title: Individual and community risks of measles and pertussis associated with personal exemptions to immunization.
abstract: BACKGROUND
  The risk of vaccine-preventable diseases among children who have philosophical and religious exemptions from immunization has been understudied.
  
  
  OBJECTIVE
  To evaluate whether personal exemption from immunization is associated with risk of measles and pertussis at individual and community levels.
  
  
  METHODS
  Population-based, retrospective cohort study using data collected on standardized forms regarding all reported measles and pertussis cases among children aged 3 to 18 years in Colorado during 1987-1998.
  
  
  METHODS
  Relative risk of measles and pertussis among exemptors and vaccinated children; association between incidence rates among vaccinated children and frequency of exemptors in Colorado counties; association between school outbreaks and frequency of exemptors in schools; and risk associated with exposure to an exemptor in measles outbreaks.
  
  
  RESULTS
  Exemptors were 22.2 times (95% confidence interval [CI], 15.9-31.1) more likely to acquire measles and 5.9 times (95% CI, 4.2-8.2) more likely to acquire pertussis than vaccinated children. After adjusting for confounders, the frequency of exemptors in a county was associated with the incidence rate of measles (relative risk [RR], 1.6; 95% CI, 1.0-2.4) and pertussis (RR, 1.9; 95% CI, 1.7-2.1) in vaccinated children. Schools with pertussis outbreaks had more exemptors (mean, 4.3% of students) than schools without outbreaks (1. 5% of students; P =.001). At least 11% of vaccinated children in measles outbreaks acquired infection through contact with an exemptor.
  
  
  CONCLUSIONS
  The risk of measles and pertussis is elevated in personal exemptors. Public health personnel should recognize the potential effect of exemptors in outbreaks in their communities, and parents should be made aware of the risks involved in not vaccinating their children.
authors.affiliation: Respiratory Diseases Branch, Centers for Disease Control and Prevention, 1600 Clifton Rd, MS-C23, Atlanta, GA 30333, USA. drf0@cdc.gov
authors.forename: D R
authors.initials: DR
authors.lastname: Feikin
authors.forename: D C
authors.initials: DC
authors.lastname: Lezotte
authors.forename: R F
authors.initials: RF
authors.lastname: Hamman
authors.forename: D A
authors.initials: DA
authors.lastname: Salmon
authors.forename: R T
authors.initials: RT
authors.lastname: Chen
authors.forename: R E
authors.initials: RE
authors.lastname: Hoffman
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D003120:Colorado / Q000453:epidemiology; D004196:Disease Outbreaks; D034462:Dissent and Disputes; D006801:Humans; D015994:Incidence; D008457:Measles / Q000453:epidemiology* / Q000517:prevention & control; D010686:Philosophy, Medical; D012068:Religion and Medicine; D012189:Retrospective Studies; D012306:Risk; D012574:Schools; D014611:Vaccination / Q000523:psychology / Q000706:statistics & numerical data; D014917:Whooping Cough / Q000453:epidemiology* / Q000517:prevention & control