Interpretive Handbook

Diphtheria occurs in 2 forms, respiratory and cutaneous, but is an uncommon disease in the United States since the advent of universal vaccination in the 1940’s. The organism is carried in the upper respiratory tract and is spread by droplet infection or hand-to mouth contact. The incubation period averages 2 to 5 days. The illness is characterized by fever, malaise, and a sore throat. A swab from beneath the thick pseudomembrane covering the posterior pharynx is the preferred specimen for culture. The organisms multiplying at the infection site produce an exotoxin that may also result in systemic complications affecting the heart, nervous system, etc. Diphtheria is treated by prompt administration of antitoxin, as well as antibiotics (penicillin or a macrolide) to eliminated the focus of infection and prevent the spread of the organism.

The diagnosis of diphtheria is based on clinical criteria and treatment must be initiated prior to laboratory confirmation. Testing is indicated to confirm a clinical diagnosis.

Confirmation of the clinical diagnosis of diphtheria

A positive result supports a diagnosis of diphtheria

A negative result is evidence against a diagnosis of diphtheria but does not definitively rule out this disease (eg, culture may be negative because of prior antimicrobial therapy)

No growth of Corynebacterium diphtheriae

Mandell GL, Bennett JE, Dolin R: In Principles and Practice of Infectious Diseases. 6th edition. Philadelphia, PA, Elsevier Inc., 2005, pp 2457-2465