Types of Diphtheria

Doctors classify diphtheria mainly by where the infection sits in the body, because the location largely decides how dangerous it is.

Respiratory diphtheria is the classic and most serious form. Within it:

• Nasal diphtheria. The mildest form, often seen in infants. It causes a runny nose that becomes blood-stained and foul-smelling, usually from one side, with little fever. It is mild because less toxin is absorbed here, but it is highly contagious to others.
• Tonsillar and pharyngeal diphtheria. The most common form. The grey pseudomembrane forms over the tonsils and throat, with sore throat, swollen neck glands and moderate fever. When the membrane spreads widely and the neck swells into the classic "bull neck", toxin absorption is heavy and the risk to the heart and nerves is highest.
• Laryngeal diphtheria. The membrane involves the voice box and windpipe, either on its own or by spreading downward. It causes hoarseness, a barking cough and noisy, laboured breathing, and it can choke the airway completely. This form most often needs emergency airway surgery.
• Malignant or hypertoxic diphtheria. A fulminant form with massive membrane spread, bleeding, collapse and severe toxin damage within days. Fortunately rare, and frequently fatal even with treatment.

Cutaneous (skin) diphtheria infects breaks in the skin and produces slow-healing, shallow ulcers with a grey membrane, most often on the legs. It is far less dangerous than the respiratory form but acts as a reservoir that can pass the bacteria to others, where it may then cause throat disease.

The practical point: a grey membrane anywhere in the airway is dangerous, but the deeper it reaches - tonsils, then throat, then voice box - the more urgent the situation becomes. Every form is contagious, and every form needs the same core treatment: antitoxin, antibiotics and isolation in a hospital.