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Internalization of non-toxigenic Corynebacterium diphtheriae by cultured human respiratory epithelial cells.

Although infection by Corynebacterium diphtheriae is a model of extracellular mucosal pathogenesis, and diphtheria is one of the most worried diseases, this microorganism can be associated also with invasive infections such as endocarditis, septic arthritis, and osteomyelitis. Invasive infections are usually caused by non-toxigenic C. diphtheriae strains. Over the last years severe pharyngitis/tonsillitis associated with the isolation of non-toxigenic C. diphtheriae have been described. Penicillin treatment failure of these infections could only partially be explained by penicillin tolerance of the causing strain. Thus, we examined the in vitro ability of non-toxigenic C. diphtheriae throat clinical isolates to adhere to, and enter human respiratory epithelial cells. Trasmission and scanning electron microscopy demonstrated intracellular C. diphtheriae in laryngeal (HEp-2 cells) and pharyngeal (Detroit D562 cells) tissue culture. Live intracellular bacteria were detectable up to 48 h post-infection. Using a variety of compound that act on eukariotic cell structures, the internalization of C. diphtheriae seems to occur via a zipper-like mechanism. It is likely that internalization of C. diphtheriae can be involved in throat colonization contributing to bacterial eradication failure and asymptomatic carriage.

Bacterial Adhesion↗

Reconstitution of active diphtheria toxin based on a hexahistidine tagged version of the B-fragment produced to high yields in bacteria.

Diphtheria toxin consists of an A-fragment that inactivates elongation factor 2 and a B-fragment that both binds to the toxin receptor and mediates translocation of the A-fragment across cellular membranes to the cytosol. Several fragments of the toxin and an inactive version of the holotoxin have been expressed in Escherichia coli, but the B-fragment alone has proven difficult to express. Only low levels of expression have been achieved. We have designed a hexahistidine tagged version of a modified diphtheria toxin B-fragment (DT-BHis) that can be expressed to high levels in E. coli. DT-BHis contains the entire diphtheria toxin B-fragment preceded by an alanine and succeeded by a leucine, a glutamic acid and a hexahistidine tag and could be purified in a single step using nickel-coated agarose beads to 85% homogeneity. DT-BHis bound specifically to the diphtheria toxin receptor and was able to compete out the effect of the wild type diphtheria toxin. Furthermore, DT-BHis was able to form pores in cellular membranes in a manner similar to the wild type B-fragment. The high yield makes DT-BHis a suitable tool in studies of diphtheria toxin interaction with cells or liposomes since functional diphtheria toxin was easily formed upon addition of A-fragment. The reconstituted diphtheria toxin showed toxicity in the same range as the wild type.

Animals↗

Physicochemical and immunochemical techniques predict the quality of diphtheria toxoid vaccines.

The most critical step in the production of diphtheria vaccines is the inactivation of the toxin by formaldehyde. Diphtheria toxoid (DTx) is produced during this inactivation process through partly unknown, chemical modifications of the toxin. Consequently, diphtheria vaccines are difficult to characterise completely and the quality of the toxoids is routinely determined with potency and safety tests. This article describes the possibility of monitoring the quality in diphtheria vaccine production with a selection of physicochemical and immunochemical tests as an alternative to established in vivo tests. To this end, diphtheria toxin was treated with increasing formaldehyde concentrations resulting in toxoid products varying in potency and residual toxicity. Differences in the quality of the experimental toxoids were also assessed with physicochemical and immunochemical techniques. The results obtained with several of these analyses, including SDS-PAGE, primary amino group determination, fluorescence spectroscopy, circular dichroism (CD) and biosensor analysis, showed a clear correlation with the potency and safety tests. A set of criteria is proposed that a diphtheria toxoid must comply with, i.e. an apparent shift of the B-fragment on SDS-PAGE, a reduction of primary amino groups in a diphtheria molecule, an increased resistance to denaturation, an increased circular dichroism signal in the near-UV region and a reduced binding to selected monoclonal antibodies. In principle, a selected set of in vitro analyses can replace the classical in vivo tests to evaluate the quality of diphtheria toxoid vaccines, provided that the validity of these tests is demonstrated in extensive validation studies and regulatory acceptance is obtained.

Animals↗

BCG vaccination among West African infants is associated with less anergy to tuberculin and diphtheria-tetanus antigens.

To examine risk factors for anergy, delayed-type hypersensitivity was assessed among 884 infants participating in a vaccine trial in Guinea-Bissau. The infants were skin-tested at 7.5 months of age with a panel of seven intradermal antigens. Risk factors for anergy to tuberculin or anergy to both the diphtheria and tetanus antigens were determined in relation to Bacillus Calmette-Guérin (BCG) vaccination, diphtheria-tetanus-pertussis (DTP) vaccination, and measles vaccination. We found sick children to be more anergic to tuberculin and diphtheria-tetanus antigens than healthy children (OR=2.49 (95% confidence interval 1.40-4.55)). There was a higher prevalence of anergy to tuberculin in the rainy season than in the dry season (OR=1.67 (1.25-2.23)). Children who had taken antimalarials within the last week had a higher prevalence of anergy to tuberculin (OR=1.41 (1.02-1.92)). BCG vaccination was significantly associated with less anergy to tuberculin and diphtheria-tetanus antigens (OR=0.42 (0.28-0.63), OR=0.77 (0.60-0.99), respectively). Children vaccinated with BCG before 1 month of age were more anergic to tuberculin than children vaccinated after 1 month (OR=1.61 (1.19-2.19)). DTP vaccination was associated with less anergy to diphtheria-tetanus antigens (OR=0.40 (0.32-0.49)), but not to tuberculin. Children with a positive reaction to tuberculin were less likely to be anergic to diphtheria-tetanus antigens (OR=0.36 (0.26-0.49)) than children with a negative tuberculin reaction. Children who were vaccinated with BCG before they received their last DTP vaccine were less anergic to diphtheria-tetanus antigens (OR=0.40 (0.16-0.88)) than other DTP-vaccinated children. In conclusion, current disease, rainy season, age below 1 month of age at the time of BCG vaccination, and administration of chloroquine or quinimax within the last 7 days were risk factors for anergy to tuberculin among 7.5-month-old infants. BCG vaccination and a positive tuberculin reaction were associated with a lower prevalence of anergy to both tuberculin and diphtheria-tetanus. Thus, BCG vaccination may contribute to better cell-mediated immune responses among infants.

BCG Vaccine↗

Immunity to diphtheria among refugees in southern Italy.

This study assessed the immune status against diphtheria of a sample of refugees (mainly Kosovars and Kurds) in southern Italy (Puglia). The 54.8% of 1128 subjects showed full protection against diphtheria, 30.1% had basic protection and 15.1% resulted seronegative for antitoxin antibody. Only from 45.9 to 73.9% of 0-10 years old refugees were fully protected while from 12.3 to 24.2% were seronegative to diphtheria with the poorest protection rate among Kurdish children from Turkey. Kosovars showed the highest protection rate to diphtheria whereas data suggest a probable endemic level of diphtheria in Iraq. The screening of refugees revealed a low coverage rate for diphtheria, especially in children, probably due to deterioration of the health service infrastructure or intermittent basic health care in the country of provenience. In terms of public health measures, there is the need of administering booster doses to all refugees coming into Italy and into other host countries to increase the coverage rate against diphtheria. The implementation of the immunization programs against diphtheria in the countries of provenience is also strongly recommended.

Adolescent↗

Immunoprecipitation and partial characterization of diphtheria toxin-binding glycoproteins from surface of guinea pig cells.

125I-Labeled membrane glycoproteins that specifically interact with diphtheria toxin and CRM197 protein--but not with diphtheria toxoid, fragment A of diphtheria toxin, or cholera toxin--were detected by use of the lactoperoxidase labeling technique followed by an immunoprecipitation system. These glycoproteins, which adhere to lentil lectin-Sepharose columns, are present on the surface of diphtheria toxin-sensitive guinea pig lymph node cells but are completely lacking on the surface of diphtheria toxin-resistant mouse L cells. The major 125I-labeled glycoprotein that interacts with diphtheria toxin exhibits anomalous behavior, characteristic of glycoproteins, when analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. This demonstration of the biochemical nature of specific diphtheria toxin binding membrane components raises the possibility that the detected components are diphtheria toxin receptors.

Animals↗

Receptor-mediated endocytosis of diphtheria toxin by cells in culture.

The binding and uptake of fluorescently labeled diphtheria toxin by cells in culture has been examined by using epifluorescence video intensification microscopy. Rhodamine-labeled diphtheria toxin retained significant toxicity on bioassay and in cell culture and was tested for uptake by human WI-38 and mouse 3T3 fibroblasts grown in culture. When added to cells at 37 degrees C, toxin was observed to become concentrated and internalized in discrete vesicles in both cell lines. The appearance of fluorescent clusters could be prevented by addition of excess unlabeled diphtheria toxin to the medium or by addition of ATP (which has been shown to block toxin binding to cells), indicating that the rhodamine-labeled toxin was binding to diphtheria toxin-specific cell surface binding sites. When the simultaneous uptake of rhodamine-labeled diphtheria toxin and fluorescein-labeled alpha 2-macroglobulin was monitored, the two proteins appeared in the same clusters indicating that the toxin undergoes receptor-mediated endocytosis. Despite the difference in susceptibility to diphtheria toxin of cells derived from sensitive (human) and resistant (mouse) tissues, the behavior of the rhodamine-labeled derivative in both cell lines was indistinguishable in terms of toxin required for formation of clusters or inhibition by unlabeled toxin or by ATP. These results demonstrate that diphtheria toxin-specific cell surface binding sites occur on both insensitive and sensitive cells and suggest that toxin is processed similarly by both cell types during its initial cell surface binding and internalization by this pathway. The possible involvement of this uptake system in the mechanism of action of diphtheria toxin in cells is discussed.

Animals↗

Evidence that diphtheria toxin and modeccin enter the cytosol from different vesicular compartments.

Inhibition of protein synthesis in Vero cells was measured at different periods of time after treatment with diphtheria toxin and the related plant toxin modeccin. Diphtheria toxin acted much more rapidly than modeccin. Cells were protected against both toxins with antiserum as well as with agents like NH4Cl, procaine, and the ionophores monensin, FCCP, and CCCP, which increase the pH of intracellular vesicles. Antiserum, which is supposed to inactivate toxin only at the cell surface, protected only when it was added within a short period of time after modeccin. Compounds that increase the pH of intracellular vesicles, protected even when added after 2 h, indicating that modeccin remains inside vesicles for a considerable period of time before it enters the cytosol. After addition of diphtheria toxin to the cells, compounds that increase the pH of intracellular vesicles protected only approximately to the same extent as antitoxin. This indicates that after endocytosis diphtheria toxin rapidly enters the cytosol. At 20 degrees C, the cells were more strongly protected against modeccin than against diphtheria toxin. The residual toxic effect of diphtheria toxin at 20 degrees C could be blocked with NH4Cl whereas this was not the case with modeccin. This indicates that at 20 degrees C the uptake of diphtheria toxin occurs by the normal route, whereas the uptake of modeccin occurs by a less efficient route than that dominating at 37 degrees C. The results indicate that after endocytosis diphtheria toxin rapidly enters the cytosol from early endosomes with low pH (receptosomes). Modeccin enters the cytosol much more slowly, possibly after fusion of the endocytic vesicles with another compartment.

Ammonium Chloride↗

Corynebacterium ulcerans and Corynebacterium pseudotuberculosis responses to DNA probes derived from corynephage beta and Corynebacterium diphtheriae.

Strains of Corynebacterium ulcerans and Corynebacterium pseudotuberculosis (Corynebacterium ovis) were examined for the production of diphtheria toxin. A majority of C. ulcerans strains (25 of 37) and 1 C. pseudotuberculosis strain (1 of 14) gave a positive Elek test for diphtheria toxin, and for all strains but 1, production of diphtheria toxin was inhibited at the same level of Fe2+ as was the Corynebacterium diphtheriae control. All Elek-positive cultures as well as two Elek-negative isolates of C. ulcerans gave a positive signal when hybridized with a DNA probe unambiguous for the diphtheria toxin gene (tox) under conditions of high stringency. The majority of probe-positive C. ulcerans strains contained three or more DNA restriction fragments that hybridized with converting corynephage beta, suggesting that in C. ulcerans as in C. diphtheriae there may be a relationship between toxinogeny and carriage of beta-related phage. Selected strains of C. diphtheriae, C. ulcerans, and C. pseudotuberculosis were examined for DNA homology by a semiquantitative technique. There was very little homology between C. diphtheriae and members of the other two species. Strains of C. ulcerans and C. pseudotuberculosis, although more closely related, appeared to belong to distinct species as well.

Bacteriophages↗

Enhancement of diphtheria toxin-induced apoptosis in Vero cells by combination treatment with brefeldin A and okadaic acid.

In the present study, we compared the abilities of ricin and diphtheria toxin to induce apoptosis in Vero cells. The cytolysis and DNA fragmentation by ricin paralleled its protein synthesis inhibitory activity. However, unlike ricin, diphtheria toxin could induce neither cytolysis nor DNA fragmentation in Vero cells up to very high concentration, in spite of the fact that Vero cells were even more sensitive to protein synthesis inhibition by diphtheria toxin than ricin. Interestingly, coexistence of brefeldin A (BFA) and okadaic acid (OA) significantly enhanced diphtheria toxin-mediated cytolysis and DNA fragmentation without affecting the activity of protein synthesis inhibition. Ammonium chloride almost completely abolished the ability of diphtheria toxin to induce apoptosis in the presence of BFA and OA as well as the protein synthesis inhibitory activity. The mutant CRM 197, which does not catalyze the ADP ribosylation of elongation factor-2 (EF-2), failed to induce apoptosis in Vero cells even in the presence of BFA and OA. Thus, translocation of diphtheria toxin into the cytosol and subsequent enzymatic inactivation of EF-2 may be necessary steps to induce apoptosis. Taken together our results suggest that protein synthesis inhibition by toxins is not sufficient to induce apoptosis, and underlying mechanisms of apoptosis induction may be distinct between ricin and diphtheria toxin. Since a morphological change in the Golgi complex was observed in Vero cells treated with BFA and OA, modulation of the Golgi complex by these reagents may be partly responsible for enhanced apoptosis induction by diphtheria toxin.

4-Chloro-7-nitrobenzofurazan↗

[Diphtheria morbidity in Russia today].

The data on diphtheria morbidity and the occurrence of carrier state for its causative agent at the period of 2001-2002 were analyzed. The rates of morbidity and detected carrier state for these years were 0.63-0.55 and 0.65-0.64 respectively. Nevertheless, in spite of the relatively low morbidity rates the presence of the toxic forms of diphtheria (400 patients for two years) and lethal cases (with lethality rate reaching 5.4%) indicated that the epidemic situation in diphtheria remained tense. The most unfavorable situation was observed in the North-Western and Central regions of Russia. In urban areas morbidity rates were still 2- to 3-fold higher in than in rural ones, but the latter showed a higher percentage of severe cases (46.6% in 2001 and 39.7% in 2002) and lethal outcomes (13.6% and 19.2%). The latter was indicative of drawbacks in the immunoprophylaxis, diagnostics and treatment of diphtheria in rural areas. In the total structure of diphtheria patients adults prevailed: 75%. The highest morbidity rates were registered among children aged 3-6 years, among adults in the age groups of 18-19 years and 50-59 years. The epidemic process developed mainly among the immunized population, which was indicated by a high proportion of vaccinated persons among those affected by this infection (62.8-66.6%) and a mild course of the disease in the majority of them. The present epidemiological situation in diphtheria was determined by patients not vaccinated against this infection. The proportion of severe cases among nonvaccinated children was 42.4-51.6% and lethal outcomes, 12.9-15.1%. Among nonimmunized adults these figures were equal to 43.1% and 9.3% respectively. The highest percentage of children, not vaccinated during the first years of their life, was registered among those in the asocial families, refugees and homeless persons. Among adults these were persons above 50 years old, as well as jobless persons of working age, pensioners and invalids, who had limited possibilities of undergoing vaccination due to their social position. It was these social and age groups that should be regarded as risk groups with respect to the severity of the course of diphtheria and lethality. To stabilize diphtheria morbidity, the full complex of prophylactic and antiepidemic measures, and primarily the immunization of the population, should be systematically carried out.

Adolescent↗

Antidiphtheria antibody responses in patients and carriers of Corynebacterium diphtheriae in the Arkhangelsk region of Russia.

Diphtheria is under control in industrialized countries. However, single cases and outbreaks still occur and the disease is not completely understood. Forty-three individuals suspected of having diphtheria who were referred to the Infectious Disease Hospital of Arkhangelsk from December 1994 to March 1995 were included in this study. Fifteen patients were diagnosed as having diphtheria and received equine hyperimmune antidiphtheria toxin antiserum, and 28 were diagnosed as carriers, 12 with nondiphtherial tonsillitis or pharyngitis and 16 without symptoms. Serum samples were obtained on admission and during the course of the disease or during follow-up of carrier status. Samples were analyzed for antibodies against diphtheria toxin with both an in vitro neutralization test (NT) and a human-specific enzyme immunoassay. All of the cases but one were confirmed by a positive culture. Twelve patients had pharyngeal diphtheria, and three had combined laryngeal and pharyngeal disease. Half of the patients had life-threatening disease, and one died. On admission, the median antibody titers measured with the NT were 0.085 IU/ml for the patients, 5.12 IU/ml for the symptomatic carriers, and 10.24 IU/ml for the healthy carriers. All of the diphtheria patients but one and nine of the carriers (six symptomatic and three healthy) had increased antibody levels during the first 7 to 10 days after admission. No obvious correlation was revealed between the antibody level or its kinetics and the course of the disease. Antibody levels on admission of >1 IU/ml were associated with a low risk of diphtheria.

Adolescent↗

Diphtheria remains a threat to health in the developing world--an overview.

Changes in the epidemiology of diphtheria are occurring worldwide. A large proportion of adults in many industrialized and developing countries are now susceptible to diphtheria. Vaccine-induced immunity wanes over time unless periodic booster is given or exposure to toxigenic Corynebacterium diphtheriae occurs. Immunity gap in adults coupled with large numbers of susceptible children creates the potential for new extensive epidemics. Epidemic emergencies may not be long in coming in countries experiencing rapid industrialization or undergoing sociopolitical instability where many of the factors thought to be important in producing epidemic such as mass population movements and difficult hygienic and economic conditions are present. The continuous circulation of toxigenic C. diphtheriae emphasizes the need to be aware of epidemiological features, clinical signs, and symptoms of diphtheria in vaccine era so that cases can be promptly diagnosed and treated, and further public health measures can be taken to contain this serious disease. This overview focused on worldwide data obtained from diphtheria with particular emphasis to main factors leading to recent epidemics, new clinical forms of C. diphtheriae infections, expression of virulence factors, other than toxin production, control strategies, and laboratory diagnosis procedures.

Adult↗

[Diphtheria immunity in the German population].

In the years 1991-1993 the diphtheria antitoxin titres of the blood serum of 2404 persons living in germany was determined by means of the ELISA test. Its aim was to to get an idea of the population's protection given by vaccination against diphtheria. It became evident that the average protection given by vaccination against diphtheria was on the decrease as people grew older. Thus only 3.8% of the 2-5-year olds did not have any protection given by vaccination (antitoxin titre < 0.01 IU/ml). The same was true for approximately 25% of the examined persons who were older than 30. Less than 10% of these persons had a thorough protection given by vaccination/(antitoxin titre > 0.1 IU/ml). In the age group of the 51-60-year olds better immunological protection than expected was found, which could be ascribed to the fact that there was a natural immunigation during the last wide-spread diphtheria epidemic in germany in the 'forties. Another aspect of this result could be a better motivation for-diphtheria vaccination in this age group. Furthermore, it was noticed that the average diphtheria antitoxin titres of women in all age groups were below those of men. In view of the great percentage of the adult population which is not sufficiently protected against diphtheria, it appears necessary to provide for more information of this population group to stimulate and motivate them to care for better protection by vaccination.

Adolescent↗

The immunization of adults against diphtheria in Sweden.

Two hundred and three women who disclaimed vaccination against diphtheria were divided into four groups and injected with either 2.0 or 6.25 Lf of a routine diphtheria toxoid or of a more purified preparation. One hundred and twenty-six of these women who did not show a secondary antibody response were given a second and a third injection one month and one year, respectively, after the first injection. Prebooster (third injection) antitoxin titres of greater than or equal to 0.01 IU ml-1 (the minimum level for protection) were found in 22 and 37% of those who received 2.0 and 6.25 Lf, respectively. Postbooster titres of greater than or equal to 1.0 IU ml-1 (calculated to give a protection of at least ten years of duration) were found in 23 and 58% of those who received 2.0 and 6.25 Lf, respectively. The rate of untoward reactions was low. Fever of short duration occurred in five women. Four out of the five women received 6.25 Lf of the more purified diphtheria toxoid and one 2 Lf of the routine toxoid. Local reactions greater than 10 cm were observed in three women. All received the higher dose, 6.25 Lf of diphtheria toxoid. Local reactions greater than 5 but less than or equal to 10 cm occurred in up to 13% (6.25 Lf of diphtheria toxoid). No significant difference between the groups of women vaccinated with routine or more purified toxoid was found. It was concluded that the diphtheria toxoids in the two doses of 2 Lf and 6.25 Lf did not induce a satisfactory immune response. To induce adequate protection the dose of diphtheria vaccine needs to be the same for adults and children, i.e. 12.5 Lf.

Adult↗

Antibody response to accelerated immunisation with diphtheria, tetanus, pertussis vaccine.

From May, 1990, a new schedule of immunisation against diphtheria, tetanus, and pertussis (at 2, 3, and 4 months) replaced the previous more widely spaced schedule. A report that children had lower concentrations of diphtheria and tetanus antibodies a month after an accelerated schedule led us to undertake a controlled study to assess antibody response and the persistence of antibodies a year after immunisation in children receiving vaccine according to widely spaced and accelerated schedules. Concentrations of antibodies to diphtheria and tetanus toxoids and to Bordetella pertussis filamentous haemagglutinin (FHA) were measured by solid-phase radioimmunoassay (SP-RIA). We studied 57 children who received accelerated immunisation at median ages of 11, 16, and 21 weeks and two control cohorts (total n = 82) who received vaccine at median ages of 15, 21, and 45 weeks. 6-8 weeks after the third dose the accelerated-schedule group had lower (p < 0.0001) geometric mean concentrations of antibody to tetanus (0.522 [95% CI 0.383-0.710] vs 3.43 [2.45-4.81] IU/mL), diphtheria (0.266 [0.179-0.396] vs 2.39 [0.616-3.53] IU/mL), and FHA (0.044 [0.030-0.063] vs 0.270 [0.196-0.374] units/mL) than the longer-schedule group. 12 months after the third dose the differences between the groups had narrowed (tetanus 0.197 vs 0.341 IU/mL, p = 0.29; diphtheria 0.100 vs 0.131 IU/mL, p = 0.64; FHA 0.014 vs 0.016 units/mL, p = 0.72). At that time all children had tetanus antibody concentrations above protective levels (0.01 IU/mL); only 2 of 31 in the accelerated-schedule group and 3 of 31 in the longer-schedule group had diphtheria antibody concentrations below the protective level. The use of an accelerated schedule of diphtheria, tetanus, and pertussis vaccination is unlikely to lead to an increase in the proportion of children unprotected against these diseases before the preschool booster.

Antibodies, Bacterial↗

Absence of protective immunity against diphtheria in a large proportion of young adults.

The schedule of vaccination recommended worldwide for diphtheria, tetanus and other diseases, provides good immunity during childhood. However, little attention has been paid to effective immunity in adults. We have collected sera from 334 Italian Army recruits and tested them for the presence of protective immunity against diphtheria and tetanus. In vivo neutralization assays were performed on rabbits and mice and values below 1/100 IU ml-1 were considered negative. Of the recruits, 22.9% were negative for diphtheria, while only 5.3% had no protective immunity against tetanus. This finding shows that a large proportion of Italian young adults are susceptible to diphtheria, and this could be dangerous if they travel to sites where this disease is still endemic, or if they come into contact with people coming from such areas. A booster vaccination of young adults against diphtheria should become common practice to avoid this risk. To reduce the side effects which are often associated with diphtheria vaccination in adults, we have developed a vaccine which contains a highly purified, non-toxic mutant of diphtheria toxin. This vaccine is combined with tetanus toxoid and can be routinely used as a booster in adults.

Adolescent↗

Immunity to diphtheria in Izmir, Turkey.

In order to assess immunity to diphtheria in Izmir, Turkey, a total of 743 persons 1-70 years of age were selected with cluster sampling. The information on socio-demographic characteristics, vaccination status and diphtheria history was gathered for each participant. Diphtheria antitoxin levels were measured qualitatively by using micro-enzyme immune assay. Of studied population, 79.1% had fully protective antitoxin levels (> or = 0.1 IU/ml). Diphtheria protection rates showed a gradual age-related decrease, reaching minimum in the 30-44 age group, in which 40.2% of these subjects had antibody titre below the full protective level. The diphtheria antitoxin geometric mean titer was highest in the 5-9 year age group (1.05 IU/ml). Then, geometric mean titer decreased with increasing age, and reached the minimum level in the 30-44 age group (0.19 IU/ml). These results suggest that in Izmir, Turkey, full serological protection against diphtheria is only detectable in 60% of the adult population. The enhancement of diphtheria immunity by booster vaccinations in adolescents and adults should be considered in Turkey.

Adolescent↗