Comparative seroepidemiology of diphtheria in six European countries and Israel

Abstract

Serological surveys for diphtheria were conducted in six European countries including Czech Republic, Hungary, Ireland, Latvia, Luxembourg, Slovakia and one country outside Europe, Israel. For each country, a nationally representative population sample was collected across the entire age range and was tested for antibodies to diphtheria toxin. Although each national laboratory used its preferred assay, the results were all standardized to those of the in vitro neutralization test and expressed in international units (IU) which allowed comparative analyses to be performed. The results showed that increasing age is related to a gradual increase in seronegative subjects (<0·01 IU/ml of diphtheria antitoxin antibodies). This may reflect waning immunity following childhood vaccination without repeated booster vaccinations in adults. Differences in seronegativity were also found according to gender. In subjects aged 1-19 years, geometric mean titres of antitoxin are clearly related to the different vaccination schedules used in the participating countries. Although clinical disease remains rare, the susceptibility to diphtheria observed in these serosurveys highlights the importance of strengthened surveillance.

Seroprevalence of diphtheria toxoid IgG antibodies in children, adolescents and adults in Poland

“…But in our studies <50% children in age 0–2 years old had protective level of antibodies whereas Edmunds et al [16] showed that >90% of 1 year olds were seropositive (various tests were used, such as ELISA, DELFIA, ToBI and the Vero cell neutralization test). A low proportion of seropositive children was also identified in the Czech Republic (using the Vero cell neutralization test) [14]. Our results together with results obtained for Czech population support the opinion of Chironna et al [17], that basic immunization without booster doses may result in unsatisfactory protection among children.…”

“…In all European countries where diphtheria seroprevalence studies were conducted, including Poland, the level of antibodies to diphtheria toxin decreases significantly in persons above 40 years old [14,16,24-29]. The most drastic decrease was observed in Poland (this study), Spain and Ireland, reaching > 67% of seronegative individuals [14,25].…”

“…The higher level of diphtheria antitoxin antibodies in the Polish population in the 1990s may have been maintained by reinforcing natural immunity and boosting through subclinical infections, as in 1990s and earlier, diphtheria was a quite common disease in Poland. Such an explanation is supported by the observation in Latvia where diphtheria is endemic and the prevalence of antibodies to diphtheria toxin is high in all age groups of the population (investigated using a commercial ELISA kit) [14]. …”

More than 20 years after re-emerging in the 1990s, diphtheria remains a public health problem in Latvia

“…From 1996 to 2003 annual seroepidemiological studies were carried out in Latvia. Studies in European countries have indicated that immunity levels below the protective level (> 0.1 IU) increased with age of adults [24]. On average in Latvia, for 23% of adults the immunity level was lower than protective and for 30% of adults it was protective.…”

Diphtheria Surveillance

“…To monitor the effectiveness of control programmes and inform policy Reviewing vaccination history on all cases through enhanced surveillance is a valuable means of monitoring the effectiveness of the vaccine. Seroprevalence studies can also be used to assess whether or not the vaccination programme is sufficiently protective, as well as monitoring the degree of waning immunity and the duration of protection (Edmunds et al 2000;Di Giovine et al 2012). A high case fatality ratio may indicate problems with late diagnosis, case management, or the availability or quality of antibiotics and/or antitoxin.…”