KEYWORD1:
pertussis, surveillance

BACKGROUND:
During 2001, 113 confirmed cases of pertussis (51 culture confirmed, 62 epi-linked) were reported in Vermont, for an average crude incidence of 18.3 cases / 100,000; nationally, 7580 cases were reported, with an incidence of 2.69 cases / 100,000. During 1997-2001, Vermont ranked either first of second nationally in pertussis incidence, with culture-confirmed cases accounting for 45%-58% of the cases. This high incidence occured even though Vermont only reports culture-confirmed and epi-linked cases to CDC, and despite Vermont's high immunization rates.

OBJECTIVE:
To describe the epidemiology of pertussis in Vermont compared with the United States, and to suggest possible reasons for observed differences.

METHOD:
Vermont and United States average pertussis incidence rates for 1997-2001 were compared by age group. Vermont incidence rates were calculated for both confirmed cases, and confirmed plus probable cases.

RESULT:
From 1997-2001, Vermont's average incidence of pertussis in children aged <1 year was 109/100,000 for confirmed cases, and 166/100,000 when probable cases were included. These rates are approximately double and triple the average national incidence of 55/100,000 in children <1 year. For all other age groups Vermont incidence rates averaged 12 times higher for confirmed cases and 20 times higher when probable cases were included.

CONCLUSION:
Given Vermont's high immunization coverage rates, it is unlikely that Vermont's "true" incidence is so much higher than the national "true" incidence. Factors that could contribute to better reporting of pertussis cases include provider alerts and education, active follow-up of potential cases, and free laboratory testing provided at the State's public health laboratory.
LEARNINGOBJECTIVES:
To describe the epidemiology of pertussis in Vermont compared with the United States, and list potential reasons for Vermont's high reported incidence and differential age distribution.