The current clinical case definition of diphtheria used by the United States' Centers for Disease Control and Prevention is based on both laboratory and clinical criteria.
- Laboratory criteria => Isolation of C. Diphtheriae from a Gram stain or throat culture from a clinical specimen,
- Histopathologic diagnosis of diphtheria by Albert's stai.
- Clinical criteria => Upper respiratory tract illness with sore throat
- Low-grade fever (above 39 °C (102 °F) is rare)
- An adherent, dense, grey pseudomembrane covering the posterior aspect of the pharynx: in severe cases, it can extend to cover the entire tracheobronchial tree.
- Case classification => Probable: a clinically compatible case that is not laboratory-confirmed and is not epidemiologically linked to a laboratory-confirmed case
- Confirmed: a clinically compatible case that is either laboratory-confirmed or epidemiologically linked to a laboratory-confirmed cas.
Empirical treatment should generally be started in a patient in whom suspicion of diphtheria is high.
The symptoms of diphtheria usually begin two to seven days after infection. Symptoms of diphtheria 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. Within two to three days, diphtheria may destroy healthy tissues in the respiratory system. The dead tissue forms a thick, gray coating that can build up in the throat or nose. This thick gray coating is called a “pseudomembrane. ” It can cover tissues in the nose, tonsils, voice box, and throat, making it very hard to breathe and swallow. Symptoms can also include cardiac arrhythmias, myocarditis, and cranial and peripheral nerve palsies.
Diphtheritic croup => Laryngeal diphtheria can lead to a characteristic swollen neck and throat, or "bull neck". The swollen throat is often accompanied by a serious respiratory condition, characterized by a brassy or "barking" cough, stridor, hoarseness, and difficulty breathing, and historically referred to variously as "diphtheritic croup", "true croup", or sometimes simply as "croup". Diphtheritic croup is extremely rare in countries where diphtheria vaccination is customary. As a result, the term "croup" nowadays most often refers to an unrelated viral illness that produces similar but milder respiratory symptoms.