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      Diagnosing swine flu: the inaccuracy of case definitions during the 2009 pandemic, an attempt at refinement, and the implications for future planning

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          Abstract

          Background  At the onset of the pandemic H1N1/09 influenza A outbreak in Australia, health authorities devised official clinical case definitions to guide testing and access to antiviral therapy.

          Objectives  To assess the diagnostic accuracy of these case definitions and to attempt to improve on them using a scoring system based on clinical findings at presentation.

          Patients/Methods  This study is a retrospective case–control study across three metropolitan Melbourne hospitals and one associated community‐based clinic during the influenza season, 2009. Patients presenting with influenza‐like illness who were tested for H1N1/09 influenza A were administered a standard questionnaire of symptomatology, comorbidities, and risk factors. Patients with a positive test were compared to those with a negative test. Logistic regression was performed to examine for correlation of clinical features with disease. A scoring system was devised and compared with case definitions used during the pandemic. The main outcome measures were the positive and negative predictive values of our scoring system, based on real‐life data, versus the mandated case definitions’.

          Results  Both the devised scoring system and the case definitions gave similar positive predictive values (38–58% using ascending score groups, against 39–44% using the various case definitions). Negative predictive values were also closely matched (ranging from 94% to 73% in the respective score groups against 83–84% for the case definitions).

          Conclusions  Accurate clinical diagnosis of H1N1/09 influenza A was difficult and not improved significantly by a structured scoring system. Investment in more widespread availability of rapid and sensitive diagnostic tests should be considered in future pandemic planning.

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          Most cited references15

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          Applied Logistic Regression

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            Predicting influenza infections during epidemics with use of a clinical case definition.

            Combined pharyngeal and nasal swab specimens were collected from 100 subjects who presented with a flu-like illness (fever >37.8 degrees C plus 2 of 4 symptoms: cough, myalgia, sore throat, and headache) of or =38.2 degrees C as well as 3 or 4 of the symptoms in the clinical case definition. Stepwise logistic regression showed that cough (odds ratio [OR], 6.7; 95% confidence interval [CI], 1.4-34.1; P=.02) and fever (OR, 3.1; 95% CI, 1.4-8.0; P=.01) were the only factors significantly associated with a positive PCR test for influenza. The positive predictive value, negative predictive value, sensitivity, and the specificity of a case definition including fever (temperature of >38 degrees C) and cough for the diagnosis of influenza infection during this flu season were 86.8%, 39.3%, 77.6%, and 55.0%, respectively.
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              Does this patient have influenza?

              Influenza vaccination lowers, but does not eliminate, the risk of influenza. Making a reliable, rapid clinical diagnosis is essential to appropriate patient management that may be especially important during shortages of antiviral agents caused by high demand. To systematically review the precision and accuracy of symptoms and signs of influenza. A secondary objective was to review the operating characteristics of rapid diagnostic tests for influenza (results available in <30 min). Structured search strategy using MEDLINE (January 1966-September 2004) and subsequent searches of bibliographies of retrieved articles to identify articles describing primary studies dealing with the diagnosis of influenza based on clinical signs and symptoms. The MEDLINE search used the Medical Subject Headings EXP influenza or EXP influenza A virus or EXP influenza A virus human or EXP influenza B virus and the Medical Subject Headings or terms EXP sensitivity and specificity or EXP medical history taking or EXP physical examination or EXP reproducibility of results or EXP observer variation or symptoms.mp or clinical signs.mp or sensitivity.mp or specificity.mp. Of 915 identified articles on clinical assessment of influenza-related illness, 17 contained data on the operating characteristics of symptoms and signs using an independent criterion standard. Of these, 11 were eliminated based on 4 inclusion criteria and availability of nonduplicative primary data. Two authors independently reviewed and abstracted data for estimating the likelihood ratios (LRs) of clinical diagnostic findings. Differences were resolved by discussion and consensus. No symptom or sign had a summary LR greater than 2 in studies that enrolled patients without regard to age. For decreasing the likelihood of influenza, the absence of fever (LR, 0.40; 95% confidence interval [CI], 0.25-0.66), cough (LR, 0.42; 95% CI, 0.31-0.57), or nasal congestion (LR, 0.49; 95% CI, 0.42-0.59) were the only findings that had summary LRs less than 0.5. In studies limited to patients aged 60 years or older, the combination of fever, cough, and acute onset (LR, 5.4; 95% CI, 3.8-7.7), fever and cough (LR, 5.0; 95% CI, 3.5-6.9), fever alone (LR, 3.8; 95% CI, 2.8-5.0), malaise (LR, 2.6; 95% CI, 2.2-3.1), and chills (LR, 2.6; 95% CI, 2.0-3.2) increased the likelihood of influenza to the greatest degree. The presence of sneezing among older patients made influenza less likely (LR, 0.47; 95% CI, 0.24-0.92). Clinical findings identify patients with influenza-like illness but are not particularly useful for confirming or excluding the diagnosis of influenza. Clinicians should use timely epidemiologic data to ascertain if influenza is circulating in their communities, then either treat patients with influenza-like illness empirically or obtain a rapid influenza test to assist with management decisions.
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                Author and article information

                Journal
                Influenza Other Respir Viruses
                Influenza Other Respir Viruses
                10.1111/(ISSN)1750-2659
                IRV
                Influenza and Other Respiratory Viruses
                Blackwell Publishing Ltd (Oxford, UK )
                1750-2640
                1750-2659
                19 June 2012
                May 2013
                : 7
                : 3 , Part 2 A(H1N1)pdm09 Papers ( doiID: 10.1111/irv.2013.7.issue-3 )
                : 403-409
                Affiliations
                [ 1 ]Infectious Diseases Department, Austin Health; Melbourne, Vic., Australia
                [ 2 ]Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Vic., Australia
                [ 3 ]Infectious Diseases Department, Alfred Health, Melbourne, Vic., Australia
                [ 4 ]Infectious Diseases Department, Northern Health, Melbourne, Vic., Australia
                [ 5 ]Nossal Institute for Global Health, Melbourne, Vic., Australia
                [ 6 ]Department of Medicine, The University of Melbourne, Melbourne, Vic., Australia.
                Author notes
                [*]Andrew Mahony, Infectious Diseases Department, Austin Health, 145 Studley Road, Heidelberg 3084, Victoria Australia. 
E‐mail: andrew.mahony@ 123456austin.org.au
                Article
                IRV398
                10.1111/j.1750-2659.2012.00398.x
                5779837
                22712880
                59be27f3-e56d-4b8c-ba02-d06c1c100b8d
                © 2012 Blackwell Publishing Ltd
                History
                Page count
                Figures: 1, Tables: 5, Pages: 7
                Categories
                Part 2 A(H1N1)pdm09 Papers
                Original Articles
                Original Article
                Custom metadata
                2.0
                May 2013
                Converter:WILEY_ML3GV2_TO_NLMPMC version:4.6.9 mode:remove_FC converted:04.11.2015

                Infectious disease & Microbiology
                case definitions,influenza a h1n1/09 subtype,roc curve
                Infectious disease & Microbiology
                case definitions, influenza a h1n1/09 subtype, roc curve

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