Swine-origin Influenza A (H1N1) Virus Infection Research Articles

Immunophenotype Expressions and Cytokine Profiles of Influenza A H1N1 Virus Infection in Pediatric Patients in 2009

Background. A novel swine-origin influenza A H1N1 virus (S-OIV) caused human infection and acute respiratory illness in 2009, resulting in an influenza pandemic. Objectives. This study characterized the immune responses of S-OIV infection in pediatric patients at risk of pulmonary complications. Methods. All enrolled pediatric patients were confirmed virologically for S-OIV infection in 2009-2010, prospectively. Changes in cellular immunophenotypes were analyzed using flow cytometry. Plasma cytokine levels associated with S-OIV infection by pulmonary and without pulmonary complications were measured using cytokine cytometric bead assay kits. Results. A total of 85 patients with a mean age of 10.3 years were recruited. The level of C-reactive protein (CRP) was high in patients exhibiting pulmonary complications. The percentage of cellular immunophenotypes did not change between patients with and without pulmonary complications. The absolute numbers of peripheral blood mononuclear cells (PBMC), CD3, CD8, and CD16CD56 decreased with acute S-OIV pulmonary complications. Acute influenza infection with pulmonary complications was associated with high plasma concentrations of IL-1β, IL-6, IL-12, and IFN-γ. Conclusion. Immunophenotype studies have reported variability in immune response to the severity of S-OIV infections. Acute phase cytokine profiles of the 2009 S-OIV infection might have contributed to the pathogenesis of the pulmonary complications.

High-resolution computed tomography findings of swine-origin influenza A (H1N1) virus (S-OIV) infection: comparison with scrub typhus

Swine-origin influenza A (H1N1) virus (S-OIV) infection and scrub typhus, also known as tsutsugamushi disease can manifest as acute respiratory illnesses, particularly during the late fall or early winter, with similar radiographic findings, such as a predominance of ground-glass opacity (GGO). To differentiate S-OIV infection from scrub typhus using high-resolution computed tomography (HRCT). We retrospectively reviewed the HRCT findings of 14 patients with S-OIV infection and 10 patients with scrub typhus. We assessed the location, cross-sectional distribution, and the presence of a peribronchovascular distribution of GGO and consolidations on HRCT. We also assessed the presence of interlobular septal thickening, bronchial wall thickening, pneumothorax, pneumomediastinum, pleural effusion, and mediastinal or axillary lymph node enlargement. Scrub typhus was more common than S-OIV in elderly patients (P < 0.001). The monthly incidences of S-OIV and scrub typhus infection reached a peak between October and November. About 86% of S-OIV patients and 80% of scrub typhus patients presented with GGO. About 67% of the GGO lesions in S-OIV had a peribronchovascular distribution, but this was absent in scrub typhus (P = 0.005). Consolidation (93% vs. 10%, P < 0.001) and bronchial wall thickening (43% vs. 0%, P = 0.024) were more frequent in S-OIV infection than scrub typhus. Interlobular septal thickening (90% vs. 36%, P = 0.013) and axillary lymphadenopathy (90% vs. 0%, P < 0.001) were more common in scrub typhus than S-OIV infection. There was considerable overlap in HRCT findings between S-OIV infection and scrub typhus. However, S-OIV showed a distinctive peribronchovascular distribution of GGO lesions. Consolidation and bronchial wall thickening were seen more frequently in S-OIV infection, whereas interlobular septal thickening and axillary lymphadenopathy were more common in scrub typhus. Thus, CT could be helpful for differential diagnosis between S-OIV infection and scrub typhus.

Serial evaluation of high-resolution CT findings in patients with pneumonia in novel swine-origin influenza A (H1N1) virus infection

The purpose of our study was to review the changes in the serial high-resolution CT (HRCT) findings from patients with novel swine-origin influenza A (H1N1) virus (S-OIV) infection. HRCT findings of 70 patients with presumed or laboratory-confirmed novel S-OIV infection were reviewed. The pattern (consolidation, ground glass, fibrosis and air trapping), distribution and extent of abnormality of the lesions on the HRCT were evaluated at different time points. To assess changes that occurred over time, the CT scans in 56 patients were examined in sequence. The most common CT findings in patients with S-OIV infection are ground-glass opacities with or without consolidation at the first week. The abnormalities peaked at the second week and resolved after that time, which resulted in substantial reduced residual disease at 4 weeks or later. The development of fibrosis was noted in the first week and peaked at the third week of illness (34.7%), then decreased slowly after that time. The mean time of air trapping being noted after the onset of symptoms was 55.5 ± 20.6 days. Comparing the findings of initial CT, most results (96.4%) of follow-up chest CT findings showed improvement (p<0.01). The abnormalities of ground-glass opacities and/or consolidation on initial CT scans tended to resolve to fibrosis, which then resolved completely or displayed substantially reduced residual disease. HRCT may show more changes in disease progression and play an important role in the evaluation of severe S-OIV.

H1N1 pneumonia: our experience in 50 patients with a severe clinical course of novel swine-origin influenza A (H1N1) virus (S-OIV).

PurposeThe authors reviewed chest radiographs (CXR) and thin-section computed tomography (CT) findings of pulmonary complications in a selected population of 50 consecutive patients with severe novel swine-origin influenza A (H1N1) virus (S-OIV) pneumonia who were seen at the Subintensive Respiratory Unit (UTSIR) and at the Intensive Care Unit (ICU) at Monaldi Hospital, Naples, Italy.Materials and methodsCXR and CT findings of 50 patients who fulfilled the World Health Organisation (WHO) criteria for S-OIV infection were reviewed by four radiologists. The final study group of 50 patients was divided into two subgroups on the basis of clinical course: group 1 consisted of 42 patients requiring noninvasive mechanical ventilation and admitted to the UTSIR; group 2 consisted of eight patients who required ICU admission and extracorporeal membrane oxygenation or advanced mechanical ventilation from October 2009 to December 2009. All patients underwent CXR and thinsection multidetector CT (MDCT) scan; the initial and follow-up radiographs and CT scans were evaluated for the presentation and follow-up pattern (consolidation, groundglass opacities, nodules, reticulation), distribution and extent of abnormality.ResultsAll patients had radiological signs of pulmonary involvement. Ground-glass opacity and consolidation, which was mainly peripheral, was the most frequent finding. In three patients, we report for the first time in viral pneumonia the reversed halo sign. Lesion extent was related to aggressiveness of the illness. More often, both lungs were involved (82%). Thoracic comorbidity was present in 18% of patients; 22% of patients was obese, and in this group, the clinical course was more aggressive than in the others with the same lesion extent at imaging. Furthermore, superinfection led to worsening of the clinical conditions.ConclusionsThe most common CXR and CT findings in patients with S-OIV infection were unilateral or bilateral ground-glass opacities with or without associated focal or multifocal areas of consolidation. On MDCT, ground-glass opacities and areas of consolidation had a predominant peribronchovascular and subpleural distribution, resembling organising pneumonia; they progressed to bilateral extensive airspace disease in severely ill patients.

Pneumonia induced by swine-origin influenza A (H1N1) infection: chest computed tomography findings in children.

PurposeThe purpose of this study was to determine the features of chest computed tomography (CT) in children with swine-origin influenza A (H1N1) virus (S-OIV).Materials and methodsThe study population consisted of 16 children with laboratory-confirmed S-OIV infection (12 boys, 4 girls), with an age range of 5–10 years (mean 6.3 years). Pneumonia was suspected in these patients based on clinical features or confirmed by radiography. All subjects underwent CT for close evaluation of pneumonia, including characteristics, distribution, extent, and other findings such as pleural effusion, pneumothorax, and pneumomediastinum.ResultsThe predominant CT finding was consolidation plus ground-grass opacity (GGO) (11/16, 69%). The consolidation-dominant pattern was found in 10 of 16 (66%) patients, and 1 (6%) was GGO-dominant. One (6%) had only GGO. In all, 7 of the 16 patients had segmental or lobar consolidation. Abnormal opacities were primarily distributed in the central lung zone (8/16, 50%) and were multifocal (15/16, 94%). Four showed atelectasis (4/16, 25%). Pneumomediastinum was observed in 4 of 16 (25%). One patient had negative radiographic findings but was positive on CT.ConclusionMultifocal consolidation with central distribution is a common CT finding in children with S-OIV, but there are few GGO-dominant cases. Widespread consolidation (segmental or lobar) is also common.

Detection of swine-origin influenza A (H1N1) viruses using a localized surface plasmon coupled fluorescence fiber-optic biosensor

Swine-origin influenza A (H1N1) virus (S-OIV) was identified as a new reassortant strain of influenza A virus in April 2009 and led to an influenza pandemic. Accurate and timely diagnoses are crucial for the control of influenza disease. We developed a localized surface plasmon coupled fluorescence fiber-optic biosensor (LSPCF-FOB) which combines a sandwich immunoassay with the LSP technique using antibodies against the hemagglutinin (HA) proteins of S-OIVs. The detection limit of the LSPCF-FOB for recombinant S-OIV H1 protein detection was estimated at 13.9 pg/mL, which is 10 3-fold better than that of conventional capture ELISA when using the same capture antibodies. For clinical S-OIV isolates measurement, meanwhile, the detection limit of the LSPCF-FOB platform was calculated to be 8.25 × 10 4 copies/mL, compared with 2.06 × 10 6 copies/mL using conventional capture ELISA. Furthermore, in comparison with the influenza A/B rapid test, the detection limit of the LSPCF-FOB for S-OIV was almost 50-fold in PBS solution and 25-fold lower in mimic solution, which used nasal mucosa from healthy donors as the diluent. The findings of this study therefore indicate that the high detection sensitivity and specificity of the LSPCF-FOB make it a potentially effective diagnostic tool for clinical S-OIV infection and this technique has the potential to be applied to the development of other clinical microbe detection platforms.

Pneumonia in novel swine-origin influenza A (H1N1) virus infection: High-resolution CT findings

Objective The purpose of our study was to review the initial high-resolution CT (HRCT) findings in pneumonia patients with presumed/laboratory-confirmed novel swine-origin influenza A (H1N1) virus (S-OIV) infection and detect pneumonia earlier. Materials and methods High-resolution CT (HRCT) findings of 106 patients with presumed/laboratory-confirmed novel S-OIV (H1N1) infection were reviewed. The 106 patients were divided into two groups according to the serious condition of the diseases. The pattern (consolidation, ground-glass, nodules, and reticulation), distribution, and extent of abnormality on the HRCT were evaluated in both groups. The dates of the onset of symptoms of the patients were recorded. Results The predominant CT findings in the patients at presentation were unilateral or bilateral multifocal asymmetric ground-glass opacities alone ( n = 29, 27.4%), with unilateral or bilateral consolidation ( n = 50, 47.2%). The consolidation had peribronchovascular and subpleural predominance. The areas of consolidation were found mainly in the posterior, middle and lower regions of the lungs. Reticular opacities were found in 6 cases of the initial MDCT scan. The extent of disease was greater in group 1 patients requiring advanced mechanical ventilation, with diffuse involvement in 19 patients (63.3%) of group 1 patients, and only 15/76 (19.7%) of group 2 patients ( p < 0.01, χ 2 test). 20 cases (19%) of the 106 patients had small bilateral or unilateral pleural effusions. None had evidence of hilar or mediastinal lymph node enlargement on CT performed at admission or later. Conclusions The most common radiographic and CT findings in patients with S-OIV infection are unilateral or bilateral ground-glass opacities with or without associated focal or multifocal areas of consolidation. On HRCT, the ground-glass opacities had a predominant peribronchovascular and subpleural distribution. CT plays an important role in the early recognition of severe S-OIV (H1N1).

Prise en charge dans un service d’urgence de l’épidémie à virus pandémique A(H1N1) 2009 à Saint-Pierre, île de La Réunion. Juillet–Août 2009

The 2009 pandemic influenza A (H1N1) virus has emerged to cause the first pandemic of the 21st century. On July 3, 2009, novel swine-origin influenza A (H1N1) virus (S-OIV) was identified in Reunion Island, French overseas department located in the southern hemisphere. The present study describes the characteristics and the impact of the epidemic on the activity of an emergency department (ED) from July 3 to August 31, 2009. Patients consulting the ED with a discharge diagnosis of influenza-like illness were analyzed. The ED activity in 2009, compared to 2008, increased by 0.5% in July and 9.7% in August. In July and August, respectively 7.1 and 20.0% cases of S-OIV infection were hospitalized. For the 394 patients studied (186 males, 36.2+/-18.5 years), 199 (50.5%) were reported to have comorbidity or risk factor (RF) for complications. Complications occurred in 112 patients (28.4%). The most common complications were bronchospasme (52.7%), pneumonia (32.1%), decompensation caused by comorbidity (17.9%). Seventy-three patients (18.5%) required hospitalization. Patients aged 65 and over accounted for 10.9% of all patients, 31.5% of hospitalized patients and 21.4% of complicated S-OIV infection. Regardless of age, comorbidity and / or RF was reported in 80.2% of complicated S-OIV infection and 86.3% of hospitalized patients. The circuit of patients with S-OIV infection was initially focused on "consultation S-OIV" localized in ED. This organization mobilized several health professionals, disorganized the various medical departments involved, and was unsuitable for the childcare or patient's monitoring with signs of poor tolerance. This organization, even identifying S-OIV patients at their arrival, referred patients to different areas of the hospital and various consultation rooms in ED. Recommendations for surveillance, prevention and policy for persons with RF, particularly respiratory disease, are justified. This feedback can raise questions about the patient's circulation in hospital and adjust plans for the organization.

CT Utilization in the Prospective Diagnosis of a Case of Swine-Origin Influenza A (H1N1) Viral Infection

The purpose of this paper is to demonstrate the potential role of CT in the early diagnosis of swine-origin influenza A (H1N1) virus (S-OIV) pneumonia. We present a case of acute influenza-like illness in which the CT findings of peribronchovascular and subpleural ground-glass opacities and consolidation resembled organizing pneumonia, and lead the radiologist to prospectively and correctly suggest the diagnosis of S-OIV infection.

CT manifestations of patients with swine-origin influenza A H1N1 QI

Objective To explore the manifestations of chest multi-slice spiral CT in patients with initial infection of swine-origin influenza A (H1N1) virus (S-OIV). Methods The chest multi-slices spirals CT images of 19 firstly diagnosed patients with swine-origin influenza A (H1N1) in our institution were retrospectively studied. CT manifestations were evaluated by three experienced radiologists. Location, appearance of lung abnormalities, abnormal distribution, pleural effusion and others (pericadiaum, lymphadenopathy and pleural thickening) were observed and quantitatively analyzed. The correlation of ground-glass and consolidation CT scores with the fever time was studied. Results The abnormal CT findings were observed bilaterally in 18 of 19 subjects including ground-glass (n= 3), consolidation (n=3 ), consolidation accompanied with ground-glass (n=12). Most of these lesions were distributed diffusively (n=14) while the others located in the middle and low lobes (n= 4). Unilateral (n=3) or bilateral (n=2) pleural effusion were observed. Lymphadenopathy (n=2), effusion of pericadium (n=1), pleural thickening (n=1) and cardiac enlargement (n=2) were also found in patients with H1N1. CT scores of ground-glass were 4. 25(n=2),3.75 (n=1),2.25(n=1),1.75(n=1),1.00(n=6),0.75(n=2), 0.50(n=2),0(n=4).CT scores of consolidation were4.25(n=1),4.00(n=1),3.75 (n=1), 2.75(n=1),1.25(n=3),1.00(n=2),0.75(n=2),0.50(n=1),0.25(n=3),0(n=4). CT scores of ground-glass were significantly correlated with the fever time (r= 0.776, P 0.01). Conclusions The most common CT findings in patients with S-OIV infection are diffuse distribution of bilateral ground-glass opacities with or without associated focal or multifocal areas of consolidation. The increasing of ground-glass's range could be the marker of progression of H1N1 pulmonary infection at initial stage. Key words: Influenza,human; Pneumonia,viral; Tomography, X-ray computed

Cytokine Profiles Induced by the Novel Swine‐Origin Influenza A/H1N1 Virus: Implications for Treatment Strategies

Background. Given the apparent high mortality associated with the novel swine-origin influenza A/H1N1 virus (S-OIV) in Mexico, we aimed to study the cytokine profiles induced by S-OIV and the effect of immunomodulators. Methods. We assayed cytokines and their messenger RNA (mRNA) levels in culture supernatants of human macrophages infected with H5N1, S-OIV California/04/2009 (S-OIV-CA), S-OIV Hong Kong/415742 (S-OIV-HK), or seasonal H1N1 with or without celecoxib and mesalazine. Results. Among the 12 cytokines showing detectable levels, levels of 8 proinflammatory cytokines (interleukin [IL] 2R, IL-6, interferon [IFN] α, macrophage inflammatory protein [MIP] α, MIP-1b, IFN-induced protein 10, regulated on activation, normal T cell expressed and secreted [RANTES], and monocyte chemotactic protein [MCP] 1) were higher in cells infected by H5N1 but similar among cells infected with H1N1, S-OIV-CA, or SOIV- HK. The levels of the other 4 cytokines were similar for H5N1, H1N1, S-OIV-CA and S-OIV-HK. Among the 8 cytokines induced by H5N1, 6 were suppressed by celecoxib and mesalazine. The mRNA levels of tumor necrosis factor a, IFN-γ, IL-6, and MCP-1 induced by H5N1 were higher than the levels of other cytokines at 12 and/or 24 h. Conclusions. No major cytokine storm, as seen in H5N1 infection, is associated with S-OIV infection of cell lines. The mainstay of treatment for uncomplicated S-OIV infections should be antiviral agents without immunomodulators. For individual S-OIV-infected patients with severe primary viral pneumonia, severe sepsis, and multiorgan failure, immunomodulators may be considered as an adjunctive therapy in clinical trials.

Swine-Origin Influenza A (H1N1) Viral Infection: Radiographic and CT Findings

The objective of our study was to review the chest radiographic and CT findings in patients with swine-origin influenza A (H1N1) virus (S-OIV) infection. The most common radiographic and CT findings in seven patients with S-OIV infection are unilateral or bilateral ground-glass opacities with or without associated focal or multifocal areas of consolidation. On MDCT, the ground-glass opacities and areas of consolidation had a predominant peribronchovascular and subpleural distribution, resembling organizing pneumonia.

Chest Radiographic and CT Findings in Novel Swine-Origin Influenza A (H1N1) Virus (S-OIV) Infection

This article reviews the chest radiographic and CT findings in patients with presumed/laboratory-confirmed novel swine-origin influenza A (H1N1) virus (S-OIV) infection. Of 222 patients with novel S-OIV (H1N1) infection seen from May 2009 to July 2009, 66 patients (30%) who underwent chest radiographs formed the study population. Group 1 patients (n = 14) required ICU admission and advanced mechanical ventilation, and group 2 (n = 52) did not. The initial radiographs were evaluated for the pattern (consolidation, ground-glass, nodules, and reticulation), distribution, and extent of abnormality. Chest CT scans (n = 15) were reviewed for the same findings and for pulmonary embolism (PE) when performed using IV contrast medium. Group 1 patients were predominantly male with a higher mean age (43.5 years versus 22.1 years in group 2; p < 0.001). The initial radiograph was abnormal in 28 of 66 (42%) subjects. The predominant radiographic finding was patchy consolidation (14/28; 50%) most commonly in the lower (20/28; 71%) and central lung zones (20/28; 71%). All group 1 patients had abnormal initial radiographs; extensive disease involving > or = 3 lung zones was seen in 93% (13/14) versus 9.6% (5/52) in group 2 (p < 0.001). No group 2 patients had > 20% overall lung involvement on initial radiographs compared with 93% of group 1 patients (13/14). PEs were seen on CT in 5/14 (36%) of group 1 patients. Chest radiographs are normal in more than half of patients with S-OIV (H1N1) and progress to bilateral extensive air-space disease in severely ill patients, who are at a high risk for PE.

Influenza A H1N1 Virus Infection in Two Hematopoietic Stem Cell Transplant Recipients.

Abstract 1169Poster Board I-191In April 2009, a novel swine-origin influenza A (H1N1) virus (S-OIV) was identified in Mexico. Since then, several cases have been reported, with subsequent cases observed in many other countries. Clinical presentation may range from mild symptomatic patients to cases of severe clinical presentation and death due to pneumonia and respiratory failure. Definition of high risk groups are thought to be similar to those defined for seasonal influenza, including young children and elderly patients, pregnant women and patients with chronic medical conditions, especially immunocompromised hosts. Hematopoietic stem cell transplant (HSCT) recipients are at high risk for infectious complications, including severe viral infections. To our knowledge, there are no reported cases of S-OIV infection in HSCT recipients to date. The clinical features and the possible consequences of this novel influenza virus in this setting remain unknown. We describe two HSCT recipients with confirmed influenza H1N1 virus infection and a benign clinical course after oseltamivir treatment. The first case is a 12 year-old male patient with diagnosis of acute myelogenous leukemia in second complete remission who underwent an unrelated umbilical cord blood transplant with two 4/6 HLA-mismatched cord blood units. Graft-versus-host disease (GVHD) prophylaxis consisted of the association of cyclosporine and mycophenolate mofetil. Additionally, he was also being treated for an invasive aspergillosis with oral voriconazole. On day+3 after transplant, he developed fever, rhinorrhea, and dry cough. A nasal wash and a nasal swab were positive for influenza A by direct immune fluorescence and for influenza A H1N1 by real-time polymerase chain reaction (RT-PCR). Computed tomography of the nasal sinus and thorax were unremarkable. Oseltamivir therapy (75 mg po twice daily for 10 days) was initiated the same day with progressive improvement of symptoms. Oseltamivir was well tolerated and there was no interference with serum levels of cyclosporine. The second case is a 30 year-old female patient with gray zone non-Hodgkin lymphoma in relapse after autologous stem cell transplant that underwent an HLA-matched related HSCT in September 2008. She relapsed 6 months after the transplant. Cyclosporine was withdrawn. Ten days later, she developed fever rhinorrhea, and myalgia. Influenza A H1N1 was confirmed by RT-PCR of a nasal wash specimen. Treatment with a 5-day course of oseltamivir (75 mg po twice daily) was initiated and the patient had a favorable clinical course, with no complications. These two cases of confirmed influenza H1N1 virus infection in HSCT recipients with a benign clinical course highlight the need for a better understanding of the clinical course and management of this novel viral agent in severely immunocompromised hosts. Disclosures:No relevant conflicts of interest to declare.

Pneumonia and Respiratory Failure from Swine-Origin Influenza A (H1N1) in Mexico

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. 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. 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. 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.

Emergence of a Novel Swine-Origin Influenza A (H1N1) Virus in Humans

On April 15 and April 17, 2009, novel swine-origin influenza A (H1N1) virus (S-OIV) was identified in specimens obtained from two epidemiologically unlinked patients in the United States. The same strain of the virus was identified in Mexico, Canada, and elsewhere. We describe 642 confirmed cases of human S-OIV infection identified from the rapidly evolving U.S. outbreak. Enhanced surveillance was implemented in the United States for human infection with influenza A viruses that could not be subtyped. Specimens were sent to the Centers for Disease Control and Prevention for real-time reverse-transcriptase-polymerase-chain-reaction confirmatory testing for S-OIV. From April 15 through May 5, a total of 642 confirmed cases of S-OIV infection were identified in 41 states. The ages of patients ranged from 3 months to 81 years; 60% of patients were 18 years of age or younger. Of patients with available data, 18% had recently traveled to Mexico, and 16% were identified from school outbreaks of S-OIV infection. The most common presenting symptoms were fever (94% of patients), cough (92%), and sore throat (66%); 25% of patients had diarrhea, and 25% had vomiting. Of the 399 patients for whom hospitalization status was known, 36 (9%) required hospitalization. Of 22 hospitalized patients with available data, 12 had characteristics that conferred an increased risk of severe seasonal influenza, 11 had pneumonia, 8 required admission to an intensive care unit, 4 had respiratory failure, and 2 died. The S-OIV was determined to have a unique genome composition that had not been identified previously. A novel swine-origin influenza A virus was identified as the cause of outbreaks of febrile respiratory infection ranging from self-limited to severe illness. It is likely that the number of confirmed cases underestimates the number of cases that have occurred.

The CDC’s Report on the New Swine-Origin Influenza A (H1N1) Virus

The CDC has published the data and epidemiology for confirmed cases of human infection with the new circulating swine-origin influenza A (H1N1) virus (S-OIV) in the U.S. The virus contains genes from swine, avian, and human influenza. This strain was detected when routine public health surveillance indicated that a collected isolate tested positive for influenza A virus but negative for human H1 or H3 subtypes. Modifications of existing assays were developed to detect S-OIV by reverse-transcriptase–polymerase chain reaction (RT-PCR). A total of 642 cases of S-OIV infection from 41 states were confirmed from April 15 through …