Diagnosis of malaria

Consider malaria in patients with a febrile illness who have visited a malarious area, particularly within the preceding year. While malaria usually occurs within a few weeks of infection, disease can occasionally be delayed for many months. For patients with suspected malaria, send a blood sample in an EDTA tube to an appropriate laboratory for examination, including thick and thin blood films.

A single negative blood film or negative antigen test does not exclude the diagnosis of malaria, particularly if the patient has taken antimalarials recently. Some antibiotics commonly used by travellers (eg trimethoprim+sulfamethoxazole, tetracyclines, quinolones) have antimalarial activity that can modify or suppress malaria symptoms, and make diagnosis by blood film more difficult.