PERTUSSIS IN MASSACHUSETTS, 1981-1991 - INCIDENCE, SEROLOGIC DIAGNOSIS, AND VACCINE EFFECTIVENESS

Massachusetts provides diphtheria-tetanus toxoid-pertussis (DTP) vaccine, and since 1980 has monitored pertussis with a statewide diagnostic service. The incidence of bacteriologically confirmed pertussis was 104.5 per 100,000 person-years in 1-month-old infants and declined progressively thereafter. Infants <6 months old experienced disproportionate morbidity: 44% of bacteriologically confirmed pertussis, 64% of hospitalizations, and 71% of hospital days. Most children with pertussis had received <3 DTP doses during childhood, whereas 87% of adolescents with pertussis had received greater than or equal to 4 doses. Serodiagnosis by single serum anti-pertussis toxin antibody ELISA increased the incidence of confirmed pertussis in persons 11-19 years old from 3.0 to 12.9 per 100,000 and in persons greater than or equal to 20 years old from 0.16 to 0.56 per 100,000. Bacteriologic methods underestimate pertussis incidence, but a single serum anti-pertussis toxin antibody ELISA is a practical method for population-based diagnosis in adolescents and adults.