Metapneumovirus-Induced Myocarditis Complicated by Klebsiella pneumoniae Co-Infection: A Case Report

BACKGROUND Human metapneumovirus (hMPV), classified in the Pneumoviridae family, is primarily known for causing lower respiratory tract infections in children, the elderly, and immunocompromised individuals. However, rare instances have shown that hMPV can also affect other systems, such as the cardiovascular system, leading to conditions like myocarditis. CASE REPORT We describe a 68-year-old man with a medical history of diabetes, hypertension, and liver cirrhosis who presented to the Emergency Department (ED) exhibiting symptoms of fever, cough, and dyspnea. His condition deteriorated rapidly, progressing to septic shock and requiring increased oxygen support, which led to his transfer to the medical intensive care unit (MICU). Diagnostic evaluations, including cardiac echocardiography and coronary angiography (CAG), confirmed the presence of myocarditis while excluding acute myocardial infarction. Despite aggressive interventions, including extracorporeal membrane oxygenation (ECMO) and intra-aortic balloon pump (IABP) therapy, the patient's condition worsened, and he died 3 days after admission. Polymerase chain reaction (PCR) testing of a throat swab confirmed hMPV infection, with Klebsiella pneumoniae simultaneously identified via sputum culture. The bacterial susceptibility report indicated that the bacteria were sensitive to piperacillin/tazobactam, which had been administered since the patient arrived at our ED, which suggests that the bacterial infection alone cannot fully explain the patient's condition. CONCLUSIONS Compared to previously reported cases of hMPV-related myocarditis, this case is the first to demonstrate notably adverse outcomes associated with the concurrent presence of bacterial infection. The rapid progression and poor outcome despite aggressive treatment emphasize the need for early diagnosis and management of such co-infections.