Epidemiology of severe pediatric patients with novel influenza A (H1N1) in Korea

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Background: Since the first outbreak of novel influenza A (H1N1) in May 2009, the virus has been spread throughout local communities. More than 4,000 diagnosed cases are being reported daily as of November 2009. One of the major infection routes is the educational institutions, so children and teenagers have high risk of viral exposure. Korea Centers for Disease Control and Prevention (KCDC) is operating nationwide monitoring system for severe hospitalization cases. The objective of this study is to highlight demographics, infection risk factors and clinical courses.

Methods: Influenza A (H1N1) patients who were hospitalized in ICU or had pneumonia in needs of intubation were categorized as severe pediatric patients. Between June and October, total of 22 cases under the age of 18 were identified as severe patients. After the medical chart review, we had an interview with the doctor in charge. All the patients were laboratory-confirmed influenza A (H1N1) virus infection by means of real-time PCR. Based on the Advisory Committee on Immunization Practices, the patients with high-risk medical conditions were defined as having higher risk for influenza complications.

Results: Among the reported 22 severe cases, 15 were male and 7 were female. Ages ranged from 2 months to 18 years old (median 7, standard deviation 5.4). Fourteen patients (63%) had high-risk medical conditions such as 1) age less than 59 months (6 cases), 2) chronic respiratory disease (3 asthma cases), 3) neuro-developmental disorder (3 cases), 4) congenital heart disease (1 case) and 5) leukemia (1 case). Total of 7 patients have expired. Patients took anti-viral agent (Tamiflu^®) average 2 days after onset. Thirteen patients received ventilator care, 7 did not and 2 were unsure. Viral pneumonia was the most common complication (17 cases, 77%) and 3 patients exacerbated into acute respiratory distress syndrome. Initial symptoms were fever and cough (18 cases, 81% each). There were 11 leukocytosis, 3 leucopenia and 3 thrombocytopenia cases on complete blood count.

Conclusion: Half of patients with high-risk medical conditions have expired. Considering current situations, we need to maintain high-risk medical conditions category and to have continuous tracking for severe pediatric patients with influenza A (H1N1).