Respiratory viruses predisposing to bacterial infections: role of neuraminidase

Streptococcus pneumoniae serotype 15A in psychiatric unit, Rhode Island, USA, 2010-2011

During a pneumococcal disease outbreak in a pediatric psychiatric unit in a hospital in Rhode Island, USA, 6 (30%) of 20 patients and staff were colonized with Streptococcus pneumoniae serotype 15A, which is not included in pneumococcal vaccines. The outbreak subsided after implementation of antimicrobial drug prophylaxis and enhanced infection control measures.

Lower nasopharyngeal epithelial cell repair and diminished innate inflammation responses contribute to the onset of acute otitis media in otitis-prone children

About 30 % of young children experience excessive, frequent episodes of middle ear infection and are classified as acute otitis media prone (OP). Streptococcus pneumoniae (Spn) is a predominant otopathogen in OP and non-OP (NOP) children. The pathogenesis of middle ear infection involves otopathogen nasopharyngeal (NP) colonization followed by an upper respiratory viral infection that modifies the NP environment to allow a sufficient inoculum of bacteria to reflux via the Eustachian tube into the middle ear space. Here, we analyzed the NP mucosal repair response between age-matched stringently defined OP (sOP) and NOP children who progressed to middle ear infection caused by Spn. We found lower epidermal growth factor, epidermal growth factor receptor, and angiogenin cytokine concentrations in nasal washes of sOP compared with NOP children. Despite higher expression of TLR2/4 transcript expression in nasal epithelium and in polymorphonuclear cells present in nasal secretions in sOP children, sOP children had lower expression of proinflammatory cytokines such as IL-6 and IL-8 in the NP. Chemotaxis-associated cytokine expression at onset of AOM in sOP children was also lower compared with NOP children, possibly indicating a lower capacity to signal the innate immune system. We conclude that lower epithelial cell repair responses during viral infection in the NP combined with diminished innate inflammatory responses potentiate Spn pathogenesis in the sOP child.

New respiratory viral infections

PURPOSE OF REVIEW

The first era in the discoveries of respiratory viruses occured between 1933 and 1965 when influenza virus, enteroviruses, adenovirus, respiratory syncytial virus, rhinovirus, parainfluenza virus and coronavirus (CoV) were found by virus culture. In the 1990s, the development of high throughput viral detection and diagnostics instruments increased diagnostic sensitivity and enabled the search for new viruses. This article briefly reviews the clinical significance of newly discovered respiratory viruses.

RECENT FINDINGS

In 2001, the second era in the discoveries of respiratory viruses began, and several new respiratory viruses and their subgroups have been found: human metapneumovirus, CoVs NL63 and HKU1, human bocavirus and human rhinovirus C and D groups.

SUMMARY

Currently, a viral cause of pediatric respiratory illness is identifiable in up to 95% of cases, but the detection rates decrease steadily by age, to 30-40% in the elderly. The new viruses cause respiratory illnesses such as common cold, bronchitis, bronchiolitis, exacerbations of asthma and chronic obstructive pulmonary disease and pneumonia. Rarely, acute respiratory failure may occur. The clinical role of other new viruses, KI and WU polyomaviruses and the torque teno virus, as respiratory pathogens is not clear.

Kinetics of coinfection with influenza A virus and Streptococcus pneumoniae

Secondary bacterial infections are a leading cause of illness and death during epidemic and pandemic influenza. Experimental studies suggest a lethal synergism between influenza and certain bacteria, particularly Streptococcus pneumoniae, but the precise processes involved are unclear. To address the mechanisms and determine the influences of pathogen dose and strain on disease, we infected groups of mice with either the H1N1 subtype influenza A virus A/Puerto Rico/8/34 (PR8) or a version expressing the 1918 PB1-F2 protein (PR8-PB1-F2(1918)), followed seven days later with one of two S. pneumoniae strains, type 2 D39 or type 3 A66.1. We determined that, following bacterial infection, viral titers initially rebound and then decline slowly. Bacterial titers rapidly rise to high levels and remain elevated. We used a kinetic model to explore the coupled interactions and study the dominant controlling mechanisms. We hypothesize that viral titers rebound in the presence of bacteria due to enhanced viral release from infected cells, and that bacterial titers increase due to alveolar macrophage impairment. Dynamics are affected by initial bacterial dose but not by the expression of the influenza 1918 PB1-F2 protein. Our model provides a framework to investigate pathogen interaction during coinfections and to uncover dynamical differences based on inoculum size and strain.

Influenza virus infected individuals often become coinfected with a bacterial pathogen and, consequently, morbidity and mortality are significantly increased. A better understanding of how these pathogens interact with each other and the host is of key importance. Here, we use data from infected mice together with mathematical modeling and quantitative analyses to understand how each pathogen influences the other, and how the 1918 influenza PB1-F2 protein and the bacterial strain and dose contribute to coinfection kinetics. We find that influenza viral titers increase when Streptococcus pneumoniae is present and that the bacteria establish and grow rapidly when influenza is present. Our model and analyses suggest that the influenza infection reduces the bacterial clearance ability of alveolar macrophages and that the subsequent S. pneumoniae infection enhances viral release from infected cells. These results provide new insights into the mechanisms of influenza coinfection and the differences in pathogenesis of influenza and S. pneumoniae strains.

Influenza and RSV make a modest contribution to invasive pneumococcal disease incidence in the UK

Objectives

The common seasonality of incidence of invasive pneumococcal disease (IPD) and viral respiratory infections has long been recognized, however, the extent to which this affects the association between the pathogens is unknown. We have analysed weekly surveillance data of IPD, influenza and respiratory syncytial virus (RSV), using ambient temperature and hours of sunshine as measures of seasonality.

Methods

Reported cases of influenza, IPD and RSV, were collected in England and Wales, from week 1 (January) 1996 to week 23 (June) 2009. The associations between IPD and respiratory viral infections were analysed using several statistical methods, including correlation coefficients and both additive and multiplicative regression models.

Results

6–7.5% of cases of IPD are attributable to influenza and 3–4% attributable to RSV. Correlation coefficients reported considerably stronger associations between IPD and the viral infections compared to regression models.

Conclusions

A small but potentially important percentage of IPD may be attributable to influenza and RSV when adjusted for seasonality by temperature. Jointly these viral infections may lead to over 10% of IPD cases. Therefore, prevention of viral respiratory infections may offer some additional benefit in reducing invasive pneumococcal infections.

New molecular virus detection methods and their clinical value in lower respiratory tract infections in children

During the past decade, several new respiratory viruses and their subgroups have been discovered. All these new viruses, as well as previously known respiratory viruses, can be detected by sensitive PCR methods, which have become popular in the diagnostic workup of respiratory viral infections. Currently, respiratory viruses can be detected in up to 95% of children with lower respiratory tract illness. On the other hand, virus detection rates in asymptomatic children are also high (up to 68%), as are coinfection rates in symptomatic children (up to 43%) and justified concerns of causality have been raised. Imposing progress has been made in developing multiplex quantitative PCR assays; here, several primer sets are run within a single PCR mixture. These PCR assays give a better understanding of the dominant viral infection, of viral infections that may be incipient and of any waning infections than does a single-target PCR. Multiplex PCR assays are also gaining popularity due to their cost-effectiveness and short throughput time compared to multiple single-target PCRs. Our understanding of the indications of virus PCRs and our ability to interpret the results from a clinical point of view have improved. This paper reviews the progress in PCR assays and discusses their role in the diagnosis of lower respiratory tract infections in children.

Potential use of Atlantic cod trypsin in biomedicine

Surface proteins of viruses and bacteria used for cell attachment and invasion are candidates for degradation by proteases. Trypsin from Atlantic cod (Gadus morhua) was previously demonstrated to have efficacy against influenza viruses in vitro and on skin. In this paper, cod trypsin is shown to be 3–12 times more effective in degrading large native proteins than its mesophilic analogue, bovine trypsin. This is in agreement with previous findings where cod trypsin was found to be the most active among twelve different proteases in cleaving various cytokines and pathological proteins. Furthermore, our results show that cod trypsin has high efficacy against herpes simplex virus type 1 (HSV-1) and the respiratory syncytial virus (RSV) in vitro. The results on the antipathogenic properties of cod trypsin are important because rhinovirus, RSV, and influenza are the most predominant pathogenic viruses in upper respiratory tract infections. Results from a clinical study presented in this paper show that a specific formulation containing cod trypsin was preferred for wound healing over other methods used in the study. Apparently, the high digestive ability of the cold-adapted cod trypsin towards large native proteins plays a role in its efficacy against pathogens and its positive effects on wounds.

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

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

Evaluation of diagnostic and therapeutic approaches for suspected influenza A(H1N1)pdm09 infection, 2009-2010

Variations between practice and national recommendations could inform clinical education in future influenza seasons.

Keywords: influenza; oseltamivir; H1N1, influenza A(H1N1)pdm09, viruses

Influenza-induced inflammation drives pneumococcal otitis media

Influenza A virus (IAV) predisposes individuals to secondary infections with the bacterium Streptococcus pneumoniae (the pneumococcus). Infections may manifest as pneumonia, sepsis, meningitis, or otitis media (OM). It remains controversial as to whether secondary pneumococcal disease is due to the induction of an aberrant immune response or IAV-induced immunosuppression. Moreover, as the majority of studies have been performed in the context of pneumococcal pneumonia, it remains unclear how far these findings can be extrapolated to other pneumococcal disease phenotypes such as OM. Here, we used an infant mouse model, human middle ear epithelial cells, and a series of reverse-engineered influenza viruses to investigate how IAV promotes bacterial OM. Our data suggest that the influenza virus HA facilitates disease by inducing a proinflammatory response in the middle ear cavity in a replication-dependent manner. Importantly, our findings suggest that it is the inflammatory response to IAV infection that mediates pneumococcal replication. This study thus provides the first evidence that inflammation drives pneumococcal replication in the middle ear cavity, which may have important implications for the treatment of pneumococcal OM.

Viral and bacterial interactions in the upper respiratory tract

Respiratory infectious diseases are mainly caused by viruses or bacteria that often interact with one another. Although their presence is a prerequisite for subsequent infections, viruses and bacteria may be present in the nasopharynx without causing any respiratory symptoms. The upper respiratory tract hosts a vast range of commensals and potential pathogenic bacteria, which form a complex microbial community. This community is assumed to be constantly subject to synergistic and competitive interspecies interactions. Disturbances in the equilibrium, for instance due to the acquisition of new bacteria or viruses, may lead to overgrowth and invasion. A better understanding of the dynamics between commensals and pathogens in the upper respiratory tract may provide better insight into the pathogenesis of respiratory diseases. Here we review the current knowledge regarding specific bacterial–bacterial and viral–bacterial interactions that occur in the upper respiratory niche, and discuss mechanisms by which these interactions might be mediated. Finally, we propose a theoretical model to summarize and illustrate these mechanisms.

Do specific virus-bacteria pairings drive clinical outcomes of pneumonia?

Bacterial pneumonia is a common contributor to severe outcomes of influenza. Epidemiological data suggest that the incidence, severity and associated bacterial pathogens differ between epidemics and by geographical location within epidemics. Data from animal models demonstrate that differences in both viral and bacterial strains alter the incidence and outcomes of pneumonia. For influenza viruses, evolutionary changes to specific virulence factors appear to alter the ability of viruses within particular lineages to prime the host for secondary bacterial infection. Although bacterial strains differ considerably in disease potential in the setting of viral co-infection, the bacterial virulence factors underlying this finding are currently unknown. The hypothesis that geographical variation exists in the prevalence of bacterial strains expressing factors that enable efficient disease potentiation during viral epidemics should be considered as one explanation for regional differences in severity. This would have implications for surveillance, vaccine development, and the conduct of clinical trials for the prevention or treatment of pneumonia.

Community-Acquired Pneumonia in the Conjugate Vaccine Era

Community-acquired pneumonia (CAP) remains one of the most common serious infections encountered among children worldwide. In this review, we highlight important literature and recent scientific discoveries that have contributed to our current understanding of pediatric CAP. We review the current epidemiology of childhood CAP in the developed world, appraise the state of diagnostic testing for etiology and prognosis, and discuss disease management and areas for future research in the context of recent national guidelines.

Viral and bacterial pathogens identification in children hospitalised for severe pneumonia and parapneumonic empyema

Pneumonia is caused by respiratory bacteria and/or viruses. Little is known if co-infections are an aggravating factor in hospitalised children with severe pneumonia. We studied the impact of respiratory pathogens on the severity of pneumonia. Between 2007 and 2009, 52 children hospitalised with a well-documented diagnosis of community-acquired pneumonia (CAP), with or without parapneumonic empyema (PPE), were enrolled in the study. The patients were classified into 2 groups: CAP + PPE (n = 28) and CAP (n = 24). The identification of respiratory viruses and bacteria in nasopharyngeal aspirates and pleural effusion samples were performed using conventional bacterial techniques and molecular assays. Using real-time multiplex PCR and antigen detection, Streptococcus pneumoniae was the main agent identified in 76% of the cases by molecular tests and BinaxNOW® in pleural fluid. A total of 8% of pleural fluid samples remained undiagnosed. In nasopharyngeal aspirates, rhinovirus, parainfluenza viruses, human metapneumovirus, and respiratory syncytial virus were detected in both CAP and CAP + PPE populations; however, the percentage of viral co-detection was significantly higher in nasopharyngeal aspirates from CAP + PPE patients (35%) compared with CAP patients (5%). In conclusion, viral co-detection was observed mainly in patients with more severe pneumonia. Molecular biology assays improved the pathogens detection in pneumonia and confirmed the S. pneumoniae detection by BinaxNOW® in pleural effusion samples. Interestingly, the main S. pneumoniae serotypes found in PPE are not the ones targeted by the heptavalent pneumococcal conjugate vaccine.

Influenza infects lung microvascular endothelium leading to microvascular leak: role of apoptosis and claudin-5

Severe influenza infections are complicated by acute lung injury, a syndrome of pulmonary microvascular leak. The pathogenesis of this complication is unclear. We hypothesized that human influenza could directly infect the lung microvascular endothelium, leading to loss of endothelial barrier function. We infected human lung microvascular endothelium with both clinical and laboratory strains of human influenza. Permeability of endothelial monolayers was assessed by spectrofluorimetry and by measurement of the transendothelial electrical resistance. We determined the molecular mechanisms of flu-induced endothelial permeability and developed a mouse model of severe influenza. We found that both clinical and laboratory strains of human influenza can infect and replicate in human pulmonary microvascular endothelium, leading to a marked increase in permeability. This was caused by apoptosis of the lung endothelium, since inhibition of caspases greatly attenuated influenza-induced endothelial leak. Remarkably, replication-deficient virus also caused a significant degree of endothelial permeability, despite displaying no cytotoxic effects to the endothelium. Instead, replication-deficient virus induced degradation of the tight junction protein claudin-5; the adherens junction protein VE-cadherin and the actin cytoskeleton were unaffected. Over-expression of claudin-5 was sufficient to prevent replication-deficient virus-induced permeability. The barrier-protective agent formoterol was able to markedly attenuate flu-induced leak in association with dose-dependent induction of claudin-5. Finally, mice infected with human influenza developed pulmonary edema that was abrogated by parenteral treatment with formoterol. Thus, we describe two distinct mechanisms by which human influenza can induce pulmonary microvascular leak. Our findings have implications for the pathogenesis and treatment of acute lung injury from severe influenza.

Bacterial neuraminidase rescues influenza virus replication from inhibition by a neuraminidase inhibitor

Influenza virus neuraminidase (NA) cleaves terminal sialic acid residues on oligosaccharide chains that are receptors for virus binding, thus playing an important role in the release of virions from infected cells to promote the spread of cell-to-cell infection. In addition, NA plays a role at the initial stage of viral infection in the respiratory tract by degrading hemagglutination inhibitors in body fluid which competitively inhibit receptor binding of the virus. Current first line anti-influenza drugs are viral NA-specific inhibitors, which do not inhibit bacterial neuraminidases. Since neuraminidase producing bacteria have been isolated from oral and upper respiratory commensal bacterial flora, we posited that bacterial neuraminidases could decrease the antiviral effectiveness of NA inhibitor drugs in respiratory organs when viral NA is inhibited. Using in vitro models of infection, we aimed to clarify the effects of bacterial neuraminidases on influenza virus infection in the presence of the NA inhibitor drug zanamivir. We found that zanamivir reduced progeny virus yield to less than 2% of that in its absence, however the yield was restored almost entirely by the exogenous addition of bacterial neuraminidase from Streptococcus pneumoniae. Furthermore, cell-to-cell infection was severely inhibited by zanamivir but restored by the addition of bacterial neuraminidase. Next we examined the effects of bacterial neuraminidase on hemagglutination inhibition and infectivity neutralization activities of human saliva in the presence of zanamivir. We found that the drug enhanced both inhibitory activities of saliva, while the addition of bacterial neuraminidase diminished this enhancement. Altogether, our results showed that bacterial neuraminidases functioned as the predominant NA when viral NA was inhibited to promote the spread of infection and to inactivate the neutralization activity of saliva. We propose that neuraminidase from bacterial flora in patients may reduce the efficacy of NA inhibitor drugs during influenza virus infection. (295 words).

Immunological pathways in virus-induced COPD exacerbations: a role for IL-15

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is characterized by high levels of antiviral type 1 cytokine interferon-γ and activated CD8(+) T cells. COPD exacerbations are the major cause of morbidity and mortality, have a prolonged and intense effect on quality of life and may result in accelerated loss of lung function. Respiratory virus infections, frequently within a state of colonization by bacteria, are the major cause of COPD exacerbations, and there is also evidence of virus latency in 'stable' disease, suggesting that latent infection might be a cause of chronic inflammation in COPD.

DESIGN

This is an update of current literature concerning the role of interleukin-15 and major histocompatibility complex class I-related chain A and B molecules in type 1 immune responses, particularly to respiratory virus infections, which are the main cause of COPD exacerbations. We also present data from our own group suggesting a role for interleukin-15 in virus-induced COPD exacerbations.

RESULTS

Type 1 cytokine interleukin-15 is produced by resident airway cells (epithelial cells and macrophages) in response to virus infection and bacteria. Virus infections modulate major histocompatibility complex class I-related chain A and B molecules in respiratory epithelial cells.

CONCLUSIONS

Interleukin-15 could play a major role in the airway inflammation in COPD directly, via its own receptors, by amplifying the type 1 immune responses and decreasing apoptosis or indirectly, via modulating molecules associated with cytotoxic activity of natural killer and CD8(+) T cells, such as major histocompatibility complex class I-related chain A and B.

Neurologic disorders among pediatric deaths associated with the 2009 pandemic influenza

OBJECTIVE

The goal of this study was to describe reported influenza A (H1N1)pdm09 virus (pH1N1)-associated deaths in children with underlying neurologic disorders.

METHODS

The study compared demographic characteristics, clinical course, and location of death of pH1N1-associated deaths among children with and without underlying neurologic disorders reported to the Centers for Disease Control and Prevention.

RESULTS

Of 336 pH1N1-associated pediatric deaths with information on underlying conditions, 227 (68%) children had at least 1 underlying condition that conferred an increased risk of complications of influenza. Neurologic disorders were most frequently reported (146 of 227 [64%]), and, of those disorders, neurodevelopmental disorders such as cerebral palsy and intellectual disability were most common. Children with neurologic disorders were older (P = .02), had a significantly longer duration of illness from onset to death (P < .01), and were more likely to die in the hospital versus at home or in the emergency department (P < .01) compared with children without underlying medical conditions. Many children with neurologic disorders had additional risk factors for influenza-related complications, especially pulmonary disorders (48%). Children without underlying conditions were significantly more likely to have a positive result from a sterile-site bacterial culture than were those with an underlying neurologic disorder (P < .01).

CONCLUSIONS

Neurologic disorders were reported in nearly two-thirds of pH1N1-associated pediatric deaths with an underlying medical condition. Because of the potential for severe outcomes, children with underlying neurologic disorders should receive influenza vaccine and be treated early and aggressively if they develop influenza-like illness.

Exogenous sialic acid transport contributes to group B streptococcus infection of mucosal surfaces

By sequence analysis of available group B streptococcus (GBS) genomes, we discovered a conserved putative operon involved in the catabolism of sialic acid, containing a tripartite transporter formed by two integral membrane components and a sugar-binding unit, named SAL0039. Expression analysis in the presence of different substrates revealed that SAL0039 was specifically upregulated by the presence of sialic acid and downregulated when bacteria were grown in human blood or in the presence of a high concentration of glucose. The role of SAL0039 in sugar transport was supported by the inability of the sal0039 deletion mutant strain to import exogenous sialic acid and to grow in semidefined medium supplemented with this sugar. Furthermore, in vivo evidence showed that the presence of exogenous sialic acid significantly increased the capacity of GBS to infect mice at the mucosal level. These findings suggest that transport of sialic acid may also contribute to GBS infections.

Pneumonia in US hospitalized patients with influenza-like illness: BioSense, 2007–2010

We used data from BioSense, a national electronic surveillance system, to describe pneumonia in hospitalized patients with influenza-like illness (ILI). Ninety-five hospitals from 20 states reported ICD-9-CM-coded inpatient final diagnosis data during the study period of September 2007 to February 2010. We compared the characteristics of persons with and without pneumonia among those with ILI-related hospitalizations. BioSense captured 26 987 ILI-related inpatient hospitalizations; 8979 (33%) had a diagnosis of pneumonia. Analysis of trends showed highest counts of pneumonia during the 2007–2008 season and the second 2009 pandemic wave. Pneumonia was more common with increasing age. Microbiology and pharmacy data were available for a subset of patients; 107 (5%) with pneumonia had a bloodstream infection and 17% of patients were prescribed antiviral treatment. Our findings demonstrate the potential utility of electronic healthcare data to track trends in ILI and pneumonia, identify risk factors for disease, identify bacteraemia in patients with pneumonia, and monitor antiviral use.

Epidemiology, microbiology, and treatment considerations for bacterial pneumonia complicating influenza

Post-influenza bacterial pneumonia is a major cause of morbidity and mortality associated with both seasonal and pandemic influenza virus illness. However, despite much interest in influenza and its complications in recent years, good clinical trial data to inform clinicians in their assessment of treatment options are scant. This paucity of evidence needs to be addressed urgently in order to improve guidance on the management of post-influenza bacterial pneumonia. The objectives of the current article are to evaluate the emergence of the 2009 H1N1 influenza pandemic and use this information as background for an in-depth review of the epidemiology of bacterial pneumonia complicating influenza, to review the bacterial pathogens most likely to be associated with post-influenza bacterial pneumonia, and to discuss treatment considerations in these patients. When determining optimal management approaches, both antiviral and antibacterial agents should be considered, and their selection should be based upon a clear understanding of how their mechanisms of action intervene in the pathogenesis of post-influenza acute bacterial pneumonia.

Deletions in the neuraminidase stalk region of H2N2 and H9N2 avian influenza virus subtypes do not affect postinfluenza secondary bacterial pneumonia

We investigated the synergism between influenza virus and Streptococcus pneumoniae, particularly the role of deletions in the stalk region of the neuraminidase (NA) of H2N2 and H9N2 avian influenza viruses. Deletions in the NA stalk (ΔNA) had no effect on NA activity or on the adherence of S. pneumoniae to virus-infected human alveolar epithelial (A549) and mouse lung adenoma (LA-4) cells, although it delayed virus elution from turkey red blood cells. Sequential S. pneumoniae infection of mice previously inoculated with isogenic recombinant H2N2 and H9N2 influenza viruses displayed severe pneumonia, elevated levels of intrapulmonary proinflammatory responses, and death. No differences between the WT and ΔNA mutant viruses were detected with respect to effects on postinfluenza pneumococcal pneumonia as measured by bacterial growth, lung inflammation, morbidity, mortality, and cytokine/chemokine concentrations. Differences were observed, however, in influenza virus-infected mice that were treated with oseltamivir prior to a challenge with S. pneumoniae. Under these circumstances, mice infected with ΔNA viruses were associated with a better prognosis following a secondary bacterial challenge. These data suggest that the H2N2 and H9N2 subtypes of avian influenza A viruses can contribute to secondary bacterial pneumonia and deletions in the NA stalk may modulate its outcome in the context of antiviral therapy.

The anticipated severity of a "1918-like" influenza pandemic in contemporary populations: the contribution of antibacterial interventions

Recent studies have shown that most of deaths in the 1918 influenza pandemic were caused by secondary bacterial infections, primarily pneumococcal pneumonia. Given the availability of antibiotics and pneumococcal vaccination, how will contemporary populations fare when they are next confronted with pandemic influenza due to a virus with the transmissibility and virulence of that of 1918? To address this question we use a mathematical model and computer simulations. Our model considers the epidemiology of both the influenza virus and pneumonia-causing bacteria and allows for co-infection by these two agents as well as antibiotic treatment, prophylaxis and pneumococcal vaccination. For our simulations we use influenza transmission and virulence parameters estimated from 1918 pandemic data. We explore the anticipated rates of secondary pneumococcal pneumonia and death in populations with different prevalence of pneumococcal carriage and contributions of antibiotic prophylaxis, treatment, and vaccination to these rates. Our analysis predicts that in countries with lower prevalence of pneumococcal carriage and access to antibiotics and pneumococcal conjugate vaccines, there would substantially fewer deaths due to pneumonia in contemporary populations confronted with a 1918-like virus than that observed in the 1918. Our results also predict that if the pneumococcal carriage prevalence is less than 40%, the positive effects of antibiotic prophylaxis and treatment would be manifest primarily at of level of individuals. These antibiotic interventions would have little effect on the incidence of pneumonia in the population at large. We conclude with the recommendation that pandemic preparedness plans should consider co-infection with and the prevalence of carriage of pneumococci and other bacteria responsible for pneumonia. While antibiotics and vaccines will certainly reduce the rate of individual mortality, the factor contributing most to the relatively lower anticipated lethality of a pandemic with a 1918-like influenza virus in contemporary population is the lower prevalence of pneumococcal carriage.

Pathogenesis and pathophysiology of pneumococcal meningitis

Pneumococcal meningitis continues to be associated with high rates of mortality and long-term neurological sequelae. The most common route of infection starts by nasopharyngeal colonization by Streptococcus pneumoniae, which must avoid mucosal entrapment and evade the host immune system after local activation. During invasive disease, pneumococcal epithelial adhesion is followed by bloodstream invasion and activation of the complement and coagulation systems. The release of inflammatory mediators facilitates pneumococcal crossing of the blood-brain barrier into the brain, where the bacteria multiply freely and trigger activation of circulating antigen-presenting cells and resident microglial cells. The resulting massive inflammation leads to further neutrophil recruitment and inflammation, resulting in the well-known features of bacterial meningitis, including cerebrospinal fluid pleocytosis, cochlear damage, cerebral edema, hydrocephalus, and cerebrovascular complications. Experimental animal models continue to further our understanding of the pathophysiology of pneumococcal meningitis and provide the platform for the development of new adjuvant treatments and antimicrobial therapy. This review discusses the most recent views on the pathophysiology of pneumococcal meningitis, as well as potential targets for (adjunctive) therapy.

Clinical impact of RT-PCR for pediatric acute respiratory infections: a controlled clinical trial

OBJECTIVE

Real-time polymerase chain reaction (RT-PCR) testing is a quick sensitive method for detecting respiratory pathogens. We evaluated the diagnostic yield of RT-PCR assays and measured the effect of rapid reporting on patient care.

METHODS

In a controlled clinical trial, nasal wash specimens were obtained from patients <12 years of age with suspected acute respiratory infections. In addition to the standard hospital protocol, RT-PCR assays for 17 pathogens were performed. The RT-PCR results were communicated to the clinicians within 12 to 36 hours in the intervention group and after 4 weeks in the control group.

RESULTS

A total of 583 patients were included (mean age: 8.1 months [range: 0-107.5 months]): 298 in the intervention group and 285 in the control group. Eighty-two percent of nasal wash specimens tested positive for ≥1 pathogen. Respiratory syncytial virus was the most frequently encountered (55%) pathogen. There were no significant differences between the groups with respect to hospital admissions (intervention group: 223 admissions; control group: 211 admissions; P = .825), length of hospital stay (mean ± SD: 3.68 ± 2.68 days [intervention group] and 3.96 ± 2.67 days [control group]; P = .178), or duration of antibiotic use (mean ± SD: 6.52 ± 2.15 days [intervention group] and 6.97 ± 2.86 days [control group]; P = .490), when antibiotic treatment had been initiated.

CONCLUSIONS

RT-PCR testing has a high yield of viral diagnoses, but rapid communication does not lead to decreases in hospital admissions, shorter hospital stays, or less antibiotic use for children with acute respiratory infections.

Pandemic influenza: certain uncertainties

For at least five centuries, major epidemics and pandemics of influenza have occurred unexpectedly and at irregular intervals. Despite the modern notion that pandemic influenza is a distinct phenomenon obeying such constant (if incompletely understood) rules such as dramatic genetic change, cyclicity, "wave" patterning, virus replacement, and predictable epidemic behavior, much evidence suggests the opposite. Although there is much that we know about pandemic influenza, there appears to be much more that we do not know. Pandemics arise as a result of various genetic mechanisms, have no predictable patterns of mortality among different age groups, and vary greatly in how and when they arise and recur. Some are followed by new pandemics, whereas others fade gradually or abruptly into long-term endemicity. Human influenza pandemics have been caused by viruses that evolved singly or in co-circulation with other pandemic virus descendants and often have involved significant transmission between, or establishment of, viral reservoirs within other animal hosts. In recent decades, pandemic influenza has continued to produce numerous unanticipated events that expose fundamental gaps in scientific knowledge. Influenza pandemics appear to be not a single phenomenon but a heterogeneous collection of viral evolutionary events whose similarities are overshadowed by important differences, the determinants of which remain poorly understood. These uncertainties make it difficult to predict influenza pandemics and, therefore, to adequately plan to prevent them.

Influenza vaccination, diagnosis, and treatment in children

Between 2009 and 2010, the influenza H1N1 pandemic swept across the globe, disproportionately affecting the pediatric population. This pandemic strain is expected to circulate again with other seasonal influenza strains during the 2010-2011 season. This article reviews the new 2010 to 2011 Centers for Disease Control and Prevention and American Academy of Pediatrics recommendations for vaccination against the influenza virus for pediatric patients. It reviews the various testing modalities and the benefits and disadvantage of each test and offers an approach to diagnostic testing. Lastly, it reviews the indications and recommendations for treatment of children with presumed or confirmed influenza infection.

New respiratory viruses and the elderly

The diagnostics of respiratory viral infections has improved markedly during the last 15 years with the development of PCR techniques. Since 1997, several new respiratory viruses and their subgroups have been discovered: influenza A viruses H5N1 and H1N1, human metapneumovirus, coronaviruses SARS, NL63 and HKU1, human bocavirus, human rhinoviruses C and D and potential respiratory pathogens, the KI and WU polyomaviruses and the torque teno virus. The detection of previously known viruses has also improved. Currently, a viral cause of respiratory illness is almost exclusively identifiable in children, but in the elderly, the detection rates of a viral etiology are below 40%, and this holds also true for exacerbations of chronic respiratory illnesses. The new viruses cause respiratory symptoms like the common cold, cough, bronchitis, bronchiolitis, exacerbations of asthma and chronic obstructive pulmonary disease and pneumonia. Acute respiratory failure may occur. These viruses are distributed throughout the globe and affect people of all ages. Data regarding these viruses and the elderly are scarce. This review introduces these new viruses and reviews their clinical significance, especially with regard to the elderly population.

Association of bacterial pneumonia and respiratory failure in children with community-acquired influenza infection

OBJECTIVE

To investigate the association of bacterial pneumonia and respiratory failure in children with community-acquired influenza infection presenting to a pediatric intensive care unit.

DESIGN

Retrospective cohort study.

SETTING

Pediatric intensive care unit at an urban academic tertiary-care children's hospital.

PATIENTS

All patients aged <18 yrs admitted to our pediatric intensive care unit with laboratory-confirmed influenza infection between October 2002 and September 2008.

INTERVENTIONS

All patients who met our clinical definitions of respiratory failure and bacterial pneumonia were identified. Patients were stratified by presence or absence of chronic medical conditions associated with an increased risk of influenza-related complications.

MEASUREMENTS AND MAIN RESULTS

There were 59 patients admitted to the pediatric intensive care unit with laboratory-confirmed community-acquired influenza during the period of study. Twenty-four patients (41%) had respiratory failure and 14 patients (24%) met the definition of bacterial pneumonia. The risk of respiratory failure was increased in the presence of bacterial pneumonia (p = .04). Adjusting for age and chronic medical conditions, patients with bacterial pneumonia had a 3.7 times greater odds (p = .04) of respiratory failure.

CONCLUSIONS

Our findings suggest that bacterial pneumonia was associated with increased odds of respiratory failure in both previously healthy children and those with chronic medical conditions. Early aggressive therapy should be considered for patients with severe influenza.

Favorable outcome after life-threatening meningococcal disease complicating influenza A(H1N1) infection

PURPOSE

Neurological complications of influenza A(H1N1) have been reported in several patients since the onset of the pandemic in 2009. However, meningococcal disease complicating influenza A(H1N1) has not been reported.

PATIENTS

Two patients were admitted to an intensive care unit (ICU) for altered mental status, fever, and rapidly spreading petechial purpura. They were diagnosed with meningococcal meningitis and/or meningococcemia and influenza A(H1N1) co-infection.

CONCLUSIONS

Meningococcal disease presenting as meningitis and/or meningococcemia is among the potential complications of influenza A(H1N1) infection. Physicians should be aware of this co-infection, as it must be detected and treated promptly with antibiotics in addition to supportive care.

Viral-bacterial co-infection in Australian Indigenous children with acute otitis media

Background

Acute otitis media with perforation (AOMwiP) affects 40% of remote Indigenous children during the first 18 months of life. Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are the primary bacterial pathogens of otitis media and their loads predict clinical ear state. Our hypothesis is that antecedent respiratory viral infection increases bacterial density and progression to perforation.

Methods

A total of 366 nasopharyngeal swabs from 114 Indigenous children were retrospectively examined. A panel of 17 respiratory viruses was screened by PCR, and densities of S. pneumoniae, H. influenzae and M. catarrhalis were estimated by quantitative real time PCR. Data are reported by clinical ear state.

Results

M. catarrhalis (96%), H. influenzae (91%), S. pneumoniae (89%) and respiratory viruses (59%) were common; including rhinovirus (HRV) (38%), polyomavirus (HPyV) (14%), adenovirus (HAdV) (13%), bocavirus (HBoV) (8%) and coronavirus (HCoV) (4%). Geometric mean bacterial loads were significantly higher in children with acute otitis media (AOM) compared to children without evidence of otitis media. Children infected with HAdV were 3 times more likely (p < 0.001) to have AOM with or without perforation.

Conclusion

This study confirms a positive association between nasopharyngeal bacterial load and clinical ear state, exacerbated by respiratory viruses, in Indigenous children. HAdV was independently associated with acute ear states.

Infection with human coronavirus NL63 enhances streptococcal adherence to epithelial cells

Understanding the mechanisms of augmented bacterial pathogenicity in post-viral infections is the first step in the development of an effective therapy. This study assessed the effect of human coronavirus NL63 (HCoV-NL63) on the adherence of bacterial pathogens associated with respiratory tract illnesses. It was shown that HCoV-NL63 infection resulted in an increased adherence of Streptococcus pneumoniae to virus-infected cell lines and fully differentiated primary human airway epithelium cultures. The enhanced binding of bacteria correlated with an increased expression level of the platelet-activating factor receptor (PAF-R), but detailed evaluation of the bacterium-PAF-R interaction revealed a limited relevance of this process.

Temporal association between rhinovirus circulation in the community and invasive pneumococcal disease in children

BACKGROUND

Mucosal coinfections with respiratory viruses and Streptococcus pneumoniae are common, but the role of rhinovirus infections in the development of invasive pneumococcal disease (IPD) in children has not been studied.

METHODS

During 1995 and 2007, we analyzed the association of IPD in children less than 5 years of age with respiratory virus epidemics by combining data from the National Infectious Disease Register, 3 prospective epidemiologic studies, and the database of the Department of Virology, University of Turku, Finland.

RESULTS

The mean IPD rate in children younger than 5 years of age in Finland was 2.9 cases per week (95% confidence interval [CI], 2.5-3.3) during periods of high rhinovirus activity, and 1.4 (95% CI, 1.2-1.6) during periods of low rhinovirus activity (P < 0.001). The IPD rate correlated with the rhinovirus activity recorded at the Department of Virology (correlation coefficient, 0.23; P = 0.001) and in the epidemiologic studies (correlation coefficients, 0.28, 0.25, and 0.31). The IPD rate was moderately increased during periods of high respiratory syncytial virus activity (mean, 2.1 cases per week; 95% CI, 1.8-2.3) compared with periods of low respiratory syncytial virus activity (mean, 1.7; 95% CI, 1.6-1.9; P = 0.008). There were no differences in the IPD rate between the periods of high and low influenza activity.

CONCLUSIONS

Rhinovirus circulation in the community had an association with IPD in children younger than 5 years of age. This study suggests that rhinovirus infection may be a contributor in the development of IPD in the population of young children.

The airway epithelium: soldier in the fight against respiratory viruses

The airway epithelium acts as a frontline defense against respiratory viruses, not only as a physical barrier and through the mucociliary apparatus but also through its immunological functions. It initiates multiple innate and adaptive immune mechanisms which are crucial for efficient antiviral responses. The interaction between respiratory viruses and airway epithelial cells results in production of antiviral substances, including type I and III interferons, lactoferrin, β-defensins, and nitric oxide, and also in production of cytokines and chemokines, which recruit inflammatory cells and influence adaptive immunity. These defense mechanisms usually result in rapid virus clearance. However, respiratory viruses elaborate strategies to evade antiviral mechanisms and immune responses. They may disrupt epithelial integrity through cytotoxic effects, increasing paracellular permeability and damaging epithelial repair mechanisms. In addition, they can interfere with immune responses by blocking interferon pathways and by subverting protective inflammatory responses toward detrimental ones. Finally, by inducing overt mucus secretion and mucostasis and by paving the way for bacterial infections, they favor lung damage and further impair host antiviral mechanisms.

Inactivated and live, attenuated influenza vaccines protect mice against influenza: Streptococcus pyogenes super-infections

Mortality associated with influenza virus super-infections is frequently due to secondary bacterial complications. To date, super-infections with Streptococcus pyogenes have been studied less extensively than those associated with Streptococcus pneumoniae. This is significant because a vaccine for S. pyogenes is not clinically available, leaving vaccination against influenza virus as our only means for preventing these super-infections. In this study, we directly compared immunity induced by two types of influenza vaccine, either inactivated influenza virus (IIV) or live, attenuated influenza virus (LAIV), for the ability to prevent super-infections. Our data demonstrate that both IIV and LAIV vaccines induce similar levels of serum antibodies, and that LAIV alone induces IgA expression at mucosal surfaces. Upon super-infection, both vaccines have the ability to limit the induction of pro-inflammatory cytokines within the lung, including IFN-γ which has been shown to contribute to mortality in previous models of super-infection. Limiting expression of these pro-inflammatory cytokines within the lungs subsequently limits recruitment of macrophages and neutrophils to pulmonary surfaces, and ultimately protects both IIV- and LAIV-vaccinated mice from mortality. Despite their overall survival, both IIV- and LAIV-vaccinated mice demonstrated levels of bacteria within the lung tissue that are similar to those seen in unvaccinated mice. Thus, influenza virus:bacteria super-infections can be limited by vaccine-induced immunity against influenza virus, but the ability to prevent morbidity is not complete.

Long-term impairment of Streptococcus pneumoniae lung clearance is observed after initial infection with influenza A virus but not human metapneumovirus in mice

Human metapneumovirus (hMPV) is a paramyxovirus responsible for respiratory tract infections in humans. Our objective was to investigate whether hMPV could predispose to long-term bacterial susceptibility, such as previously observed with influenza viruses. BALB/c mice were infected with hMPV or influenza A and, 14 days following viral infection, challenged with Streptococcus pneumoniae. Only mice previously infected with influenza A demonstrated an 8% weight loss of their body weight 72 h following S. pneumoniae infection, which correlated with an enhanced lung bacterial replication of >7 log(10) compared with pneumococcus infection alone. This enhanced bacterial replication was not related to altered macrophage or neutrophil recruitment or deficient production of critical cytokines. However, bacterial challenge induced the production of gamma interferon in bronchoalveolar lavages of influenza-infected mice, but not in those of hMPV-infected animals. In conclusion, hMPV does not cause long-term impairment of pneumococcus lung clearance, in contrast to influenza A virus.

Impact of pneumococcal conjugate vaccination of infants on pneumonia and influenza hospitalization and mortality in all age groups in the United States

A seven-valent pneumococcal conjugate vaccine (PCV7) introduced in the United States in 2000 has been shown to reduce invasive pneumococcal disease (IPD) in both vaccinated children and adults through induction of herd immunity. We assessed the impact of infant immunization on pneumococcal pneumonia hospitalizations and mortality in all age groups using Health Care Utilization Project State Inpatient Databases (SID) for 1996 to 2006 from 10 states; SID contain 100% samples of ICD9-coded hospitalization data for the selected states. Compared to a 1996–1997 through 1998–1999 baseline, by the 2005–2006 season, both IPD and pneumococcal pneumonia hospitalizations and deaths had decreased substantially in all age groups, including a 47% (95% confidence interval [CI], 38 to 54%) reduction in nonbacteremic pneumococcal pneumonia (ICD9 code 481 with no codes indicating IPD) in infants <2 years old and a 54% reduction (CI, 53 to 56%) in adults ≥65 years of age. A model developed to calculate the total burden of pneumococcal pneumonia prevented by infant PCV7 vaccination in the United States from 2000 to 2006 estimated a reduction of 788,838 (CI, 695,406 to 875,476) hospitalizations for pneumococcal pneumonia. Ninety percent of the reduction in model-attributed pneumococcal pneumonia hospitalizations occurred through herd immunity among adults 18 years old and older; similar proportions were found in pneumococcal disease mortality prevented by the vaccine. In the first seasons after PCV introduction, when there were substantial state differences in coverage among <5-year-olds, states with greater coverage had significantly fewer influenza-associated pneumonia hospitalizations among children, suggesting that PCV7 use also reduces influenza-attributable pneumonia hospitalizations.

Pneumonia is the world’s leading cause of death in children and the leading infectious cause of death among U.S. adults 65 years old and older. Pneumococcal conjugate vaccination of infants has previously been shown to reduce invasive pneumococcal disease (IPD) among seniors through prevention of pneumococcal transmission from infants to adults (herd immunity). Our analysis documents a significant vaccine-associated reduction not only in IPD but also in pneumococcal pneumonia hospitalizations and inpatient mortality rates among both vaccinated children and unvaccinated adults. We estimate that fully 90% of the reduction in the pneumonia hospitalization burden occurred among adults. Moreover, states that more rapidly introduced their infant pneumococcal immunization programs had greater reductions in influenza-associated pneumonia hospitalization of children, presumably because the vaccine acts to prevent the pneumococcal pneumonia that frequently follows influenza virus infection. Our results indicate that seven-valent pneumococcal conjugate vaccine use has yielded far greater benefits through herd immunity than have previously been recognized.

Preventing and treating secondary bacterial infections with antiviral agents

Bacterial super-infections contribute to the significant morbidity and mortality associated with influenza and other respiratory virus infections. There are robust animal model data, but only limited clinical information on the effectiveness of licensed antiviral agents for the treatment of bacterial complications of influenza. The association of secondary bacterial pathogens with fatal pneumonia during the recent H1N1 influenza pandemic highlights the need for new development in this area. Basic and clinical research into viral-bacterial interactions over the past decade has revealed several mechanisms that underlie this synergism. By applying these insights to antiviral drug development, the potential exists to improve outcomes by means other than direct inhibition of the virus.

Respiratory bacterial pathogens in the nasopharynx and lower airways of Australian indigenous children with bronchiectasis

OBJECTIVE

To test the hypothesis that bacterial density, strain diversity, and concordance of pathogens between upper and lower airways are higher in children with bronchiectasis than in those with non-bronchiectatic conditions.

STUDY DESIGN

Nasopharyngeal (NP) swabs and bronchoalveolar lavage (BAL) fluid were cultured from 45 Indigenous children with bronchiectasis and 30 non-Indigenous children with non-bronchiectatic respiratory symptoms. Lower airway infection was defined as >10(4) colony-forming units of respiratory bacteria/mL of BAL fluid. Concordance was determined by phenotype or genotype.

RESULTS

NP carriage of Streptococcus pneumoniae, nontypable Haemophilus influenzae (NTHi), and Moraxella catarrhalis, and lower airway infection by NTHi (47% vs 3%), were detected significantly more often in the children with bronchiectasis than in those without this condition. BAL specimens from the infected Indigenous children also showed greater strain diversity (71% vs 0%). Strain concordance in NP and BAL cultures was high in both infected subgroups.

CONCLUSIONS

The high density and diversity of respiratory bacteria, along with strain concordance between upper and lower airways, found in Indigenous children with bronchiectasis suggest a possible pathogenic role of recurrent aspiration of NP secretions.

Nasopharyngeal bacterial colonization during the first wheezing episode is associated with longer duration of hospitalization and higher risk of relapse in young children

The purpose of this study was to examine the association between bacterial colonization/infection and respiratory outcomes in children younger than 3 years old who were hospitalized for their first wheezing episode. This was an observational study. The primary outcome was hospitalization time and the secondary outcomes included relapses within 2 months and time to recurrent wheezing (i.e. three physician confirmed wheezing episodes) within 12 months. Bacterial antibody assays for Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Mycoplasma pneumoniae and Chlamydia pneumoniae were studied as well as nasopharyngeal bacterial culture for the three former and urine pneumococcal antigen. Nasopharyngeal bacterial culture was positive in 31/52 (60%) children, serologic evidence of bacterial infection was found in 17/96 (18%) children, urine pneumococcal antigen was positive in 24/101 (24%), and any bacterial detection method was positive in 53/106 (50%) children. The children with positive nasopharyngeal bacterial culture had longer duration of hospitalization (hazard ratio 2.4) and more often relapsed within two months than those with negative culture (odds ratio 7.3). In this study, half of the first time wheezing children had bacterial colonization or symptomatic or asymptomatic bacterial infection. The bacterial colonization (i.e. positive nasopharyngeal bacterial culture) was associated with longer duration of hospitalization and higher risk of recurrent wheezing.

Influenza enhances susceptibility to natural acquisition of and disease due to Streptococcus pneumoniae in ferrets

The role of respiratory viruses in the transmission of Streptococcus pneumoniae is poorly understood. Key questions, such as which serotypes are most fit for transmission and disease and whether influenza virus alters these parameters in a serotype-specific manner, have not been adequately studied. In a novel model of transmission in ferrets, we demonstrated that pneumococcal transmission and disease were enhanced if donors had previously been infected with influenza virus. Bacterial titers in nasal wash, the incidence of mucosal and invasive disease, and the percentage of contacts that were infected all increased. In contact ferrets, viral infection increased their susceptibility to S. pneumoniae acquisition both in terms of the percentage infected and the distance over which they could acquire infection. These influenza-mediated effects on colonization, transmission, and disease were dependent on the pneumococcal strain. Overall, these data argue that the relationship between respiratory viral infections, acquisition of pneumococci, and development of disease in humans needs further study to be better understood.

Interaction between influenza virus and Streptococcus pneumoniae in severe pneumonia

The contribution of bacterial superinfection to influenza-associated pneumonia morbidity and mortality is evident from the 1918 and 1957 influenza pandemics, and is supported by a number of murine model studies. Murine model studies have also assisted in helping to expand our understanding of the pathogenesis of the interaction between the influenza virus and subsequent susceptibility to pneumococcal superinfections. The purported impact that the pneumococcal conjugate vaccine has had on reducing the burden of confirmed influenza-associated pneumonia, as well as upon all-cause clinical pneumonia, provides additional clinical evidence of the role of superimposed pneumococcal infections as a cause of severe pneumonia in children. Using this information together with the evidence for the effectiveness of influenza vaccination against influenza-associated pneumonia, it is imperative that preventive strategies for future influenza pandemic preparedness include broad-based vaccination against pneumococci, as well as ensuring that adequate antimicrobials are available for the early treatment of influenza virus, in addition to pneumococcal and other bacterial infections.