Immunization levels and risk factors for low immunization coverage among private practices

Objectives. Previous studies have indicated that provider characteristics are an important determinant of immunization coverage. The objectives of this study were to: 1) assess immunization coverage levels among 2-year-old children receiving care in private practices in 3 California counties; and 2) evaluate practice and patient risk factors for low immunization coverage. Study Design. Cross-sectional chart review of immunization histories and provider survey of immunization policies. Setting. Forty-five randomly selected, private medical practices in 3 counties in California. Patients. Children 12 to 35 months old, followed by the participating practices. Methods. Providers underwent a detailed assessment of their immunization coverage and completed a questionnaire describing their immunization policies and procedures. Immunization data were abstracted from randomly selected medical charts of children 12 to 35 months old. Only patients who met the criteria for active status (greater than or equal to 2 visits and greater than or equal to 1 visit during the preceding 18 months) were included in analyses. Immunization coverage levels were calculated and logistic regression was used to estimate the risk of underimmunization associated with different practice and child characteristics. Results. Of the 72 eligible practices that were contacted, 45 participated in the study, yielding a participation rate of 62%. The median immunization coverage of participating offices was 54% (range: 0%-91%). Multivariate analysis revealed 5 independent risk factors for underimmunization. The strongest predictors were having fewer than 50% active children in the practice and children having fewer than 8 visits to the provider. Other significant predictors were the percentage of patients in the practice on Medicaid, administering diphtheria-tetanus-pertussis 4 at a separate visit from the Haemophilus influenzae type b booster, and practice location. Conclusions. These data provide new insights into immunization practices in an important clinical setting that has been poorly characterized previously. Immunization coverage levels were found to be low and significant risk factors for underimmunization were identified. Recommendations are made for immunization policy changes and targeting of immunization improvement interventions at practices that may be at risk for low immunization coverage.