Authors: MarieLouise von Linstow Peter Lotko Pontoppidan CarlHeinz Wirsing von König James D Cherry Birthe Hogh
Publish Date: 2010/04/08
Volume: 169, Issue: 9, Pages: 1119-1122
Abstract
We measured IgA and IgG antibodies to pertussis toxin PT and filamentous hemagglutinin FHA in sera from 203 1yearold children who had received one to three doses of a monocomponent PT toxoid vaccine Ten children 5 had IgA antibody to PT indicating recent infection seven of these children had received three doses of vaccine PT IgA responders did not have significantly longer coughing episodes than PT IgA nonresponders Since an IgA antibody response occurs in only ∼50 of infected children the actual infection rate in our cohort is estimated to ∼10 The apparent high Bordetella pertussis infection rate in Danish infants suggests that the monocomponent PT toxoid vaccine used in Denmark has limited efficacy against B pertussis infection A prospective immunization study comparing a multicomponent vaccine with the present monocomponent PT toxoid vaccine should be undertakenDespite high vaccination coverage pertussis continues to be a major cause of morbidity and mortality in Europe 16 The clinical spectrum is diverse and is affected by patient age previous exposure to the organism and immunization history 2 3 11 The heterogeneity in pertussis disease expression makes it an often unrecognized and undiagnosed disease Pertussis appears epidemically every 2 to 5 years However epidemiological data are incomplete and different reporting procedures suggest that only the tip of the iceberg is evident 2 3 11 16 Improved disease surveillance and diagnoses are essential to determine the true burden of the diseaseThe situation in Denmark is unique in that all children are vaccinated with a domestically produced DTaP DiTeKik vaccine in which toxoided pertussis toxin PT is the only pertussis component The PT toxoid vaccine replaced the wholecell pertussis vaccine in January 1997 The PT toxoid vaccine is reported to provide about 78 protection against notified pertussis after three vaccinations given at 3 5 and 12 months of age as part of the national child immunization program 9 Vaccination effectiveness for two doses of pertussis toxoid vaccine in the first year of life is reported to be 59 In September 2003 a preschool pertussis booster vaccination at 5 years of age was implemented to reduce transmission to susceptible young children Infection results in IgA and IgG antibody responses to specific Bordetella pertussis antigens whereas vaccination results in only an IgG response to these antigens 3 11Diagnosis of pertussis based on clinical symptoms is complicated by a number of factors the wide spectrum of symptoms and misdiagnosis owing to similarity between symptoms of other infections 2 3 11 16 A WHO committee in 1991 developed a primary case definition to be used in vaccine efficacy trials An illness with paroxysmal cough of ≥21 days and either cultureconfirmed infection with B pertussis or serological evidence of infection with B pertussis or household contact with a case of cultureconfirmed pertussis with onset of cough within 28 days before or after onset of cough 21In the present study we investigated whether there was evidence of circulation of B pertussis in the community This would provide baseline data on which to assess the epidemiology of B pertussis and thus direct future use of pertussis vaccines in DenmarkThe study population consisted of healthy children enrolled from the postnatal ward at Hvidovre Hospital Denmark during a 12month period from May 2004 to May 2005 19 Children were originally enrolled for the study of human metapneumovirus and respiratory syncytial virus infections in infancy Approximately 20 children were enrolled each month to ensure that the children were sampled equally throughout the year A total of 242 healthy newborns were enrolled of whom 217 were followed throughout 1 yearChildren were monitored with detailed health diaries and through monthly home visits until 1 year of age The study procedures have been previously described in detail 19 The children were scheduled to receive routine immunizations with DTaPIPVHib at 3 5 and 12 months of age Blood samples were obtained by venous puncture from 203 of the children at age 12 months and the sera kept at −80°C until further analysisTwofold dilutions of 50 µl of serum were used for the pertussis ELISA IgA and IgG antibodies to PT and filamentous hemagglutinin FHA were measured by a standardized ELISA procedure and expressed in ELISA units EU/ml with respect to reference serum 3 of the Center for Biologics Evaluation and Research/US Food and Drug Administration CBER/FDA 20 The lower levels of detection for the assays were 17 EU/ml for IgGantiPT 24 EU/ml for IgAanti PT 18 EU/ml for IgGantiFHA and 17 EU/ml for IgAantiFHA
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