RESUMEN
A 71-year-old man was admitted with confusion having been discovered on the floor of his unkempt home. Social services would later confirm that the home was infested by rats. An infection of unclear origin was suspected, and he was immediately started on broad spectrum antibiotics. He subsequently developed a swollen left knee. Two knee aspirates showed a raised white cell count but no microbiological or cytological diagnosis. Finally, samples sent for 16S rDNA PCR identified Streptobacillus monilliformis Fastidious organisms and early treatment with antibiotics can limit microbiological diagnosis through standard laboratory analysis. Newer techniques such as sequence-based testing can overcome these limitations; however, they are not widely available and require the clinician to have a high index of suspicion. Crucially, the patient continued to be treated for his clinical sepsis despite initial laboratory results being negative and conflicting specialist opinions.