Clinical features of the 2009 swine-origin influenza A (H1N1) outbreak in Japan

Abstract

To clarify the clinical symptoms of the influenza A virus during the 2009 pandemic influenza outbreak, we describe the clinical features of outpatients diagnosed with type A influenza by use of the rapid influenza diagnostic test (RIDT) from September to December 2009. Questionnaires were used to collect prospective data on 1,122 cases with influenza-like illness at our medical institutions. The independent predictors of influenza A virus were identified on the basis of demographic features and the clinical symptoms of the patients who tested positive for influenza A virus in the RIDT test. Of the 1,122 cases tested, 389 (34.7%) were positive for the influenza A virus. The median age of the influenza-positive patients was 14, and 58.9% of the patients were male. The symptoms fever, cough, rhinorrhea, and headache were statistically dominant. A history of recent contact with persons suffering from influenza or influenza-like illness at home, school, or in the workplace was significantly more common in the positive group than in the negative group. Pneumonia was observed in 2 (0.5%) of the positive patients, but the symptoms were only severe enough to require hospitalization in 1 of the 2. No deaths were observed among the 389 RIDT-positive patients. Although the spread of influenza A virus was both rapid and extensive, mainly among children under the age of 18, it seemed to be mild. Appropriate interpretation of the RIDT on the basis of recent clinical information, and early treatment with antiviral drugs might help to prevent severe illness from influenza pandemics in the future.

A Prospective Comparison of the Epidemiological and Clinical Characteristics of Pandemic (H1N1) 2009 Influenza A Virus and Seasonal Influenza A Viruses in Guangzhou, South China in 2009

“…With regards to age distribution in our study, the A(H1N1)pdm09-infected patients were younger than seasonal influenza patients. This result was consistent with previous reports from China (20) as well as other countries (24,26) such as Japan (32). The data discussed above suggests that A(H1N1)pdm09 infections appear to show seasonal variations in different climate zones but display universally similar clinical features.…”

“…In our present study, A(H1N1)pdm09-infected adolescent cases had a higher rate of contact with infected individuals, and a sharp rise in prevalence was observed after the new semester of school started at EW 36. Another possibility is that older people may have cross-immunoreactivity (32)(33)(34)(35) or long-term T cell-mediated immunity (36) against A(H1N1)pdm09, as a result of prior exposure to influenza virus that was genetically and antigenically closely related to the A(H1N1)pdm09 strain.…”

“…Clinical characteristics of influenza patients: The median age of A(H1N1)pdm09-infected patients (median [IQR], 21 [16][17][18][19][20][21][22][23][24][25][26][27][28] [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] years) (P º 0.001, by non-parametric KruskalWallis test). Moreover, comparison of the age distribution of patients in the three groups showed statistical significance (P º 0.001, by the x 2 test) ( Table 1 and Fig.…”

Clinical characteristics of influenza A H1N1 versus other influenza-like illnesses amongst outpatients attending a university health center in Oman

“…The frequencies of both these symptoms were lower than those reported by Dawood et al (25% for each symptom), 9 but higher than those reported in other studies. 21,22 In a comparison between patients infected with pandemic H1N1 (2009) influenza and those infected with seasonal influenza, Carcione et al identified diarrhea as a significant variable distinguishing H1N1-infected patients. 13 However, a study from Singapore did not confirm the same finding.…”

Analysis of the Influenza A (H1N1) 2009 Pandemic Infection in Japanese Asthmatic Patients: Using a Questionnaire-Based Survey

“…12,13 The aggressive use of antiviral agents resulted in milder disease activity and the lowered the mortality. 14 In the Niigata Prefecture specifically, variations in H1N1 pdm09 infection were different from those in the whole of Japan. The case numbers reported as H1N1 pdm09 infection (!…”