Leptospirosis and Respiratory Syncytial Virus (RSV) Co-infection: Diagnostic and Management Challenges

Leptospirosis is one of the most widespread zoonotic infections worldwide, caused by spirochetes in the genus <i>Leptospira</i>. It is typically transmitted through exposure to contaminated water or soil from infected animals and is more common in tropical settings with frequent flooding. We discuss a 60-year-old gentleman with a background of malignant melanoma on immunotherapy who presented with a three-day history of fever, night sweats, and myalgia. He had recently returned from Tobago, where he had spent time swimming in the region's surrounding lakes, and also reported being bitten by mosquitoes and other insects. His observations and examination were unremarkable, with initial investigations, including routine blood tests, showing raised inflammatory markers and leukopenia; a chest X-ray revealed no acute findings. Following this, a throat swab was found to be positive for respiratory syncytial virus (RSV). Malaria, HIV, and hepatitis screenings were negative. His symptoms remained mild, and he was discharged after 24 hours with an outpatient follow-up. A rare and imported pathogens laboratory (RIPL) geographic panel was sent to identify other possible pathogens, given his travel history. The RIPL panel, which was reported six days later, was suggestive of acute leptospirosis (positive Lip16sDNA), and he was started on a two-week course of doxycycline. The non-specific nature of his symptoms highlights the importance of ensuring a thorough travel history is taken to identify leptospirosis in returning travelers. Furthermore, even if symptoms can easily be attributed to a more commonly seen infection such as RSV, this case highlights the need for maintaining a high index of suspicion for tropical diseases such as leptospirosis.