Diphtheria is a serious bacterial infection caused by toxin-producing strains of Corynebacterium diphtheriae. It primarily affects the throat and upper airways, forming a thick membrane that can block breathing, and releases a toxin that can damage the heart and nervous system. Without treatment, nearly 1 in 3 people with diphtheria die. With antitoxin treatment, mortality drops by about 76%. Vaccination has made the disease rare in much of the world, but outbreaks continue in regions with low immunization coverage.
How Diphtheria Spreads
The bacteria spread from person to person through close respiratory contact, similar to how a cold or flu travels. Breathing in droplets from an infected person’s cough or sneeze is the primary route. Direct contact with skin sores from cutaneous (skin) diphtheria can also transmit the infection.
After exposure, symptoms typically appear within two to five days, though the incubation period can range from one to ten days. A person with diphtheria can spread the bacteria to others even before they feel sick, which is part of what makes outbreaks difficult to contain in unvaccinated communities.
What Happens Inside the Body
What makes diphtheria dangerous isn’t the bacteria themselves so much as the toxin they produce. The toxin works by shutting down protein production inside your cells. It does this in a precise, stepwise way: one part of the toxin molecule latches onto a cell’s surface, allowing the toxic portion to slip inside. Once in, it disables a key molecule (called elongation factor 2) that cells need to build proteins. This shutdown is irreversible in each affected cell, meaning the damage accumulates as the toxin spreads.
At the site of infection, usually the throat, this protein shutdown kills tissue and creates a tough, grayish membrane. As the toxin enters the bloodstream, it can reach distant organs, particularly the heart and nerves, where the toxin’s binding site is especially abundant on cell surfaces.
Signs and Symptoms
The hallmark of respiratory diphtheria is a pseudomembrane that forms within two to three days of illness. This thick, leathery coating appears over the tonsils, throat, voice box, or nasal passages and can extend down into the windpipe. It’s not like the normal mucus you’d see with a sore throat. It’s firmly attached to the tissue underneath, and attempting to remove it causes bleeding.
Early symptoms often resemble a bad sore throat: low-grade fever, swollen neck glands, and general malaise. As the membrane grows, breathing and swallowing become increasingly difficult. In severe cases, the membrane can obstruct the airway entirely. Cutaneous diphtheria, the skin form, produces ulcers or sores that are slow to heal but rarely causes the dangerous systemic effects seen with respiratory infection.
Complications: Heart and Nerve Damage
The most feared complications happen when the toxin travels through the bloodstream to the heart and nervous system. Myocarditis, or inflammation of the heart muscle, can cause life-threatening irregular heart rhythms. This complication can appear days to weeks after the initial throat infection, sometimes catching patients off guard just as they seem to be recovering.
Nerve damage typically shows up as peripheral polyneuropathy, a condition where the nerves controlling the limbs, soft palate, and even the diaphragm stop working properly. Patients may experience difficulty swallowing, slurred speech, or weakness in the arms and legs. In some cases, paralysis of the diaphragm can compromise breathing. These neurological problems can persist for weeks to months, and the progression from heart complications to nerve damage can unfold in sequence, making the recovery period unpredictable and prolonged.
Among people who develop the full membrane-forming disease, anywhere from 5% to 50% die from these complications, depending on how quickly they receive treatment, their vaccination history, and their age.
How Diphtheria Is Diagnosed
Diagnosis starts with clinical suspicion, particularly the visible pseudomembrane in the throat. But confirming diphtheria requires laboratory work that goes beyond a simple throat culture. Labs must isolate the bacteria, detect the gene responsible for toxin production, and then prove the bacteria are actually producing the toxin. That last step matters because most strains of C. diphtheriae found in the United States carry the toxin gene but don’t actually produce the toxin, meaning they won’t cause true diphtheria.
The definitive test for toxin production is called the Elek test, and in the United States, only the CDC performs it. This means samples from suspected cases often need to be shipped to the CDC for final confirmation, which can take time. In the meantime, treatment is started based on clinical judgment rather than waiting for lab results.
Treatment
Two things happen simultaneously when someone is treated for respiratory diphtheria. First, diphtheria antitoxin is administered to neutralize the toxin circulating in the bloodstream. This antitoxin doesn’t reverse damage already done, which is why early treatment matters so much. A pooled analysis in Clinical Infectious Diseases estimated that antitoxin reduces the risk of death by 76%. In the United States, the antitoxin isn’t commercially available and must be obtained directly from the CDC.
Second, antibiotics are given to kill the bacteria and stop them from producing more toxin. Only two antibiotics are recommended: erythromycin or penicillin. For cutaneous diphtheria, antibiotics alone are usually sufficient, and antitoxin typically isn’t needed.
Vaccination Schedule
Diphtheria is preventable with routine vaccination. The standard childhood series is five doses of DTaP (which also protects against tetanus and whooping cough), given at 2 months, 4 months, 6 months, 15 to 18 months, and 4 to 6 years. After age 7, a booster called Tdap is used, followed by a booster of either Td or Tdap every 10 years throughout adulthood.
Protection from the vaccine fades over time, which is why those boosters matter. Adults who skip them can gradually lose their immunity, leaving a window of vulnerability even in countries with strong childhood vaccination programs.
Where Diphtheria Still Strikes
Diphtheria has largely disappeared from countries with high vaccination rates, but it remains a serious threat in parts of Africa, South Asia, and other regions with gaps in immunization. In 2025 alone, over 20,400 suspected cases and more than 1,250 deaths were reported across eight countries in the WHO African Region between January and early November. Nigeria accounted for the largest share, with over 12,000 suspected cases and 884 deaths. Guinea had the highest fatality rate at nearly 26%, while Chad reported over 4,400 suspected cases.
Several of these countries have been dealing with ongoing outbreaks since 2023, and the situation has worsened in Mali, Mauritania, and Niger, with cases spreading geographically. The WHO considers the global risk low because most countries outside the African Region maintain established immunization programs, but these outbreaks underscore how quickly diphtheria can resurge when vaccination coverage drops.