title: Household transmission of 2009 H1N1 influenza virus in Yazd, Iran.
abstract: OBJECTIVE
  The 2009 pandemic influenza A (H1N1) virus is a public health challenge. Notably, laboratory-confirmed cases do not represent the age group most susceptible to infection. To characterize the age distribution of all cases of H1N1 influenza, we studied the personal contacts of confirmed cases to identify the age group at the highest risk.
  
  
  METHODS
  We investigated the family members of 162 laboratory-confirmed cases of 2009 H1N1 in Yazd, Iran. Family members were retrospectively asked whether they had ≥2 respiratory symptoms within 7days of the last contact with the associated index cases. The ages and symptoms of the patients as well as the interval between diagnosis and the onset of symptoms among household contacts were determined using a questionnaire.
  
  
  RESULTS
  We identified 596 family members of index cases, 83 (13.9%) of whom developed acute respiratory illness. No acute respiratory illness was found in 104 families (64%); however, there were 2 cases in 15 families (9.3%) and ≥3 cases in 4 families (24%). Household contacts from 5 to 18years old were more susceptible to acute respiratory illness than those who were ≥51years old (RR=3.174, 95% CI 1.313-7.675 P-value=0.01).
  
  
  CONCLUSIONS
  Individuals ≤18years old were most susceptible to infection by the H1N1 virus. Therefore, in low-income populations, prevention of the spread of H1N1 to this age group should be emphasized.
authors.affiliation: Shahid Sadoughi University of Medical Sciences, Yazd, Iran. fatemah.behnaz@yahoo.com
authors.forename: F
authors.initials: F
authors.lastname: Behnaz
authors.forename: M
authors.initials: M
authors.lastname: Mohammadzadeh
authors.forename: M
authors.initials: M
authors.lastname: Sadeghian
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005191:Family Characteristics; D005192:Family Health; D005260:Female; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology / Q000473:pathology / Q000635:transmission* / Q000821:virology*; D007492:Iran / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D011795:Surveys and Questionnaires; D055815:Young Adult