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

Provincial reportable disease databases have included, in the past 10 years, patient characteristics such as age, sex, and malaria species, but not the likely country of acquisition. Because 90% of all malaria cases in Canada were reported by the Provinces of British Columbia (Monica Naus [British Columbia Centre for Disease Control], pers. comm.), Ontario (Lorraine Schiedel [Ontario Ministry of Health and Long-Term Care], pers. comm.), and Quebec (Colette Colin [Ministere de la sante et des services sociaux, Quebec], pers. comm.), the present analysis focuses on their data, primarily for 1990-2002 (11). Quality assurance data for the province of Quebec (1994-2002) were provided by TDC and the Laboratoire de Sante Publique du Quebec. The federal government's notifiable disease database from 1990 to 2002 is a compilation of selected information from individual provincial databases and includes patient age and sex for each report but no malaria species or country of acquisition (Carole Scott [Division of Disease Surveillance, Health Canada], pers. comm.).

International malaria surveillance data (1990-2002) were acquired from the World Health Organization (WHO) Regional Office for South East Asia (Rakish Mani Rastogi, pers. comm.), the WHO Regional Office for Europe (12), and the United States (13-24). Malaria rates for all countries were based on population data of the U.S. Census Bureau (25).

Trends in Canadian immigration and refugee data for the years 1990-2002 were provided by Citizen and Immigration, Canada (Karen Tremblett [Medical Services Branch, Citizen and Immigration Canada], pers. comm.), data on language by Statistics Canada (26), and travel patterns of Canadians to the tropics by the World Tourism Organization, Madrid (27).

Results

TDC Database

Overall, 553 clinical cases of malaria were seen at TDC from 1981 to 2002, with some fluctuation over time but an overall gradual increase (Figure 1). In these 553 cases, 562 microscopy diagnoses were made; Plasmodium falciparum 295 (52%), P. vivax 218 (39%), P. ovale 26 (5%), P. malariae 16 (3%), and unknown species 7 (1%). Nine (2%) of the clinical cases were mixed infections, involving P. falciparum with either P malariae or P. vivax. Seven patients were seen two or three times with relapses of P. vivax (recurrence >2 months later). The relative frequency of species changed over time, with a gradual increase in the proportion of P. falciparum cases from 20% to 30% in the early 1980s to 60% to 70% in the 1990s and to 70% to 80% in the present decade (Figure 2). Over this 22-year period, only one fatality occurred (3).

[FIGURES 1-2 OMITTED]

Sixty-one countries were identified as the most likely sources of the malaria exposure. Sub-Saharan Africa was the region where most patients contracted malaria, 353 case-patients (65%), followed by south Asia (23%), Southeast Asia (6%), Central America (5%), and South America (1%). However, India, with 110 cases (20%), was the single most frequent source country. Tourists (29%), immigrants or refugees (29%), and foreign workers (24%) represented the categories most frequently reported. A shift over time occurred in the importance of sub-Saharan Africa as a source of malaria cases. In the 1980s, 50% of malaria infections were acquired in Africa; in the 90s, 70%; and, since 2000, 85%. Patients of all categories were more likely to contract P. falciparum in Africa (74.3%) while it has been an uncommon species in south Asia (5.8%). The increase in P. falciparum cases over time correlated with the increase in the total number of malaria cases contracted in Africa; P falciparum represented [approximately equal to] 30% of all cases in the early 1980s and increased to 70% in the late 1990s. From 1981 to 2002, 96% of malaria infections acquired in south Asia were non-falciparum malarias, while only 29% of infections from Africa were non-falciparum. None of the 553 cases of malaria originated from China, Malaysia, Saudi Arabia, Peru, or Venezuela, which are frequent travel destinations of Quebecers. Other common travel destinations contributed little to the 20-year malaria ease total (e.g., Philippines [1 case], South Africa [1], Costa Rica [2], Mexico [2], and Dominican Republic [3]). Malaria cases from Africa from 1992 to 2000 came predominantly (69%) from the French-speaking African countries, notably higher than the proportion of U.S. travelers (18%) who acquired malaria in these countries (13-24).