title: Age-specificity of clinical dengue during primary and secondary infections.
abstract: BACKGROUND
  This study aims to estimate the age-specific risks of clinical dengue attack (i.e., the risk of symptomatic dengue among the total number of dengue virus (DENV) infections) during primary and secondary infections.
  
  
  METHODS
  We analyzed two pieces of epidemiological information in Binh Thuan province, southern Vietnam, i.e., age-specific seroprevalence and a community-wide longitudinal study of clinical dengue attack. The latter data set stratified febrile patients with DENV infection by age as well as infection parity. A simple modeling approach was employed to estimate the age-specific risks of clinical dengue attack during primary and secondary infections.
  
  
  RESULTS
  Using the seroprevalence data, the force of infection was estimated to be 11.7% (95% confidence intervals (CI): 10.8-12.7) per year. Median age (and the 25-75 percentiles) of dengue fever patients during primary and secondary infections were 12 (9-20) and 20 (14-31) years, respectively. The estimated age-specific risk of clinical dengue increases as a function of age for both primary and secondary infections; the estimated proportion of symptomatic patients among the total number of infected individuals was estimated to be <7% for those aged <10 years for both primary and secondary infections, but increased as patients become older, reaching to 8-11% by the age of 20 years.
  
  
  CONCLUSIONS
  For both primary and secondary infections, higher age at DENV infection was shown to result in higher risk of clinical attack. Age as an important modulator of clinical dengue explains recent increase in dengue notifications in ageing countries in Southeast Asia, and moreover, poses a paradoxical problem of an increase in adult patients resulting from a decline in the force of infection, which may be caused by various factors including time-dependent variations in epidemiological, ecological and demographic dynamics.
authors.affiliation: Division of Infectious Diseases, Tropical Medicine and AIDS, Academic Medical Center, Amsterdam, The Netherlands. t.d.thai@amc.uva.nl
authors.forename: Khoa T D
authors.initials: KT
authors.lastname: Thai
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishiura
authors.forename: Phuong Lan
authors.initials: PL
authors.lastname: Hoang
authors.forename: Nga Thanh Thi
authors.initials: NT
authors.lastname: Tran
authors.forename: Giao Trong
authors.initials: GT
authors.lastname: Phan
authors.forename: Hung Quoc
authors.initials: HQ
authors.lastname: Le
authors.forename: Binh Quang
authors.initials: BQ
authors.lastname: Tran
authors.forename: Nam Van
authors.initials: NV
authors.lastname: Nguyen
authors.forename: Peter J
authors.initials: PJ
authors.lastname: de Vries
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D003715:Dengue / Q000453:epidemiology* / Q000473:pathology*; D006801:Humans; D008137:Longitudinal Studies; D012307:Risk Factors; D016036:Seroepidemiologic Studies; D014744:Vietnam / Q000453:epidemiology; D055815:Young Adult