Fever and back pain: Staphylococcus aureus bacteraemia with discitis
A 58-year-old man with type 2 diabetes treated with metformin and gliclazide presents with a five-day history of fever, rigors and severe low back pain that is worse on movement. Two weeks earlier he had cellulitis of the left leg and a peripheral cannula was inserted for intravenous antibiotics. On examination temperature 38.6 °C, pulse 104, blood pressure 128/74, respiratory rate 18, oxygen saturation 97% on air. There is tenderness over the L3/L4 region with paraspinal muscle spasm but no focal neurological deficit, no new murmur and no peripheral stigmata of endocarditis. White cell count 14.2 × 10⁹/L, CRP 210 mg/L, creatinine 96 µmol/L. Three of four blood culture bottles have grown Staphylococcus aureus sensitive to flucloxacillin after 18 hours. MRI of the lumbar spine shows abnormal signal at L3/L4 with a small anterior epidural collection, and no cord compression.
1. Why do these blood culture results change the management, and what further investigations are mandatory?
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Why it matters
Three of four bottles growing S. aureus is not contamination. S. aureus bacteraemia carries a high rate of metastatic seeding - endocarditis, vertebral osteomyelitis/discitis, epidural abscess, septic arthritis and visceral abscesses. The positive cultures convert this from “presumed discitis” into a bacteraemic deep-seated infection requiring source control, prolonged intravenous therapy and a search for endocarditis. The recent cannula and cellulitis are a plausible portal of entry.
Mandatory further work-up
- Transoesophageal echocardiography, even with a normal examination and no murmur; transthoracic echo alone can miss small vegetations. Continue until endocarditis is confidently excluded.
- Repeat blood cultures every 48 hours until negative to confirm clearance.
- Remove any indwelling device or cannula that could be the source.
- Neurological observation, including saddle sensation, anal tone and bladder function, with a low threshold for repeat imaging if anything changes.
- Baseline liver and renal function for antibiotic dosing; consider HIV testing and glucose control optimisation.
- Ophthalmology review if any visual symptoms (endogenous endophthalmitis).
Prompt TEE and source control change duration and prognosis far more than the choice of anti-staphylococcal agent.
2. Outline the antibiotic plan - agent, dose, route and duration - and what surgical input you would seek.
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Antibiotic choice
For meticillin-sensitive S. aureus: flucloxacillin 2 g intravenously every 6 hours (some centres use continuous infusion), or cefazolin 2 g every 8 hours if there is a non-anaphylactic penicillin reaction. Vancomycin is reserved for MRSA or true severe penicillin allergy; do not use it simply because it is convenient.
Duration and route
- A deep-seated bone infection with an epidural collection needs 6–8 weeks of intravenous therapy, counted from the first negative blood culture and from adequate drainage where relevant. Some patients can switch to oral therapy later under specialist guidance, but not at the outset.
- Monitor CRP/ESR, renal and liver function, and full blood count for flucloxacillin-related hepatotoxicity and neutropenia.
Surgical input
Discuss with neurosurgery and orthopaedics/spinal surgery. A small anterior epidural collection without cord compression or deficit can often be managed conservatively with close neurological observation, but any enlargement or deficit needs drainage. Also involve microbiology formally and consider whether the infected peripheral cannula site needs imaging.
Supportive care
Analgesia, thromboprophylaxis balanced against bleeding risk, tight glycaemic control and early physiotherapy.
3. What clinical developments would make you escalate urgently, and what complications would you look for?
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Neurological red flags
New leg weakness, saddle anaesthesia, urinary retention, faecal incontinence or rapidly progressive back pain suggest cauda equina syndrome or cord compression - this is a same-day emergency requiring urgent MRI and spinal surgical review, regardless of how well he otherwise looks.
Failure to improve
Persistent fever or positive blood cultures beyond 72 hours implies an undrained collection, endocarditis, a device-related source or a resistant organism. Re-examine, repeat imaging and re-discuss with microbiology and surgery rather than simply lengthening the antibiotic course.
Endocarditis
New murmur, heart failure, embolic stroke, Janeway lesions or splinter haemorrhages should prompt urgent echocardiography and cardiology/cardiac surgery involvement.
Other complications
- Septic shock or deteriorating organ function.
- Spinal instability or pathological fracture, particularly with diabetes and osteoporosis.
- Metastatic abscesses - psoas, paraspinal, renal or cerebral.
- Antibiotic toxicity: flucloxacillin hepatitis, vancomycin nephrotoxicity if used.
- Poorly controlled diabetes driving recurrence; involve the diabetes team.
Document a clear escalation plan and ensure nursing staff know to report new weakness or bladder dysfunction immediately.