Respiratory Tract Infections and their Sequelæ

Diphtheria generally begins with a sore throat, and is an acute inflammatory condition affecting the upper respiratory tract characterised by membrane formation which may block the airways. The bacteria multiply locally and produce a powerful exotoxin that causes damage to the myocardium, nerve endings and adrenal glands.

Microbiological diagnosis involves isolation of Corynebacterium diphtheriae on a selective medium such as Hoyle's medium - containing potassium tellurite. Corynebacterium diphtheriae appears as black colonies overnight. Microscopically, Corynebacterium diphtheriae contain metachromatic granules that can be visualised with special stains such as Albert's stain.

Not all strains of Corynebacterium diphtheriae possess the virulence bacteriophage, and hence not all can cause disease. It is thus important to test for toxin production. This is done using an Elek plate in which toxin from the culture and antitoxin soaked into a paper strip diffuse to form an immuno-precipitate in the agar.

Treatment for diphtheria is aimed at preventing respiratory obstruction. This may require a tracheostomy. The circulating toxin must be neutralised by administration of anti-toxin and the bacteria must be eradicated with antibiotics. Penicillin is the treatment of choice and erythromycin may be used for patients who have a penicillin allergy. Prevention is better than cure and there is a highly effective and safe vaccine which is offered to infants.