Influenza A (H1N1) pneumonia: an analysis of 63 cases by chest CT

BACKGROUND

In early April 2009, cases of human infection with 2009 pandemic influenza A (H1N1) virus were identified in Mexico. The virus then spread rapidly to other regions of the world. From October 2009, sporadic imported cases of novel influenza A (H1N1) were continuously confirmed in Suzhou. The aim of the study was to review the chest CT findings in 63 patients with laboratory-confirmed novel swine-origin influenza A (H1N1) virus (S-OIV) infection.

METHODS

Chest CT examinations were collected from 63 S-OIV infected patients during their hospital stay. Three experienced radiologists inspected images to qualitatively and quantitatively characterize S-OIV induced image changes. CT scores of lesion severity were calculated based on the percentage of affected area to determine severity of infectious lesions. Patients were divided into two groups based on the leukocyte counts. Lesion patterns, local distributions, and quantitative measures were investigated and compared between the two groups.

RESULTS

Various degrees of bilateral multifocal lesions of ground-glass opacities were found with or without consolidations on the chest CT images. The lesions were both bronchocentric and centrilobular. Patients with elevated leukocyte counts had more extensive lesions, in terms of severity and affected area, than the patients with normal leukocyte counts. The lesion severity scores of patients in the elevated leukocyte group were significantly higher than those of the normal leukocyte group in terms of the entire lung area (P < 0.01), and upper (P < 0.05) and lower (P < 0.01) lobes as well. There were changes in the CT characteristics seen at follow-up as demonstrated by lesions absorption (P < 0.01), especially in the upper lobe of the lung (P < 0.01), but less so in the middle lobe/lingual and lower lobe of the lung (P > 0.05).

CONCLUSIONS

The most common CT findings in S-OIV infection patients were bilateral multifocal distributed ground-glass opacities and consolidations. The lesions were located dominantly at bronchocentric and centrilobular areas. Lung lesions were more obviously absorbed in upper lobes between two examinations. The observations and analysis from this study provide information that may be useful in image understanding and patient management for future pandemic influenza.

Various computed tomography findings of 2009 H1N1 influenza in 17 patients with relatively mild illness

Purpose

We retrospectively analyzed the computed tomography (CT) findings of H1N1 virus infection in 17 patients with relatively mild illness.

Materials and methods

From September 2009 to January 2010, a total of 17 patients with confirmed H1N1 infection were included in the study (mean age 30.7 years). All patients were managed as outpatients or required short hospitalization without ventilation assistance. The CT scans were assessed for the presence of nodules, ground glass opacity (GGO), consolidation, bronchial wall thickening, reticulation, effusion, and lymph node enlargement. Location and distribution were evaluated.

Results

The most frequent manifestation was a mixture of nodules, consolidation, and GGO (5/17, 29.4%). In one case there was a focal area of bronchiolitis (centrilobular nodules with tree-in-bud appearance), and 10 of 17 cases (58.8%) showed bronchial wall thickening (findings of bronchitis/peribronchitis) and/or other abnormalities. In 16 of the 17 cases (94.1%) there were CT abnormalities with bilateral and random distribution without zonal predominance. Pleural effusions were seen in eight cases (47.1%).

Conclusion

In contrast to several reports so far, CT findings of H1N1 virus infection in patients with mild illness are variable, including suggestive findings of inflammation involving large and/or small airways. This study showed various CT findings overlapping with other viral, atypical, or bacterial pneumonia and even cryptogenic organizing pneumonia.

Outcome of pandemic H1N1 pneumonia: clinical and radiological findings for severity assessment

BACKGROUND/AIMS

Pandemic influenza A (H1N1) virus infection presents with variable severity. However, little is known about clinical predictors of disease severity. We studied the clinical predictors of severe pandemic H1N1 pneumonia and their correlation with radiological findings.

METHODS

We reviewed medical and radiological records of adults with pandemic H1N1 pneumonia. After classification of patients into severe and non-severe groups, the following data were evaluated: demographic data, pneumonia severity index (PSI), CURB65, risk factors, time to first dose of antiviral medication, routine laboratory data, clinical outcome, and radiological characteristics.

RESULTS

Of 37 patients with pandemic H1N1 pneumonia, 12 and 25 were assigned to the severe and non-severe groups, respectively. PSI score, serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dyhydrogenase (LDH) levels were higher in the severe group than in the non-severe group (p = 0.035, 0.0003, 0.0023, and 0.0002, respectively). AST, ALT, and LDH levels were positively correlated with the radiological findings (p < 0.0001, 0.0003, and < 0.0001, respectively) and with the number of involved lobes (p = 0.663, 0.0134, and 0.0019, respectively). The most common finding on high resolution computed tomography (HRCT) scans was ground-glass attenuation with consolidation (n = 22, 60%), which had a predominantly patchy distribution (n = 31).

CONCLUSIONS

We demonstrated a positive correlation between clinical findings, such as serum AST, ALT, and LDH levels, and radiological findings. A combination of clinical and HRCT indicators would be useful in predicting the clinical outcome of pandemic H1N1 pneumonia.

Radiological prognostic factors in patients with pandemic H1N1 (pH1N1) infection requiring hospital admission

The aim of this study was to determine the radiologic findings associated with admission to the intensive care unit (ICU) and the development of acute respiratory distress syndrome (ARDS) in patients with pH1N1 infection. One hundred and four patients (15-96 years) with laboratory-confirmed pH1N1 infection seen at the Emergency Department from July to December 2009 who underwent chest radiographs were studied. Radiographs were evaluated for consolidation, ground-glass opacities, interstitial patterns, distribution, and extent of findings. Eighty-seven (83.7%) of the patients were managed in the ward, and 17 (16.3%) patients eventually required admission to the ICU. All patients admitted to the ICU showed abnormalities on the initial radiograph. The presence of consolidation, multifocal, diffuse, and bilateral involvement on the initial radiograph was associated with a statistically higher risk of requiring ICU admission (p<0.001). There were no significant differences regarding age, sex, and presence of underlying comorbidities. Evolution to ARDS was found in eight cases that necessitated ICU care. All of them had on the initial radiograph patchy multifocal consolidations (p<0.001) with bilateral lesions in six cases. A higher number of lung zones involved and consolidation on the initial chest radiograph as well as a rapid progression of the radiological abnormalities were identified in patients requiring ICU admission and development of ARDS. Initial chest radiographs show acute abnormalities in all patients with severe disease. The findings of a multifocal patchy consolidation pattern with bilateral or diffuse lung involvement on admission should alert of the impending severity of disease and the risk of necessitating ICU admission.

Pulmonary pathology of pandemic influenza A/H1N1 virus (2009)-infected ferrets upon longitudinal evaluation by computed tomography

We investigated the development of pulmonary lesions in ferrets by means of computed tomography (CT) following infection with the 2009 pandemic A/H1N1 influenza virus and compared the scans with gross pathology, histopathology and immunohistochemistry. Ground-glass opacities observed by CT scanning in all infected lungs corresponded to areas of alveolar oedema at necropsy. These areas were most pronounced on day 3 and gradually decreased from days 4 to 7 post-infection. This pilot study shows that the non-invasive imaging procedure allows quantification and characterization of influenza-induced pulmonary lesions in living animals under biosafety level 3 conditions and can thus be used in pre-clinical pharmaceutical efficacy studies.

Computer-aided diagnosis of pulmonary infections using texture analysis and support vector machine classification

RATIONALE AND OBJECTIVES

The purpose of this study was to develop and test a computer-assisted detection method for the identification and measurement of pulmonary abnormalities on chest computed tomographic (CT) imaging in cases of infection, such as novel H1N1 influenza. The method developed could be a potentially useful tool for classifying and quantifying pulmonary infectious disease on CT imaging.

MATERIALS AND METHODS

Forty chest CT examinations were studied using texture analysis and support vector machine classification to differentiate normal from abnormal lung regions on CT imaging, including 10 patients with immunohistochemistry-proven infection, 10 normal controls, and 20 patients with fibrosis.

RESULTS

Statistically significant differences in the receiver-operating characteristic curves for detecting abnormal regions in H1N1 infection were obtained between normal lung and regions of fibrosis, with significant differences in texture features of different infections. These differences enabled the quantification of abnormal lung volumes on CT imaging.

CONCLUSION

Texture analysis and support vector machine classification can distinguish between areas of abnormality in acute infection and areas of chronic fibrosis, differentiate lesions having consolidative and ground-glass appearances, and quantify those texture features to increase the precision of CT scoring as a potential tool for measuring disease progression and severity.

[Chest radiographic findings in children with 2009 influenza A (H1N1) virus infection]

OBJECTIVE

To evaluate chest radiographic findings of children with 2009 influenza (H1N1) virus infection.

METHOD

Data of 235 patients who had microbiologically confirmed H1N1 infection and available chest radiograph obtained between May 1(st) 2009 and Jan. 31(st) 2010 were retrospectively analyzed. The final study group was divided on the basis of clinical course [group 1 mild, outpatients without hospitalization (n = 172); group 2 moderate, inpatients with brief hospitalization (n = 49); group 3 severe, ICU admission (n = 14)]. Four pediatric radiologists reviewed all the chest radiographs of lung parenchyma, airway, pleural abnormalities and also anatomic distribution of the disease.

RESULT

No significant sex or age differences were found among the study groups (P > 0.05). The mean interval between the onset of clinical symptom and the initial chest radiography was (5.91 ± 1.64) days (group 1), (3.60 ± 1.43) days (group 2) and (1.21 ± 0.41) days (group 3), respectively. The differences among the three groups were significant statistically (χ(2) = 13.368, P < 0.01). The ratio of abnormality presented at initial chest X-ray was 79.7% in group 1, 91.8% in group 2 and 100% in group 3. Radiographically, there were prominent peribronchial markings (group 1, 55.2%; group 2, 83.7%; and group 3, 78.6%), consolidation (group 1, 34.3%; group 2, 69.4%; and group 3, 100.0%), hyperinflation (group 1, 22.1%; group 2, 44.9%; and group 3, 50.0%) and ground glass opacity (group 1, 0.6%; group 2, 2.0%; and group 3, 14.3%) in the chest radiographs. The differences of presenting were statistically significant (P < 0.01). In the severe group, the lesions distributed diffusely and asymmetrically with multi-lobe involvements.

CONCLUSION

In children with 2009 influenza A H1N1 viral infection, the interval between the onset of clinical symptom and initial chest radiography, the ratio of abnormality presented at initial chest X-ray film and the severity of chest film are parallel to their clinical situation.

Chest imaging findings in children with influenza A H1N1

OBJECTIVE

To assess imaging findings at presentation in children diagnosed with influenza A (H1N1) infection.

METHODS

This is a retrospective observational cohort study conducted at The Children's Hospital affiliated to Soochow University, Suzhou, China between September 2009 and March 2010. Nasopharyngeal swabs and bronchial aspirate samples from 81 children with acute respiratory infections were tested positive for influenza A (H1N1) using quantitative real-time polymerase chain reaction. Chest imaging for these patients was analyzed retrospectively by 2 independent radiologists for the presence and distribution of abnormalities.

RESULTS

Chest radiograph findings consisted of bilateral patchy areas of consolidation (n=48), diffuse areas of air-space consolidation (n=18), and lobar consolidation (n=7). Eight chest x-rays were normal. Abnormalities were observed more frequently in the lower lobes (bilateral [n=66], unilateral [n=7]). Computed tomography (CT) scans were performed in 18 cases with air-space consolidation and interstitial opacities. Cases with diffuse areas of air-space consolidation were followed-up after 3 months by high resolution CT imaging, which showed interstitial thickening.

CONCLUSION

The predominant imaging findings in childhood influenza A (H1N1) were bilateral patchy areas of consolidation, followed by diffuse areas of air-space consolidation, normal radiographs, and lobar consolidation.

[Causes, complications and risk factors of severe influenza A (H1N1)]

Analysis of 35 deaths from A(H1N1) influenza virus infection in the Transbaikal region (autumn 2009) is reported. All the cases were under 60 years of age. Viral/bacterial pneumonia complicated by acute respiratory distress syndrome (ARDS) was the main cause of fatal outcomes. Enteroccocci were found in 83.3% of the seeded autopsy samples. Possible enterococcal infection pathways and mechanisms of ARDS development are discussed. The role of heat shock proteins is postulated. Disturbances of lipid metabolism are supposed to be major risk factors of severe influenza and its fatal outcome that may be related to obesity through common pathogenetic pathways.

[Case of novel influenza A (H1N1) pneumonia with shrinkage of a pulmonary lesion]

Fever developed in a 56-year-old man with sarcoidosis and bronchial asthma, and influenza was diagnosed. He was given zanamivir on the day of diagnosis, but he suffered a bronchial asthma attack 4 days after the diagnosis of influenza, and pneumonia developed 7 days subsequently. He was then admitted to our hospital. A rapid antigen test was positive for influenza type A, and reverse-transcriptase polymerase chain reaction results were also positive for novel influenza A (H1N1). Chest computed tomography showed homogeneous ground-glass opacities in bilateral lung fields, and novel influenza A (H1N1) pneumonia was diagnosed. The patient was treated with oseltamivir and steroid therapy for the bronchial asthma attack; however, ground-glass opacities enlarged and became consolidated. The lower lobes of both lungs showed shrinkage and persistent volume loss. Improvement in the consolidation was accompanied by improvement in his respiratory condition. We report a case with an interesting radiological course.

CT onset of influenza A (H1N1) complicated with severe pneumonia in two typical cases

The novel influenza A (H1N1) virus developed in the United States and Mexico in April 2009 and has spread worldwide rapidly. Pulmonary complications are major reason of death associated with influenza A (H1N1) infection. Thus, it is necessary to investigate characteristics on the turnover of A (H1N1) infection complicated with pneumonia. Although the chest radiographic findings of the influenza A (H1N1) pneumonia were described in a clinical report, the CT findings involving turnover of influenza A (H1N1) complicated with severe pneumonia have not yet been reported. We report two typical cases of novel influenza A (H1N1) pneumonia with chest CT findings and investigate features and turnover of influenza A(H1N1) pneumonia. From the CT appearance of two cases, we found that influenza A(H1N1) complicated with pneumonia might progress rapidly, but it would recover in two or three weeks once it was controlled effectively. The CT images in our report might help the clinician to clearly understand the patterns of onset, progression and outcomes in influenza A(H1N1) complicated with pneumonia.

Novel influenza A (H1N1) infection: chest CT findings from 21 cases in Seoul, Korea

AIM

To retrospectively evaluate the computed tomography (CT) appearances of novel influenza A (H1N1) infection.

MATERIALS AND METHODS

Chest CT images obtained at clinical presentation in 21 patients (eight men, 13 women; mean age, 37 years; age range, 6-82 years) with confirmed novel influenza A (H1N1) infection were assessed. The radiological appearances of pulmonary parenchymal abnormalities, distribution, and extent of involvement on initial chest CT images were documented. The study group was divided on the basis of age [group 1, patients <18 years old (n=8); group 2, patients ≥ 18 years old (n=13)]. Medical records were reviewed for underlying medical conditions and laboratory findings. The occurrence of recognizable CT patterns was compared for each group using the images from the initial CT examination.

RESULTS

The most common CT pattern observed in all patients was ground-glass attenuated (GGA) lesions (20/21, 95%). Bronchial wall thickening (9/21, 43%) was the second most common CT finding. Other common CT findings were consolidation (6/21, 29%), pleural effusion (6/21, 29%), pneumothorax or pneumomediastinum (5/21, 24%), and atelectasis (5/21, 24%). Among these, atelectasis and pneumomediastinum (pneumothorax) were only observed in group 1. The GGA lesions showed predilections for diffuse multifocal (10/20, 50%) or lower zone (8/20, 40%) distribution. Involvement of central lung parenchyma (12/20, 60%) was more common than a mixed peripheral and central pattern (6/20, 30%) or a subpleural pattern (2/20, 10%) at the time of presentation. Patchy GGA lesions were more frequent (18/20, 90%) than diffuse GGA lesions, and 75% (15/20) of these lesions had a bronchovascular distribution. Bilateral disease was present in all patients with GGA lesions. Bronchial wall thickening was predominantly centrally located and the distribution of the consolidation was non-specific.

CONCLUSION

The predominantly centrally located GGA lesions, with common multifocal or bilateral involvement, peribronchovascular distribution, and patchy appearance are the more distinctive CT findings of novel influenza A (H1N1) infection. Pneumomediastinum and atelectasis resulting from this disease are more common in young patients under the age of 18 years.

[The relationship between chest CT findings and viral load in patients with novel influenza A (H1N1)]

OBJECTIVE

To evaluate the value of chest CT findings and dynamic changes of viral load in patients with novel influenza A (H1N1) infection in clinical diagnosis, differential diagnosis and treatment.

METHODS

Fifty-one patients with confirmed novel influenza A (H1N1) according to the diagnostic criteria of the Ministry of Health, received chest X-ray, CT scans (HRCT) and viral load tests in our hospital from May to December of 2009. Based on whether there were signs of pneumonia in CT imaging, the patients were divided into a pneumonia group (n = 31) and a non-pneumonia group (n = 20). The relationship between chest CT changes and viral load was observed and analyzed statistically using SPSS 10.5 software.

RESULTS

Patchy consolidations of lungs were the main findings in pneumonia group with influenza A (H1N1) infection, and ground-glass opacities were the main CT findings at acute and convalescent phases. Lobular and segmental shadows of the lungs were diffusely distributed, mostly found in lower lungs, especially the left lung. In some cases, the lung diseases were accompanied with mediastinal lymphadenopathy. Co-existence of pulmonary parenchymal, interstitial and pleural diseases was observed. Peak viral load occurred at the early phase of illness, with the mean initial viral load being 7.7 copies/ml and 4.2 copies/ml in the pneumonia and the non-pneumonia groups respectively. The viral nucleic acid became negative 4 days after antiviral treatment (course of 6 days). Dynamic observation of 3 patients with novel influenza A (H1N1) pneumonia showed that, the viral clearance period preceded the absorption of lung lesions in 2 cases, but viral clearance period of a young patient was significantly prolonged.

CONCLUSION

In patients with the novel influenza A (H1N1) infection, the viral load in the pneumonia group was significantly higher than that in the group with normal chest imaging. Dynamic observation on chest imaging and viral load may be beneficial for clinicians to start prompt and effective treatment.

Radiological findings of pneumonia in patients with swine-origin influenza A virus (H1N1)

Purpose

During spring 2009, a pandemic swine-origin influenza A (H1N1) virus (S-OIV) emerged and spread globally. We describe the chest X-ray and computed tomography (CT) findings of 40 patients with pneumonia due to S-OIV observed in our institution.

Material and methods

Among 534 patients with S-OIV, according to the US Centers for Disease Control and Prevention case definition, seen between June and November 2009, 121 underwent chest X-ray and 40 (median age 44 years, range 16–79) had pneumonia. The initial chest radiographs were evaluated for pattern, distribution and extent of lung abnormalities. Unenhanced chest CT scans were performed in two patients and were reviewed for the same findings. Underlying medical conditions were present in 42% of patients (17/40).

Results

Our patients had predominantly mild illness, and pneumonia was observed in 40 individuals (40/121 patients who had chest X-rays, 33%; and 40/534 patients with S-OIV, 7.5%). However, S-OIV can cause severe illness requiring admission to the intensive care unit for advanced mechanical ventilation and extracorporeal life support, including adult respiratory distress syndrome (ARDS) and death. The major radiological abnormalities observed were interstitial changes (60.0%), with (22.0%) or without patchy ground-glass appearance, mostly bilateral, and located in the lower lung zones (7.5%). Extensive disease was seen in 37.5% (15/40), and ARDS was observed in three individuals (0.30%)with underlying medical conditions. Subtle pleural effusion was noted in four patients.

Conclusions

In our series, the most frequent pneumonia patterns observed during S-OIV (H1N1) virus were interstitial changes and patchy ground-glass appearance, mostly bilateral, and located in the lower lung zones. CT, performed in severely ill patients, confirmed the ARDS identified with chest X-rays, better depicting the features and extent of lung abnormalities.

[The changes of chest imaging and clinical features in patients with severe infection of new influenza A (H1N1)]

OBJECTIVE

To study the clinical features and the pulmonary imaging changes of severe cases of new influenza A (H1N1).

METHODS

This study included 10 severe cases with new influenza A (H1N1) infection in the Forth People's Hospital of Taiyuan from 20 Oct. 2009 to 22 Nov 2009.Six patients were males and 4 were females, with an average age of 19.3 years (range 5 - 41 years). The laboratory study included blood routine, blood gas analysis, liver and renal function tests, myocardium enzymology, chest radiograph and CT.

RESULTS

The prominent clinical features included fever, cough and dyspnea. The pulmonary imaging changes were varied, including ground-glass opacity, consolidation, atelectasis, fluid pneumothorax and pleural effusion, and manifestations of acute pneumonia and interstitial pneumonia simultaneously. Extensive pulmonary infiltration developed quickly, and acute lung injury (ALI) occurred in 5 patients and acute respiratory distress syndrome (ARDS) in 3 cases. Oseltamivir, oxygen therapy and antibiotic therapy were effective for improvement of the disease and final recovery of all these patients.

CONCLUSIONS

The severe cases of new influenza A (H1N1) infection has imaging manifestations of acute pneumonia and interstitial pneumonia. The disease progresses quickly and may lead to ALI/ARDS.

Severe novel influenza A (H1N1) infection in cancer patients

Background: The natural history and consequences of severe H1N1 influenza infection among cancer patients are not yet fully characterized. We describe eight cases of H1N1 infection in cancer patients admitted to the intensive care unit of a referral cancer center.

Patients and methods: Clinical data from all patients admitted with acute respiratory failure due to novel viral H1N1 infection were reviewed. Lung tissue was submitted for viral and bacteriological analyses by real-time RT-PCR, and autopsy was conducted on all patients who died.

Results: Eight patients were admitted, with ages ranging from 55 to 65 years old. There were five patients with solid organ tumors (62.5%) and three with hematological malignancies (37.5%). Five patients required mechanical ventilation and all died. Four patients had bacterial bronchopneumonia. All deaths occurred due to multiple organ failure. A milder form of lung disease was present in the three cases who survived. Lung tissue analysis was performed in all patients and showed diffuse alveolar damage in most patients. Other lung findings were necrotizing bronchiolitis or extensive hemorrhage.

Conclusions: H1N1 viral infection in patients with cancer can cause severe illness, resulting in acute respiratory distress syndrome and death. More data are needed to identify predictors of unfavorable evolution in these patients.

Reduction of natural killer but not effector CD8 T lymphocytes in three consecutive cases of severe/lethal H1N1/09 influenza A virus infection

Background

The cause of severe disease in some patients infected with pandemic influenza A virus is unclear.

Methodology/Principal Findings

We present the cellular immunology profile in the blood, and detailed clinical (and post-mortem) findings of three patients with rapidly progressive infection, including a pregnant patient who died. The striking finding is of reduction in natural killer (NK) cells but preservation of activated effector CD8 T lymphocytes; with viraemia in the patient who had no NK cells. Comparison with control groups suggests that the reduction of NK cells is unique to these severely ill patients.

Conclusion/Significance

Our report shows markedly reduced NK cells in the three patients that we sampled and raises the hypothesis that NK may have a more significant role than T lymphocytes in controlling viral burden when the host is confronted with a new influenza A virus subtype.

Hospital triage system for adult patients using an influenza-like illness scoring system during the 2009 pandemic--Mexico

BACKGROUND

Pandemic influenza A (H1N1) virus emerged during 2009. To help clinicians triage adults with acute respiratory illness, a scoring system for influenza-like illness (ILI) was implemented at Hospital Civil de Guadalajara, Mexico.

METHODS

A medical history, laboratory and radiology results were collected on emergency room (ER) patients with acute respiratory illness to calculate an ILI-score. Patients were evaluated for admission by their ILI-score and clinicians' assessment of risk for developing complications. Nasal and throat swabs were collected from intermediate and high-risk patients for influenza testing by RT-PCR. The disposition and ILI-score of those oseltamivir-treated versus untreated, clinical characteristics of 2009 pandemic influenza A (H1N1) patients versus test-negative patients were compared by Pearson's Chi(2), Fisher's Exact, and Wilcoxon rank-sum tests.

RESULTS

Of 1840 ER patients, 230 were initially hospitalized (mean ILI-score = 15), and the rest were discharged, including 286 ambulatory patients given oseltamivir (median ILI-score = 11), and 1324 untreated (median ILI-score = 5). Fourteen (1%) untreated patients returned, and 3 were hospitalized on oseltamivir (median ILI-score = 19). Of 371 patients tested by RT-PCR, 104 (28%) had pandemic influenza and 42 (11%) had seasonal influenza A detected. Twenty (91%) of 22 imaged hospitalized pandemic influenza patients had bilateral infiltrates compared to 23 (38%) of 61 imaged hospital test-negative patients (p<0.001). One patient with confirmed pandemic influenza presented 6 days after symptom onset, required mechanical ventilation, and died.

CONCLUSIONS

The triaging system that used an ILI-score complimented clinicians' judgment of who needed oseltamivir and inpatient care and helped hospital staff manage a surge in demand for services.