Predominant role of bacterial pneumonia as a cause of death in pandemic influenza: implications for pandemic influenza preparedness

An influenza A H1N1 virus revival - pandemic H1N1/09 virus

In April 2009, a novel H1N1 influenza A virus, the so-called pandemic H1N1/09 virus (former designations include swine influenza, novel influenza, swine-origin influenza A [H1N1] virus [S-OIV], Mexican flu, North American Flu) was identified in Mexico. The virus has since spread throughout the world and caused an influenza pandemic as defined by the criteria of the World Health Organization. This represents the first influenza A virus pandemic since the emergence of H3N2 (''Hong Kong'' Flu) in 1968. Vaccine production has started, and vaccines are expected to become available during the course of 2009. Although the pandemic H1N1/09 virus originates from the triple-reassortant swine influenza (H1) virus circulating in North American pigs, it is not epidemic in pigs. Although the H1N1/09 virus pandemic is currently mild, concerns remain that it may become more aggressive during spreading. The distribution of proper information to the public on the status of the H1N1/09 virus pandemic will be important to achieve a broad awareness of the potential risks and the optimum code of behavior during the pandemic. Here, the features of pandemic H1N1/09 virus are discussed within the framework of knowledge gained from previous influenza A virus pandemics.

Protection of racial/ethnic minority populations during an influenza pandemic

Racial/ethnic minority populations experience worse health outcomes than do other groups during and after disasters. Evidence for a differential impact from pandemic influenza includes both higher rates of underlying health conditions in minority populations, increasing their risk of influenza-related complications, and larger socioeconomic (e.g., access to health care), cultural, educational, and linguistic barriers to adoption of pandemic interventions. Implementation of pandemic interventions could be optimized by (1) culturally competent preparedness and response that address specific needs of racial/ethnic minority populations, (2) improvements in public health and community health safety net systems, (3) social policies that minimize economic burdens and improve compliance with isolation and quarantine, and (4) relevant, practical, and culturally and linguistically tailored communications.

Chinchilla as a robust, reproducible and polymicrobial model of otitis media and its prevention

There is compelling evidence that many infectious diseases of humans are caused by more than one microorganism. Multiple diverse in vitro systems have been used to study these complex diseases, and although the data generated have contributed greatly to our understanding of diseases of mixed microbial etiology, having rigorous, reproducible and relevant animal models of human diseases are essential for the development of novel methods to treat or prevent them. All animal models have inherent limitations; however, they also have important advantages over in vitro methods, including the presence of organized organ systems and an intact immune system, which promote our ability to characterize the pathogenesis of, and the immune response to, sequential or coinfecting microorganisms. For the highly prevalent pediatric disease otitis media, or middle-ear infection, the chinchilla (Chinchilla lanigera) has served as a gold-standard rodent host system in which to study this multifactorial and polymicrobial disease.

Understanding influenza transmission, immunity and pandemic threats

Abstract  The current pandemic threat can be best understood within an ecological framework that takes account of the history of past pandemics caused by influenza A, the relationships between pandemic and seasonal spread of influenza viruses, and the importance of immunity and behavioural responses in human populations. Isolated populations without recent exposure to seasonal influenza seem more susceptible to new pandemic viruses, and much collateral evidence suggests that this is due to immunity directed against epitopes shared between pandemic and previously circulating strains of inter‐pandemic influenza A virus. In the highly connected modern world, most populations are regularly exposed to non‐pandemic viruses, which can even boost immunity without causing influenza symptoms. Such naturally‐induced immunity helps to explain the low attack‐rates of seasonal influenza, as well as the moderate attack‐rates in many urbanized populations affected by 1918–1919 and later pandemics. The effectiveness of immunity, even against seasonal influenza, diminishes over time because of antigenic drift in circulating viruses and waning of post‐exposure immune responses. Epidemiological evidence suggests that cross‐protection against a new pandemic strain could fade even faster. Nevertheless, partial protection, even of short duration, induced by prior seasonal influenza or vaccination against it, could provide important protection in the early stages of a new pandemic.

An early 'classical' swine H1N1 influenza virus shows similar pathogenicity to the 1918 pandemic virus in ferrets and mice

The 1918 pandemic influenza virus has demonstrated significant pathogenicity in animal models and is the progenitor of 'classical' swine and modern seasonal human H1N1 lineages. Here we characterize the pathogenicity of an early 'classical' swine H1N1 influenza A virus isolated in 1931 compared to the pathogenicity of the 1918 pandemic virus and a seasonal H1N1 virus in mice and ferrets. A/Swine/Iowa/31 (Sw31) and the 1918 influenza viruses were uniformly lethal in mice at low doses and produced severe lung pathology. In ferrets, Sw31 and 1918 influenza viruses caused severe clinical disease and lung pathology with necrotizing bronchiolitis and alveolitis. The modern H1N1 virus caused little disease in either animal model. These findings revealed that in these models the virulence factors of the 1918 influenza virus are likely preserved in the Sw31 virus and suggest that early swine viruses may be a good surrogate model to study 1918 virulence and pathogenesis.

Intervention strategies for an influenza pandemic taking into account secondary bacterial infections

Influenza infections often predispose individuals to consecutive bacterial infections. Both during seasonal and pandemic influenza outbreaks, morbidity and mortality due to secondary bacterial infections can be substantial. With the help of a mathematical model, we investigate the potential impact of such bacterial infections during an influenza pandemic, and we analyze how antiviral and antibacterial treatment or prophylaxis affect morbidity and mortality. We consider different scenarios for the spread of bacteria, the emergence of antiviral resistance, and different levels of severity for influenza infections (1918-like and 2009-like). We find that while antibacterial intervention strategies are unlikely to play an important role in reducing the overall number of cases, such interventions can lead to a significant reduction in mortality and in the number of bacterial infections. Antibacterial interventions become even more important if one considers the--very likely--scenario that during a pandemic outbreak, influenza strains resistant to antivirals emerge. Overall, our study suggests that pandemic preparedness plans should consider intervention strategies based on antibacterial treatment or prophylaxis through drugs or vaccines as part of the overall control strategy. A major caveat for our results is the lack of data that would allow precise estimation of many of the model parameters. As our results show, this leads to very large uncertainty in model outcomes. As we discuss, precise assessment of the impact of antibacterial strategies during an influenza pandemic will require the collection of further data to better estimate key parameters, especially those related to the bacterial infections and the impact of antibacterial intervention strategies.

Mortality and morbidity burden associated with A/H1N1pdm influenza virus: Who is likely to be infected, experience clinical symptoms, or die from the H1N1pdm 2009 pandemic virus ?

Here we use lessons from past influenza pandemics and recent information about the H1N1pdm pandemic to discuss variations in H1N1pdm disease burden with age, underlying risk factors, and geography.

Pneumococcal pneumonia and influenza: a deadly combination

Significant morbidity due to pneumococcal co-infection is associated with viral respiratory infections. Pneumonia is the leading cause of death in children worldwide. The incidence of clinical pneumonia among children in the United States decreased 39% following the introduction of a seven-valent pneumococcal conjugate vaccine (PCV). PCVs have also reduced hospitalisations associated with influenza in children. The majority of the mortality associated with the influenza pandemic of 1918 was attributable to bacterial infections, especially the pneumococcus. Vaccination with PCV for children and pneumococcal polysaccharide vaccine for adults should be considered essential to pandemic influenza preparedness.

Adaptive vaccination strategies to mitigate pandemic influenza: Mexico as a case study

In this modeling work, we explore the effectiveness of various age-targeted vaccination strategies to mitigate hospitalization and mortality from pandemic influenza, assuming limited vaccine supplies. We propose a novel adaptive vaccination strategy in which vaccination is initiated during the outbreak and priority groups are identified based on real-time epidemiological data monitoring age-specific risk of hospitalization and death. We apply this strategy to detailed epidemiological and demographic data collected during the recent swine A/H1N1 outbreak in Mexico. We show that the adaptive strategy targeting age groups 6-59 years is the most effective in reducing hospitalizations and deaths, as compared with a more traditional strategy used in the control of seasonal influenza and targeting children under 5 and seniors over 65. Results are robust to a number of assumptions and could provide guidance to many nations facing a recrudescence of A/H1N1v pandemic activity in the fall and likely vaccine shortages.

Pneumococcal surface protein A contributes to secondary Streptococcus pneumoniae infection after influenza virus infection

We compared the growth of Streptococcus pneumoniae mutants with a disruption in the gene for either pneumococcal surface protein A (PspA-), neuraminidase A (NanA-), or hyaluronidase (Hyl-) to that of the parental strain D39 by means of a competitive growth model in mice with and those without prior influenza virus infection. The numbers of total bacteria recovered from mice with prior influenza virus infection were significantly greater than those recovered from mice without prior influenza virus infection. Although the Hyl- and NanA- mutants did not display attenuation in mice with or without prior influenza virus infection, the PspA- mutant exhibited attenuation both in mice with and in mice without prior influenza virus infection. This defect was severe in influenza virus-infected mice, for which growth of the PspA- mutant was 1800-fold lower than that of the parental strain D39. Furthermore, PspA immunization significantly reduced secondary bacterial lung burdens and concentrations of specific markers of lung damage in mice receiving serotypes 2, 3, and 4 pneumococci. Our findings indicate that PspA contributes to secondary S. pneumoniae infection after influenza virus infection and that PspA immunization mitigates early secondary pneumococcal lung infections.

Pneumonia and respiratory failure from swine-origin influenza A (H1N1) in Mexico

BACKGROUND

In late March 2009, an outbreak of a respiratory illness later proved to be caused by novel swine-origin influenza A (H1N1) virus (S-OIV) was identified in Mexico. We describe the clinical and epidemiologic characteristics of persons hospitalized for pneumonia at the national tertiary hospital for respiratory illnesses in Mexico City who had laboratory-confirmed S-OIV infection, also known as swine flu.

METHODS

We used retrospective medical chart reviews to collect data on the hospitalized patients. S-OIV infection was confirmed in specimens with the use of a real-time reverse-transcriptase-polymerase-chain-reaction assay.

RESULTS

From March 24 through April 24, 2009, a total of 18 cases of pneumonia and confirmed S-OIV infection were identified among 98 patients hospitalized for acute respiratory illness at the National Institute of Respiratory Diseases in Mexico City. More than half of the 18 case patients were between 13 and 47 years of age, and only 8 had preexisting medical conditions. For 16 of the 18 patients, this was the first hospitalization for their illness; the other 2 patients were referred from other hospitals. All patients had fever, cough, dyspnea or respiratory distress, increased serum lactate dehydrogenase levels, and bilateral patchy pneumonia. Other common findings were an increased creatine kinase level (in 62% of patients) and lymphopenia (in 61%). Twelve patients required mechanical ventilation, and seven died. Within 7 days after contact with the initial case patients, a mild or moderate influenza-like illness developed in 22 health care workers; they were treated with oseltamivir, and none were hospitalized.

CONCLUSIONS

S-OIV infection can cause severe illness, the acute respiratory distress syndrome, and death in previously healthy persons who are young to middle-aged. None of the secondary infections among health care workers were severe.

The innate immune rheostat: influence on lung inflammatory disease and secondary bacterial pneumonia

The activity of innate immunity is not simply dictated by the presence of an antigen but also by the balance between negative regulatory and immune potentiator pathways. Even in the absence of antigen, innate immunity can 'inflame' if negative regulators are absent. This resting state is adaptable and dictated by environmental influences, host genetics and past infection history. A return to homoeostasis post inflammation may therefore not leave the tissue in an identical state to that prior to the inflammatory event. This adaptability makes us all unique and also explains the variable outcome experienced by a diverse population to the same inflammatory stimulus. Using murine models we have identified that influenza virus causes a long-term modification of the lung microenvironment by a de-sensitization to bacterial products and an increase in the myeloid negative regulator CD200R (CD200 receptor). These two events prevent subsequent inflammatory damage while the lung is healing, but also they may predispose to bacterial colonization of the lower respiratory tract should regulatory mechanisms overshoot. In the extreme, this leads to bacterial pneumonia, sepsis and death. A deeper understanding of the consequences arising from innate immune cell alteration during influenza infection and the subsequent development of bacterial complications has important implications for future drug development.

Novel swine-origin influenza A virus in humans: another pandemic knocking at the door

Influenza A viruses represent a continuous pandemic threat. In April 2009, a novel influenza A virus, the so-called swine-origin influenza A (H1N1) virus (S-OIV), was identified in Mexico. Although S-OIV originates from triple-reassortant swine influenza A (H1) that has been circulating in North American pig herds since the end of the 1990s, S-OIV is readily transmitted between humans but is not epidemic in pigs. After its discovery, S-OIV rapidly spread throughout the world within few weeks. In this review, we sum up the current situation and put it into the context of the current state of knowledge of influenza and influenza pandemics. Some indications suggest that a pandemic may be mild but even "mild" pandemics can result in millions of deaths. However, no reasonable forecasts how this pandemic may develop can be made at this time. Despite stockpiling by many countries and WHO, antiviral drugs will be limited in case of pandemic and resistances may emerge. Effective vaccines are regarded to be crucial for the control of influenza pandemics. However, production capacities are restricted and development/production of a S-OIV vaccine will interfere with manufacturing of seasonal influenza vaccines. The authors are convinced that S-OIV should be taken seriously as pandemic threat and underestimation of the menace by S-OIV to be by far more dangerous than its overestimation.

Staphylococcus aureus activates type I IFN signaling in mice and humans through the Xr repeated sequences of protein A

The activation of type I IFN signaling is a major component of host defense against viral infection, but it is not typically associated with immune responses to extracellular bacterial pathogens. Using mouse and human airway epithelial cells, we have demonstrated that Staphylococcus aureus activates type I IFN signaling, which contributes to its virulence as a respiratory pathogen. This response was dependent on the expression of protein A and, more specifically, the Xr domain, a short sequence-repeat region encoded by DNA that consists of repeated 24-bp sequences that are the basis of an internationally used epidemiological typing scheme. Protein A was endocytosed by airway epithelial cells and subsequently induced IFN-beta expression, JAK-STAT signaling, and IL-6 production. Mice lacking IFN-alpha/beta receptor 1 (IFNAR-deficient mice), which are incapable of responding to type I IFNs, were substantially protected against lethal S. aureus pneumonia compared with wild-type control mice. The profound immunological consequences of IFN-beta signaling, particularly in the lung, may help to explain the conservation of multiple copies of the Xr domain of protein A in S. aureus strains and the importance of protein A as a virulence factor in the pathogenesis of staphylococcal pneumonia.

Confronting the next influenza pandemic with anti-inflammatory and immunomodulatory agents: why they are needed and how they might work

Despite the best efforts of influenza scientists, companies and health officials to prepare for the next pandemic, most of the world's people will not have access to affordable supplies of vaccines and antiviral agents. They will have to rely on 19th century public health 'technologies' to see them through. In the 21st century, science ought to be able to provide something better. Influenza scientists study the molecular characteristics of influenza viruses and their signaling effects in cell culture and animal models of infection. While these studies have been enormously informative, they have been unable to explain the system-wide effects of influenza on the host, the increased mortality of younger adults in the 1918 influenza pandemic and the much lower mortality rates in children who were more commonly infected with the 1918 virus. Experiments by non-influenza scientists have defined common cell signaling pathways for acute lung injury caused by different agents, including inactivated H5N1 influenza virus. These pathways include several molecular targets that are up-regulated in acute lung injury and down-regulated by anti-inflammatory and immunomodulatory agents, including statins, fibrates, and glitazones. These agents also help reverse the mitochondrial dysfunction that accompanies multi-organ failure, something often seen in fatal Influenza. Observational studies suggest that statins are beneficial in treating patients with pneumonia (there are no such studies for fibrates and glitazones). Other studies suggest that these agents might be able to 'roll back' the self-damaging host response of young adults to the less damaging response of children and thus save lives. Research is urgently needed to determine whether these and other agents that modify the host response might be useful in managing H5N1 influenza and the next pandemic.

Applications of high-throughput genomics to antiviral research: evasion of antiviral responses and activation of inflammation during fulminant RNA virus infection

Host responses can contribute to the severity of viral infection, through the failure of innate antiviral mechanisms to recognize and restrict the pathogen, the development of intense systemic inflammation leading to circulatory failure or through tissue injury resulting from overly exuberant cell-mediated immune responses. High-throughput genomics methods are now being used to identify the biochemical pathways underlying ineffective or damaging host responses in a number of acute and chronic viral infections. This article reviews recent gene expression studies of 1918 H1N1 influenza and Ebola hemorrhagic fever in cell culture and animal models, focusing on how genomics experiments can be used to increase our understanding of the mechanisms that permit those viruses to cause rapidly overwhelming infection. Particular attention is paid to how evasion of type I IFN responses in infected cells might contribute to over-activation of inflammatory responses. Reviewing recent research and describing how future studies might be tailored to understand the relationship between the infected cell and its environment, this article discusses how the rapidly growing field of high-throughput genomics can contribute to a more complete understanding of severe, acute viral infections and identify novel targets for therapeutic intervention.

Emergence and pandemic potential of swine-origin H1N1 influenza virus

Influenza viruses cause annual epidemics and occasional pandemics that have claimed the lives of millions. The emergence of new strains will continue to pose challenges to public health and the scientific communities. A prime example is the recent emergence of swine-origin H1N1 viruses that have transmitted to and spread among humans, resulting in outbreaks internationally. Efforts to control these outbreaks and real-time monitoring of the evolution of this virus should provide us with invaluable information to direct infectious disease control programmes and to improve understanding of the factors that determine viral pathogenicity and/or transmissibility.

Influenza H1N1 and the world wide economic crisis--a model of coherence?

A recent published model described the phenomenon of a global panic reaction (GPR) on the stock markets based on two remarkable stock market crashes in the months of January and March [Sperling W, Bleich S, Reulbach U, Black Monday on stock markets throughout the world - a new phenomenon of collective panic disorder? A psychiatric approach. Med Hypotheses; 2008]. This model was completed by a therapeutic approach following typical elements of cognitive behavioural therapy (CBT) [Sperling W, Biermann T, Maler JM, Global panic reaction - a therapeutic approach to a world-wide economic crisis. Med Hypotheses; 2009]. The phenomenon of a global panic reaction due to economic crises seems to have even larger implications on human health as well. It is well known that acute and chronic distress is competent to suppress the immune system by various mechanisms that are discussed in detail. This global panic reaction - that has also been observed in former times - might therefore be responsible for the new variation of recent influenza pandemic coming from Mexico.

An improvised oxygen supply system for pandemic and disaster use

BACKGROUND

Current disaster planning for pandemic influenza anticipates overwhelming numbers of patients in need of hospitalization. The anticipated use of extra, or "surge," beds is common in both hospital and community disaster response planning. In a pandemic of respiratory illness, supplemental oxygen will be a life-saving intervention. There are currently few options to provide these proposed surge beds with the necessary oxygen.

OBJECTIVES

A method of providing an improvised oxygen delivery system for use in a disaster was developed and tested. This system was designed to use readily available commercial materials to assemble an oxygen delivery system.

METHODS

The study consisted of a laboratory design, assembly, and testing of an improvised oxygen system.

RESULTS

A liquid oxygen (LOX) Dewar container was used to supply oxygen systems built from inexpensive commercially available plastic tubing and fittings. The system will drive ventilators without significant pressure drop or ventilator malfunction. The final developed system will supply 30 patients with up to 6 L/min (l pm) oxygen each by nasal cannula from a single oxygen Dewar.

CONCLUSIONS

An improvised system to deliver oxygen for patient beds or ventilator use can be easily assembled in the event of a disaster. This could be life-saving in the event of a pandemic of respiratory illness.

Pneumococcal vaccine in the elderly: a useful but forgotten vaccine

Pneumococcal disease in the elderly is a major concern emphasizing the need for prevention. The review focuses on a literature-based analysis of the efficacy ("does the vaccine works?") and/or the effectiveness ("does vaccination help older population?") of pneumococcal vaccines 14- or 23-valent (PPV23) in the elderly. In the setting of Streptococcus pneumoniae pneumonia, there is still no conclusive evidence decisively confirming the efficacy of pneumococcal vaccine against pneumococcal pneumonia in the elderly populations. However, the efficacy of pneumococcal vaccination has been demonstrated in the prevention of invasive pneumococcal disease (IPD) such as bacteremia, which is the main complication of pneumonia. In the setting of IPD in the elderly, analysis of the current literature provides evidence for both the efficacy and effectiveness of PPV23, but most of the clinical studies failed to demonstrate a substantial reduction in all-cause mortality rate. The community-acquired pneumonia guidelines in the industrialized countries include recommendations for pneumococcal vaccine by PPV23 for adults aged 65 years and over. Taking into account the preventive effect of PPV23 on IPD and the threat of a pandemic flu, the increase of PPV23 vaccination coverage in elderly patients should be strongly considered.

Immune dysregulation in severe influenza

Among previously healthy children with severe influenza, the mechanisms leading to increased pathology are not understood. We hypothesized that children with severe influenza would have high levels of circulating cytokines. To examine this, we recruited patients with severe influenza and examined plasma cytokine levels as well as the ability of peripheral blood cells to respond to stimuli. Ten patients with severe influenza were enrolled during the 2005-2007 influenza seasons. We evaluated plasma cytokine levels, circulating NK cells, and responses to TLR ligands during the illness. We compared these patients with five patients with moderate influenza, six patients with respiratory syncytial virus (RSV), and 24 noninfected controls. Patients with influenza showed depressed responses to TLR ligands when compared with RSV patients and healthy controls (P<0.05). These normalized when retested during a convalescent phase. Plasma levels of IL-6, IL-12, and IFN- were elevated in influenza patients compared with controls (P<0.05). A compromised ability to produce TNF- was reproduced by in vitro infection, and the magnitude of the effect correlated with the multiplicity of infection and induction of IFN regulatory factor 4 expression. Aberrant, systemic, innate responses to TLR ligands during influenza infection may be a consequence of specific viral attributes such as a high inoculum or rapid replication and may underlie the known susceptibility of influenza-infected patients to secondary bacterial infections.

Acute bacterial pneumonia is associated with the occurrence of acute coronary syndromes

A link between acute infections and the development of acute coronary syndromes (ACS) has been proposed. We used retrospective cohort and self-controlled case series analyses to define the closeness of the association between acute bacterial pneumonia due to Streptococcus pneumoniae or Haemophilus influenzae and ACS. For the retrospective cohort analysis we included a control group of patients with admission diagnoses other than pneumonia or ACS. For the self-controlled case series analysis, we made within-person comparisons of the risk for ACS during the 15 days after admission for pneumonia with that of 365 days before and after that event. In 206 pneumonia patients (144 S. pneumoniae, 62 H. influenzae) we identified 22 (10.7%) cases of ACS, which compared to 6 (1.5%) among 395 controls resulted in an odds ratio (OR) of 7.8 (95% confidence interval [CI], 3.1-19.4). With multivariate logistic regression analysis, the OR for ACS in the pneumonia group remained elevated (OR, 8.5; 95% CI, 3.4-22.2). By the self-controlled case series method, the risk of ACS remarkably increased during the first 15 days after the diagnosis of pneumonia (incidence rate ratio, 47.6; 95% CI, 24.5-92.5). The characteristics and strength of these associations suggest a causal role for the acute infection in this relationship.

Disaster planning: potential effects of an influenza pandemic on community healthcare resources

The federal government states that local communities are primarily responsible for public health planning and implementation during a severe pandemic. Accordingly, an assessment of the current healthcare capabilities in these communities and planning for deficiencies is required. This article assesses the impact and healthcare capabilities of a specific model local community in a mid-Atlantic state. Two statistical models demonstrate the likely impact of both mild and severe pandemics on local healthcare resources. Both models reveal significant deficiencies that local communities may face. In the event of a severe 1918-type pandemic influenza or a mild influenza pandemic, many local community healthcare systems will likely have inadequate resources to respond to the crisis; such a healthcare emergency would likely overwhelm local community resources and current public health practices. Proper planning at the community level is critical for being truly prepared for such a public health emergency.

Animal models for the study of influenza pathogenesis and therapy

Influenza A viruses causes a variety of illnesses in humans. The most common infection, seasonal influenza, is usually a mild, self-limited febrile syndrome, but it can be more severe in infants, the elderly, and immunodeficient persons, in whom it can progress to severe viral pneumonitis or be complicated by bacterial superinfection, leading to pneumonia and sepsis. Seasonal influenza also occasionally results in neurologic complications. Rarely, viruses that have spread from wild birds to domestic poultry can infect humans; such "avian influenza" can range in severity from mild conjunctivitis through the rapidly lethal disease seen in persons infected with the H5N1 virus that first emerged in Hong Kong in 1997. To develop effective therapies for this wide range of diseases, it is essential to have laboratory animal models that replicate the major features of illness in humans. This review describes models currently in use for elucidating influenza pathogenesis and evaluating new therapeutic agents.

Pandemic influenza--including a risk assessment of H5N1

Influenza pandemics and epidemics have apparently occurred since at least the Middle Ages. When pandemics appear, 50% or more of an affected population can be infected in a single year, and the number of deaths caused by influenza can dramatically exceed what is normally expected. Since 1500, there appear to have been 13 or more influenza pandemics. In the past 120 years there were undoubted pandemics in 1889, 1918, 1957, 1968, and 1977. Although most experts believe we will face another influenza pandemic, it is impossible to predict when it will appear, where it will originate, or how severe it will be. Nor is there agreement about the subtype of influenza virus most likely to cause the next pandemic. The continuing spread of H5N1 highly pathogenic avian influenza viruses has heightened interest in pandemic prediction. Despite uncertainties in the historical record of the pre-virology era, study of previous pandemics may help guide future pandemic planning and lead to a better understanding of the complex ecobiology underlying the formation of pandemic strains of influenza A viruses.

Bacterial complications during pandemic influenza infection

Evaluation of: Morens DM, Taubenberger JK, Fauci AS: Predominant role of bacterial pneumonia as a cause of death in pandemic influenza: implications for pandemic influenza preparedness. J. Infect. Dis. 198(7), 962-970 (2008). Secondary bacterial pneumonia is a common occurrence following lung influenza virus infection and leads to a significantly worse prognosis. This recent re-analysis of postmortem specimens and a vast number of reports from past influenza pandemics shows an extremely high frequency of lung colonization by bacterial species that are commonly found in the nasopharynx. This polymicrobial condition occurred in the preantibiotic era 1918-1919 influenza pandemic, but there is also evidence of bacterial co-infections in those outbreaks that occurred after antibiotic introduction. As such, antibiotic treatment should be included in any pandemic preparedness strategy. However, the choice of which antibiotic to use is important since some may even heighten morbidity and mortality.

Parapneumonic empyema deaths during past century, Utah

Vaccine strategies and antimicrobial drug stockpiling to control empyema will increase preparedness as we prepare for the next influenza pandemic.

Bacterial pneumonia with empyema is a serious complication of influenza and commonly resulted in death during the 1918 influenza pandemic. We hypothesize that deaths caused by parapneumonic empyema are increasing in Utah once again despite advances in critical care and the availability of antimicrobial drugs and new vaccines. In this study, we analyzed the historical relationship between deaths caused by empyema and influenza pandemics by using 100 years of data from Utah. Deaths caused by empyema have indeed increased from 2000–2004 when compared with the historic low death rates of 1950–1975. Vaccine strategies and antimicrobial drug stockpiling to control empyema will be important as we prepare for the next influenza pandemic.

Increased susceptibility for superinfection with Streptococcus pneumoniae during influenza virus infection is not caused by TLR7-mediated lymphopenia

Influenza A virus (IAV) causes respiratory tract infections leading to recurring epidemics with high rates of morbidity and mortality. In the past century IAV induced several world-wide pandemics, the most aggressive occurring in 1918 with a death toll of 20-50 million cases. However, infection with IAV alone is rarely fatal. Instead, death associated with IAV is usually mediated by superinfection with bacteria, mainly Streptococcus pneumoniae. The reasons for this increased susceptibility to bacterial superinfection have not been fully elucidated. We previously demonstrated that triggering of TLR7 causes immune incompetence in mice by induction of lymphopenia. IAV is recognized by TLR7 and infections can lead to lymphopenia. Since lymphocytes are critical to protect from S. pneumoniae it has long been speculated that IAV-induced lymphopenia might mediate increased susceptibility to superinfection. Here we show that sub-lethal pre-infections of mice with IAV-PR8/A/34 strongly increased their mortality in non-lethal SP infections, surprisingly despite the absence of detectable lymphopenia. In contrast to SP-infection alone co-infected animals were unable to control the exponential growth of SP. However, lymphopenia forced by TLR7-triggering or antibody-mediated neutropenia did not increase SP-susceptibility or compromise the ability to control SP growth. Thus, the immune-incompetence caused by transient lympho- or leukopenia is not sufficient to inhibit potent antibacterial responses of the host and mechanisms distinct from leukodepletion must account for increased bacterial superinfection during viral defence.

The influenza virus enigma

Both seasonal and pandemic influenza continue to challenge both scientists and clinicians. Drug-resistant H1N1 influenza viruses have dominated the 2009 flu season, and the H5N1 avian influenza virus continues to kill both people and poultry in Eurasia. Here, we discuss the pathogenesis and transmissibility of influenza viruses and we emphasize the need to find better predictors of both seasonal and potentially pandemic influenza.

Encephalitis lethargica and influenza. I. The role of the influenza virus in the influenza pandemic of 1918/1919

An investigation of the characteristics of influenza epidemics in the nineteenth and early twentieth centuries was undertaken, principally in order to analyze the role of the 1918/1919 influenza pandemic in the etiology of encephalitis lethargica. Expectations regarding a future influenza pandemic derive principally from experiences in the 1918 epidemic. It is proposed that this pandemic was atypical with respect to many of its features, and that these have not been appropriately regarded in mapping expectations and responses of a future pandemic. Both a longer historical viewpoint (incorporating knowledge from all major nineteenth and twentieth century epidemics) and closer examination of individual epidemics at the town level is essential for producing an accurate picture of the challenge.

Guidelines on management of human infection with the novel virus influenza A (H1N1)--a report from the Hospital das Clínicas of the University of São Paulo

The pandemic novel influenza A (H1N1) infection was considered widespread in Brazil on July, 2009. Since then, 9.249 cases were confirmed in Brazil, most of them concentrated in São Paulo. The Hospital das Clínicas of the University of São Paulo is a reference center for H1N1 cases in São Paulo. The purpose of this review is to analyze the evidence concerning diagnosis, prevention, and treatment of novel influenza A (H1N1) infection. In addition, we propose guidelines for the management of this pandemic emphasizing Hospital das Clínicas "bundles" for the control of the pandemic novel influenza A (H1N1).

Emerging infections: a perpetual challenge

Emerging and re-emerging infectious diseases, and their determinants, have recently attracted substantial scientific and popular attention. HIV/AIDS, severe acute respiratory syndrome, H5N1 avian influenza, and many other emerging diseases have either proved fatal or caused international alarm. Common and interactive co-determinants of disease emergence, including population growth, travel, and environmental disruption, have been increasingly documented and studied. Are emerging infections a new phenomenon related to modern life, or do more basic determinants, transcending time, place, and human progress, govern disease generation? By examining a number of historically notable epidemics, we suggest that emerging diseases, similar in their novelty, impact, and elicitation of control responses, have occurred throughout recorded history. Fundamental determinants, typically acting in concert, seem to underlie their emergence, and infections such as these are likely to continue to remain challenges to human survival.