Diphtheria is an acute toxin-mediated systemic disease caused by the bacterium Corynebacterium diphtheriae. Infection remains localised to the throat or skin but disease is mainly due to local inflammation and/or systemic toxaemia. Pharyngeal diphtheria presents with a membranous inflammation of the upper respiratory tract, which may be extensive enough to cause laryngeal obstruction. Damage to other organs including the myocardium, nervous system and kidneys, caused by the organism’s exotoxin, may complicate pharyngeal or cutaneous diphtheria.43,44 Non-toxigenic C. diphtheriae usually causes mild throat or skin infection, which is occasionally complicated by invasive disease including endocarditis or arthritis. Corynebacterium ulcerans, a bacterium found in cattle and more recently in cats, can also express diphtheria toxin and cause a zoonotic infection in humans that is similar to diphtheria.45,46
See Appendix 6 for pre 2004 definition
National definition from January 2004:11
Isolation of toxigenic Corynebacterium diphtheriae or toxigenic C. ulcerans (confirmed case)
Isolation of Corynebacterium diphtheriae or C. ulcerans (toxin production unknown) and one of the following presentations as clinical evidence:
The ICD-10-AM code used to identify hospitalisations was A36 (diphtheria).
The ICD-10 code A36 (diphtheria) was used to identify deaths.
Notifications, hospitalisations and deaths
There were no notifications of diphtheria during January 2003 to December 2005 and no deaths due to diphtheria in 2003–2004. For the three year period 2002/2003 to 2004/2005, there were 66 hospitalisations coded as diphtheria. Of these, most were cutaneous (A36.3; n=39), with the remainder coded as other (A36.8; n=16) or unspecified (A36.9; n=11) diphtheria. There were no hospitalisations coded as pharyngeal or laryngeal diphtheria. Of the hospitalisations, unspecified diphtheria was given as the principal diagnosis in three cases. Although numbers are low, the group with the most admissions coded as diphtheria were males aged 25–29 years (n=12).
Diphtheria has become rare in Australia. A cutaneous toxigenic case acquired in East Timor and notified in 2001 was the first case notified since 1993. Culture positive cutaneous and throat infections with non-toxigenic C. diphtheriae are endemic in the Northern Territory,47 but these are not classified as diphtheria in the absence of relevant symptoms.
From 2004, all toxigenic isolates, including those from cutaneous cases, became notifiable. This report includes, for the first time, all ICD codes for diphtheria in hospitalisation data (previously restricted to codes for pharyngeal or nasopharyngeal diphtheria and laryngeal diphtheria in order to be consistent with notification data). In the absence of any notifications during the period 2003–2005, the 66 hospitalisations (three principal diagnosis) were presumably non-toxigenic or culture negative suspected diphtheria cases or coding errors.
Diphtheria is still a global problem with 21 countries in Asia, South America, Africa and Europe reporting 10 or more cases of diphtheria to the World Health Organization (WHO) in 2005,48 with a total of 8,229 cases reported globally in 2005. In 2002, WHO estimated that there were 5,000 deaths due to diphtheria. The large outbreak of diphtheria in the Newly Independent States (NIS) of the former Soviet Union in the 1990s49 has been gradually brought under control (from a peak of 50,425 cases in 1995 to 176 cases in the European Region in 2004). Four key strategies have been identified to maintain diphtheria control in the region: (1) ensuring high population immunity; (2) strengthened surveillance; (3) early diagnosis and high quality case management; and (4) rapid investigation and management of close contacts.50 The NIS outbreak underscores the risk of diphtheria returning when high vaccination coverage in children (who are critical vectors of respiratory transmission) is not maintained.
In countries with high childhood vaccination coverage against diphtheria, such as Australia, the United Kingdom, Germany, the USA and Canada, cutaneous lesions are the most likely manifestation of C. diphtheriae infection. Cutaneous infection may be caused by local circulating non-toxigenic strains51 (which can also cause invasive disease, including bacteraemia, endocarditis and arthritis, particularly in persons with risk factors such as homelessness, alcoholism, or diabetes)52 or by imported toxigenic types due to overseas travel.53,54 Cutaneous C. diphtheriae infection (due to toxigenic or non-toxigenic strains) may be difficult to diagnose due to a low index of suspicion, may cause chronic infection and may serve as a reservoir for ongoing transmission with greater efficiency than respiratory infection.51,53 Unfortunately, the frequency of international travel now means that even in countries such as Australia, where diphtheria is rare, exposure to a toxigenic strain may occur, with potentially fatal consequences in unvaccinated individuals, or in those whose vaccine induced immunity has waned.55,56 Waning immunity may be more of a problem in the small percentage of children of mothers born in countries overseas where cutaneous diphtheria is common, resulting in mothers having more circulating antibody, which, in turn, can reduce infant immune responses to vaccination through greater placental antibody transfer.57 Australian serosurveillance data indicate that, whilst childhood protection is excellent (>99%), waning immunity in adults has resulted in a susceptible population.58 Australians travelling to countries where diphtheria remains a problem should ensure that they are protected against diphtheria through booster immunisation as necessary.