title: Density of day cares in relation to reported pertussis incidence in Philadelphia.
abstract: OBJECTIVE
  Reported pertussis incidence has increased markedly in recent years. In addition to the documented increase in under-immunization and waning immunity, the increase may be related to the more frequent use of child care services by parents over the last few decades. Additionally, clustering of outbreaks may be related to neighborhood characteristics not previously identified.
  
  
  METHODS
  We conducted a citywide case-control study of children in Philadelphia aged birth through six years, between 2001 and 2013. Cases were reported as probable pertussis diagnoses to the Health Department. Controls were sampled from the city's immunization information system and matched to the cases by date of birth.
  
  
  METHODS
  Multilevel logistic regression was used to isolate the independent contributions of individual and neighborhood risk factors and the corresponding relative odds of pertussis. The density of day cares in each neighborhood served as the main exposure and reported incident cases of confirmed and probable pertussis was the main outcome.
  
  
  RESULTS
  Between 2001 and 2013, 410 cases of confirmed and probable pertussis were included with four controls matched per case yielding a final sample of 2050 children from 45 Philadelphia neighborhoods. There was a 30% increase in the risk of pertussis based solely on the neighborhood where the children resided (median odds ratio 1.3, 95% credible interval 1.1, 1.6). The density of day cares in each neighborhood was unrelated to the distribution of pertussis cases.
  
  
  CONCLUSIONS
  Pertussis clustering was observed at the neighborhood level in Philadelphia, but was unrelated to the neighborhood's day care density. From a Health Department perspective, the highest risk neighborhoods should be targeted for vaccine campaigns and further research to identify the etiologic risk factors.
authors.affiliation: Department of Epidemiology and Biostatistics, Drexel University Dornsife School of Public Health, Philadelphia, PA 19104, United States. Electronic address: ng338@drexel.edu.
authors.forename: N D
authors.initials: ND
authors.lastname: Goldstein
authors.affiliation: Division of Disease Control, Philadelphia Department of Public Health, Philadelphia, PA 19146, United States.
authors.forename: E C
authors.initials: EC
authors.lastname: Newbern
authors.affiliation: Department of Epidemiology and Biostatistics, Drexel University Dornsife School of Public Health, Philadelphia, PA 19104, United States.
authors.forename: L P
authors.initials: LP
authors.lastname: Tabb
authors.affiliation: Department of Epidemiology and Biostatistics, Drexel University Dornsife School of Public Health, Philadelphia, PA 19104, United States.
authors.forename: S L
authors.initials: SL
authors.lastname: Welles
mesh_terms: D016022:Case-Control Studies; D002648:Child; D002656:Child Day Care Centers / Q000706:statistics & numerical data*; D002675:Child, Preschool; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D016015:Logistic Models; D008297:Male; D015143:Philadelphia / Q000453:epidemiology; D012111:Residence Characteristics / Q000706:statistics & numerical data*; D012307:Risk Factors; D014917:Whooping Cough / Q000453:epidemiology*
keywords: Day care/child care; Multilevel modeling; Neighborhood; Pertussis; Vaccination