What Is Diphtheria and Where Does It Occur Today
Diphtheria is a contagious bacterial disease caused by strains of bacteria called Corynebacterium diphtheriae, which are tiny organisms that can enter the body through the nose, mouth, or even broken skin. What makes this infection particularly dangerous is not just the bacteria themselves, but a powerful poison called a toxin that these bacteria produce. This toxin can travel through the bloodstream and damage vital organs throughout the body, including the heart, kidneys, and nervous system.[1][2]
The disease has become extraordinarily rare in the United States and other developed nations. In the early 1920s, diphtheria was a major public health crisis in America, with the epidemic peaking in 1921 when 206,000 cases were reported. Today, the situation is dramatically different. The transformation happened because children began receiving routine vaccinations against diphtheria starting in the 1940s, and this practice has continued ever since.[2][9]
However, diphtheria has not disappeared from the world. The disease remains common in regions where healthcare systems are limited or vaccination programs are not widely available. Southeast Asia, India, parts of Africa, South America, and eastern Europe continue to see cases of diphtheria. In 2015, approximately 4,500 cases were reported worldwide, resulting in around 2,100 deaths. These numbers likely represent only a fraction of actual cases, as many areas with diphtheria outbreaks have limited disease surveillance systems.[4][6]
Recent years have seen a concerning trend. The COVID-19 pandemic disrupted routine immunization services and surveillance activities across many countries. These setbacks left numerous children without protection against vaccine-preventable diseases like diphtheria. As a result, outbreaks have been occurring with increasing frequency in areas where vaccination coverage has dropped, reminding us that no region is completely free from the risk of diphtheria returning.[4]
How Diphtheria Spreads From Person to Person
Understanding how diphtheria spreads is important for protecting yourself and others. The bacteria most commonly travel through the air when an infected person coughs or sneezes. These actions release tiny droplets into the air that contain the bacteria, and when another person breathes in these droplets, they can become infected. This is called respiratory droplet transmission, and it’s the most common way diphtheria spreads from one person to another.[3][2]
Direct contact with someone who has diphtheria also poses a risk. If a person has the skin form of the disease, touching their open sores or ulcers can transmit the bacteria. Additionally, touching objects that an infected person has recently handled, such as cups, utensils, clothing, or bedding, can potentially spread the infection. This type of transmission through contaminated objects, called fomite transmission, is less common but still possible.[3][9]
One particularly concerning aspect of diphtheria transmission involves people called carriers. These are individuals who have the bacteria in their body but don’t feel sick or show any symptoms. Despite appearing healthy, carriers can still spread diphtheria to others for approximately six weeks. Because they don’t know they’re infected, carriers may unknowingly expose many people before anyone realizes there’s a problem. As the number of carriers in a community decreases, the overall number of diphtheria cases tends to decline as well.[1][7]
After someone is exposed to diphtheria bacteria, it typically takes between two and five days before symptoms appear. However, this incubation period can range anywhere from one to ten days. During this time, even before symptoms develop, an infected person may be able to spread the disease to others. Without antibiotic treatment, a person with diphtheria remains contagious for two to six weeks.[1][2]
Recognizing the Signs and Symptoms
The symptoms of diphtheria can vary depending on which part of the body is affected. When the infection affects the respiratory system, which includes the nose, throat, and windpipe, it’s called respiratory diphtheria. This is the most common and dangerous form of the disease. When diphtheria affects the skin, it’s called cutaneous diphtheria, which tends to be less severe.[2]
Respiratory diphtheria often starts with symptoms that can be mistaken for a common sore throat or cold. Early signs include a mild fever, usually around 100-101°F, along with general tiredness and a feeling of being unwell. The throat becomes sore, and the glands in the neck may swell, creating visible lumps on either side of the neck. Some people experience a runny nose, and children may seem particularly fussy or irritable.[1][2]
What makes diphtheria different from other throat infections is the development of a distinctive thick membrane. This coating is typically grey or white, sometimes appearing fuzzy or with a black tint. It forms over the throat, tonsils, and sometimes the nose. This membrane is made up of dead cells, bacteria, and other substances, and it adheres firmly to the tissues underneath. If someone tries to remove it, the tissue may bleed. As this membrane grows, it can partially or completely block the airway, making breathing increasingly difficult.[1][2]
As the disease progresses, additional symptoms may appear. The voice may become husky or hoarse. Breathing problems worsen, and some people develop a high-pitched breathing sound called stridor due to narrowing of the upper airways. The neck may swell significantly, sometimes described as a “bull neck” appearance. In severe cases, people may show signs of shock, including pale and cold skin, rapid heartbeat, sweating, and an anxious appearance.[2][7]
Cutaneous diphtheria presents differently. Instead of throat symptoms, this form causes skin problems. Yellow spots or sores appear on the skin, often on the legs, feet, or hands. These sores may look similar to another skin condition called impetigo. The sores are typically painful and may be surrounded by red, inflamed skin. They can develop into ulcers covered by a grey membrane. This type of diphtheria is more common in tropical climates and tends to occur among people living in crowded conditions with poor hygiene.[1][2]
It’s important to note that some people infected with diphtheria bacteria experience only mild symptoms or no symptoms at all. These individuals still carry and can spread the bacteria to others, making them unknowing sources of infection in their communities.[1]
Who Is Most at Risk
Not everyone faces the same level of risk when it comes to diphtheria. The primary risk factor is lack of vaccination. People who have never received the diphtheria vaccine or who haven’t completed the full series of shots are most vulnerable to infection. Even those who were vaccinated as children can become susceptible over time, because immunity from the vaccine gradually weakens. This is why booster shots are recommended every ten years for adults.[2][3]
Age plays a role in risk and severity. Children under five years old and adults over 60 are particularly vulnerable to severe diphtheria and its complications. Young children’s immune systems are still developing, while older adults may have weakening immune systems or other health conditions that make fighting off infection more difficult. Historically, diphtheria was known as a childhood disease because it most commonly affected unvaccinated children.[2][18]
People with weakened immune systems face higher risk regardless of age. This includes individuals with conditions like HIV/AIDS, those receiving chemotherapy for cancer, people taking medications that suppress the immune system after organ transplants, and anyone with chronic illnesses that compromise immunity. For these individuals, diphtheria is more likely to cause severe disease and complications.[2]
International travel significantly increases exposure risk. Nearly all diphtheria cases in the United States are associated with international travel to regions where the disease is more common. Travelers visiting Africa, South America, India, Southeast Asia, or Eastern Europe face higher risk, especially if their vaccinations aren’t up to date. Even brief visits to these areas can result in exposure.[3][9]
Living conditions and social factors also matter. People living in overcrowded housing, those with poor hygiene access, and individuals in communities with low overall vaccination rates face increased risk. Low herd immunity, which refers to the protection that occurs when enough people in a community are vaccinated, allows diphtheria bacteria to circulate more easily. Poor nutrition can also make someone more susceptible to infection and severe disease.[2][7]
Close contact with someone who has diphtheria dramatically increases risk. This includes household members, people who frequently spend time with an infected person, anyone directly exposed to secretions from the infected person’s mouth or nose, and those exposed to discharge from infected skin wounds. Healthcare workers caring for diphtheria patients also face occupational exposure risk.[3]
Dangerous Complications That Can Develop
What makes diphtheria particularly dangerous is not just the local infection in the throat or on the skin, but the serious complications that can develop when the toxin spreads throughout the body. Even with treatment, diphtheria can cause severe, potentially fatal complications, which is why early diagnosis and treatment are so critical.[1]
The most immediate life-threatening complication is airway blockage. As the thick grey membrane grows in the throat, it can completely obstruct the windpipe, preventing air from reaching the lungs. This can lead to suffocation and death if emergency measures aren’t taken. In some cases, doctors must perform an emergency procedure called a tracheostomy, creating an opening in the neck directly into the windpipe to allow breathing.[2][10]
Heart damage represents another major complication. The diphtheria toxin can inflame and damage the heart muscle, a condition called myocarditis. This inflammation affects the heart’s ability to pump blood effectively throughout the body. Myocarditis can cause irregular heartbeats, slow heart rate, or rapid heart rate. In severe cases, it leads to complete heart failure. Heart complications from diphtheria can occur even weeks after the initial infection and are a leading cause of death in diphtheria patients.[1][2]
The nervous system is also vulnerable to diphtheria toxin. Nerve damage, called neuropathy or neuritis, can affect various nerves throughout the body. The specific effects depend on which nerves are damaged. Some people develop difficulty swallowing or double vision because nerves controlling these functions are affected. Others may experience weakness or paralysis in their arms and legs. Nerve damage typically appears several weeks after the initial infection and may take months to fully resolve. In some cases, permanent nerve damage occurs.[1][2]
Kidney damage is another serious complication. The toxin can cause kidney inflammation and failure, reducing the kidneys’ ability to filter waste products from the blood. This can lead to dangerous buildups of toxins in the body and require emergency dialysis treatment.[1][2]
Bleeding problems may develop if the toxin affects blood platelets, the cell fragments that help blood clot. This can result in abnormal bleeding or difficulty stopping bleeding from wounds.[6]
How Doctors Diagnose Diphtheria
Diagnosing diphtheria quickly is essential because treatment must begin as soon as possible to prevent serious complications. Doctors often start by looking for the telltale signs of diphtheria based on symptoms and physical examination. If a doctor sees a child or adult with a sore throat and notices a grey membrane covering the throat and tonsils, they may immediately suspect diphtheria and begin treatment even before test results are available.[2][10]
To confirm the diagnosis, doctors collect a sample from the area where diphtheria is suspected. For respiratory diphtheria, this involves using a swab to take a sample from the back of the throat or from the nose. For skin diphtheria, the doctor takes a sample from the infected wound or sore. These samples are sent to a laboratory where technicians try to grow and identify any bacteria present. This process is called culturing.[2][3]
However, growing bacteria in the laboratory takes time, often several days. Because diphtheria can worsen rapidly, doctors don’t wait for laboratory confirmation before starting treatment if they strongly suspect the disease. This is especially true for respiratory diphtheria, where delays in treatment can be deadly.[10][11]
Even if Corynebacterium diphtheriae bacteria are found in the laboratory culture, additional testing is needed. Not all strains of these bacteria produce the dangerous toxin. Laboratory technicians must perform special tests to determine whether the bacteria found in a patient’s sample are toxin-producing strains. This testing typically involves coordination with local or state public health authorities and is often supported by the Centers for Disease Control and Prevention (CDC).[3][11]
The medical history also plays an important role in diagnosis. Doctors will ask about recent travel to areas where diphtheria is common, whether the person has been in contact with anyone known to have diphtheria, and about vaccination history. These details help doctors assess the likelihood of diphtheria and guide treatment decisions.[3]
Treatment Approaches and Recovery
Treating diphtheria requires immediate and aggressive medical intervention. Because of the potential for serious complications and death, doctors begin treatment as soon as they suspect diphtheria, without waiting for laboratory test results. Treatment typically requires hospitalization, often in an intensive care unit, because patients need close monitoring and isolation to prevent spread to others.[10][14]
The cornerstone of respiratory diphtheria treatment is diphtheria antitoxin, a medication that neutralizes the toxin produced by the bacteria. This antitoxin is made from horse serum and contains antibodies that bind to and inactivate the diphtheria toxin before it can enter and damage body cells. The antitoxin can only neutralize toxin that is still circulating in the bloodstream; it cannot reverse damage that has already occurred to tissues. This is why early administration is so critical.[3][10]
In the United States, diphtheria antitoxin must be obtained directly from the CDC through a special investigational new drug protocol, as it is not routinely stocked at hospitals. Before giving the antitoxin, doctors perform skin allergy tests because some people may have allergic reactions to the horse-derived serum. The dose and method of administration depend on the severity and location of the disease.[10][14]
Antibiotics are the second essential component of treatment. While antibiotics kill the bacteria and stop toxin production, they do not neutralize toxin that has already been produced, which is why antitoxin is also needed. The antibiotics most commonly used are erythromycin or penicillin. These medications help clear the infection, reduce the time a person remains contagious, and prevent spread to others. Treatment with antibiotics typically lasts about two weeks.[10][11]
For cutaneous diphtheria, treatment usually involves antibiotics alone, as antitoxin is typically not necessary for skin infections. The infected wounds must be thoroughly cleaned as part of treatment.[3][11]
Supportive care is crucial during treatment. Doctors must ensure the patient can breathe adequately. If the throat membrane threatens to block the airway, emergency measures may be needed, including intubation or tracheostomy to secure an airway. Patients need close cardiac monitoring because of the risk of heart damage. Any cardiac complications require prompt treatment. Adequate rest is essential, especially in the first two to three weeks, to reduce strain on the heart.[10][14]
Isolation is necessary to prevent spread. Patients with respiratory diphtheria must remain in isolation with droplet precautions until they complete their antibiotic treatment and two consecutive throat cultures taken 24 hours apart come back negative for the bacteria. For skin diphtheria, contact precautions are used until cultures are negative.[11]
Recovery time varies depending on disease severity and whether complications developed. Skin ulcers from cutaneous diphtheria usually heal within two to three months but may leave scars. Nerve damage may take months to resolve, and some people experience permanent effects. Even after recovery, patients need to complete or update their diphtheria vaccination, because having the disease doesn’t guarantee future immunity.[10][11]
Preventing Diphtheria Through Vaccination
The most effective way to prevent diphtheria is through vaccination. The diphtheria vaccine has been one of modern medicine’s great success stories, transforming a once-common killer into a rare disease in countries with strong vaccination programs. The vaccine works by training the immune system to recognize and fight off diphtheria bacteria and neutralize their toxin.[3][9]
Diphtheria vaccine is not given alone but is combined with vaccines for other diseases. For babies and children, it’s part of the DTaP vaccine, which also protects against tetanus and pertussis (whooping cough). The childhood vaccination schedule includes doses at 2 months, 4 months, 6 months, 12-18 months, and 4-6 years. This series of five shots provides strong protection during childhood.[3][23]
Preteens and teens receive a booster shot called Tdap at age 11-12 years. This booster is necessary because immunity from childhood vaccines gradually weakens over time. Adults need a booster every ten years throughout their life, either Tdap or Td (which protects against tetanus and diphtheria but not pertussis). Many adults fall behind on these boosters, which puts them at risk if exposed to diphtheria.[3][23]
Pregnant women should receive the Tdap vaccine during the second half of each pregnancy, even if they’ve had it before. This protects both the mother and passes antibodies to the newborn, providing the baby with some protection during the first few months of life before the baby can receive their own vaccinations.[23]
The diphtheria vaccine is very effective at preventing disease, though it cannot prevent all cases. Vaccinated people who are exposed to diphtheria typically have milder illness and much lower risk of serious complications or death compared to unvaccinated individuals. Studies have shown that the vaccine’s effectiveness remains high when people stay up to date with their boosters.[7][23]
Most people tolerate the diphtheria vaccine well. Common side effects are mild and temporary, including soreness, redness, or swelling where the shot was given, mild fever, tiredness, and headache. Serious reactions are very rare. The benefits of protection against diphtheria far outweigh the small risk of side effects for the vast majority of people.[23]
For travelers, ensuring vaccination is up to date before visiting areas where diphtheria is common is essential. If more than ten years have passed since your last diphtheria-containing vaccine, you should receive a booster before traveling to higher-risk regions. This provides maximum protection during your trip.[9]
Beyond vaccination, other prevention measures include avoiding close contact with people known to have diphtheria, practicing good hygiene including frequent handwashing, and not sharing personal items like cups, utensils, or towels with others. If you’ve been exposed to someone with diphtheria, immediate medical attention is necessary. Prophylactic antibiotics and testing may be recommended, along with vaccination if you’re not up to date.[11]
Global Vaccination Coverage and Challenges
While diphtheria has been nearly eliminated in many developed countries, global vaccination coverage remains incomplete. In 2023, an estimated 84% of children worldwide received the recommended three doses of diphtheria-containing vaccine during infancy. While this represents substantial progress, it also means that 16% of children—millions of kids—have no protection or incomplete protection against diphtheria. There is wide variation in coverage between and within countries.[4]
Low vaccination rates in some regions create pockets where diphtheria bacteria can circulate freely, putting unvaccinated people at risk and allowing outbreaks to occur. These outbreaks can then spread to other areas, including through international travel. This is why maintaining high vaccination rates everywhere is important not just for individual communities but for global health security.[4]
Understanding How Diphtheria Affects the Body
To understand why diphtheria is so dangerous, it helps to know what happens in the body during infection. When diphtheria bacteria enter the respiratory system, they attach to the lining of the airways, particularly in the throat. Unlike many bacteria that invade deeper into tissues, Corynebacterium diphtheriae tend to stay on the surface of mucous membranes.[2]
Once attached, the bacteria that carry the special toxin gene begin producing diphtheria toxin. This toxin is a protein that is extremely poisonous to human cells. The toxin works by entering cells and shutting down their ability to make proteins, which are essential for cell survival and function. Without protein production, cells die.[3][13]
In the throat, dying cells combine with bacteria, white blood cells, and other debris to form the characteristic thick grey membrane. This membrane adheres tightly to underlying tissues. Attempts to remove it cause bleeding because it’s stuck so firmly to the damaged tissue underneath. As more cells die and the membrane grows, it can extend to cover large areas of the throat, tonsils, and even the nasal passages. If it grows large enough or breaks loose, it can completely block the airway, causing suffocation.[2]
The toxin doesn’t stay localized to the throat. It enters the bloodstream and circulates throughout the body, reaching organs far from the initial infection site. The toxin has a particular affinity for heart muscle cells and nerve cells, which is why these organs are most commonly damaged by diphtheria. In the heart, the toxin kills heart muscle cells, causing inflammation and reducing the heart’s pumping ability. In nerves, it damages the protective covering around nerve fibers called the myelin sheath, disrupting nerve signal transmission and causing weakness or paralysis.[2][6]
The kidneys can also be affected as they work to filter the toxin from the blood, becoming inflamed and damaged in the process. Different organs may be affected to different degrees depending on how much toxin is produced, how quickly treatment is started, and individual patient factors.[2]
In skin diphtheria, the process is similar but localized to the skin. The bacteria enter through cuts or breaks in the skin and produce toxin locally, causing cell death and ulcer formation. While systemic toxin spread can occur from skin infections, it’s less common than with respiratory diphtheria.[1]
Understanding this disease process explains why early treatment with antitoxin is so critical. The antitoxin can neutralize toxin that is circulating in the blood before it reaches and damages organs. However, once the toxin has entered cells and caused damage, the antitoxin cannot reverse those effects. This is why every hour counts in treating diphtheria—the sooner antitoxin is given, the less damage the toxin can cause to vital organs.[3]