Beyond the gut: a case report of Shigella-associated myocarditis

Shigellosis is a faecal-oral-transmitted gram-negative bacterial infection caused by Shigella species. Though it commonly presents with self-limiting diarrhoea, bloodstream infection and extra-intestinal complications, such as myocarditis, are rare. Rising incidence among gay, bisexual, and other men who have sex with men (gbMSM) has been associated with antimicrobial resistance.

A 36-year-old gbMSM presented with a 3-day history of bloody diarrhoea, dehydration, and hypotension. Initial management included fluid resuscitation and empiric antibiotics. Blood and stool cultures later confirmed Shigella flexneri bacteraemia, prompting escalation to meropenem and intensive care unit admission for septic shock. On Day 5, the patient developed chest pain, electrocardiogram changes, and elevated troponin. Computed tomography (CT) coronary angiography excluded obstructive coronary artery disease. Cardiac magnetic resonance imaging (MRI) revealed septal mid-wall late gadolinium enhancement (LGE), compatible with a clinical diagnosis of probable acute myocarditis. He was managed with guideline-directed medical therapy and completed 14 days of targeted antibiotics. At 6-month follow-up, he remained asymptomatic. Repeat cardiac MRI showed no evidence of oedema on T2-weighted sequences and near-complete resolution of LGE on T1-weighted sequences, with improved left ventricular ejection fraction from 44.6% to 49%.

This rare case of S. flexneri-associated myocarditis reinforces the need to consider bacterial causes of myocarditis in the context of systemic infection. Cardiac MRI was instrumental in establishing the diagnosis and monitoring recovery. In line with European Society of Cardiology and American College of Cardiology guidelines, repeat imaging provided essential prognostic data. This case highlights the potential for invasive Shigella infection in gbMSM and underscores the crucial role of cardiac MRI in myocarditis diagnosis and follow-up.