[1] In severe cases, a grey or white patch develops in the throat,[2][1] which can block the airway, and create a barking cough similar to what is observed in croup.

They include fever of 38 °C (100.4 °F) or above; chills; fatigue; bluish skin coloration (cyanosis); sore throat; hoarseness; cough; headache; difficulty swallowing; painful swallowing; difficulty breathing; rapid breathing; foul-smelling and bloodstained nasal discharge; and lymphadenopathy.

It can cover tissues in the nose, tonsils, voice box, and throat, making it very hard to breathe and swallow.

As a result, the term "croup" nowadays most often refers to an unrelated viral illness that produces similar but milder respiratory symptoms.

[26] The disease may remain manageable, but in more severe cases, lymph nodes in the neck may swell, and breathing and swallowing are more difficult.

The Centers for Disease Control and Prevention (CDC) recommends[29] either: In cases that progress beyond a throat infection, diphtheria toxin spreads through the blood, and can lead to potentially life-threatening complications that affect other organs, such as the heart and kidneys.

[7] Better standards of living, mass immunization, improved diagnosis, prompt treatment, and more effective health care have led to a decrease in cases worldwide.

[31] In 1613, Spain experienced an epidemic of diphtheria, referred to as El Año de los Garrotillos (The Year of Strangulations).

In 1826, Pierre Bretonneau gave the disease the name diphthérite (from Greek διφθέρα, diphthera 'leather'), describing the appearance of pseudomembrane in the throat.

[42][43] In 1890, Shibasaburō Kitasato and Emil von Behring immunized guinea pigs with heat-treated diphtheria toxin.

Behring used this antitoxin (now known to consist of antibodies that neutralize the toxin produced by C. diphtheriae) for human trials in 1891, but they were unsuccessful.

This was the first ever standardization of a biological product, and played an important role in future developmental work on sera and vaccines.

This incident, coupled with a tetanus outbreak in Camden, New Jersey,[49] played an important part in initiating federal regulation of biologic products.

[citation needed] In 1905, Franklin Royer, from Philadelphia's Municipal Hospital, published a paper urging timely treatment for diphtheria and adequate doses of antitoxin.

[51] In 1906, Clemens Pirquet and Béla Schick described serum sickness in children receiving large quantities of horse-derived antitoxin.

As a part of the campaign, 85 million pieces of literature were distributed by the Metropolitan Life Insurance Company, with an appeal to parents to "Save your child from diphtheria."

[53] In 1919, in Dallas, Texas, 10 children were killed and 60 others made seriously ill by toxic antitoxin which had passed the tests of the New York State Health Department.

[55] In 1926, Alexander Thomas Glenny increased the effectiveness of diphtheria toxoid (a modified version of the toxin used for vaccination) by treating it with aluminum salts.

In Nazi Germany, where authorities preferred treatment and isolation over vaccination (until about 1939–1941), cases rose over the same period from 6.1 to 9.6 per 100,000 inhabitants.

[60] Between June 1942 and February 1943, 714 cases of diphtheria were recorded at Sham Shui Po Barracks, resulting in 112 deaths because the Imperial Japanese Army did not release supplies of anti-diphtheria serum.

[citation needed] During 1948 in Kyoto, 68 of 606 children died after diphtheria immunization due to improper manufacture of aluminum phosphate toxoid.

[62] In 1974, the World Health Organization included DPT vaccine in their Expanded Programme on Immunization for developing countries.

[65] After the breakup of the former Soviet Union in 1991, vaccination rates in its constituent countries fell so low that an explosion of diphtheria cases occurred.

[68] In early June 2015, a case of diphtheria was diagnosed at Vall d'Hebron University Hospital in Barcelona, Spain.

[72] In June 2016, a three-year-old, five-year-old, and seven-year-old girl died of diphtheria in Kedah, Malacca, and Sabah, Malaysia.

[74][75] In 2017, outbreaks occurred in a Rohingya refugee camp in Bangladesh, and amongst children unvaccinated due to the Yemeni Civil War.

[80] In October 2022, there was an outbreak of diphtheria at the former Manston airfield, a former Ministry of Defence (MoD) site in Kent, England, which had been converted to an asylum seeker processing centre.

The Home Office, the government department responsible for asylum seekers, refused to confirm the number of cases.

The agency said it is working closely with local and national partners "to ensure all necessary public health measures are implemented" following the discovery of the new case.

The statement added: "We have conducted a risk assessment and close contacts of the case have been identified and where appropriate, vaccination and advice will be given to prevent the spread of the infection.