Severe Streptococcus zooepidemicus infection in a gardener

A 79-year-old man presented with 5 days of right-leg pain, high fever, severe headache and deteriorating conscious state. He was previously fit and healthy and took no medications. The patient appeared unwell, had a temperature of 39.5°C, moderate irritability and depressed conscious state. There was marked neck stiffness and his left wrist and right knee joints appeared swollen and inflamed. There was a cardiac systolic murmur, but no stigmata of bacterial endocarditis.

Aspirates of the left wrist and right knee yielded purulent fluid containing numerous gram-positive cocci. The patient was admitted to the intensive care unit and treated with high dose benzylpenicillin plus vancomycin. A cerebral computed tomography scan was normal; lumbar puncture was not performed. The affected joints were washed out within 24 hours. All cultures of blood and synovial fluid yielded a Lancefield Group C β-haemolytic streptococcus, identified further using the ID 32 Strep strip (BioMerieux, Marcy l’Etoile, France) as Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) based on its ability to ferment sorbitol and not trehalose. This isolate was shown to be sensitive to penicillin (minimum inhibitory concentration, < 0.1 mg/L). Intravenous penicillin therapy was continued. Transoesophageal echocardiography showed echodensities close to the aortic valve which suggested vegetations.

The patient’s condition improved steadily, and he ultimately received intravenous antibiotics for 6 weeks. Further history revealed that the patient collected fresh horse manure for his garden daily from a local paddock. He reported no direct contact with animals or ingestion of unpasteurised dairy products. S. zooepidemicus could not be cultured from a single specimen of horse manure collected from the paddock, and it was not possible to collect clinical specimens directly from any of the horses that used the paddock.