Diphtheria is a potentially fatal, contagious disease that usually involves the nose, throat, and air passages, although it may also infect the skin. Its most striking feature is the formation of a grayish membrane covering the tonsils and upper part of the throat.



Diphtheria is spread most often by droplets from the coughing or sneezing of an infected person or carrier. The incubation period is two to seven days, with an average of three days. It is vital to seek medical help at once when diphtheria is suspected, because treatment requires emergency measures for adults as well as children.

Risk factors

Risk factors for developing diphtheria include:

Causes and symptoms

The symptoms of diphtheria are caused by toxins produced by the diphtheria bacillus, Corynebacterium diphtheriae (from the Greek for rubber membrane). Toxin production is related to infections of the bacillus itself with a virus. The infection destroys healthy tissue in the upper area of the throat around the tonsils or in open wounds in the skin. Fluid and dying cells clot to form the telltale gray or grayish-green membrane. In very young children, this membrane can grow to the point where it closes off the airway, and the child becomes unable to breathe. Inside the membrane, the bacteria produce an exotoxin, which is a poisonous secretion that causes the life-threatening symptoms of diphtheria. The exotoxin is carried throughout the body in the bloodstream, destroying healthy tissue in other parts of the body.

The most serious complications caused by the exotoxin are inflammations of the heart muscle (myocarditis) and damage to the nervous system. The risk of serious complications is increased as the time between onset of symptoms and the administration of antitoxin increases and as the size of the membrane formed increases. Myocarditis may cause disturbances in the heart rhythm (arrhythmias) and may result in heart failure. Symptoms of nervous system involvement can include having double vision (diplopia), experiencing painful or difficult swallowing (dysphagia), and having slurred speech or loss of voice, which are all indications of the exotoxin's effect on nerve functions. The exotoxin may also cause severe swelling in the neck (so-called bull neck).

The signs and symptoms of diphtheria vary according to the location of the infection. Some adults can be carriers of the disease without showing significant symptoms.


Nasal diphtheria produces few symptoms other than a watery or bloody discharge. On examination, there may be a small visible membrane in the nasal passages. Nasal infection rarely causes complications by itself, but it is a public health problem because it spreads the disease more rapidly than other forms of diphtheria.


Pharyngeal diphtheria gets its name from the pharynx, which is the part of the upper throat that connects the mouth and nasal passages with the voice box (larynx). This is the most common form of diphtheria, causing the characteristic grayish throat membrane. The membrane often bleeds if it is scraped or cut. It is important not to try to remove the membrane because the trauma may increase the body's absorption of the exotoxin. Other signs and symptoms of pharyngeal diphtheria are mild sore throat, fever of 101–102 °F (38.3–38.9 °C), a rapid pulse, and general body weakness.


Laryngeal diphtheria, which involves the voice box or larynx, is the form most likely to produce serious complications. The fever is usually higher in this form of diphtheria (103–104 °F or 39.4–40 °C) and the patient is very weak. Patients may have a severe cough, have difficulty breathing, or lose their voice completely. The development of a so-called bull neck indicates a high level of exotoxin in the bloodstream. Obstruction of the airway may result in difficulty breathing, respiratory compromise, and death.



Because diphtheria must be treated as quickly as possible, doctors usually make the diagnosis based on the visible symptoms without waiting for test results. However, because diphtheria is rare in the developed world, many physicians have never seen a case and may have difficulty making a visual diagnosis.


In making the diagnosis, the doctor examines the patient's eyes, ears, nose, and throat to rule out other diseases that may cause fever and sore throat, such as infectious mononucleosis, a sinus infection, or strep throat. The most important single symptom that suggests diphtheria is the membrane. When a patient develops skin infections during an outbreak of diphtheria, the doctor will consider the possibility of cutaneous diphtheria and take a smear to confirm the diagnosis.


The diagnosis of diphtheria can be confirmed by the results of a culture obtained from the infected area. Material from the swab is put on a microscope slide and stained using a procedure called Gram's stain. The diphtheria bacillus is called Gram-positive because it holds the dye after the slide is rinsed with alcohol. Under the microscope, diphtheria bacilli look like beaded rod-shaped cells, grouped in patterns that resemble Chinese characters. Another laboratory test involves growing the diphtheria bacillus on a special material called Loeffler's medium.


Diphtheria is a serious disease that may require hospital treatment in an intensive care unit if the patient has developed respiratory symptoms. Treatment includes a combination of medications and supportive care.


The most important step is prompt administration of diphtheria antitoxin. Diphtheria antitoxin is made from horse serum that contains antibodies against the bacterium. It works by neutralizing any circulating exotoxin. The doctor must first test the patient for sensitivity to animal serum. Patients who are sensitive (about 10%) must be desensitized with diluted antitoxin, since the antitoxin is the only specific substance that will counteract diphtheria exotoxin. No other type of antitoxin is available for the treatment of diphtheria.

An antibody against an exotoxin, usually derived from horse serum.
A rod-shaped bacterium, such as the diphtheria bacterium.
A person who may harbor an organism without symptoms and may transmit it to others.
Located in the skin.
Diphtheria-tetanus-pertussis (DTP)—
The standard preparation used to immunize children against diphtheria, tetanus, and whooping cough. A so-called acellular pertussis vaccine (aP) has been used since it was licensed in the mid-1990s in a combined vaccine known as DTaP.
A poisonous secretion produced by bacilli that is carried in the bloodstream to other parts of the body.
Gram's stain—
A dye-staining technique used in laboratory tests to determine the presence and type of bacteria.
Loeffler's medium—
A special substance used to grow diphtheria bacilli to confirm a diagnosis.
Inflammation of the heart tissue.
A preparation made from inactivated exotoxin, used in immunization.

The dose of antitoxin ranges from 20,000–100,000 units, depending on the severity and length of time the symptoms have occurred before treatment. Diphtheria antitoxin is usually given intravenously. It must be obtained from the U.S. Centers for Disease Control and Prevention (CDC) and may not be available in some parts of the world.


Antibiotics are given to kill the bacteria, to prevent the spread of the disease, and to protect the patient from developing pneumonia. They are not a substitute for treatment with antitoxin. Both adults and children may be given penicillin, ampicillin, or erythromycin. Erythromycin appears to be more effective than penicillin in treating people who are carriers because of better penetration into the infected area.

Cutaneous diphtheria is usually treated by cleansing the wound thoroughly with soap and water and giving the patient antibiotics for ten days.

Supportive care

Diphtheria patients need bed rest with intensive nursing care, including extra fluids, oxygenation, and monitoring for possible heart problems, airway blockage, or involvement of the nervous system. Patients with laryngeal diphtheria are kept in a croup tent or high-humidity environment; they may also need throat suctioning or emergency surgery if their airway is blocked.

Patients recovering from diphtheria should rest at home for a minimum of two to three weeks, especially if they have heart complications. In addition, patients should be immunized against diphtheria after recovery, because having the disease does not always induce antitoxin formation or protect against reinfection.

Prevention of complications

Diphtheria patients who develop myocarditis may be treated with oxygen and with medications to prevent irregular heart rhythms. An artificial pacemaker may be needed. Patients with difficulty swallowing can be fed through a tube inserted into the stomach through the nose. Patients who cannot breathe are usually put on mechanical respirators.

Public health role and response

Public health responders are generally not the first responders to suspected cases of diphtheria. Instead, they receive information about such cases from primary-care physicians, emergency department personnel, and other healthcare workers. Public health workers then contact the infected person to obtain information about possible sources of the disease and contact information regarding individuals who may have transmitted the diseases. Vaccination histories may also be collected to see if the individual may have been associated with others who have not been vaccinated. Diphtheria is a reportable disease. Physicians and public health workers must report all cases to the state health department, other public health agencies, and other health organizations that use such information to prevent the spread of the disease.


The prognosis depends on the size and location of the membrane and on when treatment with antitoxin is obtained; the longer the delay, the higher the death rate. The most vulnerable patients are children under age five and those who develop pneumonia or myocarditis. Death rates generally range from 5%–10% and may reach as high as 20% in young children and older adults. Nasal and cutaneous diphtheria are rarely fatal.



Prevention of diphtheria involves four factors: immunization, isolation, identification and treatment, and reporting.


Universal immunization is the most effective means of preventing diphtheria. The standard course of immunization for healthy children as of 2018 is inoculation with DTaP (diphtheria-tetanus-acellular pertussis) vaccine. A total of five doses are required for full immunization and are given at 2, 4, and 6 months, between 15 and 18 months, and a final dose between 4 and 6 years. Adults should be immunized once with Tdap (lower case letters indicate a reduced dosage of that component) and then at 10-year intervals with Td (tetanus-diphtheria). Pregnant women are given a single dose of Tdap around 30 weeks of pregnancy. This dose is repeated with each pregnancy.

Isolation of patients Identification and treatment of contacts

Because diphtheria is highly contagious and has a short incubation period, family members and other contacts of diphtheria patients must be watched for symptoms and tested to see if they are carriers. They are usually given antibiotics for seven days and a booster shot of diphtheria/tetanus toxoid.

Reporting cases to public health authorities

Reporting is necessary to track potential epidemics, to help doctors identify the specific strain of diphtheria, and to see if resistance to penicillin or erythromycin has developed.

See also Communicable diseases ; Vaccination .



Davidson, Tish. Vaccines: History, Science, and Issues. Santa Barbara, CA: Greenwood Press, 2017.


National Library of Medicine. “Diphtheria.” MedlinePlus. https://medlineplus.gov/diphtheria.html (accessed March 22, 2018).

United States Centers for Disease Control and Prevention. “Diphtheria.” https://www.cdc.gov/diphtheria/index . html (accessed March 22, 2018).

World Health Organization. “Diphtheria.” http://www.who.int/topics/diphtheria/en (accessed March 22, 2018).


United States Centers for Disease Control and Prevention (CDC), 1600 Clifton Rd., Atlanta, GA, 30329-4027, (404) 639-3534, (800) 232-4636; TTY: 888-232-6348, http://www.cdc.gov .

World Health Organization (WHO), Avenue Appia 20, 1211 Geneva 27, Switzerland, +2241 791 21 11, Fax: +2241 791 31 11, info@who.int, http://www.who.int .

Rebecca J. Frey, PhD
Revised by Tish Davidson, AM

  This information is not a tool for self-diagnosis or a substitute for professional care.