Malaria epidemics and surveillance systems in Canada

Emerging Infectious Diseases, July, 2004 by J. Dick MacLean, Anne-Marie Demers, Momar Ndao, Evelyne Kokoskin, Brian J. Ward, Theresa W. Gyorkos

In the past decade, fluctuations in numbers of imported malaria cases have been seen in Canada. In 1997 to 1998, malaria case numbers more than doubled before returning to normal. This increase was not seen in any other industrialized country. The Canadian federal malaria surveillance system collects insufficient data to interpret these fluctuations. Using local (sentinel), provincial, federal, and international malaria surveillance data, we evaluate and interpret these fluctuations. Several epidemics are described. With an ever-increasing immigrant and refugee population of tropical origin, improved surveillance will be necessary to guide public health prevention policy and practice. The Canadian experience is likely to be generalizable to other industrialized countries where malaria is a reportable disease within a passive surveillance system.

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Malaria has been a reportable communicable disease in Canada since 1929, when a surveillance system for communicable diseases was first developed. Although no longer endemic in Canada, malaria has remained an important imported disease, principally in immigrants and travelers (1-3). Rarely, it has been transmitted in blood products (4). Published reports document delays in clinical and laboratory diagnoses of malaria and lack of understanding of malaria prophylaxis and fever management in travelers (3). The Canadian infectious disease surveillance system has reported an average of 538 malaria cases per year since 1990, and Statistics Canada reported an average of one death per year (5,6, Carole Scott [Division of Disease Surveillance, Health Canada], pers. comm.). The present federal surveillance system reports the age and sex of a patient and does not document malaria death rate, malaria species, nor the likely country of acquisition. While malaria-related deaths may be few, that any exist is a matter of concern. The continued incidence of malaria cases and deaths in Canada suggests that the malaria surveillance system should be strengthened and used more proactively to help identify appropriate preventive measures.

All 10 provincial and 3 territorial health authorities in Canada are required by law to report diagnoses of malaria and other selected diseases to federal authorities at Health Canada (2). Summary reports of these diseases are published by both levels of reporting in provincial and territorial news bulletins and by Health Canada in the Canada Communicable Diseases Report.

In several instances over the past decade, malaria incidence in Canada as a whole, or in individual provinces, reached epidemic levels (7). Why some were not immediately identified and why no comprehensive analysis has been published as part of government surveillance systems are questions that will be addressed. Failing to recognize these epidemics has bruited the ability of public health officials to assess and intervene appropriately to control the illness and death associated with imported malaria in Canada.

This study evaluated and summarized data collected over the past 22 years by local, provincial, and federal malaria surveillance systems, from Canadian federal immigration and refugee data resources and from international tourist resources, to identify and explore the causes of malaria epidemics. In addition, geographic patterns and Plasmodium spp. profiles of malaria are examined. This analysis led us to conclude that changes are needed in both the surveillance reporting instruments and how these surveillance results are analyzed and used.

Methods

The databases used for the present analysis include 22 years of records from a local malaria reference center in Montreal, Canada (the McGill University Centre for Tropical Diseases [TDC]) and up to 13 years of quality assurance and notifiable disease surveillance databases of the provincial and federal governments of Canada, France, India, Switzerland, the United States, and the United Kingdom. TDC is a clinical and laboratory facility that provides care to 800 to 1,100 new patients per year (approximately 60% primary cases and 40% consult cases), drawn mainly from the Montreal region. The TDC database from 1981 to 2002 has allowed previous detailed reviews of changing patterns of malaria in its patient populations (8-10). Malaria-relevant data captured include category of traveler (tourist, immigrant, refugee, expatriate, missionary, and volunteer), countries visited, and malaria species. A diagnosis of malaria is made if parasites are noted on a blood smear (thin, thick, or buffy coat) or if, in the last 5 years, the patient had a positive result on a malaria antigen-capture test (e.g., Macromed [Nova Century Scientific, Inc., Burlington, Ontario, Canada], ICT Malaria P.f. [ICT Diagnostics, Brookvale, New South Wales, Australia], or OptiMAL [Flow Inc., Portland, OR]). While active surveillance studies during this period included polymerase chain reaction (PCR) as a screening tool, PCR-positive cases were not included in any of the passive surveillance statistics unless they were also independently confirmed by either malaria antigen capture or smear.