A Man With Fever, Fatigue, and a Trip to Nigeria

Making the Diagnosis

Every febrile traveler returning from malaria-endemic areas should be tested as soon as possible for malaria, with results available within 24 hours of presentation. The clinical presentation of malaria can vary widely, from asymptomatic to critically ill. In nonendemic areas such as the United States, travelers returning with malaria are likely to progress to serious and potentially life-threatening disease without appropriate diagnosis and treatment.

Microscopic examination of thick and thin blood smears is the recommended test because this provides information on presence of the malaria parasite, the parasite species, and percentage of red blood cells infected (percent parasitemia or parasite density). Parasite species and percent parasitemia are key pieces of information needed to select the appropriate treatment. Because the number of parasites in the blood at any one time can vary considerably, multiple smears are required to rule out a diagnosis of malaria infection.

A patient is considered to not have malaria after three blood smears — each drawn 12-24 hours apart — all fail to show any parasites. If assistance with malaria microscopy is needed, state health departments or CDC can assist.

This patient previously tested negative for malaria with an RDT. However, RDTs available in the United States for malaria diagnosis are not sensitive enough to definitively rule out infection; up to 15% of patients presenting with malaria in the United States may have false-negative results. Although RDTs can be useful when timely microscopy is not available, microscopy should be done as soon as possible to confirm the RDT results and, if positive, determine species of malaria and percent parasitemia.

Alternative methods such as polymerase chain reaction are not recommended because of the long time required from specimen collection to reporting of results.

Choosing the Appropriate Treatment

The clinical microbiologist calls with preliminary results of the patient's blood smears: "Intracellular parasitic forms consistent with Plasmodium falciparum are identified within erythrocytes. Final parasitemia is pending but is no less than 6%."

The patient's appearance is unchanged. He is diaphoretic but alert and without apparent distress.