Improving the Clinical Diagnosis of Influenza—a Comparative Analysis of New Influenza A (H1N1) Cases

Abstract

BackgroundThe presentation of new influenza A(H1N1) is broad and evolving as it continues to affect different geographic locations and populations. To improve the accuracy of predicting influenza infection in an outpatient setting, we undertook a comparative analysis of H1N1(2009), seasonal influenza, and persons with acute respiratory illness (ARI) in an outpatient setting.Methodology/Principal FindingsComparative analyses of one hundred non-matched cases each of PCR confirmed H1N1(2009), seasonal influenza, and ARI cases. Multivariate analysis was performed to look for predictors of influenza infection. Receiver operating characteristic curves were constructed for various combinations of clinical and laboratory case definitions. The initial clinical and laboratory features of H1N1(2009) and seasonal influenza were similar. Among ARI cases, fever, cough, headache, rhinorrhea, the absence of leukocytosis, and a normal chest radiograph positively predict for both PCR-confirmed H1N1-2009 and seasonal influenza infection. The sensitivity and specificity of current WHO and CDC influenza-like illness (ILI) criteria were modest in predicting influenza infection. However, the combination of WHO ILI criteria with the absence of leukocytosis greatly improved the accuracy of diagnosing H1N1(2009) and seasonal influenza (positive LR of 7.8 (95%CI 3.5–17.5) and 9.2 (95%CI 4.1–20.3) respectively).Conclusions/SignificanceThe clinical presentation of H1N1(2009) infection is largely indistinguishable from that of seasonal influenza. Among patients with acute respiratory illness, features such as a temperature greater than 38°C, rhinorrhea, a normal chest radiograph, and the absence of leukocytosis or significant gastrointestinal symptoms were all positively associated with H1N1(2009) and seasonal influenza infection. An enhanced ILI criteria that combines both a symptom complex with the absence of leukocytosis on testing can improve the accuracy of predicting both seasonal and H1N1-2009 influenza infection.

Factors promoting the prolonged shedding of the pandemic (H1N1) 2009 influenza virus in patients treated with oseltamivir for 5 days

“…In our present study, the shedding of 2009 H1N1 virus was assessed in 173 patients: after 5 days of oseltamivir treatment, 88 patients (50·8%) still had a positive RT‐PCR result. These results agree with those of recent studies that found that patients admitted to hospital with the pandemic influenza 2009 H1N1 virus had a longer duration of viral shedding than adults who were hospitalized with a seasonal influenza virus infection 12, 13, 14…”

“…A pH1N1 infection was suspected if the patient had an influenza‐like illness, namely a temperature of ≥37·5°C and at least one of the following symptoms: sore throat, cough, rhinorrhea, or nasal congestion 13. RT‐PCR was performed within 12 hours of sampling (without freezing) using Real‐Time Ready Inf A/H1N1 detection kits (Roche Diagnostics, Rotkreuz, Switzerland) and multiwell plate‐based real‐time PCR platforms (LightCycler ® 480 Real‐Time PCR System; Roche Diagnostics) as previously described 14. All patients admitted to isolation rooms underwent repeated RT‐PCR testing after 5 days of oseltamivir therapy.…”

Resource Burden at Children’s Hospitals Experiencing Surge Volumes During the Spring 2009 H1N1 Influenza Pandemic

“…Frequency distributions for patient characteristics for all ED visits with an IRI code were calculated for all 23 hospitals during the period when the CDC surveillance identified circulating 2009 H1N1 influenza (Calendar Weeks [16][17][18][19][20][21][22][23][24][25][26][27][28][29]. To describe the hospital-level variation in influenza-related utilization, we first performed hospitallevel analyses.…”

“…Due to nonspecific or delayed symptoms and limited use and accuracy of viral testing, 16,17 few persons with IRI receive a confirmed diagnosis. We therefore used the Electronic Surveillance System for the Early Notification of Community-Based Epidemics (ESSENCE) II list of International Classification of Diseases, 9th revision (ICD-9), codes developed for influenza syndromic surveillance in the military 18,19 and validated for the 2009 H1N1 influenza pandemic.…”

A Systematic Review of Clinical Decision Rules for the Diagnosis of Influenza

“…The search was initially performed on January 26, 2010, and was repeated on July 8, 2010, as part of the revision of this article. One potential study 25 was identifi ed during that fi nal search, but was not included because it did not meet the inclusion criterion of prospective data collection.…”