Patterns of imported malaria at the Academic Medical Center, Amsterdam, the Netherlands

Background. In the Netherlands, cases of imported malaria peaked in the late 1990s to around 500 (60% Plasmodium falciparum) annually. About 30% to 40% of all cases and 57% to 69% of the falciparum cases presented in the Academic Medical Center, Amsterdam. In 1991 to 1994, a shift in population groups to more semi-immune patients, mostly settled immigrants visiting friends and relatives (VFRs), was noticed, when compared to 1979 to 1988. This study shows the ongoing trend in 2000 to 2002. Methods. All the patients diagnosed with malaria in the Academic Medical Center, Amsterdam, during 2000 to 2002 were analyzed. Nonimmune and semi-immune patients were analyzed separately. Results. A total of 302 patients were diagnosed with malaria: 207 (69%) were male; mean age was 34.0 years (range 1-74 years). Of the 302 patients, 105 (35%) were nonimmune travelers and 197 (65%) were considered semi-immune. In 248 (82%) patients, P falciparum was found. In 28 (9.3%),15 (5.0%), and 6 (2.0%) cases, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae were diagnosed, respectively. Of the 248 falciparum cases, 233 (94%) were infected in sub-Saharan Africa; 90% of them had a parasitemia and <2 and 4% had a parasitemia exceeding 5% (maximum 43.7%). The majority of the falciparum cases (96%) were diagnosed within 30 days after return. The number of nonimmune patients with falciparum malaria decreased sharply from 42 in 2000 to 31 in 2001 to 13 in 2002, accounting for the decrease in all malaria cases, from 118 in 2000 to 82 in 2002. Fifty-four percent of vivax infections were acquired in Southeast Asia and 46% in Latin America and sub-Saharan Africa; 71% of the patients presented after 30 days (delayed primary attacks). All the P ovale infections were acquired in sub-Saharan Africa (73% delayed primary attacks). Conclusions. During 2000 to 2002, the total number of patients with falciparum malaria was steadily decreasing due to a decrease in nonimmune patients. The number of semi-immune patients, mostly VFRs and visitors, remained stable. The increasing use of more convenient chemoprophylactic drugs, like atovaquone/proguanil, appears to improve compliance in those who can afford the drug.