Susanna Taormina

Analogous IgG subclass response to pertussis toxin in vaccinated children, healthy or affected by whooping cough.

The study of antigen specific IgG subclass distribution during disease, or during any other natural or artificial immunisation, can provide useful information on the kind of the immune response and the expected levels of protection. This is particularly true for diseases, such as pertussis in which the mechanisms underlying specific defence are still not completely understood. An investigation was therefore performed to evaluate the IgG subclass response to pertussis toxin (PT) in sera from 89 healthy vaccinated children and 131 vaccinated or unvaccinated children convalescent after a confirmed B. pertussis symptomatic infection. Antibody titres were expressed in arbitrary ELISA units/ml, and statistical analyses were performed. In unvaccinated convalescent children IgG1 and IgG3 were prevalent whereas in children immunised with two different acellular pertussis (aP) vaccines, both healthy and convalescent, IgG1, IgG2 and IgG4 antibodies were mainly produced. Maintenance of the same anti-PT antibody response pattern in healthy acellular pertussis vaccine recipients and in vaccinated children who later acquire the disease is an interesting result indicative of the priming effect induced by these vaccines in the direction of a relatively higher Th2 cell-polarisation of the immune response.

European Sero-Epidemiology Network 2: standardisation of immunoassay results for pertussis requires homogeneity in the antigenic preparations.

A standardisation process, already developed during the earlier European Sero-Epidemiology Network (ESEN) project, was employed with a more robust algorithm to harmonise results of pertussis serological assays performed in 12 European and non-European countries. Initially, results from each countrys own assay were compared with those obtained at the reference laboratory by means of an in-house pertussis toxin (PT)-based ELISA: seven countries used in-house or commercial PT-ELISAs; the other countries used assays based on Bordetella pertussis whole cell extracts (WCE) (three countries) or on combined PT-FHA (filamentous haemagglutinin) antigenic preparations (two countries). The WCE assays, although admitted for diagnostic purposes, confirmed their low correlation with the PT-ELISAs and their results could not be used for standardisation; the PT-FHA ELISAs gave results that were suitable for standardisation in one country but unsatisfactory in the other; the use of purified PT in serological assays confirmed its better reliability than other preparations and all PT-ELISAs results could be calibrated against those of the reference centre. In the standardisation process two high-titre cut-offs indicative of likelihood of recent infection (from within 4 weeks of disease onset up to 1 year after) were included for evaluations as they are suggested to be more useful, for the sero-epidemiological assays of immunity to pertussis, than the cut-off of protection, commonly employed, but still not defined for pertussis. Providing PT-ELISAs are used, standardisation of pertussis assay results is always possible and, when standardisation is performed, evaluation and comparison of the impact of different interventions can be also allowed, by measuring at the distribution of high antibody titres in the populations.

Seroepidemiology of pertussis infection in an urban childhood population in Cameroon

In 1989, the prevalence of IgG antibodies to pertussis toxin (PT) in a sample of 367 unvaccinated apparently healthy children 5–14 years old was estimated by ELISA in Kumba City (Cameroon). Children were recruited using a systematic random sampling from six primary schools located in different districts of the city. The sample was representative of the various socio-economic classes.The overall prevalence was 75%; it increased from 62% in 5 year old children to 81% in children 12–14 years old (P < 0.01). IgG antibody prevalence was positively related to the family size. Children belonging to households of nine or more members had a 2.2-fold risk (C.I. 95 per cent =1.1–4.6) of previous exposure to B. pertussis infection. No association was found with the fathers occupation (O.R. = 1). These findings demonstrate a great impact of pertussis infection in Cameroon, with a nearly total exposure by late childhood.

Prevalence of pertussis IgG antibodies in children in Palermo, Italy

SummaryThe prevalence of IgG antibodies toBordetella pertussis in a sample of 615 1–12-year-old unvaccinated children in Palermo was estimated by ELISA. The overall prevalence was 56%; it increased from 24% in one to three-year-old children to 67% in 11–12-year-old children (p<0.01). IgG antibody prevalence was not associated with the fathers years of schooling (OR 1), nor with the family size (OR 1.3; C.I. 95%=0.8−2.2). For children aged one the three years, serological results showed that the history of pertussis reported by parents in questionnaires gave high specificity (93.2%) and negative predictive value (85.4%). Our seroepidemiological study evidences a great exposure of children toB. pertussis in Palermo, with a high proportion of infections occurring after three years of age.ZusammenfassungBei 615 ein bis zwölf Jahre alten Kindern, die in Palermo leben und nicht gegen Pertussis geimpft wurden, wurde die Prävalenz von IgG-Antikörpern gegenBordetella pertussis mittels ELISA bestimmt. Die Gesamtprävalenz betrug 65%; sie nahm von 24% bei ein bis drei Jahre alten Kindern auf 67% bei 11–12jährigen zu (p < 0,01). Es bestand keine Beziehung zwischen der IgG-Antikörperprävalenz und der Schulbildung des Vaters (OR 1) oder der Größe der Familie (OR 1,3; C.I. 95%=0,8−2.2). Bei ein- bis dreijährigen Kindern zeigten die serologischen Ergebnisse, daß die auf den Fragebogen von den Eltern angegebene Pertussisanamnese hochspezifisch war (93,2%) und einen hohen negativen prädiktiven Wert hatte (85,4%). Unsere seroepidemiologische Studie belegt, daß Kinder in Palermo dem KeuchhustenerregerB. pertussis stark ausgesetzt sind und ein großer Teil der Infektionen nach dem dritten Lebensjahr auftritt.