A 32‐year‐old Australian‐born, human immunodeficiency virus (HIV) negative man presented to hospital with 3 days of cramping abdominal pain, diarrhoea and fevers, 5 days after having unprotected receptive anal intercourse. Regular medications were tenofovir disoproxil fumarate and emtricitabine for pre‐exposure prophylaxis (PrEP), with complete adherence. On examination, he had left lower quadrant abdominal tenderness. White cell count was 7.3 × 109/L (reference range [RR], 3.9–12.7 × 109 cells/L) and C‐reactive protein (CRP) 164 mg/L (RR, 0–5 mg/L). A presumptive diagnosis of infective colitis was made, and he was empirically commenced on intravenous ceftriaxone 2 g daily. He initially improved with resolution of fever and abdominal pain. A sexually transmissible infection screen was performed, which was negative, including HIV serology. Faecal cultures returned positive for Shigella flexneri serotype 3a. The patient completed 5 days of ceftriaxone therapy and was discharged home improved, with a CRP of 28 mg/L.
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