A startling resurgence of diphtheria among migrant populations in Europe has drawn urgent attention from the global scientific community. A comprehensive study, recently published in the prestigious New England Journal of Medicine, provides unprecedented insights into the largest diphtheria epidemic recorded in Western Europe over the past seventy years. This epidemic, initially identified in 2022 and extending into 2023, has predominantly affected vulnerable groups such as migrants and homeless populations across multiple European nations. The findings challenge previous assumptions by pinpointing transmission events along migration routes or within European reception centers, rather than in migrants’ countries of origin. This revelation reshapes the epidemiological narrative surrounding Corynebacterium diphtheriae and underscores mounting public health imperatives.
Diphtheria is an acute infectious disease caused by Corynebacterium diphtheriae, a Gram-positive bacterium capable of producing a potent exotoxin that damages respiratory tissues and other organs. Historically, widespread vaccination campaigns had relegated diphtheria to a rarity in Western Europe, rendering it a controlled and manageable disease. However, the sudden increase in cases reported in recent years among marginalized populations warns against complacency. In 2022 alone, the European Centre for Disease Prevention and Control (ECDC) cataloged 362 confirmed cases, predominantly affecting young males recently arrived from conflict regions such as Afghanistan and Syria. The epidemic’s survival beyond emergency intervention reflects both the challenges of controlling infectious diseases in mobile populations and the necessity for robust, cross-border health strategies.
Molecular epidemiology has been central to deciphering the dynamics of this outbreak. Researchers at the Institut Pasteur, collaborating with Santé publique France and other European public health bodies, conducted whole-genome sequencing on 363 bacterial isolates collected from affected individuals. The striking genomic similarity among isolates from disparate countries revealed that transmission likely occurred after migrants had left their original homelands. This genetic homogeneity indicates a common point or series of points where infection was contracted, probably along migratory corridors or within asylum facilities. The genomic data also linked the 2022 epidemic strain with a diphtheria outbreak detected in Germany in 2025, suggesting a silent, ongoing circulation of the bacterium within Western Europe that had gone unnoticed until recently.
Epidemiologically, the epidemic exhibits notable demographic characteristics. A vast majority of infections occurred in males, with a median age of 18, emphasizing a young, predominantly male migrant profile. Clinically, the infections were overwhelmingly cutaneous, accounting for approximately 77% of cases, while respiratory diphtheria—a more severe manifestation—was observed in 15%. Cutaneous diphtheria often presents as skin lesions that can serve as bacterial reservoirs, complicating outbreak containment due to subtler symptoms and reduced clinical suspicion. This clinical pattern complicates diagnosis and underlines the necessity for healthcare providers to maintain heightened vigilance, especially when treating vulnerable individuals and migrant populations with limited healthcare access.
Understanding the origin and pathways of transmission remains a critical hurdle. Although the countries of origin were initially suspected as epidemic reservoirs, the absence of genetic diversity in bacterial strains says otherwise. Instead, the study posits that contamination events occurred during transit or within European host countries’ reception centers. These findings raise pressing questions about the sanitary conditions, healthcare infrastructure, and screening measures along migratory routes. Moreover, the mobility and often informal living conditions of migrants hinder comprehensive epidemiological surveillance, rendering the true scope of the epidemic difficult to gauge and control. This uncertainty calls for innovative approaches in field epidemiology and public health outreach.
Public health officials are responding with renewed urgency. The study asserts that effective vaccination programs within the general population have substantially limited larger spread, but stresses persistent vulnerabilities in specific demographic groups. Maintaining high vaccination coverage remains paramount, alongside increased screening efforts targeted at at-risk populations—particularly migrants, homeless people, injecting drug users, and unvaccinated elderly individuals with comorbidities. The international collaboration facilitating rapid data sharing and coordinated responses is cited as a critical factor in adapting prevention and treatment protocols in real time. This model of open cross-border communication exemplifies modern epidemiological practice in addressing infectious threats.
Clinicians’ awareness is emphasized as a frontline defense against this persistent health challenge. Symptoms of diphtheria, especially the cutaneous form, may be subtle and easily overlooked outside endemic contexts. Consequently, heightened suspicion is warranted when treating vulnerable groups closely linked to migrant communities, including healthcare workers and social service providers. Prompt identification, testing, and administration of appropriate antibiotic therapy, combined with diphtheria antitoxin when indicated, are crucial. The awareness of professional risks among individuals with sustained contact to these communities adds another layer of prevention to curtail potential nosocomial or community transmission.
From a research perspective, the outbreak highlights the enduring need to scrutinize bacterial genomic evolution and antimicrobial resistance. Although current treatment regimens remain effective, the specter of emerging antibiotic resistance necessitates continual surveillance of Corynebacterium diphtheriae strains circulating in these populations. Monitoring genetic changes informs both clinical decision-making and public health policies, guiding vaccination strategies and antibiotic stewardship. The Institut Pasteur and associated reference laboratories underscore the value of integrating molecular biology techniques in epidemiological frameworks.
International cooperation, as demonstrated by this study, represents a crucial pillar for successful outbreak management. The National Reference Center (CNR) for diphtheria, newly appointed as part of the European Reference Laboratory network, plays a pivotal role in unifying diagnostic standards and data aggregation across Europe. This harmonization strengthens the continent’s capacity to promptly detect and respond to diphtheria cases, reducing the window for uncontrolled propagation. Partnerships between research entities, healthcare institutions, and public health authorities exemplify the holistic approach necessary to manage infectious diseases in an era marked by unprecedented human mobility.
In conclusion, this unprecedented diphtheria outbreak among migrant populations in Western Europe serves as a potent reminder of the vulnerabilities that remain despite decades of successful infection control. It exemplifies how socio-political factors, such as mass migration and social marginalization, interact with microbial evolution to shape emerging public health crises. The study’s findings compel sustained vigilance, investment in targeted vaccination, improved surveillance among vulnerable groups, and enhanced clinical awareness. By integrating state-of-the-art genomics with pragmatic public health interventions, European institutions demonstrate a model of resilience and adaptability in combating infectious diseases in complex modern contexts.
Subject of Research: People
Article Title: Corynebacterium diphtheriae outbreak among migrant populations in Europe
News Publication Date: 4-Jun-2025
Image Credits: Institut Pasteur
Keywords: Microbial genetics, Bacterial pathogens
