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

Clinical manifestations, therapy and outcome of pandemic influenza a (H1N1) 2009 in hospitalized patients

Background/Aim. Increasing number of epidemiological and clinical studies to date showed that the pandemic influenza A (H1N1) 2009, by its characteristics, significantly differs from infection caused by seasonal influenza. Therefore, the information about clinical spectrum of manifestations, risk factors for severe form of the disease, treatment and outcome in patients with novel flu are still collected. Methods. A total of 98 patients (mean age 32 ? 15 years, range 14-88 years) with the signs and symptoms of novel influenza were treated in the Clinic for Infectious and Tropical Diseases, Military Medical Academy. There were 74 (75.5%) patients with suspected influenza A (H1N1) 2009, 10 (10.2%) with the likelihood and 14 (14.3%) with the confirmed influenza. In all the patients we registered the basic demographic data, risk factors for severe disease, symptoms and signs of influenza, laboratory tests and chest radiography. We analyzed antiviral therapy use and disease outcome (survived, died). Results. The average time from the beginning of influenza A (H1N1) to the admission in hospital was 3 days (0-16 days) and from the moment of hospitalization to the Intensive Care Unit (ICU) admission was 2 days (0-5 days). There were 49 (50.0%) patients, 20-29 years of age and 5 (5.1%) patients older than 65. A total of 21 (21.4%) patients were with underlying disease, 18 (18.4%) were obese, 19 (19.4%) were cigarette smokers. All of the patients had fever, 81 (82.6%) cough, while dyspnea and diarrhea were registered in ? of the patients. In more than 75% of the patients laboratory tests were within normal limits. The realtime polymerase chain reaction (PCR) test for identification of influenza A (H1N1) 2009 was positive in 14 (77.8%), while pneumonia was verified in 30 (30.7%) of the patients. Six (6.1%) patients, mean age of 45 ? 14 years (31-59 years) were admitted to the ICU, of whom five (5.1%) had Adult Respiratory Distress Syndrome (ARDS). Risk factors were registered more frequently in the patients with acute respiratory failure (14.2% vs 4.9%, p < 0.05). A total of 67 (68.4%) patients received oseltamivir, 89 (90.1%) was applied to antibiotics and 64 (65.3%) were treated with a combined therapy. Antiviral therapy was applied to 43 (43.3%) patients in the first 48 hours from the onset of the disease, of whom only one (3.4%) developed ARDS. Fatal outcome was noted in 2.0% of the patients (2 of 98 patients) and in 33.3% of the patients treated in the ICU. Conclusion. Novel influenza A (H1N1) is most commonly manifested as a mild acute respiratory disease, which usually affects young healthy adults. A small number of the patients develop severe illness with acute respiratory failure and death. Patients seem to have benefit from antiviral therapy especially in first 48 hours.

Disease Mongering and the Fear of Pandemic Influenza

The catastrophic H1N1 pandemic of 1918, which killed tens of millions, is now legendary, and influenza policy has centered on preventing another such disaster. There is reason for concern about influenza A. It can rapidly alter its genetic makeup to increase virulence and can jump from other species to humans. Nonetheless, ignorance about influenza in 1918, the lack of effective vaccines or antibacterial and antiviral drugs, and the social disruption caused by World War I also contributed heavily to the lethality, and it is unlikely that influenza of similar destructiveness will recur. The stupefying publicity over the threat of influenza has been generated partly by those, such as the pharmaceutical industry and influenza researchers, who benefit from the increased expenditures the publicity provokes. It is, in effect, disease mongering, the promotion of disease or dread of disease for one's own gain. Huge expenditures on influenza preparedness have produced little demonstrable benefit and some harm, independent of the wasted resources. Disease mongering, including spreading fear of influenza, is widespread and unhealthy and should be vigorously opposed.

Healthcare system cost evaluation of antiviral stockpiling for pandemic influenza preparedness

Healthcare workers need to be protected during a severe influenza outbreak; therefore, we evaluated 4 different antiviral strategies: (1) using antiviral medication for outbreak prophylaxis of all hospital employees; (2) using antiviral medication for postexposure prophylaxis (PEP) or treatment of all hospital employees; (3) using a combination of antiviral medication for outbreak prophylaxis of high-risk clinical staff and postexposure prophylaxis or treatment for all other staff; and (4) using antiviral medication for postexposure prophylaxis or treatment of high-risk clinical staff only. Three different purchasing options were applied to each of the 4 antiviral strategies: (1) just-in-time purchase during a severe influenza outbreak, (2) prepandemic stockpiling, or (3) stockpiling through contracts with pharmaceutical manufacturers to reserve a predetermined antiviral supply. Although outbreak prophylaxis of all hospital employees would offer the maximum protection, the large costs associated with such a purchase make this option unrealistic and impractical. In addition, even though postexposure prophylaxis or treatment of only high-risk clinical staff would incur the least expense, the assumed level of protection if these options were offered only to high-risk clinical staff may not be sufficient to maintain routine hospital operations, since needed non-high-risk staff would not be protected. Considering the potential benefits and drawbacks of stockpiling antiviral medication from a cost perspective, it does not appear feasible for hospitals to stockpile antiviral medication in large quantities prior to a severe influenza outbreak. This article focuses on the financial viability of stockpiling antiviral medication, but the potential impact of other factors on the decision to stockpile was also considered and will be explored in future analyses. While legal hurdles related to prescribing, storing, and dispensing antiviral medication can be addressed, unavailability of a suitable vaccine supply may strongly support a decision to stockpile antiviral medication. Other issues to be addressed include antiviral resistance specifically related to the efficacy of oseltamivir, coupled with a high frequency of secondary bacterial infections; uncertainties about the degree of government assistance; potential government seizures of stockpiled assets; and legal and ethical concerns related to fair access to stockpiled medication. These issues may all be perceived as barriers to the feasibility of stockpiling antiviral medication.

Pathology of the swine-origin influenza A (H1N1) flu

Pathological studies would aid in finding the real causes of death and in outlining adequate strategies for treatment regarding patients with poor clinical outcome of influenza A H1N1 swine flu. We describe the autopsy findings of six cases of influenza A H1N1 swine flu. The lungs in these cases had an alveolitis with hyaline membranes. Immunohistochemistry for influenza was positive only in lungs (in pneumocytes, in macrophages, in some multinucleate cells in alveoli, and in blood vessel walls) of two cases. Disseminated petechial brain hemorrhage was observed in four of the cases and focally in one case. Focal myocarditis was observed in one case. Coagulation infarcts (ischemic) were observed in the pancreas of two cases and in the spleen of two cases. Our results indicate that there was marked replication of the virus in alveoli in the more recently infected cases, which could explain the extensive diffuse alveolar damage. In our cases, there were important vascular phenomena that resulted in hemorrhage and thrombosis, but without marked decrease of platelet count and coagulation cascade disruptions. This would be attributed to hemodynamic disruption. However, it is possible that the hemorrhagic petechial lesions in the brain are due to vascular lesions or to an increase of endothelial permeability.

Seasonal FluMist vaccination induces cross-reactive T cell immunity against H1N1 (2009) influenza and secondary bacterial infections

T cell epitopes have been found to be shared by circulating, seasonal influenza virus strains and the novel pandemic H1N1 influenza infection, but the ability of these common epitopes to provide cross-protection is unknown. We have now directly tested this by examining the ability of live seasonal influenza vaccine (FluMist) to mediate protection against swine-origin H1N1 influenza virus infection. Naive mice demonstrated considerable susceptibility to H1N1 Cal/04/09 infection, whereas FluMist-vaccinated mice had markedly decreased morbidity and mortality. In vivo depletion of CD4(+) or CD8(+) immune cells after vaccination indicated that protective immunity was primarily dependent upon FluMist-induced CD4(+) cells but not CD8(+) T cells. Passive protection studies revealed little role for serum or mucosal Abs in cross-protection. Although H1N1 influenza infection of naive mice induced intensive phagocyte recruitment, pulmonary innate defense against secondary pneumococcal infection was severely suppressed. This increased susceptibility to bacterial infection was correlated with augmented IFN-γ production produced during the recovery stage of H1N1 influenza infection, which was completely suppressed in mice previously immunized with FluMist. Furthermore, susceptibility to secondary bacterial infection was decreased in the absence of type II, but not type I, IFN signaling. Thus, seasonal FluMist treatment not only promoted resistance to pandemic H1N1 influenza infection but also restored innate immunity against complicating secondary bacterial infections.

Elevated influenza-related excess mortality in South African elderly individuals, 1998-2005

BACKGROUND

Although essential to guide control measures, published estimates of influenza-related seasonal mortality for low- and middle-income countries are few. We aimed to compare influenza-related mortality among individuals aged ≥65 years in South Africa and the United States.

METHODS

We estimated influenza-related excess mortality due to all causes, pneumonia and influenza, and other influenza-associated diagnoses from monthly age-specific mortality data for 1998-2005 using a Serfling regression model. We controlled for between-country differences in population age structure and nondemographic factors (baseline mortality and coding practices) by generating age-standardized estimates and by estimating the percentage excess mortality attributable to influenza.

RESULTS

Age-standardized excess mortality rates were higher in South Africa than in the United States: 545 versus 133 deaths per 100,000 population for all causes (P<.001) and 63 vs 21 deaths per 100,000 population for pneumonia and influenza (P=.03). Standardization for nondemographic factors decreased but did not eliminate between-country differences; for example, the mean percentage of winter deaths attributable to influenza was 16% in South Africa and 6% in the United States (P<.001). For all respiratory causes, cerebrovascular disease, and diabetes, age-standardized excess death rates were 4-8-fold greater in South Africa than in the United States, and the percentage increase in winter deaths attributable to influenza was 2-4-fold higher.

CONCLUSIONS

These data suggest that the impact of seasonal influenza on mortality among elderly individuals may be substantially higher in an African setting, compared with in the United States, and highlight the potential for influenza vaccination programs to decrease mortality.

Identification of Unique Blood and Urine Biomarkers in Influenza Virus and Staphylococcus aureus Co-infection: A Preliminary Study

Each year, there are estimated to be approximately 200,000 hospitalizations and 36,000 deaths due to influenza in the United States. Reports have indicated that most deaths are not directly due to influenza virus, but to secondary bacterial pneumonia, predominantly staphylococcal in origin. Here we identify the presence of candidate blood and urine biomarkers in mice with Staphyococcus aureus and influenza virus co-infection. In this pilot study, mice were grouped into four treatments: co-infected with influenza virus and S. aureus, singly infected with influenza virus or S. aureus, and a control group of uninfected mice (PBS treated). Gene expression changes were identified by DNA-microarrays from blood samples taken at day five post infection. Proteomic changes were obtained from urine samples collected at three and five days post infection using 2-D DIGE followed by protein ID by mass spectrometry. Differentially expressed genes and/or proteins were identified as candidate biomarkers for future validation in larger studies.

Cost-effectiveness of stockpiling 23-valent pneumococcal polysaccharide vaccine to prevent secondary pneumococcal infections among a high-risk population in the United States during an influenza pandemic

BACKGROUND

Secondary bacterial infections (especially pneumococcal infections) were a major cause of death during prior influenza pandemics. One strategy to prevent pneumococcal infections in adults during a future pandemic is to stockpile 23-valent pneumococcal polysaccharide vaccine (PPSV23). Stockpiling a pneumococcal vaccine can ensure that it is available when needed most-that is, at the onset of a pandemic.

OBJECTIVE

The purpose of this article was to project the health and economic impact of stockpiling PPSV23 to prevent secondary pneumococcal infections among high-risk adults aged 18 to 64 years during an influenza pandemic within the United States.

METHODS

A cost-effectiveness model was developed to evaluate the health and economic effects of stockpiling PPSV23 versus not stockpiling this vaccine for preventing secondary pneumococcal infections among 20 million high-risk US adults aged 18 to 64 years during an influenza pandemic. The model was used to project the number of pneumococcal cases, hospitalizations, deaths, and days of work loss averted. Three health outcomes (deaths, hospitalizations, and outpatient care) were estimated from secondary pneumococcal infections. To assess the overall effectiveness of the different strategies, the quality-adjusted life-year (QALY) was used as a measure of these 3 health outcomes. The results are presented for 3 scenarios based on the pandemic severity and anticipated prepandemic influenza vaccine availability: base case, more-severe case, and less-severe case.

RESULTS

In the base-case scenario, vaccinating 20 million high-risk adults with PPSV23 avoided 2858 deaths, 878 hospitalizations, 41,881 pneumococcal pneumonia cases, and 232,891 days of work loss during a pandemic. Under the more-severe case scenario, vaccination avoided 21,921 deaths, 10,280 hospitalizations, 70,345 pneumococcal cases, and approximately 1.12 million days of work loss. Under the less-severe case scenario, pneumococcal vaccination avoided 715 deaths, 219 hospitalizations, 10,470 pneumococcal cases, and 58,235 days of work loss. The incremental cost-effectiveness ratio for stockpiling PPSV23 versus no stockpiling for the base-case and less-severe case scenarios was $39,946 and $198,653 per QALY, respectively. For the more-severe case scenario, stockpiling PPSV23 was cost saving. Probabilistic sensitivity analyses found that the range of incremental cost-effectiveness ratio values was broad due to the large uncertainty regarding the timing and impact of the next pandemic. In addition, the shelf life of PPSV23 and stockpile management substantially influenced the cost-effectiveness ratio.

CONCLUSIONS

For severe pandemics or pandemics in which prepandemic influenza vaccine is unavailable, stockpiling of PPSV23 can be a cost-effective strategy for reducing the health and economic burden associated with secondary pneumococcal infections in a high-risk US population. However, for a mildly severe pandemic in which prepandemic influenza vaccine is available, stockpiling of PPSV23 may not be cost-effective.

Hospitalised patients with Influenza A (H1N1) in the Royal Hospital, Oman: Experience of a tertiary care hospital, July-December 2009

OBJECTIVES

The aim of this study was to describe the clinical characteristics, risk factors, laboratory investigations and outcome of hospitalised patients with positive Influenza A (H1N1) at the Royal Hospital in Oman.

METHODS

We extracted data from the retrospective medical charts, radiological and laboratory findings of 131 patients who were confirmed as positive for Influenza A (H1N1) by real-time reverse-transcriptase-polymerase- chain-reaction from 21 July to 23 December 2009.

RESULTS

The median age was 24 years with 34.4% in the paediatric age group. Most (63%) of hospitalised patients were female. Symptoms at presentation included mainly fever (93.9%) and respiratory symptoms (89.3%). 83% of the patients had at least one risk factor and pregnancy was the most common associated condition (22.9%). Most of the patients had reduced lymphocytic count (57.3%) and high levels of serum C-reactive protein, aspartate transaminase and lactate dehydrogenase (75.7%, 75% and 70.8% respectively). The majority of the patients (64.5%) had evidence of pneumonia and radiological findings constituted mainly bi-lateral infiltrates (60.6%). Antiviral therapy was administered to 95.4% of the patients who mostly received it 48 hours after disease onset. Death occurred in 6.9% of patients. Out of these, 88.9% required Intensive Care Unit (ICU) care and mechanical ventilation.

CONCLUSION

Influenza A (H1N1) infection mainly affected those of younger age and females. Associated medical conditions were common, with pregnancy being interestingly the commonest risk factor. The infection caused severe illness that required ICU admission and led to death in 6.9% of patients.

Older adults have a low capacity to opsonize pneumococci due to low IgM antibody response to pneumococcal vaccinations

Since the 23-valent pneumococcal polysaccharide vaccine (PPV23) is less effective for older adults than for young adults, it is important to investigate the immunologic basis for the reduced efficacy of PPV23 among older adults. We determined the effectiveness of PPV23 among young (n = 55) and older (n = 44) adults by measuring the serum IgG, IgM, and IgA concentrations and opsonic capacities against serotypes 14, 18C, and 23F. While young and older adults showed no difference in levels of IgG antibodies against pneumococcal polysaccharide (PPS), older adults had lower IgA and IgM antibody levels than young adults for all three serotypes. In both age groups, anti-PPS IgA or IgM antibody levels were much lower than anti-PPS IgG antibody levels. Young adults showed higher opsonic capacities than older adults for serotypes 14 and 23F. In order to determine the effects of anti-PPS IgA or IgM antibodies on the functional difference between young and older adults, anti-PPS IgA or IgM antibodies were removed from immune sera by affinity chromatography. The difference in opsonic capacity between young and older adults disappeared for serotypes 14 and 23F (but not for serotype 18C) when IgM antibody was removed. However, there was no significant difference between the two age groups when IgA antibody was removed. In conclusion, even though anti-PPS IgG antibody levels are high compared with anti-PPS IgM antibody levels, the low levels of anti-PPS IgM antibody alone can explain the functional difference observed between young and older adults immunized with PPV23 with regard to some pneumococcal serotypes.

The seasonality of pandemic and non-pandemic influenzas: the roles of solar radiation and vitamin D

OBJECTIVES

Seasonal variations in ultraviolet B (UVB) radiation cause seasonal variations in vitamin D status. This may influence immune responses and play a role in the seasonality of influenza.

METHODS

Pandemic and non-pandemic influenzas in Sweden, Norway, the USA, Singapore, and Japan were studied. Weekly/monthly influenza incidence and death rates were evaluated in view of monthly UVB fluences.

RESULTS

Non-pandemic influenzas mostly occur in the winter season in temperate regions. UVB calculations show that at high latitudes very little, if any, vitamin D is produced in the skin during the winter. Even at 26°N (Okinawa) there is about four times more UVB during the summer than during the winter. In tropical regions there are two minor peaks in vitamin D photosynthesis, and practically no seasonality of influenza. Pandemics may start with a wave in an arbitrary season, while secondary waves often occur the following winter. Thus, it appears that a low vitamin D status may play a significant role in most influenzas.

CONCLUSIONS

In temperate latitudes even pandemic influenzas often show a clear seasonality. The data support the hypothesis that high fluences of UVB radiation (vitamin D level), as occur in the summer, act in a protective manner with respect to influenza.

Efficacy of whole-cell killed bacterial vaccines in preventing pneumonia and death during the 1918 influenza pandemic

BACKGROUND

Most deaths in the 1918 influenza pandemic were caused by secondary bacterial pneumonia.

METHODS

We performed a systematic review and reanalysis of studies of bacterial vaccine efficacy (VE) in preventing pneumonia and mortality among patients with influenza during the 1918 pandemic.

RESULTS

A meta-analysis of 6 civilian studies of mixed killed bacterial vaccines containing pneumococci identified significant heterogeneity among studies and estimated VE at 34% (95% confidence interval [CI], 19%-47%) in preventing pneumonia and 42% (95% CI, 18%-59%) in reducing case fatality rates among patients with influenza, using random-effects models. Using fixed-effect models, the pooled VE from 3 military studies was 59% (95% CI, 43%-70%) for pneumonia and 70% (95% CI, 50%-82%) for case fatality. Military studies showed less heterogeneity and may provide more accurate results than civilian studies, given the potential biases in the included studies. Findings of 1 military study using hemolytic streptococci also suggested that there was significant protection.

CONCLUSIONS

Despite significant methodological problems, the systematic biases in these studies do not exclude the possibilities that whole-cell inactivated pneumococcal vaccines may confer cross-protection to multiple pneumococcal serotypes and that bacterial vaccines may play a role in preventing influenza-associated pneumonia.

Co-infection of Influenza B and Streptococci causing severe pneumonia and septic shock in healthy women

Background

Since the Influenza A pandemic in 1819, the association between the influenza virus and Streptococcus pneumoniae has been well described in literature. While a leading role has been so far attributed solely to Influenza A as the primary infective pathogen, Influenza B is generally considered to be less pathogenic with little impact on morbidity and mortality of otherwise healthy adults. This report documents the severe synergistic pathogenesis of Influenza B infection and bacterial pneumonia in previously healthy persons not belonging to a special risk population and outlines therapeutic options in this clinical setting.

Case Presentation

During the seasonal influenza epidemic 2007/2008, three previously healthy women presented to our hospital with influenza-like symptoms and rapid clinical deterioration. Subsequent septic shock due to severe bilateral pneumonia necessitated intensive resuscitative measures including the use of an interventional lung assist device. Microbiological analysis identified severe dual infections of Influenza B with Streptococcus pyogenes in two cases and Streptococcus pneumoniae in one case. The patients presented with no evidence of underlying disease or other known risk factors for dual infection such as age (< one year, > 65 years), pregnancy or comorbidity.

Conclusions

Influenza B infection can pose a risk for severe secondary infection in previously healthy persons. As patients admitted to hospital due to severe pneumonia are rarely tested for Influenza B, the incidence of admission due to this virus might be greatly underestimated, therefore, a more aggressive search for influenza virus and empirical treatment might be warranted. While the use of an interventional lung assist device offers a potential treatment strategy for refractory respiratory acidosis in addition to protective lung ventilation, the combined empiric use of a neuraminidase-inhibitor and antibiotics in septic patients with pulmonary manifestations during an epidemic season should be considered.

Radiographic study of severe Influenza-A (H1N1) disease in children

OBJECTIVE

To characterize the radiographic findings of pediatric patients with severe Influenza-A (H1N1) disease.

METHODS

A retrospective study of data from chest X-ray, CT and MRI exam of 29 pediatric patients treated in intensive care unit for severe Influenza-A (H1N1) disease.

RESULTS

Disease developed quickly at early stage. Here are four types of radiographic findings. The disease continued to progress for 2-3 days and X-ray showed that all 29 patients had increased solid lesions with the existence of interstitial lesions. Four days later, all lung lesions showed absorption to certain degree. Fifteen days later, X-ray and CT showed complete or significant absorption in 19 cases (85.5%); delayed recovery was identified in 8 cases (27.6%), pulmonary fibrosis was found in 3 cases (10.3%), and 3 patients (10.3%) died. But the latter identified more lesions. Cranial CT and MRI were performed for 8 patients who had neurological symptoms. Of them, 3 cases (10.3%) were abnormal, showed symmetrical long T1 and T2 signal shadow in bilateral thalamus and longer T1 and T2 signals in the between. 3 cases had autopsy completed.

CONCLUSION

The severe Influenza-A (H1N1) among children progression was generally rapid in the first 3 days. The overall radiographic findings are similar to acute respiratory distress syndrome (ARDS). A small portion of the patients occurred acute necrotizing encephalopathy and plastic bronchitis.

Control of Streptococcus pneumoniae serotype 5 epidemic of severe pneumonia among young army recruits by mass antibiotic treatment and vaccination

During an outbreak of severe pneumonia among new army recruits, an epidemiological investigation combined with repeated nasopharyngeal/oropharyngeal cultures from sick and healthy contacts subjects was conducted. Fifteen pneumonia cases and 19 influenza-like illness cases occurred among 596 recruits over a 4-week period in December 2005. Pneumonia attack rates reached up to 5.5%. A single pneumococcus serotype 5 clone was isolated from blood or sputum cultures in 4 patients and 30/124 (24.1%) contacts. Immunization with 23-valent polysaccharide vaccine supplemented with a 2-dose azithromycin mass treatment rapidly terminated the outbreak. Carriage rates dropped to <1%, 24 and 45 days after intervention.

Activation of the innate immune system provides broad-spectrum protection against influenza A viruses with pandemic potential in mice

The efficacy of a stabilized chemical analog of double-stranded ribonucleic acid (RNA), PIKA, as prophylaxis against infection with 5 different influenza A virus subtypes, including the 2009 swine-origin pandemic H1N1 virus, was evaluated in mice. Intranasal treatment with PIKA resulted in a significant reduction of viral replication in the respiratory tract. The inhibitory effect was mediated by rapid infiltration of immune cells into the lungs, and production of inflammatory cytokines. While TLR3 is important for the optimal production of these inflammatory cytokines, inhibition of viral replication was still observed in TLR3(-/-) mice. In addition, a significant synergistic effect in inhibiting H5N1 virus replication was observed when PIKA was coadministered with oseltamivir. The broad-spectrum protection provided by PIKA makes it an attractive option for prophylaxis from infection with influenza A viruses.

Novel findings from the second wave of adult pH1N1 in the United States

OBJECTIVE

To describe the impact of novel pH1N1 virus in Atlanta, GA, for inpatient and intensive care services, including lung lavage data and determinants of disease outcome, from the earliest group of infected US population after initial cases.

DESIGN

An observational review of all patients with laboratory-confirmed pH1N1 disease hospitalized in four Atlanta hospitals from August 1 through October 31, 2009. Data reviewed included demographics, anthropometrics, clinical laboratory, and respiratory physiology.

SETTING

Four hospitals in urban Atlanta, Georgia.

PATIENTS

Consecutively admitted patients between August 1 and October 31, 2009 with laboratory confirmed pH1N1 infection.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total of 109 patients were admitted during the surveillance period and intensive care unit care was required in 23 patients (21%) among which there were six deaths (26%). Only eight of the 109 (7%) patients were without medical comorbidity; 34% of the 65 female patients were pregnant and none died or required intensive care unit care. Patients with respiratory failure undergoing bronchoalveolar lavage exhibited neutrophilic predominance (average 64%) and negative bacterial cultures. Body mass index was > 30 kg/m in 35 of 81 (43%) of patients with anthropometric data and 16 of 23 (70%) patients requiring intensive care unit care (p = .03). The 16 patients who required mechanical ventilation (70% of intensive care unit patients) were characterized by severe hypoxemia (requiring high levels of inspired oxygen and positive end-expiratory pressures), reduced lung compliance, and high lung injury scores.

CONCLUSIONS

This first report of the second wave of US pH1N1 disease from Atlanta, GA, shares epidemiologic characteristics of earlier cohorts but differs by having an even greater prevalence of obesity and fewer patients who were free from chronic medical conditions. Importantly, lung lavage fluid in severe pH1N1 disease is predominantly neutrophilic and culture-negative. Further reports are needed to validate these new findings regarding pH1N1 disease in the United States.

Community-acquired respiratory coinfection in critically ill patients with pandemic 2009 influenza A(H1N1) virus

BACKGROUND

Little is known about the impact of community-acquired respiratory coinfection in patients with pandemic 2009 influenza A(H1N1) virus infection.

METHODS

This was a prospective, observational, multicenter study conducted in 148 Spanish ICUs.

RESULTS

Severe respiratory syndrome was present in 645 ICU patients. Coinfection occurred in 113 (17.5%) of patients. Streptococcus pneumoniae (in 62 patients [54.8%]) was identified as the most prevalent bacteria. Patients with coinfection at ICU admission were older (47.5±15.7 vs 43.8±14.2 years, P<.05) and presented a higher APACHE (Acute Physiology and Chronic Health Evaluation) II score (16.1±7.3 vs 13.3±7.1, P<.05) and Sequential Organ Failure Assessment (SOFA) score (7.0±3.8 vs 5.2±3.5, P<.05). No differences in comorbidities were observed. Patients who had coinfection required vasopressors (63.7% vs 39.3%, P<.05) and invasive mechanical ventilation (69% vs 58.5%, P<.05) more frequently. ICU length of stay was 3 days longer in patients who had coinfection than in patients who did not (11 [interquartile range, 5-23] vs 8 [interquartile range 4-17], P=.01). Coinfection was associated with increased ICU mortality (26.2% vs 15.5%; OR, 1.94; 95% CI, 1.21-3.09), but Cox regression analysis adjusted by potential confounders did not confirm a significant association between coinfection and ICU mortality.

CONCLUSIONS

During the 2009 pandemics, the role played by bacterial coinfection in bringing patients to the ICU was not clear, S pneumoniae being the most common pathogen. This work provides clear evidence that bacterial coinfection is a contributor to increased consumption of health resources by critical patients infected with the virus and is the virus that causes critical illness in the vast majority of cases.

Prevalence and clinical features of pneumonia in patients with laboratory-confirmed pandemic influenza A H1N1 2009 infection in South Korea

During the early stages of the pandemic influenza A H1N1 2009 (pH1N1) outbreak in South Korea, the government recommended antiviral therapy with laboratory confirmation in specialized hospitals. Hence we had a unique opportunity to test all patients suspected to have pH1N1, including those who initially presented with a mild illness, such as those who were not in at-risk groups and who had an uncomplicated illness. We therefore evaluated the proportion and clinical features of pneumonia in patients with laboratory-confirmed pH1N1. Of the 3253 patients who visited Asan Medical Center, Seoul, South Korea, between 24 August and 19 October 2009 for a suspected pH1N1 infection (temperature ≥ 37.5°C and at least 1 of the following symptoms: sore throat, cough, rhinorrhoea and nasal congestion), 553 (17%) were positive for pH1N1 by real-time reverse-transcriptase polymerase chain reaction. Chest radiographs were performed in 96 (17%) of the 553 patients. Of the 553 patients, 30 (5%; 95% confidence interval (CI) 4-8%) had pneumonia, including 26 (86%) with viral pneumonia and 4 (14%) with bacterial pneumonia. So, the proportion of pneumonia in patients with laboratory-confirmed pH1N1 was at least 5%. Multivariate analysis indicated that dyspnoea (odds ratio (OR) 57.8, p < 0.001), wheezing (OR 19.3, p = 0.02), vomiting (OR 18.5, p < 0.001) and diarrhoea (OR 11.0, p = 0.001) were independently associated with pneumonia. Antiviral therapy at >48 h after the onset of symptoms (OR 2.1, p = 0.09) tended to be more common in patients with pneumonia than in those without pneumonia.

Association of 2009 pandemic influenza A (H1N1) infection and increased hospitalization with parapneumonic empyema in children in Utah

BACKGROUND

During previous influenza pandemics, many deaths were associated with secondary bacterial infection. In April 2009, a previously unknown 2009 influenza A virus (2009 H1N1) emerged, causing a global influenza pandemic. We examined the relationship between circulating 2009 H1N1 and the occurrence of secondary bacterial parapneumonic empyema in children.

METHODS

Children hospitalized with parapneumonic empyema from August 2004 to July 2009, including a period when the 2009 H1N1 circulated in Utah, were identified using International Classification of Diseases, Ninth Revision codes. We compared the average number of children diagnosed with influenza A and the number of admissions for empyema per month for the previous 4 seasons to rates of empyema during the 2009 H1N1 outbreak. We identified causative bacteria using culture and polymerase chain reaction (PCR).

RESULTS

We observed an increase in hospitalization of children with pneumonia complicated by empyema during a severe outbreak of 2009 H1N1 during the spring and summer of 2009, compared with historical data for the previous 4 seasons. Streptococcus pneumoniae and Streptococcus pyogenes were the predominant bacteria identified.

CONCLUSIONS

Similar to previous pandemics, secondary bacterial infection with S. pneumoniae and S. pyogenes were associated with the 2009 H1N1 outbreak. There is an urgent need to better understand bacterial complications of pandemic influenza. In the interim, influenza vaccines, antiviral agents, and pneumococcal vaccines should be used to prevent cases of secondary bacterial pneumonia whenever possible.

The Streptococcus pyogenes proteome: maps, virulence factors and vaccine candidates

Streptococcus pyogenes is an important cause of human morbidity and mortality worldwide. A wealth of genomic information related to this pathogen has facilitated exploration of the proteome, particularly in response to environmental conditions thought to mimic various aspects of pathogenesis. Proteomic approaches are also used to identify immunoreactive proteins for vaccine development and to identify proteins that may induce autoimmunity. These studies have revealed new mechanisms involved in regulating the S. pyogenes proteome, which has opened up new avenues in the study of S. pyogenes pathogenesis. This article describes the methods used, and progress being made towards characterizing the S. pyogenes proteome, including studies seeking to identify potential vaccine candidates.

[Clinical and sociological prospectives on pandemic (H1N1) 2009]

A new pandemic influenza A (H1N1) virus has emerged and rapidly spread throughout the world. The clinical and pathological findings associated with severe illness in Pandemic (H1N1) 2009 and the risk factors are similar to the high pathogenic avian influenza (H5N1). The effective treatment methods for severe influenza in Pandemic (H1N1) 2009 could strongly refer to the treatment method for human H5N1 infection. In this article, the experiences, the investigation and our collaboration studies for Pandemic (H1N1) 2009 in Mexico and Avian Influenza (H5N1) in Vietnam and the examination for the past pandemic influenza will be described. The effective treatments for critical pneumonia caused by influenza will be discussed from the medical, regional and global point-of-view which can be applied to any type of pandemic influenza.

The role of radiology in influenza: novel H1N1 and lessons learned from the 1918 pandemic

The pandemic of swine-origin H1N1 influenza that began in early 2009 has provided evidence that radiology can assist in the early diagnosis of severe cases, raising new opportunities for the further development of infectious disease imaging. To help define radiology's role in present and future influenza outbreaks, it is important to understand how radiologists have responded to past epidemics and how these outbreaks influenced the development of imaging science. The authors review the role of radiology in the most severe influenza outbreak in history, the "great pandemic" of 1918, which arrived only 23 years after the discovery of x-rays. In large part because of the coincidental increase in the radiologic capacity of military hospitals for World War I, the 1918 pandemic firmly reinforced the role of radiologists as collaborators with clinicians and pathologists at an early stage in radiology's development, in addition to producing a radical expansion of radiologic research on pulmonary infections. Radiology's solid foundation from the 1918 experience in medical practice and research now affords significant opportunities to respond to the current H1N1 pandemic and future epidemics through similar interdisciplinary strategies that integrate imaging science with pathology, virology, and clinical studies. The broad range of current imaging capabilities will make it possible to study influenza at the cellular level, in animal models, and in human clinical trials to elucidate the pathogenesis of severe illness and improve clinical outcomes.

2009 H1N1 influenza: a twenty-first century pandemic with roots in the early twentieth century

A swine-origin H1N1 triple-reassortant influenza A virus found to be a distant relative of the 1918 "Spanish flu" virus emerged in April 2009 to give rise to the first influenza pandemic of the 21st century. Although disease was generally mild and similar to seasonal influenza, severe manifestations including respiratory failure were noted in some, particularly those with underlying conditions such as asthma, pregnancy and immunosuppression. Children and younger adults accounted for most cases, hospitalizations and deaths. A reverse transcriptase-polymerase chain reaction assay was superior to antigen-based rapid tests for diagnosis. All 2009 H1N1 pandemic influenza strains were susceptible to 1 or more neuraminidase inhibitors. Monovalent, unadjuvanted 2009 H1N1 vaccines were licensed in the United States in September 2009 and initially targeted to younger individuals, pregnant women, caretakers of infants and healthcare providers. The 2009 H1N1 pandemic highlights the need for modernization of influenza vaccines, improved diagnostics and more rigorous evaluation of mitigation strategies.

Clinical pathological characteristics and management of acute respiratory distress syndrome resulting from influenza A (H1N1) virus

Young adults, especially pregnant woman and patients with pre-existing medical conditions, appear to be at risk for the development of severe acute respiratory distress syndrome (ARDS) from influenza A (H1N1) infection, leading to critical hypoxemia. This may require high ventilator settings, the use of nonconventional modes, and extracorporeal membrane oxygenation in some cases. This severe ARDS may be related to prolonged and virulent viral infection, inducing ongoing aberrant immune responses and leading to extensive lung damage. Duration of antiviral therapy, the timing of steroid introduction, and moving away from standard ventilation techniques in ARDS may be key points in disease management.

Comparative pathology of select agent influenza a virus infections

Influenza A virus infections may spread rapidly in human populations and cause variable mortality. Two of these influenza viruses have been designated as select agents: 1918 H1N1 virus and highly pathogenic avian influenza (HPAI) virus. Knowledge of the pathology of these virus infections in humans, other naturally infected species, and experimental animals is important to understand the pathogenesis of influenza, to design appropriate models for evaluation of medical countermeasures, and to make correct diagnoses. The most important complication of influenza in humans is viral pneumonia, which often occurs with or is followed by bacterial pneumonia. Viremia and extrarespiratory disease are uncommon. HPAI viruses, including HPAI H5N1 virus, cause severe systemic disease in galliform species as well as in anseriform species and bird species of other orders. HPAI H5N1 virus infection also causes severe disease in humans and several species of carnivores. Experimental animals are used to model different aspects of influenza in humans, including uncomplicated influenza, pneumonia, and virus transmission. The most commonly used experimental animal species are laboratory mouse, domestic ferret, and cynomolgus macaque. Experimental influenza virus infections are performed in various other species, including domestic pig, guinea pig, and domestic cat. Each of these species has advantages and disadvantages that need to be assessed before choosing the most appropriate model to reach a particular goal. Such animal models may be applied for the development of more effective antiviral drugs and vaccines to protect humans from the threat of these virus infections.

Influenza infectious dose may explain the high mortality of the second and third wave of 1918-1919 influenza pandemic

Background

It is widely accepted that the shift in case-fatality rate between waves during the 1918 influenza pandemic was due to a genetic change in the virus. In animal models, the infectious dose of influenza A virus was associated to the severity of disease which lead us to propose a new hypothesis. We propose that the increase in the case-fatality rate can be explained by the dynamics of disease and by a dose-dependent response mediated by the number of simultaneous contacts a susceptible person has with infectious ones.

Methods

We used a compartment model with seasonality, waning of immunity and a Holling type II function, to model simultaneous contacts between a susceptible person and infectious ones. In the model, infected persons having mild or severe illness depend both on the proportion of infectious persons in the population and on the level of simultaneous contacts between a susceptible and infectious persons. We further allowed for a high or low rate of waning immunity and volunteer isolation at different times of the epidemic.

Results

In all scenarios, case-fatality rate was low during the first wave (Spring) due to a decrease in the effective reproduction number. The case-fatality rate in the second wave (Autumn) depended on the ratio between the number of severe cases to the number of mild cases since, for each 1000 mild infections only 4 deaths occurred whereas for 1000 severe infections there were 20 deaths. A third wave (late Winter) was dependent on the rate for waning immunity or on the introduction of new susceptible persons in the community. If a group of persons became voluntarily isolated and returned to the community some days latter, new waves occurred. For a fixed number of infected persons the overall case-fatality rate decreased as the number of waves increased. This is explained by the lower proportion of infectious individuals in each wave that prevented an increase in the number of severe infections and thus of the case-fatality rate.

Conclusion

The increase on the proportion of infectious persons as a proxy for the increase of the infectious dose a susceptible person is exposed, as the epidemic develops, can explain the shift in case-fatality rate between waves during the 1918 influenza pandemic.

Advances in the prevention, management, and treatment of community-acquired pneumonia

Despite the availability of powerful antibiotics, community-acquired pneumonia (CAP) remains one of the leading reasons for morbidity and mortality worldwide, and despite the availability of powerful antibiotics, there has been only little improvement in case fatality rates for many years. Consequently, it cannot be expected that novel antibiotics will substantially improve outcomes in CAP. Therefore, this review focuses on novel approaches that may reduce CAP-related mortality: the impact of immunomodulation by macrolides and fluoroquinolones and the prevention of CAP by pneumococcal vaccines.

PB1-F2 proteins from H5N1 and 20 century pandemic influenza viruses cause immunopathology

With the recent emergence of a novel pandemic strain, there is presently intense interest in understanding the molecular signatures of virulence of influenza viruses. PB1-F2 proteins from epidemiologically important influenza A virus strains were studied to determine their function and contribution to virulence. Using 27-mer peptides derived from the C-terminal sequence of PB1-F2 and chimeric viruses engineered on a common background, we demonstrated that induction of cell death through PB1-F2 is dependent upon BAK/BAX mediated cytochrome c release from mitochondria. This function was specific for the PB1-F2 protein of A/Puerto Rico/8/34 and was not seen using PB1-F2 peptides derived from past pandemic strains. However, PB1-F2 proteins from the three pandemic strains of the 20^th century and a highly pathogenic strain of the H5N1 subtype were shown to enhance the lung inflammatory response resulting in increased pathology. Recently circulating seasonal influenza A strains were not capable of this pro-inflammatory function, having lost the PB1-F2 protein's immunostimulatory activity through truncation or mutation during adaptation in humans. These data suggest that the PB1-F2 protein contributes to the virulence of pandemic strains when the PB1 gene segment is recently derived from the avian reservoir.

There is presently great interest in understanding how influenza viruses cause disease. In this paper, we explore the role of the influenza virus PB1-F2 protein in disease. We show that the ability of the protein to cause cell death is mediated through a mitochondrial death pathway controlled by proteins called BAX or BAK. However, this function of the protein only seems to be relevant to a restricted set of viruses and not past pandemic strains. Instead, the ability to generate inflammation in the lung proves to be a common trait of all past pandemic strains as well as the H5N1 highly pathogenic avian influenza strains which remain a significant pandemic threat. It appears likely that this pro-inflammatory phenotype is a characteristic of viruses emerging from the avian reservoir and is therefore important for new strains that cross the species barrier and establish themselves in humans. During circulation and adaptation in the mammalian lung, this function is typically lost. Of note, the novel 2009 H1N1 pandemic strain does not express a full-length PB1-F2. Were it to acquire a fully functional, inflammatory PB1-F2 through reassortment, this could herald greatly enhanced disease potential.

Features of the new pandemic influenza A/H1N1/2009 virus: virology, epidemiology, clinical and public health aspects

PURPOSE OF REVIEW

The emergence of the pandemic A/H1N1/2009 influenza virus has enabled preexisting pandemic influenza plans to be put into action. This review examines the clinical and public health impact of this new virus.

RECENT FINDINGS

Although early figures suggested that this pandemic virus was causing higher morbidity and mortality than seasonal influenza viruses, subsequent studies have found it to cause milder disease in most cases. Yet, there are some groups with increased risk of serious disease from this new pathogen. The widespread use of antiviral agents, prophylactically and therapeutically, has led to the sporadic emergence of drug resistance, though this is still rare. Nonpharmacological public health interventions for containment and mitigation have been relatively ineffective in limiting the rapid, global spread of this pathogen. Recently, the focus has been on the manufacture and distribution of various specific vaccines against this new virus, and the care of severely ill patients admitted to intensive care.

SUMMARY

As this virus continues to infect new members of the global population, it may eventually become just one of the annual circulating seasonal influenza viruses. Until then, it will be prudent to continue to monitor it closely for any signs of enhanced transmissibility and virulence.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Differences in the epidemiological characteristics and clinical outcomes of pandemic (H1N1) 2009 influenza, compared with seasonal influenza

BACKGROUND

There are limited data comparing the clinical presentations, comorbidities, and outcomes of patients with infections due to seasonal influenza with patients with infections due to pandemic (H1N1) 2009 influenza.

OBJECTIVE

To compare the epidemiological characteristics and outcomes of pandemic (H1N1) 2009 influenza with those of seasonal influenza.

METHODS

A cross-sectional study was conducted among patients who received diagnoses during emergency department and inpatient encounters at 2 affiliated academic medical centers in Philadelphia, Pennsylvania. Cases of seasonal influenza during the period November 1, 2005, through June 1, 2008, and cases of pandemic influenza during the period from May 1, 2009, through August 7, 2009, were identified retrospectively.

RESULTS

Forty-nine cases of pandemic influenza and 503 cases of seasonal influenza were identified. Patients with pandemic H1N1 were younger (median age, 29 years) than patients with seasonal influenza (median age, 59 years) (P<.001). More patients with pandemic H1N1 (35 [71%] of 49) were African American, compared with patients with seasonal influenza (267 [53%] of 503; P=.02). Several symptoms were more common among patients with pandemic influenza infections than among patients with seasonal influenza infections: cough (98% vs 83%; P=.007), myalgias (71% vs 46%; P=.001), and pleuritic chest pain (45% vs 15%; P<.001). Pregnancy was the only comorbidity that occurred significantly more often in the pandemic influenza group than in the seasonal influenza group (16% vs 1%; P<.001). There were no significant differences in frequencies of deaths of hospitalized patients, intensive care unit admission, or length of hospitalization between groups.

CONCLUSION

Other than pregnancy, there were few clinically important differences between infections due to seasonal influenza and those due to pandemic influenza. The greater rate of lower respiratory tract symptoms in pandemic cases might serve to differentiate pandemic influenza from seasonal influenza.

Influenza virus evolution, host adaptation, and pandemic formation

Newly emerging or "re-emerging" viral diseases continue to pose significant global public health threats. Prototypic are influenza viruses that are major causes of human respiratory infections and mortality. Influenza viruses can cause zoonotic infections and adapt to humans, leading to sustained transmission and emergence of novel viruses. Mechanisms by which viruses evolve in one host, cause zoonotic infection, and adapt to a new host species remain unelucidated. Here, we review the evolution of influenza A viruses in their reservoir hosts and discuss genetic changes associated with introduction of novel viruses into humans, leading to pandemics and the establishment of seasonal viruses.

Swine flu - lessons learnt in Australia

What did we do well in the first year of pandemic (H1N1) 2009, and what can we do better?

H1N1 influenza: initial chest radiographic findings in helping predict patient outcome

PURPOSE

To retrospectively evaluate whether findings on initial chest radiographs of influenza A (H1N1) patients can help predict clinical outcome.

MATERIALS AND METHODS

Institutional review board approval was obtained; informed consent was waived. All adult patients admitted to the emergency department (May to September 2009) with a confirmed diagnosis of H1N1 influenza who underwent frontal chest radiography within 24 hours were included. Radiologic findings were characterized by type and pattern of opacities and zonal distribution. Major adverse outcome measures were mechanical ventilation and death.

RESULTS

Of 179 H1N1 influenza patients, 97 (54%) underwent chest radiography at admission; 39 (40%) of these had abnormal radiologic findings likely related to influenza infection and five (13%) of these 39 had adverse outcomes. Fifty-eight (60%) of 97 patients had normal radiographs; two (3%) of these had adverse outcomes (P = .113). Characteristic imaging findings included the following: ground-glass (69%), consolidation (59%), frequently patchy (41%), and nodular (28%) opacities. Bilateral opacities were common (62%), with involvement of multiple lung zones (72%). Findings in four or more zones and bilateral peripheral distribution occurred with significantly higher frequency in patients with adverse outcomes compared with patients with good outcomes (multizonal opacities: 60% vs 6%, P = .01; bilateral peripheral opacities: 60% vs 15%, P = .049).

CONCLUSION

Extensive involvement of both lungs, evidenced by the presence of multizonal and bilateral peripheral opacities, is associated with adverse prognosis. Initial chest radiography may have significance in helping predict clinical outcome but normal initial radiographs cannot exclude adverse outcome.

Inducible innate resistance of lung epithelium to infection

Most studies of innate immunity have focused on leukocytes such as neutrophils, macrophages, and natural killer cells. However, epithelial cells play key roles in innate defenses that include providing a mechanical barrier to microbial entry, signaling to leukocytes, and directly killing pathogens. Importantly, all these defenses are highly inducible in response to the sensing of microbial and host products. In healthy lungs, the level of innate immune epithelial function is low at baseline. This is indicated by low levels of spontaneous microbial killing and cytokine release, reflecting low constitutive stimulation in the nearly sterile lower respiratory tract when mucociliary clearance mechanisms are functioning effectively. This contrasts with the colon, where bacteria are continuously present and epithelial cells are constitutively activated. Although the surface area of the lungs presents a large target for microbial invasion, activated lung epithelial cells that are closely apposed to deposited pathogens are ideally positioned for microbial killing.

Structured regulation of inflammation during respiratory viral infection

Innate immune cells including macrophages, dendritic cells, and granulocytes are resident within or patrol very different microenvironments in the host. Their activity or responsiveness to antigen is dictated by site-specific factors. Because of the constant exposure to environmental antigens and commensal microorganisms, mucosal immunity needs to be more constrained than peripheral counterparts to prevent unnecessary inflammation. The epithelial surfaces that dominate all mucosal tissues provide an ideal regulator since innate immune cells are often in intimate contact with, or lie immediately beneath, them and a breach in epithelial integrity would signal a damaging event and release innate immunity from their influence. We discuss the role of the respiratory epithelium in raising the threshold of innate immune cell activation at homoeostasis, how its absence triggers innate immunity, and how inflammatory resolution often produces an altered homoeostatic environment that can affect the next inflammatory event at this site.

Complications of seasonal and pandemic influenza

Influenza is a seasonal viral infection associated with significant morbidity and mortality. In 2009, a novel H1N1 influenza A virus emerged and has been classified as a pandemic. In contrast to seasonal influenza, severe disease from pandemic H1N1 seems concentrated in older children and young adults, with almost no cases reported in patients older than 60 yrs. Although patients with underlying cardiopulmonary disease remain at risk, most complications have occurred among previously healthy individuals, with obesity and respiratory disease as the strongest risk factors. Pulmonary complications are common. Primary influenza pneumonia occurs most commonly in adults and may progress rapidly to acute lung injury requiring mechanical ventilation. Secondary bacterial infection is more common in children. Staphylococcus aureus, including methicillin-resistant strains, is an important cause of secondary bacterial pneumonia with a high mortality rate. Treatment of pneumonia should include empirical coverage for this pathogen. Neuromuscular and cardiac complications are unusual but may occur.

Bench-to-bedside review: bacterial pneumonia with influenza - pathogenesis and clinical implications

Seasonal and pandemic influenza are frequently complicated by bacterial infections, causing additional hospitalization and mortality. Secondary bacterial respiratory infection can be subdivided into combined viral/bacterial pneumonia and post-influenza pneumonia, which differ in their pathogenesis. During combined viral/bacterial infection, the virus, the bacterium and the host interact with each other. Post-influenza pneumonia may, at least in part, be due to resolution of inflammation caused by the primary viral infection. These mechanisms restore tissue homeostasis but greatly impair the host response against unrelated bacterial pathogens. In this review we summarize the underlying mechanisms leading to combined viral/bacterial infection or post-influenza pneumonia and highlight important considerations for effective treatment of bacterial pneumonia during and shortly after influenza.

Severity of pneumonia due to new H1N1 influenza virus in ferrets is intermediate between that due to seasonal H1N1 virus and highly pathogenic avian influenza H5N1 virus

Background. The newly emerged influenza A(H1N1) virus (new H1N1 virus) is causing the first influenza pandemic of this century. Three influenza pandemics of the previous century caused variable mortality, which largely depended on the development of severe pneumonia. However, the ability of the new H1N1 virus to cause pneumonia is poorly understood.

Methods. The new H1N1 virus was inoculated intratracheally into ferrets. Its ability to cause pneumonia was compared with that of seasonal influenza H1N1 virus and highly pathogenic avian influenza (HPAI) H5N1 virus by using clinical, virological, and pathological analyses.

Results. Our results showed that the new H1N1 virus causes pneumonia in ferrets intermediate in severity between that caused by seasonal H1N1 virus and by HPAI H5N1 virus. The new H1N1 virus replicated well throughout the lower respiratory tract and more extensively than did both seasonal H1N1 virus (which replicated mainly in the bronchi) and HPAI H5N1 virus (which replicated mainly in the alveoli). High loads of new H1N1 virus in lung tissue were associated with diffuse alveolar damage and mortality.

Conclusions. The new H1N1 virus may be intrinsically more pathogenic for humans than is seasonal H1N1 virus.

Influenza: The Once and Future Pandemic

Influenza A viruses infect large numbers of warm-blooded animals, including wild birds, domestic birds, pigs, horses, and humans. Influenza viruses can switch hosts to form new lineages in novel hosts. The most significant of these events is the emergence of antigenically novel influenza A viruses in humans, leading to pandemics. Influenza pandemics have been reported for at least 500 years, with inter-pandemic intervals averaging approximately 40 years.

Influenza: the once and future pandemic

Influenza A viruses infect large numbers of warm-blooded animals, including wild birds, domestic birds, pigs, horses, and humans. Influenza viruses can switch hosts to form new lineages in novel hosts. The most significant of these events is the emergence of antigenically novel influenza A viruses in humans, leading to pandemics. Influenza pandemics have been reported for at least 500 years, with inter-pandemic intervals averaging approximately 40 years.