Suspected infection requiring hospitalisation has highly heterogenous presentation. Yet, variances in host response and its implications are largely unknown. In this multicentre cohort of 3802 individual patients presenting to the Emergency Department (ED) with suspected infection requiring hospitalisation, we apply uniform manifold approximation and projections and K-means clustering to 29 plasma proteins to identify biologically discrete host response clusters. In this work, we first describe two large clusters, called “Dysregulated” and “Undifferentiated”, with abnormal protein concentrations and adverse outcomes in the former. Through further clustering, we identify 4 sub-clusters in the Dysregulated cluster, each with discrete biological signatures, clinical correlates, and outcomes. Clusters 3 and 4 are characterised by renal impairment and viral infections respectively. Clusters 5 and 6 are associated with bacterial culture positivity, with the former consistent with an immunosu

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