A 47-year-old male presented with fever, myalgia, arthralgia, and a rash following a rat bite, initially raising suspicion for dengue due to a positive IgM rapid test. However, further investigation, including blood cultures and 16S rRNA gene sequencing, ultimately identified Streptobacillus moniliformis as the causative agent of rat-bite fever. The patient responded well to doxycycline. This case highlights the potential for false-positive dengue serology in other febrile illnesses, emphasizing the importance of comprehensive diagnostic workup beyond initial rapid tests, especially when clinical suspicion for an alternative diagnosis is high.
Key note: False-positive dengue IgM results can occur in other febrile illnesses like rat-bite fever, necessitating thorough diagnostic evaluation.