Victorian statutory requirement
Diphtheria (Group A disease) must be notified immediately by telephone or fax followed by written notification within five days.
School exclusion is relevant for cases and contacts:
Cases should be excluded until a medical certificate of recovery is received following at least two negative throat swabs. The first should be 24 hours or more after finishing a course of antibiotics and the second 48 hours later.
Contacts should be excluded until cleared to return by the Department of Health.
Infectious agent
Corynebacterium diphtheriae of the gravis, mitis or intermedius biotypes is an aerobic gram-positive bacillus. Toxin production results when the bacteria are infected by a bacteriophage containing the diphtheria toxin gene tox.
Identification
Clinical features
Diphtheria is an acute bacterial infection caused by toxigenic strains of Corynebacterium diphtheriae. It primarily affects the tonsils, pharynx, nose and larynx. Other mucous membranes, skin, and rarely the vagina or conjunctivae can also be involved. The toxin causes local tissue destruction and membrane formation.
The characteristic lesion in the throat is an adherent greyish-white membrane that first occurs on the tonsils, but may spread up onto the palate and involve the pharynx and result in respiratory obstruction.
The onset is insidious with early symptoms of malaise, sore throat, anorexia and low-grade fever. Patients with severe pharyngeal disease may develop neck swelling giving a characteristic ‘bull neck appearance’. Systemic absorption of the toxin can result in neuropathy and cardiomyopathy, resulting in early death or later neurological complications.
Laryngeal diphtheria can present as a slowly progressive croup which can result in death if the airway obstruction is not relieved.
Non-toxigenic strains of C. diphtheriae rarely cause local lesions but may cause infective endocarditis.
Cutaneous diphtheria presents with lesions of variable appearance but which may resemble impetigo.
Non-cutaneous diphtheria has a case fatality rate of 5–10% with higher rates in children under five years and adults over 40 years of age.
Method of diagnosis
Diagnosis is usually based on observation of the classical greyish-white membrane overlying the tonsils or pharynx.
Specimens for C. diphtheriae culture should be obtained from the nose and throat and from any other suspicious lesions. Swabs should be obtained from the pharyngeal membrane, or a portion of the membrane itself could be submitted for culture.
Selective medium is required to culture C. diphtheriae so the testing laboratory should be notified that the disease is clinically suspected. All isolates should be sent to a public health reference laboratory for C. diphtheriae toxin detection by polymerase chain reaction (PCR).
Incubation period
The incubation period is two to five days but occasionally longer.