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Volume: 24S3 - July 1998
Guidelines for the Control of Diphtheria in Canada
STRATEGIES FOR DIPHTHERIA CONTROL
Immunity against diphtheria: maintaining high levels of immunization
in the Canadian population
Strategies
- Efforts should be made to achieve, maintain and document high levels
of immunization coverage among children. The national goals of 97% up-to-date
coverage by the second birthday and 99% coverage by the seventh birthday
by 1997(23) have not been met. Estimated coverage levels
in 1997 are 84% by the second birthday (receipt of four doses) and 79%
by the seventh birthday (receipt of five doses).
- Uptake of Td boosters among adolescents and adults should also be
increased by promoting minimal use of single antigen tetanus toxoid
and by improving public and provider awareness of booster recommendations.
Although the available data indicate an increase in the use of Td toxoid
for adults, limited surveys of adult populations have found low diphtheria
vaccine coverage overall. NACI recommends that children receive the
recommended series of doses, including the school leaving dose
at 14 to 16 years of age, and that adults complete primary immunization
as a first priority(17). NACI recommendations for primary
and booster immunizations for all ages are further described on pages
5 and 6.
- Information systems need to be developed to monitor immunization levels
and to identify pockets of low coverage, which should be targeted for
catch-up immunization. Ideally, the systems should be based on immunization
registries; however, coverage surveys may be used as an alternative.
Surveillance: strengthening the infrastructure for
the surveillance of diphtheria
Strategies
- Efforts should be made to ensure that clinicians and public-health
workers are informed through provincial and territorial public-health
authorities about international outbreaks of diphtheria and the potential
for importation to Canada, as well as the existence of any high-risk
groups in their jurisdictions. It is important to recognize that because
of the success of control programs, most practising clinicians no longer
see cases of diphtheria. Therefore, the diagnosis of cases and initiation
of the appropriate investigation and treatment are likely to be delayed
without a high index of suspicion.
- Revised surveillance case definitions (1997) as presented below should
be used for national notification.
Confirmed case - laboratory identification of toxigenic C.
diphtheriae, or epidemiologic link (contact within 2 weeks before
onset of symptoms) to a laboratory-confirmed case, plus one of
the following:
- upper respiratory tract infection (nasopharyngitis, laryngitis, or
tonsillitis) with or without a nasal, tonsillar, pharyngeal and/or laryngeal
membrane, with or without gradually increasing hoarseness or stridor,
cardiac (myocarditis) and/or neurologic involvement (motor and/or sensory
palsies) 1 to 6 weeks after onset, or death with no other known cause
- systemic manifestations compatible with diphtheria in a person with
an upper respiratory tract infection or infection at another site.
Probable case - upper respiratory tract infection (nasopharyngitis,
laryngitis, or tonsillitis) with or without a nasal, tonsillar, pharyngeal
and/or laryngeal membrane, plus at least one of the following:
- gradually increasing hoarseness or stridor
- cardiac (myocarditis) and/or neurologic involvement (motor and/or
sensory palsies) 1 to 6 weeks after onset
- death, with no other known cause.
Suspect case - upper respiratory tract infection (nasopharyngitis,
laryngitis, or tonsillitis) with a nasal, tonsillar, pharyngeal and/or
laryngeal membrane.
Laboratory support: ensuring adequate laboratory support
for diagnosis and follow-up of cases and contacts
Strategies
- Current laboratory practices for identification of C. diphtheriae
and toxigenicity testing should be reviewed to ensure that diphtheria
infections are recognized promptly. A program is being developed to
provide reference services for culturing and toxigenicity testing where
provincial and territorial laboratories do not have the appropriate
resources and training.
Special considerations: improving immunity
of travellers and immigrants
Strategies
- Efforts should be made to ensure that travellers to potentially endemic
regions are aware of the recommendations for booster immunization and
that they update their immunization prior to travel to reduce their
risk of acquiring diphtheria. NACI recommends that persons who are travelling
to areas where they are likely to be exposed to diphtheria may be offered
a booster dose of Td if > 10 years have elapsed since their most
recent booster(17).
- The diphtheria status of immigrants to Canada should be reviewed as
part of the medical examination required for immigration and upon their
arrival in Canada. Immunizations should be updated as appropriate for
age. This is particularly important for all immigrant children and for
adult immigrants who are likely to travel to endemic regions.
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