In a setting where malaria, dengue, typhoid, leptospirosis, scrub typhus and bacterial sepsis all present as an unwell adult with fever, the duration and shape of the fever narrows the field faster than any single test available on the first day.
Under five days with no localising signs keeps dengue, malaria and early bacterial infection open. Beyond seven days, typhoid, tuberculosis, abscess and rickettsial disease rise and dengue falls away. A fever that broke and returned is a different problem from one that never broke. Whether it began abruptly or crept up over a week is worth asking directly, because patients volunteer the current temperature and not the history.
The corollary matters just as much: find out what has already been taken. A course of azithromycin from the pharmacy will blunt a rickettsial illness and confuse everything that follows, and paracetamol taken four-hourly hides the pattern you are trying to read.
- Ask for the day the fever started, not how many days the patient thinks they have been unwell.
- Ask whether the fever ever broke completely, and whether it returned.
- Ask what medicines were already taken, including from a pharmacy without prescription.
- Record onset as abrupt or gradual - it is rarely asked and rarely recovered later.
- Examine for an eschar in any undifferentiated fever; it is easily missed in skin folds and hair.
Why it matters
On day one of an undifferentiated fever the history discriminates better than any test you can get back that afternoon.
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