Clinical and epidemiological characteristics of 245 cases of influenza A (H3N2)

Abstract

Objective: To investigate the clinical and epidemiological characteristics of influenza A (H3N2) infected patients in Jinhua area, and therefore to improve the understanding of infection with H3N2 influenza virus. Methods: The pharynx swab specimens for pathogenic detection were collected from acute respiratory infection (ARI) cases in the fever clinic of the sentinel hospital in Jinhua area from 2014 to 2017. Descriptive statistics method was used to analyze the clinical features and pathogenics characteristics of the patients infected with H3N2 influenza virus. The t test or χ(2) test of independent samples were used for comparison between groups. Results: A total of 3 803 cases of acute respiratory infection (ARI) were reported in the sentinel hospital in Jinhua area from 2014 to 2017. Among them, 245 cases (6.4%) of H3N2 influenza were diagnosed, including 153 males (62.4%) and 92 females (37.6%), aged from 0.5 to 95 years, with an average age of (50.1+15.7) years. They were divided into 5 age groups, with 107 (43.7%) patients aged 60 years and older. The incidence of major diseases was 43.7%. There was no significant difference in the gender in different age groups (χ(2)=4.581, P=0.333). The seasonal peak of H3N2 influenza A virus infection was mainly in summer (In June-September), but was also seen in other months. In the 4 years from 2014 to 2017, there were a total of 4 peaks, which occurred in July-September, July-August, June-August, and June-August. The body temperature of most patients (73.1%) was between 38.0 and 38.9 ℃. The main positive signs of H3N2 influenza A virus infection were different degrees of pharyngeal hyperemia and tonsillar enlargement. Fever (>38 ℃), cough, dizziness, fatigue, sore throat, headache, chills, shortness of breath, runny nose, myalgia, expectoration, nasal congestion were the main symptoms of H3N2 cases. The proportion of abnormal X-ray/CT manifestations in H3N2 influenza A virus infection cases was lower than that of other influenza viruses. 89.8% of the patients were positive for H3N2 influenza A. The average lymphocyte count was (1.1±0.5) × 10(9)/L, total platelet count (157±39) × 10(9)/L in H3N2 influenza A infection group, which were lower than those in other influenza positive patients [(1.2±0.6)×10(9)/L and (165±42) × 10(9)/L], while the neutrophil count (3.6±0.8) × 10(9)/L was higher than that in other influenza positive patients (3.4±1.0) × 10(9)/L(all P<0.05). Conclusions: Patients with H3N2 influenza A in Jinhua mostly presented with throat congestion and tonsillar enlargement in varying degrees, fever (>38 ℃), cough and sputum production. The seasonal peak of influenza A was in summer (June-September). Elderly aged 60 years or older were the susceptible group.