage was required. After hospitalization, antibiotics (Ampicillin/Sulbactam 12 g/day) were also administered based on Gram-stain findings from the drainage fluid, which showed Gram-positive cocci resembling a string of beads. A culture of the drainage fluid identified Streptococcus agalactiae. Aggressive abscess drainage and early antibiotic therapy resulted in a favorable response. She was discharged without complications on the 33rd hospital day. DNM is well known as a rare but lethal disease. In this case, the presence of diabetes mellitus and post-influenza infection might have been risk factors for a serious S. agalactiae infection. Early aggressive therapy and adequate drainage are recommended for patients with DNM.

Cigarette smoking as a risk factor for influenza-associated mortality: evidence from an elderly cohort

Please cite this paper as: Wong et al. (2012) Cigarette smoking as a risk factor for influenza‐associated mortality: evidence from an elderly cohort. Influenza and Other Respiratory Viruses 7(4), 531–539.

Background  The effects of individual lifestyle factors on the mortality risk after influenza infection have not been explored.

Objectives  In this study, we assessed the modifying effects of cigarette smoking on mortality risks associated with influenza in a cohort of Hong Kong elders with a follow‐up period of 1998–2009.

Methods  We used the Cox proportional hazards model with time‐dependent covariates of weekly proportions of specimens positive for influenza (termed as influenza virus activity), to calculate the hazard ratio of mortality associated with a 10% increase in influenza virus activity for never, ex‐ and current smokers. Other individual lifestyle and socioeconomic factors as well as seasonal confounders were also added into the models.

Results  The overall hazard ratio associated with influenza was 1·028 (95% confidence interval, 1·006, 1·051) for all natural cause mortality and 1·035 (1·003, 1·068) for cardiovascular and respiratory mortality. We found that influenza‐associated hazard ratio was greater in current and ex‐smokers than in never smokers for mortality of all natural causes, cardiovascular and respiratory diseases.

Conclusions  The findings suggest that smoking might increase influenza‐associated mortality risks among elders.

Invasive bacterial infections in relation to influenza outbreaks, 2006-2010

BACKGROUND

We aimed to define the excess morbidity associated with bloodstream infections (BSIs), imposed by pandemic H1N1 influenza during 2009-2010 (pH1N1/2009-2010) and seasonal influenza.

METHODS

Eight hospitals, accounting for 33% of hospitalizations in Israel, provided data on BSI during 2006-2010. The age-specific incidence of BSI due to Streptococcus pneumoniae, Staphylococcus aureus, and Streptococcus pyogenes was determined. BSI incidence rate ratios (IRRs) during seasonal and pH1N1 influenza seasons were assessed.

RESULTS

Regular influenza seasons were characterized by increased rates of S. pneumoniae BSI but with no increase in S. aureus and S. pyogenes BSI rates. The pH1N1/2009-2010 influenza outbreak was characterized by (1) higher rates of S. pneumoniae bacteremia among children but not among adults (IRRs for S. pneumoniae BSI among children aged 0-4 years during the summer and winter of 2009-2010 were 14.8 [95% confidence interval {CI}, 5-43.7] and 6.5 [95% CI, 3.6-11.8], compared with 2006-2009 summers and influenza-active winter weeks, respectively [P < .0001]), higher rates of S. aureus BSI in all age groups (IRRs during the summer and winter of 2009-2010 were 1.6 [95% CI, 1.4-1.9] and 1.5 [95% CI, 1.2-1.7], compared with 2006-2009 summers and influenza-active weeks, respectively [P < .0001]), higher rates of S. pyogenes BSI during 2009-2010 influenza season (IRR 2.7 [95% CI, 1.6-4.6] and 3.3 [95% CI, 1.9-5.8] during the summer and winter of 2009-2010, compared with 2006-2009 summers and influenza-active weeks, respectively [P < .0001]).

CONCLUSIONS

pH1N1 influenza seasons were characterized by marked increases in invasive S. aureus and S. pyogenes infections among children and adults, with the highest increase in S. pneumoniae BSI among children.

Lethal synergism of 2009 pandemic H1N1 influenza virus and Streptococcus pneumoniae coinfection is associated with loss of murine lung repair responses

Secondary bacterial infections increase disease severity of influenza virus infections and contribute greatly to increased morbidity and mortality during pandemics. To study secondary bacterial infection following influenza virus infection, mice were inoculated with sublethal doses of 2009 seasonal H1N1 virus (NIH50) or pandemic H1N1 virus (Mex09) followed by inoculation with Streptococcus pneumoniae 48 h later. Disease was characterized by assessment of weight loss and survival, titration of virus and bacteria by quantitative reverse transcription-PCR (qRT-PCR), histopathology, expression microarray, and immunohistochemistry. Mice inoculated with virus alone showed 100% survival for all groups. Mice inoculated with Mex09 plus S. pneumoniae showed severe weight loss and 100% mortality with severe alveolitis, denuded bronchiolar epithelium, and widespread expression of apoptosis marker cleaved caspase 3. In contrast, mice inoculated with NIH50 plus S. pneumoniae showed increased weight loss, 100% survival, and slightly enhanced lung pathology. Mex09-S. pneumoniae coinfection also resulted in increased S. pneumoniae replication in lung and bacteremia late in infection. Global gene expression profiling revealed that Mex09-S. pneumoniae coinfection did not induce significantly more severe inflammatory responses but featured significant loss of epithelial cell reproliferation and repair responses. Histopathological examination for cell proliferation marker MCM7 showed significant staining of airway epithelial cells in all groups except Mex09-S. pneumoniae-infected mice. This study demonstrates that secondary bacterial infection during 2009 H1N1 pandemic virus infection resulted in more severe disease and loss of lung repair responses than did seasonal influenza viral and bacterial coinfection. Moreover, this study provides novel insights into influenza virus and bacterial coinfection by showing correlation of lethal outcome with loss of airway basal epithelial cells and associated lung repair responses.

Secondary bacterial pneumonias lead to increased disease severity and have resulted in a significant percentage of deaths during influenza pandemics. To understand the biological basis for the interaction of bacterial and viral infections, mice were infected with sublethal doses of 2009 seasonal H1N1 and pandemic H1N1 viruses followed by infection with Streptococcus pneumoniae 48 h later. Only infection with 2009 pandemic H1N1 virus and S. pneumoniae resulted in severe disease with a 100% fatality rate. Analysis of the host response to infection during lethal coinfection showed a significant loss of responses associated with lung repair that was not observed in any of the other experimental groups. This group of mice also showed enhanced bacterial replication in the lung. This study reveals that the extent of lung damage during viral infection influences the severity of secondary bacterial infections and may help explain some differences in mortality during influenza pandemics.

Pandemic influenza A (H1N1) 2009: chest radiographic findings from 147 proven cases in the Montreal area

OBJECTIVE

To describe chest radiographic findings in patients with isolated and complicated acute novel influenza A (H1N1) virus infection.

METHODS

Retrospective study of 147 patients (64 men, mean age 41) with reverse-transcriptase polymerase chain reaction confirmed acute influenza A (H1N1) infection, who also had a chest radiograph <72 hours of viral specimen collection. Radiographs were analysed for acute findings. A correlation with bacterial cultures results was performed. The unpaired 2-sample equal-variance Student t test was applied to continuous variables and the Pearson χ(2) test of association to discrete variables.

RESULTS

In 71% of cases, chest radiograph was normal. The presence of acute imaging findings was associated with older age (P < .05), increased number of comorbidities (most commonly, chronic obstructive pulmonary disease, diabetes, asthma) (P < .05), higher rate of hospitalization (P < .05) and intensive care unit admission, and increased mortality. Predominant acute radiographic finding in isolated influenza A (H1N1) was alveolar opacity (88%), either unifocal or multifocal, most often in the lower lobes. In the subgroup of patients with positive imaging findings and for whom nonviral microbiologic data was available, 62% had superimposed bacterial or fungal infection.

CONCLUSION

In the majority of patients with acute influenza A (H1N1) infection, the chest radiograph is normal. Acute imaging findings are associated with older age, an increased number of comorbidities, and a higher rate of complications and mortality. The predominant radiographic finding of isolated primary influenza A (H1N1) infection is alveolar opacity. Superimposed bacterial infection is frequent and must be excluded in patients with abnormal imaging.