A Fever That Will Not Break
A 30-year-old returns from a tropical region with a five-day history of fever to 39.5 C, headache, muscle aches, and a normal chest examination. Blood tests show a normal white cell count, mildly low platelets, and raised liver enzymes. A rapid test for one common cause is negative. The patient took a course of antibiotics before travel for an unrelated infection. He reports no rash, no neck stiffness, and no diarrhoea. His heart rate is 96 bpm and blood pressure is normal. A clinician reasons: 'Rapid test is negative, so it is a viral illness; send him home.'
1. Identify at least two reasons the negative rapid test does not rule out the suspected infection, and explain the reasoning.
Read the worked answer
First, rapid tests for many tropical infections have limited sensitivity, especially early in illness or at low parasite/antigen loads, so a negative result lowers but does not eliminate the probability. Second, recent antibiotic use can suppress the organism and reduce the test's ability to detect it, producing a false negative. Third, the clinical picture (fever, headache, myalgia, low platelets, raised liver enzymes, normal white count) fits the infection better than a generic viral illness, and the pretest probability is raised by travel to an endemic area. A negative test in a patient with a high pretest probability should prompt a second, more sensitive test (e.g., microscopy or a different assay) rather than closing the case. The reasoning to avoid is treating a single test result as definitive when the prior probability is high.
2. Which features argue against simple viral illness, and what would you do next?
Read the worked answer
The combination of low platelets and raised liver enzymes with a normal white cell count is a pattern seen in several systemic infections and is not typical of a common cold or flu. Persistent high fever for five days with myalgia and headache in a returning traveller also fits a systemic infection. Against simple viral illness: the duration and height of fever, the platelet and liver abnormalities, and the failure to improve. Next steps: repeat and broaden testing with a more sensitive method, take a careful exposure and medication history (including the antibiotics and any malaria prophylaxis), check for other travel-related causes, and arrange follow-up and safety-netting. If the patient deteriorates, admission for observation is warranted. The key judgement is that a negative test does not equal absence of disease when the clinical picture is suggestive.
3. The patient's heart rate is only 96 bpm despite a temperature of 39.5 C. Is that reassuring? Explain.
Read the worked answer
Normally heart rate rises roughly 10 bpm per 1 C of fever, so a temperature of 39.5 C would predict a heart rate well above 100 bpm. A rate of 96 is relatively slow for that temperature, which can be a warning sign rather than a reassurance in some infections (a relative bradycardia). It should not be dismissed as 'he is not that unwell'. It is one more reason to look carefully rather than send the patient home on a viral label, and to arrange review and repeat testing. The broader lesson is to compare the observed vital signs with what the fever predicts, not just to check whether each value is inside the normal range.