Toxigenic Strains Of Corynebacterium Diphtheriae Research Articles

Balto and Togo during the cold winter of Alaska (1925): the two canine heroes in the fight against diphtheria.

In recent years, diphtheria has re-emerged in areas with inadequate vaccination coverage, and Europe has not been spared with several cases among migrants. Diphtheria is a potentially fatal infection caused mainly by toxigenic strains of Corynebacterium diphtheriae. Due to the high mortality rate, especially among young children, the fight against diphtheria is considered one of the first conquests of immunization. In the history of medicine, there is a unique case of an unconventional response to a diphtheria outbreak in which sled dogs were used to overcome the supply difficulties of diphtheria antitoxin. The mass media followed the medical response to the outbreak and raised audience awareness of public health issues. The facts of Nome, Alaska, in 1925 can serve as a catalyst to rethink conventional responses to diphtheria outbreaks in low-income countries today and promote mass media awareness of public health importance.

EPIDEMIOLOGICAL INVESTIGATION DIPTHERIA CASES IN KEDIRI DISTRICT IN 2022

Background: Diphtheria is a type of infectious disease that can be prevented by immunization. The cause of diphtheria is the toxigenic strain of Corynebacterium diphtheriae. East Java is the province with the most diphtheria cases in Indonesia. The number of diphtheria cases in East Java increased in 2018 by 695 cases. In 2019 diphtheria cases decreased to 358 cases, in 2020 to 94 cases, and in 2021 by 45 cases. Objective: Knowing the number of diphtheria cases and their prevention. Method: descriptive qualitative research with a case study approach. The definition of a case is a person with symptoms of fever, sore throat, swelling in the neck, and pseudomembranes. Data collection was conducted in five villages, namely Keling Village, Kanigoro Village, Kras Village, Jemekan Village, and Bogem Village in the period from October to November 2022. Results: Clinical symptoms, 100% or all five patients experienced symptoms of fever and sore throat as initial symptoms. Four patients had a fever as the initial symptom, and one started with a sore throat. 40% of patients had symptoms of neck swelling and shortness of breath. The five patients were also found to have pseudomembranes. Conclusion: There were 5 diphtheria suspects found in Kediri District in 2022. The clinical symptoms experienced by the five patients were fever, sore throat, neck swelling, shortness of breath, and pseudomembranes.

Diphtheria in Children- A Clinical Profile of Cases during an Outbreak in Kerala, India

Introduction: Diphtheria is an acute potentially fatal infectious disease caused by the toxigenic strains of Corynebacterium diphtheriae. Acute respiratory obstruction, toxic myocarditis and neurologic weakness are the most important complications of diphtheria. The clinical presentation and severity of diphtheria vary in immunized and non-immunized children. Early diagnosis and prompt treatment including administration of diphtheria antitoxin and antibiotics minimize mortality. Aim: To observe the changing trends in the clinical presentation of diphtheria during the 2016 outbreak and its association with immunization status and antitoxin administration. Materials and Methods: This Longitudinal prospective study conducted among children admitted to Government Medical College, Kozhikode, Kerala, a tertiary care centre with a diagnosis of diphtheria during January 2016 to December 2016. Details of socio-demographic data, clinical presentation, investigations, immunization status, treatment and complications were collected using a semi-structured performa. These children were managed by an interim guideline provided by the state authorities. They were followed-up for 3 months. The data was analyzed using Statistical Package for Social Sciences (SPSS), version 18.0. Results: Among 76 children, 62(82%) were from Malappuram and Kozhikode districts, which have relatively low immunization coverage. Most admissions were in July 2016. Majority (58, 76.3%) of children belonged to Muslim community. The mean age was 8.1 years with male to female ratio 1.53:1. Most of the children (47, 62%) were unimmunized or partially immunized. Cultures were positive for C. diphtheriae in 20 children. Complications were noted in 36 children, which included asymptomatic myocarditis in 31, symptomatic myocarditis in one, palatal palsy in nine, loss of accommodation in four and distal weakness in five. Only one child who received antitoxin within 72 hours of disease onset developed neurological complications. Complications were common in children who received less than minimum three doses of diphtheria vaccines compared to those who received three or more doses (54% vs. 44%). There was no mortality. Conclusion: There was an upward shift in age of affected children. Neurological complications were significantly less in those who received antitoxin within 72 hours of disease onset. Regular monitoring helped to detect asymptomatic myocarditis. The outbreak highlighted the need to improve awareness about diphtheria and better vaccination coverage, especially in older children.

Diphtheria: characteristics of the pathogen and laboratory diagnostics (lecture).

The problem of diphtheria infection remains relevant, since the circulation of toxigenic strains of Corynebacterium diphtheriae persists in the body of bacterial carriers, despite ongoing vaccination. The lecture presents modern ideas about the properties of the pathogen, its pathogenicity factors (toxin, pili, surface proteins (67-72P (or DIP0733), DIP1281, etc.) and their role in the pathogenesis of the disease.. Information about the clinical and epidemiological characteristics and modern methods of laboratory diagnostics of diphtheria is presented. The algorithm of bacteriological research and methods for determining the toxigenic properties of the pathogen are described. The basics of diphtheria vaccination as the only effective means of preventing mass outbreaks of this disease are considered in the framework of the proposed lecture. Knowledge of the peculiarities of the circulation of strains of Corynebacterium diphtheria in modern conditions, pathogenetic and clinical-epidemiological features of diphtheria, as well as modern methods of laboratory diagnostics is important and necessary for students of medical schools and infectious diseases doctors, pediatricians, bacteriologists, therapists, pulmonologists, epidemiologists, etc.

Characterization of toxigenic Corynebacterium diphtheriae strains isolated in Russia

The aim of the study was to characterize toxigenic strains of Corynebacterium diphtheriae by examining 12 toxigenic strains of C. diphtheriae isolated in Russia between January, 2017 to June, 2019. The morphological, toxigenic and biochemical properties of C. diphtheriae was studied. Genotyping of C. diphtheriae strains was performed using MLST and dtxR gene sequencing with subsequent phylogenetic analysis. Results. Toxigenic strains of C. diphtheriae were isolated in the Novosibirsk, Samara and Chelyabinsk Regions, the Khanty-Mansi Autonomous Okrug — Yugra as well as the Republic of Northern Ossetia — Alania. Among these strains, 5 were isolated from diphtheria patients (moderate disease found in one case, mild course — remaining patients) and 7 strains were isolated from bacterial carriers. In two cases C. diphtheriae from diphtheria patients were identified as ST25 sequence type, gravis variant; in one case — ST8 type, gravis variant; two cases — ST67 sequence type, mitis variant. In asymptomatic carriers of tox-positive C. diphtheriae strains they belonged to ST25 sequence type, gravis variant — in two cases, ST67 type, mitis variant — in four cases. A sequencing type was not identified in one case. All sequence types were widespread globally being presented by a large number of isolates in the PubMLST and characterized by a substantial amount of derivative sequence types. At the same time, they belonged to different clonal complexes and differed markedly from each other contributing to their reliable difference as assessed by MLST. Study of gene dtxR sequence diversity showed that all allelic variants were typical for the representatives of these sequence types. New alleles of gene dtxR were not revealed in strains examined. It was shown that non-synonymous substitution C440T leading to A147V amino acid substitution was found solely in one allele distributed in ST8, ST185, ST195 and ST451 types suggesting at late mutation. In contrast, the polymorphism C640A resulting in the amino acid substitution L214I was found not only in the same allele, but also in the basal tree branches indicating that isoleucine was in the ancestral sequence of the protein.

Diphtheria

Diphtheria is a potentially fatal infection mostly caused by toxigenic Corynebacterium diphtheriae strains and occasionally by toxigenic C. ulcerans and C. pseudotuberculosis strains. Diphtheria is generally an acute respiratory infection, characterized by the formation of a pseudomembrane in the throat, but cutaneous infections are possible. Systemic effects, such as myocarditis and neuropathy, which are associated with increased fatality risk, are due to diphtheria toxin, an exotoxin produced by the pathogen that inhibits protein synthesis and causes cell death. Clinical diagnosis is confirmed by the isolation and identification of the causative Corynebacterium spp., usually by bacterial culture followed by enzymatic and toxin detection tests. Diphtheria can be treated with the timely administration of diphtheria antitoxin and antimicrobial therapy. Although effective vaccines are available, this disease has the potential to re-emerge in countries where the recommended vaccination programmes are not sustained, and increasing proportions of adults are becoming susceptible to diphtheria. Thousands of diphtheria cases are still reported annually from several countries in Asia and Africa, along with many outbreaks. Changes in the epidemiology of diphtheria have been reported worldwide. The prevalence of toxigenic Corynebacterium spp. highlights the need for proper clinical and epidemiological investigations to quickly identify and treat affected individuals, along with public health measures to prevent and contain the spread of this disease.

Improved quadruplex real-time PCR assay for the diagnosis of diphtheria.

Introduction. Diphtheria is caused by toxigenic strains of Corynebacterium diphtheriae, Corynebacterium ulcerans and Corynebacterium pseudotuberculosis. For diagnostic purposes, species identification and detection of toxigenic strains (diphtheria toxin (tox)-positive strains) is typically performed using end-point PCR. A faster quadruplex real-time PCR (qPCR) was recently developed (De Zoysa et al. J . Med . Microbiol. 2016;65(12):1521-1527).Aims. We aimed to improve the quadruplex method by adding a 16S rRNA gene target as an internal processing control, providing confirmation of the presence of bacterial DNA in the assays, thus avoiding the possibility of false-negative reporting.Methodology. Universal 16S rRNA gene primers and a probe were defined. The novel method was tested using 36 bacterial isolates and 17 clinical samples. Experimental robustness to temperature and reagent concentration variations was assessed.Results. The method allows detection of the tox gene and distinguishing C. diphtheriae (including the newly described species Corynebacterium belfantii) from C. ulcerans and C. pseudotuberculosis. Complete diagnostic specificity, sensitivity and experimental robustness were demonstrated. The lower limit of detection for C. diphtheriae, C. ulcerans and tox targets was 1.86 genome copies per 5 µl reaction volume. The method was successfully used on two distinct qPCR technologies (LightCycler 480, Roche Diagnostics and Rotor-Gene Q, Qiagen) and in two laboratories (Institut Pasteur, Paris, France and Public Health England - National Infection Service, London, UK).Conclusion. This work describes validation of the improved qPCR quadruplex method and supports its implementation for the biological diagnosis of diphtheria.

Corynebacterium diphtheria, Adhesion, Type and Biofilm Cultures

Relevance. It is now known that toxigenic strains of Corynebacterium diphtheriae are capable not only of adhesion, but also of invasion into epithelial cells of the upper respiratory tract. In addition, Corynebacteria have the ability to form biofilms, as a part of which they can change to some extent their properties (sizes of bacterial cells, antibiotic sensitivity), which can affect their adhesion and invasive properties. Aims. Identification and comparative analysis of adhesive and invasive activity of typical and biofilm cultures of various toxigenic strains of C. diphtheriae. Materials & Methods. Abstract adhesive and invasive properties of standard and biop^nochnyh (120- and 720-hour) cultures of toxigenic strains of C. diphtheriae gravis tox + № 665, № 6765, C. diphtheriae mitis tox + № 269, derived from NISC L.A. Tarasevich, strain C. diphtheriae gravis tox +, isolated from patients with a diagnosis of "localized form of diphtheria" bacteriological laboratory FSI «1002 CSSE SNCMD» Ministry of defence of the Russian Federation, C. diphtheriae gravis strain with a “silent" tox-gene provided by the MBUZ “GB № 1 them. ON. Semashko Rostov-on-Don " on culture pharyngeal epithelial carcinoma cells Hep-2. Results. The identification and comparative analysis of the adhesive and invasive activity of typical an biofilm cultures of various toxigenic strains of C. diphtheriae was carried out. The adhesive and invasive properties of typical and biofilm (120- and 720-hour) cultures of toxigenic C. diphtheriae strains were studied on the culture of Hep-2 carcinoma cells of the pharyngeal epithelium. The ability to adhere type cultures of all toxigenic strains of corynebacteria increased by the 8th and 18th hours of cultivation, and the dynamics of their invasive properties correlated with adhesion. The most pronounced adhesive-invasive potential was found in the circulating strain of C. diphtheriae gravis tox +. Adhesion processes prevailed over invasion in the C. diphtheriae gravis tox + strains № 6765, C. diphtheriae gravis with the “silent" tox-gene and C. diphtheriae mitis tox + № 269. When biofilm was formed, adhesion of corynebacterium increased, and invasiveness decreased dramatically. Conclusion All studied toxigenic strains of C. diphtheriae had adhesive and invasive activity. These properties were most pronounced in the circulating strain of C. diphtheriae gravis tox +. Conclusions. Adhesion and invasion of the causative agent of diphtheria play a significant role in the early stages of the infectious process, whereas subsequently, during the formation of a biofilm, the adhesion of corynebacteria increases and the invasiveness decreases sharply.

A study on clinical and epidemiological profile of patients admitted with white patch in throat to Sir Ronald Ross Institute of Tropical and Communicable Diseases, Hyderabad, India

Background: One of the most common differential diagnosis for a white patch in throat is diphtheria. Diphtheria is an acute infectious disease caused by toxigenic strains of corynebacterium diphtheriae. These bacilli release powerful exotoxin which is responsible for formation of white or greyish or yellowish membrane commonly over tonsils, pharynx or larynx. The objectives of the study were to determine the clinical and epidemiological factors of cases admitted with white patch in throat; to assess the microbiological confirmation rate of diphtheria among cases with white patch in throat; to identify the mortality and morbidity among study population.Methods: A cross sectional record based retrospective study was carried out at Sir Ronald Ross Institute of Tropical & Communicable Diseases, Hyderabad. All the cases admitted in year 2016 with a white/grey/yellowish patch in throat were included in the study. The study was carried out for 2 months.Results: A total of 230 cases were reported and 46.1% of cases were in the age group of 11-20 years. Males constituted about 48.3% and females 51.7% of study population. The most common clinical presentation was Sore throat, fever and a pseudo membrane over tonsils/pharynx. A total of 12 deaths occurred among 230 cases.Conclusions: Deaths occurred most commonly in the younger age group and in the non-immunized. Recovery was faster and the course of illness was uncomplicated in the older age group and in completely immunized individuals.

Possibilities of application of the liquid transport medium for capture of pathological material at laboratory diagnosis of a diphtheria infection.

The main objective of laboratory diagnosis of a diphtheria is identification of the causative agent by means of the minimum quantity of diagnostic tests for obtaining the authentic answer in the most short time. One of the major stages is capture and delivery of pathological material on which the efficiency of carrying out and timeliness of issue of the final answer depends. Considering emergence in the market of commercial liquid transport mediums, assessment of their efficiency for diagnosis of diphtheria is advisable. In the real work the pilot studies allowing to predict efficiency of use of the commercial transport liquid medium ∑-Transwab® with the liquid medium of Ames in two systems - with the standard applicator (system 1) and with the thin extended tampon for sampling from narrow cavities - urethral and nazofarengialny are conducted (system 2). In a research used a control toxigenic strain of Corynebacterium diphtheriae of a biovar of gravis No. 665. In an experiment "imitated" operating conditions of the medical organizations for storage of tampons with pathological material on diphtheria before their transportation in laboratory - on a table at the room temperature (6 and 20 hours), in the refrigerator (6 and 20 hours), in the thermostat (6 and 20 hours). After an incubation all tampons sowed the environment for primary crops of pathological material on a blood tellurite agar.. Accounting of results was carried out in 24 and 48 hours of growth. It is established that the commercial transport liquid medium of Ames can be used for capture of pathological material on diphtheria in the second half of the working day at storage in the conditions of the refrigerator. At the same time, it is necessary to consider a tampon form as the best results on a identification of the causative agent of diphtheria have been received when using a universal tampon.

Strengthening the laboratory diagnosis of pathogenic Corynebacterium species in the Vaccine era.

Over the last three decades, successful implementation of the diphtheria vaccination in the developed and developing countries has reduced the infections caused by the toxigenic strains of Corynebacterium diphtheriae, but a concomitant increase in the invasive infections due to the nontoxigenic strains was seen. In addition, the recent reports on the emergence of nontoxigenic toxin gene-bearing strains, having the potential to revert back to toxigenic form poses a significant threat to human beings. Besides infections caused by C. diphtheriae, the emergence of the respiratory, cutaneous and invasive infections by related pathogenic Corynebacterium species like C. ulcerans and C. pseudotuberculosis, complicate the diagnosis and management of infection. These observations together with the widespread prevalence of diphtheria in the vaccine era, necessitates the strengthening of the epidemiological surveillance and laboratory diagnosis of the pathogen. This review provides the overview of the advantages and limitations of different molecular methods and the role of MALDI-TOF in the laboratory diagnosis of Diphtheria. The contribution of next generation sequencing technology and different genotyping techniques in understanding the pathogenicity, transmission dynamics and epidemiology of the C. diphtheriae is discussed.

<i>Mycobacterium bovis</i> BCG as a Delivery System for the <i>dtb</i> Gene Antigen from Diphtheria Toxin

Diphtheria is a fulminant bacterial disease caused by toxigenic strains of Corynebacterium diphtheriae whose local and systemic manifestations are due to the action of the diphtheria toxin (DT). The vaccine which is used to prevent diphtheria worldwide is a toxoid obtained by detoxifying DT. Although associated with high efficacy in the prevention of disease, the current anti-diphtheria vaccine, one of the components of DTP (diphtheria, tetanus and pertussis triple vaccine), may present post vaccination effects such as toxicity and reactogenicity resulting from the presence of contaminants in the vaccine that originated during the process of production and/or detoxification. Therefore, strategies to develop a less toxic and at the same time economically viable vaccine alternatives are needed to improve existing vaccines in use worldwide. In this study, the Moreau substrain of BCG which is used in Brazil as a live vaccine against human tuberculosis was genetically modified to carry and express the gene encoding for the diphtheria toxin fragment B (DTB). As such, the DNA sequence encoding the dtb gene was cloned into the pUS977 shuttle vector for cytoplasmic expression and successfully introduced into BCG cells by electroporation. Mice immunized with recombinant BCG expressing DTB showed seroconversion with the detection of specific antibodies against DTB. Also, rBCGs stably expressing DTB persisted up to 60 days in the absence of selective pressure in mice and cell viability did not change significantly during the period tested. Finally, immune sera from BALB/c mice vaccinated with rBCGpUS977dtbPW8 were preliminarily tested for their capacity of neutralizing the diphtheria toxin in the Vero Cells assay.

Diphtheria in Europe: Current Problems and New Challenges

Diphtheria, caused by toxigenic strains of Corynebacterium diphtheriae, is an ancient disease with high incidence and mortality that has always been characterized by epidemic waves of occurrence. Whilst towards the beginning of the 1980s, many European countries were progressing towards the elimination of diphtheria, an epidemic re-emergence of diphtheria in the Russian Federation and the Newly Independent States of the former Soviet Union demonstrated a continuous threat of the disease into the 1990s. At present, the epidemic is under control and only sporadic cases are observed in Europe. However, the circulation of toxigenic strains is still observed in all parts of the world, posing a constant threat to the population with low levels of seroprotection. More recently, Corynebacterium ulcerans has been increasingly isolated as emerging zoonotic agent of diphtheria from companion animals such as cats or dogs, indicating the enduring threat of this thought-to-be controlled disease.

Polymerase Chain Reaction for Detection of Toxigenic Strains of Corynebacterium diphtheriae in Milk and Some Milk Products

Polymerase Chain Reaction for Detection of Toxigenic Strains of Corynebacterium diphtheriae in Milk and Some Milk Products

Screening for Corynebacterium diphtheriae and Corynebacterium ulcerans in patients with upper respiratory tract infections 2007–2008: a multicentre European study

AbstractDiphtheria is now rare in most European countries but, when cases do arise, the case fatality rate is high (5–10%). Because few countries continue to routinely screen for the causative organisms of diphtheria, the extent to which they are circulating amongst different European populations is largely unknown. During 2007–2008, ten European countries each screened between 968 and 8551 throat swabs from patients with upper respiratory tract infections. Six toxigenic strains of Corynebacterium diphtheriae were identified: two from symptomatic patients in Latvia (the country with the highest reported incidence of diphtheria in the European Union) and four from Lithuania (two cases, two carriers); the last reported case of diphtheria in Lithuania was in 2002. Carriage rates of non-toxigenic organisms ranged from 0 (Bulgaria, Finland, Greece, Ireland, Italy) to 4.0 per 1000 (95% CI 2.0–7.1) in Turkey. A total of 28 non-toxigenic strains were identified during the study (26 C. diphtheriae, one Corynebacterium ulcerans, one Corynebacterium pseudotuberculosis). The non-toxigenic C. ulcerans strain was isolated from the UK, the country with the highest reported incidence of cases due to C. ulcerans. Of the eleven ribotypes detected, Cluj was seen most frequently in the non-toxigenic isolates and, amongst toxigenic isolates, the major epidemic clone, Sankt-Petersburg, is still in circulation. Isolation of toxigenic C. diphtheriae and non-toxigenic C. diphtheriae and C. ulcerans in highly-vaccinated populations highlights the need to maintain microbiological surveillance, laboratory expertise and an awareness of these organisms amongst public health specialists, microbiologists and clinicians.

Patterns of adherence to HEp-2 cells and actin polymerisation by toxigenic Corynebacterium diphtheriae strains

Corynebacterium diphtheriae strains displayed different degrees of attachment to HEp-2 cell monolayers with two distinct adherence patterns, termed localised (LA) and diffuse (DA). The LA phenotype predominated over the DA phenotype. The non-sucrose fermenting strains expressing DA pattern adhered mostly with high index values (≥10 bact/cell). Low adhesion index (<10 bact/cell) was mainly observed among sucrose fermenting strains. The fluorescein isothiocyanate (FITC)-labelled phalloidin assay (fluorescent-actin staining test) showed positive results for microorganisms of both LA and DA phenotypes. The FITC-labelled C. diphtheriae non-fimbrial surface proteins 67–72p interacted directly with HEp-2 cell membranes. Therefore, toxigenic C. diphtheriae exhibited LA and DA adherence patterns and ability to induce actin polymerisation. The experimental evidences also pointed to 67–72p as putative adhesins of C. diphtheriae to HEp-2 cells.

Intracellular viability of toxigenic Corynebacterium diphtheriae strains in HEp-2 cells

Corynebacterium diphtheriae, generally considered an extracellular coloniser, was evaluated for its ability to enter and survive within HEp-2 monolayers by gentamicin protection assay. Intracellular viability of HC01 strain, isolated from endocarditis, was more expressive (2.59%) than observed in 241 (0.21%) and CDC-E8392 (1.93%) strains. Electron microscopy of C. diphtheriae-infected HEp-2 cells revealed intracellular bacteria inside membrane-bound vacuoles. Bacterial internalisation was totally inhibited by 5 μM cytochalasin E and significantly inhibited by 100 μM genistein ( P<0.05). Therefore, C. diphtheriae presents the ability to survive within cultured epithelial cells and signalling cascade as well as actin polymerisation are required for entry of diphtheria bacilli into HEp-2 cells.

Epidemiology of Diphtheria in the 1990s

Introduction Respiratory diphtheria, a severe systemic illness caused by toxigenic strains of Corynebacterium diphtheriae, was one of the most common causes of death among children in the pre-vaccine era. Diphtheria toxoid vaccine was developed in the 1920s. Widespread immunization led to the virtual elimination of diphtheria in developed countries by the 1960s and to a marked reduction of diphtheria cases in developing countries in the 1980s. The control of diphtheria has resulted in a larger proportion of adults lacking immunity as a result of failure to vaccinate or waning immunity among the vaccinated in the absence of exposure to infection. In the early 1990s, epidemic diphtheria re-emerged in the Newly Independent States (NIS) of the former Soviet Union after 30 years of control and caused thousands of deaths, primarily among adults. This paper briefly reviews the epidemiology of diphtheria in developed and developing countries, focusing on the 1990s, and comments on recent laboratory developments.

Diphtheria in the Russian Federation in the 1990s.

A resurgence of diphtheria spread throughout the Russian Federation in the early 1990s; diphtheria had been well controlled, but circulation of toxigenic strains of Corynebacterium diphtheriae had persisted since the implementation of universal childhood vaccination in the late 1950s. More than 115,000 cases and 3,000 deaths were reported from 1990 to 1997, and, in contrast to the situation in the prevaccine era, most of the cases and deaths occurred among adults. Contributing factors included the accumulation of susceptible individuals among both adults and children and probably the introduction of new strains of C. diphtheriae. Vaccine quality, vaccine supply, or access to vaccine providers did not significantly contribute to the epidemic. Mass vaccination of adults and improved childhood immunization controlled the epidemic. High levels of population immunity, especially among children, will be needed to prevent and control similar outbreaks in the future.

Diphtheria in Lithuania, 1986-1996.

Diphtheria reappeared in Lithuania in 1986 and rose to epidemic levels by 1992. Between 1991 and 1996, 110 cases of diphtheria were registered, with an incidence of 0.03-1.15/100,000 population. Most cases (84%) and all 17 deaths occurred among persons >/=15 years, most of whom had never been vaccinated. Persons 40-49 years old had the highest average annual age-specific morbidity (1.70/100,000) and mortality (0.53/100,000) rates. Low levels of immunity among individuals 40-49 years old and migration to epidemic areas in Russia and Belarus contributed to the epidemic's occurrence. Between 1991 and 1995, toxigenic Corynebacterium diphtheriae strains were isolated from 84 of all registered patients (76%), and nontoxigenic strains were isolated from 13 (12%). By 1996, two mass vaccination campaigns, which provided one dose of vaccine to individuals 25-30 years old and three doses of vaccine to persons 31-60 years old, helped reduce the number of cases. The first campaign achieved 69% coverage; the second achieved 48% coverage.