Overview
Diphtheria is a bacterial infection of the throat, nose or skin. The bacteria produce a toxin that kills tissue, forming a thick grey coating across the back of the throat that can block breathing.
The toxin also travels in the blood and can damage the heart, the nerves and the kidneys. This is why treatment uses an antitoxin as well as antibiotics, and why it is started on suspicion rather than waiting for a laboratory result.
Disease Summary
- Category
- Infectious Disease
- Cause
- Corynebacterium diphtheriae
- Transmission
- Respiratory droplets and contact with skin sores
- Body System
- Respiratory System
- Preventable
- Yes
- Curable
- Yes
Symptoms
Common Symptoms
Symptoms usually appear 2 to 5 days after exposure, with a range of 1 to 10 days. The illness begins gradually and can be mistaken for an ordinary sore throat.
Sore Throat
Listed by both WHO and CDC among the commonest symptoms of respiratory diphtheria.
Mild Fever
CDC describes a low-grade fever with gradual onset, which is part of why the illness is underestimated early.
Thick Grey Coating in the Throat or Nose
CDC describes a thick grey coating of dead tissue that builds up in the nose and throat and can make breathing and swallowing very hard. This is the hallmark sign.
Swollen Glands in the Neck
Swelling of the neck glands is listed by both WHO and CDC.
Weakness and Malaise
General weakness and loss of appetite accompany the local throat symptoms.
Difficulty Swallowing
The coating in the throat makes swallowing painful and difficult.
Hoarseness
CDC notes hoarseness when the voice box is involved, which signals the infection is extending downwards.
Skin Sores in Cutaneous Diphtheria
CDC describes an open sore or ulcer with a clear edge, pain, scaling or peeling skin, redness and swelling. Skin sores heal slowly.
Danger Signs
Seek urgent medical attention immediately if any of the following symptoms develop.
Difficulty Breathing
CDC states that airway blockage is a deadly complication of respiratory diphtheria and it can develop quickly.
Bull Neck
Marked swelling of the neck, described by CDC as bull neck, is a feature of severe disease.
Signs of Heart Involvement
Chest pain, breathlessness or an irregular heartbeat can mean the toxin has reached the heart muscle.
Weakness, Double Vision or Difficulty Swallowing Later in the Illness
These suggest nerve damage from the toxin and can appear after the throat symptoms have improved.
Reduced Urine Output
CDC lists kidney failure among the complications once the toxin enters the bloodstream.
Diagnosis
Clinical Recognition and Immediate Treatment
CDC states that providers assess the clinical signs and start treatment for respiratory cases immediately, without waiting for laboratory confirmation.
Finding the Adherent Membrane
The case definition rests on an upper airway illness with an adherent membrane on the nose, throat, tonsils or voice box. The membrane bleeds if you try to remove it.
Exposure History
CDC advises seeking care immediately if someone has symptoms and has been exposed to a case, and monitoring close contacts for 7 to 10 days after last exposure.
Identifying the Site
Respiratory diphtheria involves the throat, tonsils, voice box or nose. Skin diphtheria is assessed separately, and CDC states antitoxin is not usually needed for it.
Laboratory Confirmation Afterwards
Confirmation requires growing the bacterium and proving that it produces toxin. This follows treatment rather than preceding it.
Laboratory Tests
Culture from the Throat, Nose or Skin
Identifies the bacterium. CDC advises collecting the specimen before antibiotics start where possible, because treatment reduces the chance of growing the organism.
Toxigenicity Testing
Shows whether the bacterium actually produces diphtheria toxin. This is what defines a reportable case, because non-toxin-producing strains do not cause diphtheria.
PCR for the Toxin Gene
Detects the gene for the toxin and is useful when antibiotics were given before the swab. CDC cautions that PCR alone does not confirm that toxin is being produced and must be paired with a toxigenicity test.
Clearance Cultures
CDC states a patient is no longer contagious after two consecutive negative cultures taken 24 hours apart, once the antibiotic course is complete.
Heart and Kidney Monitoring
Used to detect toxin effects on the heart muscle and kidneys early, since these develop after the throat symptoms.
Treatment
Diphtheria Antitoxin
WHO states the antitoxin neutralises toxin circulating in the blood. CDC states it is given without waiting for laboratory confirmation, and that it is not usually needed for skin diphtheria. It cannot reverse toxin already bound to tissue, which is why hours matter.
Antibiotics
WHO states antibiotics stop the bacteria multiplying and so stop further toxin being made. CDC states that only erythromycin or penicillin is recommended.
Airway Support and Isolation
Severe cases may need the airway protected. Droplet precautions continue for respiratory disease, and contact precautions for skin disease, until cultures are clear.
Monitoring and Treating Toxin Effects
Heart and nerve complications are watched for and managed as they appear, because they can develop after the throat has improved.
Vaccination During Recovery
WHO recommends vaccination after recovery, because having diphtheria does not reliably protect against getting it again.
Prevention
Complete the childhood vaccine series
WHO recommends a full primary series plus three booster doses for long-term protection, starting in infancy.
Keep boosters up to date
Protection fades over time. WHO notes that only 83 countries include all three recommended booster doses in their national programmes.
Treat and protect close contacts
CDC advises monitoring close contacts for 7 to 10 days after last exposure, giving preventive antibiotics, and giving an additional vaccine dose where the last one was more than 5 years ago.
Seek care early for a sore throat with a coating
Early treatment protects the patient and stops the chain of transmission.
Isolate cases until cultures are clear
CDC states a patient is no longer contagious after two consecutive negative cultures taken 24 hours apart once antibiotics are complete.
Reach under-vaccinated communities
WHO identifies low immunisation coverage, damaged health infrastructure, conflict and overcrowded conditions as where outbreaks concentrate.
Risk Factors
Unvaccinated and Under-Vaccinated People
WHO states that any person who is not immune is at risk of illness from diphtheria.
- Children who missed doses or never started the series
- Adults whose boosters have lapsed
- People with an unknown vaccination history
- WHO reports case fatality around 30% in unvaccinated people who go untreated
Young Children
WHO states that children under five are at higher risk of death.
- Children under 5 years, in whom CDC reports case fatality up to 20%
- Children in households where the series was not completed
- Infants too young to have finished the primary series
- Children in crowded living conditions
People in Outbreak and Displacement Settings
WHO identifies the conditions in which diphtheria returns.
- Communities with low immunisation coverage
- Areas with damaged health infrastructure or ongoing conflict
- Overcrowded settings with poor hygiene
- Places where laboratory confirmation and antitoxin are hard to access
Complications
Airway Obstruction
CDC states that airway blockage is a deadly complication of respiratory diphtheria.
Inflammation of the Heart Muscle
The circulating toxin can damage the heart muscle, which CDC lists among the major complications.
Nerve Damage
The toxin can damage nerves, causing weakness, double vision and difficulty swallowing, often after the throat symptoms have settled.
Kidney Damage
CDC lists kidney failure among the complications once the toxin enters the bloodstream.
Low Platelet Count
The circulating toxin can reduce the platelets that help blood to clot.
Slow-Healing Skin Ulcers
CDC states that skin infections heal slowly and may leave ulcers with clearly defined edges.
When to Seek Medical Care
Symptoms Plus a Known Exposure
CDC states to seek medical care immediately if you or your child has symptoms and has been exposed to someone with diphtheria.
A Sore Throat With a Grey Coating
A visible grey coating at the back of the throat is not an ordinary sore throat and needs same-day assessment.
Any Difficulty Breathing or Swallowing
These indicate the airway is threatened and need emergency care.
Visible Swelling of the Neck
Marked neck swelling is a sign of severe disease.
Do Not Wait for Test Results
CDC states treatment begins immediately for respiratory cases, because the antitoxin works only on toxin that has not yet bound to tissue.
Prognosis
Good With Early Antitoxin and Antibiotics
Treatment given before the toxin has spread widely prevents most of the serious complications.
Mortality Remains Significant
CDC gives an overall case fatality rate of 5% to 10%, rising to up to 20% in people under 5 and over 40, and states that about 1 in 10 people with respiratory diphtheria die even with treatment.
Recovery Takes Weeks
Nerve effects in particular can take weeks to months to resolve.
Infection Does Not Guarantee Immunity
WHO recommends vaccination after recovery, because having had diphtheria does not reliably protect against a second episode.
Differential Diagnosis
Streptococcal or Viral Sore Throat
Far more common, and lacks the grey adherent membrane that bleeds when disturbed.
Infectious Mononucleosis
Causes fever, sore throat and swollen glands, but does not usually produce the grey adherent membrane.
Epiglottitis
Causes rapid airway compromise like severe diphtheria, but without the membrane, and is diagnosed by careful airway assessment.
Retropharyngeal Abscess
Produces high fever and difficulty swallowing from a collection of pus rather than a membrane, and is seen on imaging.
Oral Thrush
Produces a whitish coating rather than the greyish membrane of diphtheria, and wipes away more easily.
References
World Health Organization: Diphtheria
WHO fact sheet on cause, symptoms, treatment, vaccination and global coverage.
CDC: Diphtheria Symptoms and Complications
Symptoms of respiratory and skin diphtheria and the complications of the toxin.
CDC: Clinical Features of Diphtheria
Case definitions, the pseudomembrane, complications and case fatality.
World Health Organization: Diphtheria in the African Region
WHO outbreak report covering cases, deaths and vaccination status across eight African countries.
Frequently Asked Questions
How long after being around someone with diphtheria would symptoms start?
CDC states it usually takes 2 to 5 days for symptoms to appear, with a range of 1 to 10 days. CDC advises monitoring close contacts for 7 to 10 days after last exposure.
Is diphtheria still around?
Yes. WHO states that no WHO region is completely free from diphtheria and that outbreaks have been occurring with increasing frequency because of under-vaccination. WHO reported more than 20 000 suspected cases and over 1 200 deaths across eight African countries between January and early November 2025.
Is diphtheria treatable?
Yes. WHO states cases are treated with diphtheria antitoxin, which neutralises toxin in the blood, together with antibiotics that stop the bacteria making more toxin. CDC states treatment begins immediately for respiratory cases without waiting for laboratory confirmation.
How many vaccine doses protect against diphtheria?
WHO recommends a full primary series in infancy plus three additional booster doses for long-term protection. Exact ages differ between national schedules, so check what applies where you live.
Can you get diphtheria on your skin?
Yes. CDC describes skin diphtheria as an open sore or ulcer with a clear edge, pain, scaling or peeling skin, redness and swelling, and states that people can be infected by touching these sores. CDC states skin infections generally receive antibiotics only, and that antitoxin is not usually needed.