title: Pandemic 2009 H1N1 virus infection in children and adults: A cohort study at a single hospital throughout the epidemic.
abstract: BACKGROUND
  In 2009, there was an influenza pandemic in South Korea. The aim of this study was to evaluate the epidemiological, clinical and laboratory characteristics of this infection in children and adults.
  
  
  METHODS
  We evaluated the epidemiologic characteristics of patients infected with the 2009 H1N1 influenza A virus (4,463 patients, age range from 2 mo to 86 y), and the clinical and laboratory findings of 373 inpatients (80/217 children, ≤ 15 y, had pneumonia and 36/156 adults, > 16 y, had pneumonia) in a single hospital during the epidemic.
  
  
  RESULTS
  The majority of infected patients (94%) were less than 40 y, and greater than 90% of cases occurred during a two-month period. The rates of admission and pneumonia were 8.4% (373/4,463) and 2.5% (116/4,463), respectively. The rates of admission and pneumonia, total duration of fever, the frequency of underlying diseases, and the values of C-reactive protein and erythrocyte sedimentation rate tended to increase as age increased; highest rates were found in the ≥ 65 y group. Pneumonia was founded more boys than girls in children, but more female than male in adults. The adult patients with pneumonia had higher leukocyte counts with lower lymphocyte differentials than the group without pneumonia, as shown in children group.
  
  
  CONCLUSIONS
  Our results suggest that the immunologic reaction to viral insults may be associated with age, sex and underlying diseases, and that unknown herd immunity may affect populations. The patients with underlying diseases, especially in older patients may have immunologic insufficiency that is associated with immunologic consumption by the underlying diseases.
authors.affiliation: Departments of Pediatrics, College of Medicine, The Catholic University of Korea, 505 Banpo-dong, Seocho-gu, Seoul 137-701, Republic of Korea. leekyungyil@catholic.ac.kr.
authors.forename: Jung-Woo
authors.initials: JW
authors.lastname: Rhim
authors.forename: Eun-Ji
authors.initials: EJ
authors.lastname: Go
authors.forename: Kyung-Yil
authors.initials: KY
authors.lastname: Lee
authors.forename: You-Sook
authors.initials: YS
authors.lastname: Youn
authors.forename: Myung-Sook
authors.initials: MS
authors.lastname: Kim
authors.forename: Sun Hee
authors.initials: SH
authors.lastname: Park
authors.forename: Ji-Chang
authors.initials: JC
authors.lastname: Kim
authors.forename: Jin-Han
authors.initials: JH
authors.lastname: Kang