Key messages

  • Diphtheria is an ‘urgent’ notifiable condition that must be notified immediately to the department by medical practitioners and pathology services. Exclusion periods apply to both cases and contacts.
  • Diphtheria is an acute bacterial infection caused by toxigenic strains of Corynebacterium diphtheriae.
  • Illness is now rare in highly immunised communities, including Australia. Diphtheria vaccination is part of the standard childhood immunisation schedule.
  • Case management involves diphtheria antitoxin, antibiotic therapy and infection control.

Notification requirement for diphtheria

Diphtheria is an ‘urgent’ notifiable condition and must be notified by medical practitioners and pathology services immediately by telephone upon initial diagnosis (presumptive or confirmed). Pathology services must follow up with written notification within 5 days. 

This is a Victorian statutory requirement.

Primary school and children’s services centre exclusion for diphtheria

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.

Infectious agent of diphtheria

Corynebacterium diphtheriae of the gravis, mitis, intermedius or belfanti biotypes is an aerobic gram-positive bacillus. Toxin production results when the bacteria are infected by a bacteriophage containing the diphtheria toxin gene tox+. Rarely, other Corynebacterium species that cause disease in animals can infect humans, usually farm workers, and Corynebacterium ulcerans may be toxigenic.

Identification of diphtheria

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, resulting in respiratory obstruction. The membrane bleeds when swabbed, unlike that in typical streptococcal pharyngitis or infectious mononucleosis.

The onset is insidious, with early symptoms of malaise, sore throat, anorexia and low-grade fever (rarely >39.1 °C). Patients with severe pharyngeal disease may develop massive lymphadenopathy, giving a characteristic ‘bull neck’ appearance. Systemic absorption of the toxin can result in acute renal failure, neuropathy (cranial, palatal or peripheral motor) and cardiomyopathy, resulting in early death or later neurological complications.

Laryngeal diphtheria can present as a slowly progressive croup, which can result in death from suffocation if the airway obstruction is not relieved.

Nontoxigenic strains of C. diphtheriae rarely cause local lesions, but may cause infective endocarditis.

Cutaneous diphtheria presents with lesions of variable appearance, which may resemble impetigo. It is rarely a toxic illness in itself but can potentially spread to contacts’ respiratory tracts.

Noncutaneous diphtheria has a case-fatality rate of 5–10 per cent, with higher rates in children under 5 years and adults over 40 years of age.

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 of Corynebacterium diphtheriae

The incubation period is 2–5 days but occasionally longer.

Public health significance and occurrence of diphtheria

Diphtheria occurs worldwide and is more prevalent in winter months in temperate zones. Illness is now rare in highly immunised communities. An epidemic began in the Russian Federation in 1990, involving all of the countries of the former Soviet Union and Mongolia. The epidemic declined after a peak in 1995 but was responsible for more than 140,000 cases and more than 4,000 deaths. More than 70 per cent of cases were aged 15 years or older.

Diphtheria is now a very rare infection in Australia but may occur in unimmunised people who are recent travellers, or their contacts. The last reported case in Victoria occurred in 1991. Importation of the infection from other affected countries remains a concern in Australia, with the potential to affect unimmunised children and adults, as well as adults with waning immunity post-vaccination.

Reservoir of Corynebacterium diphtheriae

Humans are the reservoir, and carriers are usually asymptomatic.

Mode of transmission of Corynebacterium diphtheriae

Transmission is droplet spread from the respiratory tract. More rarely, transmission can occur from contact with articles soiled with discharges from infected lesions.

Period of communicability of diphtheria

Transmission may occur for as long as virulent bacilli are present in discharges and lesions. The time is variable but is usually 2 weeks or less, and seldom more than 4 weeks without antibiotics. Appropriate antibiotic therapy promptly terminates shedding. The rare chronic carrier may shed organisms for 6 months or more.

Susceptibility and resistance to diphtheria

Infants born of immune mothers are relatively immune, but passive immunity is usually lost by 6 months of age. Lifelong immunity is usually, but not always, acquired after disease or inapparent infection. A primary course of toxoid vaccination provides long-lasting, but not lifelong, immunity. Vaccinated individuals may become colonised by C. diphtheriae in the nasopharynx while still being protected from clinical disease.

Control measures for diphtheria

Preventive measures

Diphtheria vaccination is part of the standard childhood immunisation schedule. Primary vaccination is achieved with three doses of a diphtheria toxoid–containing vaccine at 2, 4 and 6 months of age. Booster doses are currently recommended. They are given as DTPa at 4 years of age and as adult/adolescent formulation dTpa at 12–17 years of age. Before the 8th birthday, DTP-containing vaccines should be used. After the 8th birthday, smaller doses of toxoid (adult/adolescent formulation dTpa or dT-containing vaccines) should be given.

Adults who have been fully vaccinated in the past should receive a booster dose of adult diphtheria toxoid–containing vaccine (dT [‘ADT’] or dTpa) at the age of 50 years unless a booster dose has been documented in the previous 10 years.

For routine and ‘catch-up’ diphtheria immunisation schedules for children and adults, refer to the current edition of The Australian immunisation handbook (National Health and Medical Research Council).

Control of case

Management of cases involves diphtheria antitoxin, antibiotic therapy and infection control. Consult the current version of Therapeutic guidelines: antibiotic. Specialist infectious diseases advice should always be sought on clinical suspicion of a case of diphtheria.

Diphtheria antitoxin should be given if there is strong clinical suspicion, immediately after specimens are taken and without waiting for laboratory confirmation. The dosage will depend on severity, which is assessed by the extent of the pharyngeal membrane and duration of disease. Patients must be tested for hypersensitivity before administration. Co-administration of antitoxin with corticosteroids may be recommended for patients with hypersensitivity to antitoxin. Antitoxin is available through the Special Access Scheme.

Parenteral antibiotic treatment is usually required initially, and can be either erythromycin or penicillin. These can be substituted with equivalent oral formulations once the patient can swallow comfortably. Antibiotics should be continued to complete a total of 14 days of treatment.

Natural infection with C. diphtheriae does not guarantee ongoing immunity. The patient should begin or complete active immunisation with an age-appropriate diphtheria toxoid–containing vaccine during convalescence.

Use standard precautions with additional respiratory precautions for respiratory tract diphtheria, and standard precautions with additional contact precautions for cutaneous diphtheria, until the case is shown to be clear of carriage via two negative cultures taken at least 24 hours apart, collected at least 24 hours after completing antibiotics. The disease is usually not highly contagious after 48 hours of antibiotic therapy.

Control of contacts

All close contacts of the case, including all household contacts and other people directly exposed to oral secretions from the case, should have swabs taken for culture from their throat and nose.

A prophylactic course of 7 days of oral erythromycin or a single dose of benzathine penicillin IM is recommended for close contacts. Such contacts should also be kept under surveillance for 7 days, regardless of their immunisation status.

Contacts are excluded from childcare and school until cleared by the department. Other contacts are advised to exclude themselves from work, and particularly food handling, until bacteriologic examination shows that they are not carriers of the organism.

Unvaccinated contacts should be commenced on their primary course of vaccine.

Vaccinated contacts should be given a booster injection of vaccine if more than 5 years have elapsed since their previous dose.

For close contacts identified as diphtheria carriers:

  • ensure that prophylactic antibiotic therapy has been given (as above for close contacts)
  • exclude until two negative swabs are obtained, the first not less than 24 hours after finishing the antibiotics and the other 48 hours later.

If either of the repeat cultures is positive, an additional 10-day course of erythromycin or penicillin is recommended, followed by two repeat cultures.

Extensive swabbing to detect diphtheria carriers apart from close contacts is not recommended.

Control of environment

Not applicable.

Outbreak measures for diphtheria

Outbreaks of diphtheria require immunising the largest possible proportion of the population involved, emphasising the need for protection of infants and preschool children. In outbreaks among adults, immunise groups that are most affected and at high risk. Repeat immunisations may be recommended after 1 month.

Outbreak investigations involve enhanced case surveillance, with laboratory confirmation of all suspected cases, as well as identification and appropriate management of close contacts and asymptomatic carriers (see Control of contacts, above).


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