Imported Malaria Treated in Melbourne, Australia: Epidemiology and Clinical Features in 246 Patients

Background: Imported malaria is increasing in nonendemic countries, including Australia. The objective of this study was to describe the epidemiology and clinical features of travelers with imported malaria presenting to a specialist infectious diseases hospital.

Methods: A retrospective case series of 246 consecutively admitted inpatients with laboratory confirmed malaria. The main outcome measures were the proportion of patients infected with each malaria species, and relationship between species and country of birth, area of acquisition, adequacy of chemoprophylaxis, clinical features, laboratory investigations, and treatment.

Results: Plasmodium vivax caused 182 (68.9%) episodes, Plasmodium falciparum caused 71 (26.9%), Plasmodium ovale caused 5 (1.9%), and Plasmodium malariae 1 (0.4%). Fifty-six percent of patients reported chemoprophylaxis use. People born in a country with endemic malaria (36.6%) were less likely to have used chemoprophylaxis. Malaria was most commonly acquired in Papua New Guinea and Southeast Asia. The median times to diagnosis after return to Australia for P. falciparum and P. vivax infections were 1 and 9 weeks respectively. The longest interval between last arrival in Australia and presentation with P. falciparum malaria was 32 weeks. Fever (96%), headache (74%), and a tender or palpable spleen (40%), were the most common clinical features. Diarrhea was more common in P. falciparum, and rigors in P. vivax infections. Thrombocytopenia (71%), abnormal liver function tests and an elevated C-reactive protein (85%) were common. Six patients had severe falciparum malaria but no deaths occurred during the study period.

Conclusion: Malaria remains a health threat for those traveling in endemic areas and is associated with failure to use chemoprophylaxis appropriately. Nonspecific clinical features may lead to delayed diagnosis and misdiagnosis. Malaria should be suspected in the febrile traveler, regardless of birthplace, prophylaxis, symptomatology, or the time that has elapsed since leaving the malarious area.