Prevalence of diphtheria carriers in a population with disappearing clinical diphtheria

Modifiable risk factors for diphtheria: A systematic review and meta-analysis

Objective

To identify modifiable risk factors for diphtheria and assess their strengths of association with the disease.

Methods

This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement. Electronic databases and grey literature were searched from inception until January 2023. Studies had to report on diphtheria cases and estimates of association for at least one potential risk factor or sufficient data to calculate these. The quality of non-ecological studies was assessed using the Newcastle-Ottawa Scale (NOS), while the quality of evidence was evaluated using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) criteria.

Results

The search yielded 37,705 papers, of which 29 were ultimately included. All the non-ecological studies were of moderate to high quality. Meta-analysis of 20 studies identified three factors increasing the risk of diphtheria: incomplete vaccination (<3 doses) (pooled odds ratio (POR) = 2.2, 95% confidence interval (CI) = 1.4-3.4); contact with a person with skin lesions (POR = 4.8, 95% CI = 2.1-10.9); and low knowledge of diphtheria (POR = 2.4, 95% CI = 1.2-4.7). Contact with a case of diphtheria; sharing a bed or bedroom; sharing utensils, cups, and glasses; infrequent bathing; and low parental education were associated with diphtheria in multiple studies. Evidence for other factors was inconclusive. The quality of evidence was low or very low for all the risk factors.

Conclusions

Findings from the review suggest that countries seeking to control diphtheria need to strengthen surveillance, improve vaccination coverage, and increase people's knowledge of the disease. Future research should focus on understudied or inconclusive risk factors.

Corynebacterium species nasopharyngeal carriage in asymptomatic individuals aged ≥ 65 years in Germany

PURPOSE

The prevalence of protective anti-diphtheria toxin antibodies decreases with age. Therefore, the elderly might serve as reservoir for potentially toxigenic Corynebacterium (C.) species (C. diphtheriae, C. ulcerans, and C. pseudotuberculosis). This study aimed to examine the colonization rate of the nasopharynx with corynebacteria of individuals aged 65 years and older.

METHODS

In the period from October 2012 to June 2013, nasal and throat swabs were taken from 714 asymptomatic subjects aged 65-106 years (average age 77.2) at three regions in Germany and investigated for Corynebacterium species.

RESULTS

A total of 402 strains of Corynebacterium species were isolated from 388 out of 714 asymptomatic subjects (carriage rate 54.3%). The carriage rate was significantly higher in study participants living in retirement homes (68.4%) compared to those living autonomously at home (51.1%). Strains were isolated mostly from the nose (99%). Corynebacterium accolens was the most often isolated species (39.8%), followed by C. propinquum (24.1%), C. pseudodiphtheriticum (19.4%), and C. tuberculostearicum (10.2%). No C. diphtheriae, C. ulcerans, and C. pseudotuberculosis strains were isolated. A subsample of 74 subjects was tested serologically for anti-diphtheria antibodies. Protective anti-diphtheria toxin antibodies were found in 29.7% of the subjects; 70.3% showed no protective immunity.

CONCLUSIONS

These results suggest that carriage of potentially toxigenic corynebacteria is very rare among people aged 65 and older in Germany. However, the low prevalence of protective anti-diphtheria toxin antibodies might pose a risk for acquiring diphtheria especially for the elderly.

The Mighty World of Microbes: An Overview

The world of microbes on our planet is vast and diverse. This includes the normal bacterial flora present on the skin and mucous membranes of humans. The human microbiome project (HMP) was launched by NIH in 2007 as a part of a road map for medical research. The HMP serves as a template for researchers who are studying more than 1,000 microbial genomes with a focus on their role in health and disease. The study samples have been derived from five human body regions that are known to be inhabited by microbial flora. These include the gastrointestinal tract, female urogenital tract, mouth, nose, and skin. The techniques being used include finger printing, sequencing, dynamic range, and comparison of multiple samples. It is now well accepted that there are more microbial cells than human cells in the human body. Just the gastrointestinal tract harbors more than tenfold microbial cells than the number of human cells in the entire body. The understanding of the relationship between microbes and humans is at best rudimentary at this point in time. Similarly, the relationship between humans and microbes in the environment and environmental surfaces is poorly understood except for a few pathogenic microbes.

Serological survey on the immunity to diphtheria of the northern Greek population

The recent outbreak of diphtheria in the Newly Independent States (NIS) of the former USSR and the immigration from these high risk areas to Greece prompted us to determine the diphtheria antitoxin levels by enzyme-linked immunosorbent assays (ELISA) in 509 healthy individuals (307 males and 202 females) from northern Greece. The population under study was divided in ten age groups from 1 day to > 60 years old. Diphtheria antitoxin levels of > or = 0.1 IU/ml were considered as protective ones. 44.6% of the examined people were found susceptible. The children up to their twenties seem to be immune to diphtheria in a high proportion (86-88.4%). The diphtheria antitoxin levels declined sharply above this age (17.6% in the age group 21-30 years old). The level of protection in adults appeared to be higher in the oldest group (49%). According to these results, the adults are not properly protected. Booster doses of vaccine for them are recommended to improve the resistance of the northern Greek population from possible infection by toxigenic stains of Corynebacterium diphtheriae, imported or endogenous.

Characterization of bacteriophages from tox-containing, non-toxigenic isolates of Corynebacterium diphtheriae

Non-toxigenic strains of Corynebacterium diphtheriae continue to cause disease within immunized populations. A subset of these corynebacteria carry the diphtheria toxin gene but in a cryptic form. To determine whether such strains might contribute to the re-emergence of functional toxin genes, the phages and tox mutations within three clone types were examined. tox-containing, beta-related phages were isolated from two of the strain types. The third isolate appeared to harbour a defective prophage. One of the tox- phages encoded truncated, yet enzymatically-active, forms of diphtheria toxin, suggesting that it had sustained a point mutation within the latter half of its toxin gene. In contrast, the other mutant phage did not elicit the production of either a cross-reacting material or an ADP-ribosylating activity. Complementation tests employing a series of double lysogens confirmed that the mutations responsible for the non-toxigenic phenotype of all of the phages were cis dominant. Given these findings, it is reasonable to hypothesize that tox+ genes can arise within human populations by either homologous recombination between two distinct tox- phages or spontaneous reversion within a single mutant allele.

Clinical and molecular study of Corynebacterium diphtheriae systemic infections in France. Coryne Study Group

Diphtheria is a disease with a long history that almost completely disappeared from developed countries. In addition, until 1987, systemic infections involving Corynebacterium diphtheriae were rare. However, in 1990, an epidemic occurred in Russia. These two circumstances have provided the stimulus to gain insight into the situation in France. In fact, between 1987 and 1993, a total of 59 C. diphtheriae strains were isolated. Epidemiological data were collected for patients from whom 40 strains were isolated from normally sterile sites, including 34 from blood cultures, and half of the bacteremic patients developed endocarditis. Osteoarticular involvement was noted in 11 of these 40 patients, including 5 bacteremic patients. The fatality rate following bacteremia was 36%, despite specific antibiotic treatment (beta-lactams and aminoglycosides). The mean age of the participants was 38 years, with half of the patients subsisting under low socioeconomic conditions and suffering from homelessness or alcoholism. Apparently, the skin turned out to be the major route of transmission in this reemerging disease. Eighty-eight percent of the isolates belonged to the C. diphtheriae biotype mitis. These were found predominantly in the Paris area, and most were of the same ribotype. Those isolates originating from the overseas territories (Guyana and New Caledonia) belonged to C. diphtheriae biotype gravis. No strains were positive for the tox gene by PCR. This study attests to the persistent circulation in France of C. diphtheriae in the form of systemic infections. The matter is especially significant since these strains are nontoxigenic and are of a unique ribotype. The strains are, however, sensitive to most antibiotics, although 20% are rifampin resistant.

Diphtheria: changing patterns in the developing world and the industrialized world

In the past, diphtheria was considered one of the most serious childhood diseases because it took a heavy toll in health and life among preschool-aged children. Prior to the widespread availability of diphtheria toxoid, nearly 70% of cases were in children younger than 15 years of age. In the industrialized countries, immunization against diphtheria became widespread in the 1940s and 1950s. This led to a marked decrease in the incidence of diphtheria. There was also a decrease in circulating toxigenic Corynebacterium diphtheriae organisms, resulting in less natural boosting of antibody levels. This had led to gaps in the immunity of the adult population. Since 1990, diphtheria has made a spectacular comeback in several European countries, with a high proportion of cases in adults. In developing countries, immunization of infants with diphtheria toxoid was introduced with the Expanded Programme on Immunization in the late 1970s. Coverage rose slowly to 46% in 1985 and 79% in 1992. Because the pool of immunized persons is not yet large, the process of maintaining immunity still operates through natural mechanisms, including frequent skin infections caused by C. diphtheriae. But recently, several developing countries where coverage has been high for 5-10 years have reported diphtheria outbreaks. These outbreaks have been characterized by high case fatality rates, a large proportion of patients with complications, and their occurrence in both young and older age groups. In all countries, priority should be given to efforts to reach at least 90% coverage with three doses of diphtheria toxoid in children below one year of age. In countries where diphtheria has been successfully controlled, immunity levels should be maintained by booster doses.

Molecular epidemiology of nasopharyngeal corynebacteria in healthy adults from an area where diphtheria vaccination has been extensively practiced

In addition to conventional biochemical tests, a DNA probe specific for Corynebacterium diphtheriae was used to characterize 53 cystinase-positive and urease-negative corynebacteria strains isolated from pharyngeal and nasal swabs obtained from 515 healthy adults living in an urban area of central Italy. No Corynebacterium diphtheriae strain was found. Six "atypical" strains were isolated, which could not be classified in any of the species so far defined in the Corynebacterium genus. These strains appeared to be biochemically close to Corynebacterium pseudodiphtheriticum and genetically close to Corynebacterium diphtheriae, since their DNAs strongly hybridized, under relatively low stringency conditions, with a Corynebacterium diphtheriae-specific probe and since insertion sequences which are usually found in Corynebacterium diphtheriae genomes were also found to be present in their genomes. No one of these six strains was either toxigenic or susceptible to lysogenization by beta-corynephage carrying the tox gene. Therefore, they do not seem to have any epidemiological relevance as possible hosts for beta-phages.

Immunity to diphtheria, six to 15 years after a basic three-dose immunization schedule

The results of a study of the immunity to diphtheria of 283 girls (9-18 years of age) vaccinated at the age of two years with three doses of vaccine, are reported. The rabbit skin test was used to determine the titre of serum diphtheria antitoxin. 55.8% of the subjects were found to be protected (titre greater than or equal to 0.1 IU/ml), 38.9% were only relatively immune (titre greater than or equal to 0.01- less than 0.01 IU/ml), and 5.3% were unprotected (titre less than 0.01 IU/ml). The antitoxin titres showed a tendency to decrease with time. Even so, 6-15 years after vaccination, the percentages of protected and partially protected subjects were still high (95%).