Background: Outbreaks of pertussis continue to occur despite declines in other vaccine-preventable diseases, with morbidity and mortality primarily in the ≤ two year olds. Idaho had the highest reported incidence of pertussis last year in the nation and the lowest pertussis vaccination coverage levels according to the 1996 National Immunization Survey.

Objectives: To investigate vaccination levels and access to healthcare in children ≤2 years of age who had pertussis and their contacts(≤2 years of age) in a rural district in Idaho which had the largest outbreak in the nation.

Methods: We examined all confirmed and probable cases of pertussis to identify those ≤ 2 years of age. We then interviewed families to identify contact children ≤ 2 years of age who had been exposed to pertussis. For the subject population (cases and contacts), we acquired the following information: provider-verified vaccination status, vaccine refusals, disease severity, and provider type.

Results: of the 141 confirmed and probable cases, 24 were ≤2 years of age and who had exposed 53 children ≤2 years of age who did not get pertussis, for a total subject population of 77. The overall vaccination level at the time of the outbreak was 74% and age-appropriate vaccination level at 7 months was 59%. Eigthy-seven percent of the children had at least three doses of a pertussis-containing vaccine at the outset of the outbreak. These vaccination levels were similar to the general population in the district based on findings from a concurrent birth certificate study. All children regardless of vaccination status had an immunization provider. Eighty-six percent of the children had received their last set of vaccinations in the private sector; however, the age-appropriate coverage at seven months of age was lower for those seeing a public provider (64% vs. 27%, p<.05). Vaccine refusal was 1.3%. There was one death (unvaccinated seven week old infant) and three hospitalizations (none with ≥three doses of pertussis vaccine).

Conclusion: Relatively high vaccination levels were not sufficient to prevent the outbreak, but segments of the population were at risk because of undervaccination. All deaths and hospitalizations were among those with <3 doses of pertussis vaccine. All cases and contacts were enrolled with a provider. Efforts are needed at the provider level to increase the age-appropriate vaccination levels in rural areas.