RISK OF SERIOUS ACUTE NEUROLOGICAL ILLNESS AFTER IMMUNIZATION WITH DIPHTHERIA-TETANUS-PERTUSSIS VACCINE - A POPULATION-BASED CASE-CONTROL STUDY

Objective.-To evaluate the association between serious acute neurological illness and receipt of whole-cell pertussis vaccine, given as diphtheria-tetanus-pertussis (DTP) vaccine. Design.-Population-based case-control study. Setting.-Outpatient and inpatient hospital settings, physician practices, and the general population in Washington and Oregon states. Subjects.-A total of 424 confirmed cases of neurological illness were identified prospectively during a 12-month period by statewide active surveillance from the population of 218 000 children 1 to 24 months of age living in Washington and Oregon (estimated 368 000 DTP immunizations given). Each case child was matched to two population control children by birth date (+/-5 days), gender, and county of birth. Written immunization records were used to determine whether illness occurred within 7 days of immunization in case children, or within 7 days of the same reference date in control children, thus qualifying as exposed. Main Outcome Measures.-Outpatient and inpatient cases of complex febrile seizures, seizures without fever, infantile spasms, and acute encephalitis/encephalopathy confirmed by an expert panel masked to immunization history. Results.-The estimated odds ratio (OR) for onset of serious acute neurological illness within 7 days for young children exposed to DTP vaccine was 1.1 (95% confidence interval [CI], 0.6 to 2.0). When the analysis was restricted to children with encephalopathy or complicated seizures and adjusted for factors possibly affecting vaccine administration, the OR was 3.6 (95% Cl, 0.8 to 15.2). Odds ratios for specific study diagnoses varied, but all CIs included 1. No elevated risk was observed for the largest group of illnesses studied, nonfebrile seizures (OR, 0.5; 95% CI, 0.2 to 1.5). Conclusions.-This study did not find any statistically significant increased risk of onset of serious acute neurological illness in the 7 days after DTP vaccine exposure for young children.