The outbreak of pertussis in a refinery as described by John Hoey in a recent article on pertussis in adults1 is interesting but pales in comparison with outbreaks recently reported from Vancouver Island, where well over 100 positive cases (by both culture and polymerase chain reaction) were diagnosed in adolescents and adults,2 and from Quebec, where the severity of pertussis in older adults was well characterized.3 Rarely, pertussis can lead to severe complications, even in a healthy adult.4
The case-fatality rate of 0.8% reported by Hoey actually represents cases in infants under 2 years of age admitted to hospital.5 The overall case fatality rate is unknown but is undoubtedly lower.
There are a number of differences between the United States and Canada in recommendations for treatment and chemoprophylaxis of pertussis contacts. In Canada, treatment and chemoprophylaxis with erythromycin are recommended for 10 days rather than 14, and the maximum daily dose is 1 g rather than 2 g.6 Also, chemoprophylaxis is recommended in this country only in households or other environments where there is an infant under 1 year of age. Canadian guidelines will soon be revised according to the recommendations of the National Consensus Conference on Pertussis (held in May 2002). On the basis of results from 4 randomized controlled trials, the recommended treatment for pertussis will be 7 days of erythromycin,7 5 days of azithromycin8 or 7 days of clarithromycin,9 and chemoprophylaxis will be limited to households with an infant under 1 year of age (because of lack of benefit in modifying the development of clinical disease in contacts10).
The recommendations for vaccination presented by Hoey were those of the US Centers for Disease Control and Prevention. In Canada, an adolescent/adult formulation of acellular pertussis vaccine combined with diphtheria and tetanus toxoids (known by the abbreviation TdaP; Adacel, Aventis Pasteur) is licensed for use in people 12 to 50 years of age. The National Advisory Committee on Immunization recommends that all adolescents receive TdaP in place of Td.11 More extensive use of this vaccine beyond adolescence may be beneficial in controlling the increasing burden of disease in adults.
Scott A. Halperin Head, Pediatric Infectious Diseases Dalhousie University IWK Health Centre Halifax, NS
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