[Table of Contents]

Volume: 24S3 - July 1998

Guidelines for the Control of Diphtheria in Canada

PUBLIC-HEALTH ISSUES

To develop strategies for diphtheria control, three issues were identified and are discussed below.

Is there a potential for the reintroduction of diphtheria in epidemic proportions?

As previously described, the conversion of non-toxigenic strains to toxigenic ones is thought to be the most likely method of transmission in highly immunized populations, most likely resulting in limited transmission⁽⁵⁾. The experiences of Sweden in the 1980s and Finland in the 1990s seem to support this theory. Thus, an imported case of diphtheria (or an indigenous one) in the general Canadian population is unlikely to result in a large outbreak or sustained transmission of toxigenic strains. However, ongoing isolation of toxigenic strains in association with mild or moderate illness (mostly in Aboriginal populations) and the results of recent serosurveys indicate that geographic pockets of susceptible people may exist, among older adults and also among groups that abuse drugs and alcohol. It has been argued that the low levels of diphtheria antitoxin observed over time in the adult population have not been associated with an increased number of cases⁽²²⁾. What is not so clear is whether the absence of clinical cases is due to vaccine-induced immunity or a lack of challenge with toxigenic strains.

What is the current level of circulation of toxigenic C. diphtheriae in the Canadian population?

A better understanding of the level of circulation of toxigenic C. diphtheriae should help to clarify this question of population "immunity" to infection. The current surveillance of diphtheria does not adequately assess the actual level of circulation of toxigenic organisms, as there is no uniform reporting of mild respiratory cases or cutaneous cases. Further, laboratories in Canada do not routinely culture for C. diphtheriae, and very few have the ability to perform toxigenicity testing ( Dr. J. Huang, Bureau of Microbiology, LCDC; personal communication, January 1997). There should be more emphasis put on the epidemiologic significance of non-classical cases and carriers of toxigenic strains (and less on clinically typical cases) as an indicator of diphtheria activity. Such an approach to surveillance should be useful in monitoring progress towards elimination of indigenous infection in Canada.

What is the level of readiness to deal with potential importation of diphtheria with secondary transmission of toxigenic organisms?

Currently, there are no national recommendations for the management of clinical diphtheria and the prevention of secondary transmission. A number of provinces have developed or are developing guidelines for use within their jurisdiction. The last part of this document presents recommendations for the management of cases and control measures to prevent secondary transmission from indigenous or imported cases.

Additional issues that have to be addressed include improving the awareness of health-care professionals (clinical and public-health) about the global epidemiology of diphtheria and the ongoing threat of importations, encouraging a high index of suspicion for diphtheria among clinicians, and ensuring adequate immunization of travellers to diphtheria endemic zones.

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