Laboratory features of common causes of fever in returned travelers

There can be considerable overlap in the clinical presentation and laboratory features of dengue, malaria, and enteric fever, three important causes of fever in returned travelers. Routine laboratory tests including full blood examination (FBE), liver function tests (LFTs), and C-reactive protein (CRP) are frequently ordered on febrile patients, and may help differentiate between these possible diagnoses.

Adult travelers returning to Australia who presented to the Royal Melbourne Hospital with confirmed diagnosis of dengue, malaria, or enteric fever between January 1, 2000 and March 1, 2013 were included in this retrospective study. Laboratory results for routine initial investigations performed within the first 2 days were extracted and analyzed.

There were 304 presentations including 58 with dengue fever, 187 with malaria, and 59 with enteric fever, comprising 56% of all returned travelers with a febrile systemic illness during the study period. Significant findings included 9-fold and 21-fold odds of a normal CRP in dengue compared with malaria and enteric fever, respectively. The odds of an abnormally low white cell count (WCC) were also significantly greater in dengue versus malaria or enteric fever. Approximately one third of dengue presentations and almost half of the malaria presentations had platelet counts <100 × 10(9) /L. A normal CRP with leukopenia and/or thrombocytopenia occurred in 21% to 30% of dengue presentations, but not in malaria or enteric fever presentations.

There is a wide differential diagnosis for imported fever, but the non-specific findings of a normal CRP with a low WCC and/or low platelet count may provide useful information in addition to clinical clues to suggest dengue over malaria or enteric fever. Further systematic prospective studies among travelers could help define the potential clinical utility of these results in assisting the clinician when deciding for or against commencement of empiric antimicrobial therapy while awaiting confirmatory tests.