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

Objectives. Previous studies have indicated that provider characteristics a re an important determinant of immunization coverage. The objectives of thi s study were to: 1) assess immunization coverage levels among 2-year-old ch ildren 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 pr ovider survey of immunization policies. Setting. Forty-five randomly selected, private medical practices in 3 count ies in California. Patients. Children 12 to 35 months old, followed by the participating pract ices. Methods. Providers underwent a detailed assessment of their immunization co verage and completed a questionnaire describing their immunization policies and procedures. Immunization data were abstracted from randomly selected m edical charts of children 12 to 35 months old. Only patients who met the cr iteria for active status (greater than or equal to 2 visits and greater tha n or equal to 1 visit during the preceding 18 months) were included in anal yses. Immunization coverage levels were calculated and logistic regression was used to estimate the risk of underimmunization associated with differen t 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 an alysis revealed 5 independent risk factors for underimmunization. The stron gest 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, adm inistering diphtheria-tetanus-pertussis 4 at a separate visit from the Haem ophilus 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 previousl y. Immunization coverage levels were found to be low and significant risk f actors for underimmunization were identified. Recommendations are made for immunization policy changes and targeting of immunization improvement inter ventions at practices that may be at risk for low immunization coverage.