The sequence that causes harm is investigating the interesting diagnosis before excluding the lethal one. In anyone with fever who has been in a malarious area within the past year — and that includes much of India, not only the obvious destinations — the first test is a malaria smear or rapid diagnostic test, before the blood cultures come back and before the chest film is reviewed.
One negative test does not clear it. Parasitaemia in falciparum infection fluctuates, so a negative smear in a patient who remains febrile and unwell needs repeating at 12 and 24 hours before malaria is set aside. A rapid diagnostic test positive for the pan-malarial antigen but negative for the falciparum-specific one still means malaria; it means a different species.
And take the travel history properly. Ask where, when, for how long, what prophylaxis and whether it was actually taken, what the accommodation was, and what happened in the two weeks before departure. Incubation period narrows the differential faster than any test: fever beginning more than three weeks after return effectively excludes dengue and the viral haemorrhagic fevers, while a fever within a week of return from a rural area does not exclude malaria at all.
- Send a malaria test on every post-travel fever before pursuing other diagnoses
- Repeat a negative smear at 12 and 24 hours if the patient stays febrile
- Record dates of travel and return — incubation period does more diagnostic work than most tests
- Ask whether prophylaxis was taken, not whether it was prescribed
- Treat a falciparum diagnosis as an emergency regardless of how well the patient looks
Why it matters
Falciparum malaria kills patients who looked well at the first assessment, and one negative smear is the commonest reason it was missed.
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