Diphtheria in England: 2024
Updated 24 April 2025
Applies to England
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This report summarises the epidemiology of diphtheria in England for 2024 and reiterates current recommendations on diagnosis and clinical management of diphtheria.
Main messages
The main points arising from this report are that:
- diphtheria is a vaccine-preventable disease that can be life-threatening
- from January to December 2024, toxigenic corynebacteria were isolated from 12 human individuals in England; 2 Corynebacterium diphtheriae (C. diphtheriae) cases and 10 Corynebacterium ulcerans (C. ulcerans) cases; there were no deaths
- both C. diphtheriae cases presented with cutaneous symptoms
- there were no toxigenic C. diphtheriae cases amongst asylum seekers with recent arrival in England, compared with 13 cases in 2023 and 72 cases in 2022
- 7 of the 10 toxigenic C. ulcerans cases presented with cutaneous symptoms; 2 cases had mild respiratory symptoms and the remaining case presented with infective endocarditis
- there were no non-toxigenic tox gene-bearing (NTTB) cases, compared to 0 and 1 in the two years prior
- four cases of non-toxigenic C. diphtheriae associated with infective endocarditis were reported by clinicians in England
Background
Diphtheria is a very rare infection in England due to the success of the routine immunisation programme introduced in 1942, when the average annual number of cases was about 60,000 with 4,000 deaths (1). Over the past decade, the number of diphtheria cases in England has increased from an average of 2 to more than 10 cases per year (with the exception of 2020).
Diphtheria vaccine is an inactivated toxoid vaccine available as a combination vaccine that is highly effective in protecting individuals from the effects of toxin-producing corynebacteria.
There are three Corynebacterium species that can potentially produce toxin:
- C. diphtheriae
- C. ulcerans
- Corynebacterium pseudotuberculosis (C. pseudotuberculosis)
The latter two are both less common globally and traditionally associated with farm animal contact and dairy products and more recently, for C. ulcerans, with companion animal contact (2, 3).
Although there is no direct evidence of person-to-person transmission of C. ulcerans infection, there have been incidents that suggest this mode of transmission is possible (3) and therefore contact tracing is carried out as for cases of toxigenic C. diphtheriae.
Diphtheria can present with a range of clinical presentations. Classic respiratory diphtheria is characterised by a swollen ‘bull neck’ and strongly adherent pseudomembrane which obstructs the airways; a milder respiratory form of the disease where patients present with sore throat or pharyngitis can occur in immunised or partially immunised individuals (2).
Cutaneous presentations, characterised by ‘rolled edge’ ulcers, are also common, particularly in tropical regions (3).
Treatment involves prompt administration of diphtheria anti-toxin (DAT) for severe cases to prevent the late complications from circulating toxin and appropriate antibiotics for clearance of the organism from the nasopharynx. Public health management of clinical cases of diphtheria in England is provided by local health protection teams (HPTs), including identification, assessment and prophylaxis of close contacts (3).
Laboratory confirmation of diphtheria is usually made by detection of the expression of diphtheria toxin in isolates of C. diphtheriae, C. ulcerans or C. pseudotuberculosis or initially using PCR for species confirmation and detection of the diphtheria toxin gene.
The determination of toxigenicity in England requires submission of isolates of these three species to UK Health Security Agency’s (UKHSA) Vaccine Preventable Bacteria Section (VPBS), within the Respiratory and Vaccine Preventable Bacteria Reference Unit (RVPBRU), which is the National Reference Laboratory (NRL) for diphtheria. Identification and the presence of the toxin (tox) gene are tested for using real-time PCR. If the tox gene is detected, the isolate is tested for expression of diphtheria toxin using the Elek test (4). Public health actions proceed on the basis of the results from PCR testing.
The availability of both PCR and Elek testing has identified a number of C. diphtheriae isolates carrying the tox gene (PCR-positive) but not expressing the toxin (Elek-negative), termed non-toxigenic tox gene-bearing (NTTB) strains (3). The pathogenesis and clinical significance of isolation of this organism are not yet well understood; NTTB are not thought to cause diphtheria and therefore, as reversion to toxin expression is considered highly unlikely, guidelines recommend such cases are managed as non-toxigenic strains with antibiotic therapy only if clinically indicated (3).
Cases of diphtheria in England in 2024
This 2024 review updates a previous annual review of diphtheria cases in England for 2023 (5). Data sources for the enhanced surveillance of diphtheria include notifications, reference and NHS laboratory reports, death registrations, and individual case details such as vaccination history, source of infection, and severity of disease obtained from hospital records and general practitioners.
During 2024, toxigenic strains of corynebacteria were identified from 12 persons by the NRL (2 C. diphtheriae; 10 C. ulcerans).
This compares with toxigenic strains identified from:
- 27 persons in 2023 (16 C. diphtheriae, of which: 13 were among asylum seekers with recent arrival in England; and 11 C. ulcerans)
- 87 persons in 2022 (76 C. diphtheriae, of which 72 were among asylum seekers; and 11 C. ulcerans)
- 10 toxigenic strains in 2021 (7 C. ulcerans and 3 C. diphtheriae)
- 1 toxigenic strain in 2020 (C. ulcerans)
- 10 toxigenic strains in 2019 (all C. ulcerans), and
- 11 toxigenic strains in 2018 (3 C. ulcerans and 8 C. diphtheriae).
No NTTB C. diphtheriae strains were identified in 2024, compared to none in 2023; 1 in both 2022 and 2021; and 2 in each of the years 2020, 2019 and 2018.
Diphtheria is a notifiable disease in accordance with the amended Public Health (Control of Disease) Act 1984 and accompanying regulations (6). Suspected cases are reported to UKHSA via the Notifications of Infectious Diseases (NOIDs) system: by registered medical practitioners, based on clinical suspicion; or by local microbiology laboratories via the Second-Generation Surveillance System (SGSS) on identification of a notifiable organism.
In 2024, there were 22 diphtheria notifications received from NOIDs for England. Laboratory investigation identified:
- 1 toxigenic C. diphtheriae infection
- 2 non-toxigenic C. diphtheriae infections, and
- 1 toxigenic C. ulcerans infection.
The 18 remaining notifications were submitted presumptively in the absence of identification of corynebacteria by local testing. Sixteen were subsequently found not to be a corynebacterial infection, and 2 cases were not tested after being deemed clinically incompatible with diphtheria. Both toxigenic cases were formally notified to UKHSA through direct referral of isolates to the NRL.
During 2024, the NRL received a total of 352 isolates for confirmation and toxigenicity testing from 325 individual cases for investigation (135 human and 190 animal) from England.
This compares with:
- 328 isolates from 278 individual cases (170 human and 108 animal) in 2023
- 253 isolates from 242 individual cases (202 human and 40 animal) in 2022
- 50 isolates (25 human and 4 animal) in 2021, and
- 29 individual isolates (25 human and 4 animal) in 2020
Ten individuals were identified as being infected by toxigenic C. ulcerans, and 2 individuals by toxigenic C. diphtheriae, only 2 of which were formally notified (Table 1). Toxigenic C. ulcerans strains were confirmed amongst a further 89 isolates from 78 animals, 2 of which were epidemiologically linked to a human case.
Of the remaining isolates: 125 were non-toxigenic C. diphtheriae; 94 were non-toxigenic C. ulcerans; 7 were non-toxigenic C. pseudotuberculosis; and 24 were not C. diphtheriae, C. ulcerans or C. pseudotuberculosis.
Table 1. Summary of (a) Diphtheria notifications (NOIDs) (b) Toxigenic corynebacteria by strain, and (c) NRL toxigenicity testing: England, 2024
| (a) Total diphtheria notifications in 2024 | |
|---|---|
| Number due to toxigenic C. diphtheriae | 1 |
| Number due to toxigenic C. ulcerans | 1 |
| Number due to non-toxigenic C. diphtheriae | 2 |
| Notified but did not meet possible case classification | 18 |
| (b) All toxigenic corynebacteria isolates from human cases in 2024 | |
|---|---|
| Toxigenic C. diphtheriae | 2 |
| Toxigenic C. ulcerans | 10 |
| NTTB C. diphtheriae | 0 |
| (c) All toxigenic corynebacteria isolates submitted to the NRL in 2024 | |
|---|---|
| Toxigenic C. diphtheriae | 3 |
| NTTB C. diphtheriae | 0 |
| Non-toxigenic C. diphtheriae [note 1] | 125 |
| Toxigenic C. ulcerans [note 2] | 99 |
| Non-toxigenic C. ulcerans [note 3] | 94 |
| Non-toxigenic C. pseudotuberclerosis | 7 |
| Other – Not C. diphtheriae, C. ulcerans or C. pseudotuberclerosis [note 4] | 24 |
Note 1. Includes multiple isolates from 4 individuals
Note 2. Includes 89 isolates from 78 animals
Note 3. Includes 87 isolates from 82 animals
Note 4. Includes 5 isolates from animals
Toxigenic Corynebacterium diphtheriae
In 2024, toxigenic C. diphtheriae strains from 2 individuals were identified in England. The cases among residents in England were aged 70 to 75 years, with symptom onset during recent travel to Pakistan and Somalia, respectively. One case had unknown immunisation history and the other was partially immunised prior to infection. Both cases were hospitalised with symptoms consistent with cutaneous diphtheria.
Initial contact tracing for the 2 cases identified 23 close contacts, two of which were healthcare workers (HCWs) whose personal protective equipment (PPE) was deemed insufficient. All identified close contacts were offered antibiotic prophylaxis and vaccinations (as necessary). HCWs were individually risk assessed and excluded from work until negative diphtheria test results were obtained, as appropriate.
In 2022, an outbreak of diphtheria was reported among migrants in Europe (7) with a similar increase in cases identified among individuals arriving by small boat to England (8). This continued into 2023, though there was a marked decrease in cases.
In 2024, no toxigenic C. diphtheriae strains were identified amongst asylum seekers.
Toxigenic Corynebacterium ulcerans
There were 10 toxigenic C. ulcerans isolates from 10 individuals identified in 2024, of which 7 had a cutaneous presentation, 2 had a sore throat (with isolation from a throat swab) and 1 presented with sepsis and infective endocarditis. The age range of these cases was 26 to 86 years.
Two of the cases were hospitalised, neither was treated with DAT, and there were no fatalities. Both individuals were recorded to have contact with animals, though only one of the animal contacts tested positive for C. ulcerans. One case was fully vaccinated and the other partially vaccinated.
Contact tracing for all cases was carried out, with all identified close contacts being offered antibiotic prophylaxis and vaccinations (as necessary). Healthcare workers (HCW) with significant exposure were identified where insufficient personal protective equipment (PPE) was used. HCW close contacts were risk assessed individually and excluded from work until a negative diphtheria test was returned, as appropriate. All were offered antibiotic prophylaxis and a dose of diphtheria-containing vaccine.
Table 2. Clinical presentation of diphtheria cases and causative organism, England 2024
| Clinical presentation of cases | Toxigenic C. diphtheriae | Toxigenic C. ulcerans | Total |
|---|---|---|---|
| Severe respiratory diphtheria (sore throat with exudate or membrane) | – | – | 0 |
| Mild respiratory diphtheria (sore throat/pharyngitis) | – | 2 | 2 |
| Cutaneous diphtheria | 2 | 7 | 9 |
| Cutaneous and respiratory diphtheria | – | – | 0 |
| Asymptomatic/respiratory carrier | – | – | 0 |
| Other | – | 1 | 1 |
Non-toxigenic Corynebacterium diphtheriae with infective endocarditis
There were 4 cases of non-toxigenic C. diphtheriae, with imaging evidence of infective endocarditis, identified in England between July and December 2024. The cases were largely among young males (although ages ranged between 20 and 55 years) with a history of smoking or nasal insufflation of heroin or cocaine. All cases emerged from London and neighbouring regions, with three cases experiencing homelessness or living in shared accommodation. Thus far, no clear epidemiological link between cases has been identified.
The UKHSA stood up a national response in January 2025 to co-ordinate the public health response and ongoing investigation.
Further information
Microbiological laboratories are requested to promptly submit all suspected isolates of C. diphtheriae, C. ulcerans and C. pseudotuberculosis to the UKHSA NRL, RVPBRU, Colindale, London, using the laboratory request form R3 (9).
From 1 April 2014, the test result which helps inform public health actions is a real-time PCR result which confirms the identity of C. diphtheriae, C. ulcerans or C. pseudotuberculosis and determines whether the gene for the diphtheria toxin (tox) is present.
If the tox gene is detected, the isolate is then subjected to the Elek test to confirm expression of toxin (4). The NRL also provides advice on all aspects of laboratory testing for diphtheria and related infections. Advice on immunisation against diphtheria, provision of vaccine and provision of diptheria antitoxin for therapeutic use is available from the UKHSA Colindale Immunisation and Vaccine Preventable Diseases Division and in the recently revised guidance for public health control and management of diphtheria (3).
As a disease becomes rare, the completeness and accuracy of surveillance information become more important and each clinical diagnosis (that is, notification) needs to be confirmed by laboratory diagnosis. In addition to notifications, enhanced surveillance for diphtheria incorporates data from reference and NHS laboratories, death registration, and individual case details such as vaccination history, source of infection and severity of disease obtained from hospital records, general practitioners and local incident team reports.
Linkage of notified cases of suspected diphtheria and confirmatory laboratory data shows that most notifications are cases of pharyngitis associated with isolation of non-toxigenic strains of C. diphtheriae. Interpretation of notification data should therefore be undertaken with caution.
References
1. UKHSA (2013). ‘Diphtheria: the Green Book, chapter 15’
2. Wagner KS, White JM, Crowcroft NS, De Martin S, Mann G, Efstratiou A. ‘Diphtheria in the United Kingdom, 1986-2008: the increasing role of Corynebacterium ulcerans’. Epidemiology and Infection 2010: volume 138, issue 11, pages 1,519 to 1,530
3. UKHSA (2024). ‘Public health control and management of diphtheria in England: 2024 guidelines’
4. De Zoysa A, Efstratiou A, Mann G, Harrison TG, Fry NK (2016). ‘Development, validation and implementation of a quadruplex real-time PCR assay for identification of potentially toxigenic corynebacteria’. Journal of Medical Microbiology 2016: volume 65, issue 12, pages 1,521 to 1,527
5. UKHSA (2023). ‘Diphtheria in England: 2023’. Health Protection Report: volume 18, number 7
6. UKHSA. ‘Notifiable diseases and causative organisms: how to report’
7. European Centre for Disease Prevention and Control (October 2022). ‘Increase of reported diphtheria cases among migrants in Europe due to Corynebacterium diphtheriae, 2022’
8. UKHSA (2022). ‘Diphtheria: cases among asylum seekers in England (data to 25 November 2022)’
9. UKHSA. ‘R3: Vaccine preventable bacteria section request form’