Antibiotic Stewardship in Hospitalized Patients, Part 2: S. aureus Bacteremia, Endocarditis, Meningitis, and Vertebral Osteomyelitis

Bottom line

What these infections have in common

• Each has a deep or endovascular focus that antibiotics alone reach slowly, so the course is counted in weeks and the plan includes a defined source-control decision (catheter removal, valve surgery, abscess drainage).
• Each has a mandatory diagnostic bundle that is easy to skip — repeat cultures and echocardiography, lumbar puncture with the right sequence around antibiotics, or biopsy before antibiotics — and skipping it changes the outcome.
• Each has a short list of triggers for urgent surgery or ICU care that the ward team must watch for daily, and each warrants infectious diseases involvement.

S. aureus bacteremia: the mandatory bundle

• Repeat blood cultures (two sets) every 48 hours until documented clearance; the first negative set starts the treatment clock, and bacteremia persisting beyond 48–72 hours on effective therapy defines complicated disease.
• Remove any short-term catheter or PICC the same day — source control is the single most important intervention, and salvage of an S. aureus-infected line is not attempted. Place new long-term access only after cultures are documented negative.
• Echocardiography in every patient: transthoracic first, then transesophageal if the transthoracic study is non-diagnostic or positive, or with any high-risk feature — persistent bacteremia or fever beyond 72 hours, community-acquired or unknown-source bacteremia, a prosthetic valve or intracardiac device, pacemaker or ICD, hemodialysis, prior endocarditis, a new murmur, embolic stigmata, or injection drug use. Transesophageal sensitivity is about 90% versus 50–70% for transthoracic.
• Examine daily for metastatic foci — back pain (MRI for epidural abscess or vertebral osteomyelitis), joints, skin, a new murmur, CNS findings — and image what the exam or persistent bacteremia suggests.
• Consult infectious diseases on every case; involvement is consistently associated with guideline-concordant care and lower mortality.
• Uncomplicated bacteremia requires all of: endocarditis excluded, no prosthetic material (valve, graft, pacemaker, joint), follow-up cultures at 2–4 days negative, defervescence within 72 hours of effective therapy and source removal, and no metastatic infection. It is treated for 14 days IV from the first negative culture. Failing any criterion makes it complicated: 4–6 weeks IV, and 6 weeks or more for endocarditis, vertebral osteomyelitis, epidural abscess, or an undrained focus, with source control.
• Definitive therapy: MSSA — cefazolin 2 g IV every 8 hours (3 g if over 120 kg) or nafcillin or oxacillin 2 g IV every 4 hours, preferred with CNS involvement; cefazolin is better tolerated (less interstitial nephritis, hepatitis, rash). Beta-lactams are clearly superior to vancomycin for MSSA, so stop vancomycin the moment susceptibility returns. MRSA — vancomycin dosed to an AUC/MIC of 400–600 (about 15–20 mg/kg every 8–12 hours, loading dose in severe illness) or daptomycin 8–10 mg/kg IV daily; daptomycin is inactivated by surfactant and must not be used when pneumonia is a possible focus. No gentamicin or rifampin for uncomplicated native-valve or catheter-related bacteremia. Oral step-down is not standard.
• The contrast with uncomplicated gram-negative bacteremia: with a controlled source (for example a urinary source) and clinical response, 7 days is non-inferior to 14, repeat cultures and echocardiography are not routine, and early oral step-down to a fluoroquinolone or TMP-SMX is appropriate.

Infective endocarditis

• Suspect it with persistent bacteremia or fever beyond 72 hours on appropriate therapy, community-acquired or unknown-source S. aureus bacteremia, a prosthetic valve or intracardiac device, a new regurgitant murmur or heart failure, embolic or immunologic stigmata, prior endocarditis, injection drug use, or hemodialysis. Apply the modified Duke criteria; S. aureus in two sets counts as a typical organism for a major criterion.
• Organisms by setting: native valve — S. aureus most common overall, then viridans streptococci, enterococci, coagulase-negative staphylococci, and HACEK organisms. Early prosthetic-valve endocarditis (within 12 months of surgery) — coagulase-negative staphylococci, S. aureus, gram-negative bacilli, and Candida; late prosthetic-valve disease resembles native-valve disease. Injection drug use — S. aureus with tricuspid involvement, plus Pseudomonas, other gram-negatives, polymicrobial infection, and Candida.
• Empiric therapy while cultures pend: native valve — vancomycin plus ceftriaxone (a broader antipseudomonal beta-lactam with injection drug use or healthcare exposure); prosthetic valve — vancomycin plus gentamicin plus rifampin, with cefepime for gram-negative coverage. Narrow immediately once the organism and susceptibilities return; rifampin is reserved for retained prosthetic material.
• Vegetation, abscess, or new regurgitation on echocardiography means 6 weeks of IV therapy from the first negative culture, a daily cardiac exam, an EKG for new conduction delay, and early cardiac surgery consultation.
• Surgical indications: valve dysfunction causing heart failure; uncontrolled infection (annular or aortic abscess, fistula, new heart block, a destructive penetrating lesion); persistent bacteremia or fever beyond 5–7 days despite appropriate therapy; fungal or highly resistant organisms; most prosthetic-valve endocarditis with dysfunction or relapse; recurrent emboli with a persistent vegetation, or a large mobile vegetation over 10 mm, particularly on the anterior mitral leaflet after an embolic event. Early surgical consultation improves outcomes; do not wait to complete antibiotics.

Bacterial meningitis

• Organisms by age and host: adults 18–50 — Streptococcus pneumoniae and Neisseria meningitidis. Adults over 50, and anyone with alcohol use or cirrhosis, pregnancy, malignancy, steroids or immunosuppression, or chronic renal failure — add Listeria monocytogenes. Post-neurosurgical or nosocomial meningitis — Pseudomonas, other gram-negatives, and staphylococci.
• Sequence: two sets of blood cultures immediately (yield 50–70%, often the only microbiologic diagnosis if lumbar puncture is delayed), plus CBC, CMP, coagulation studies, lactate, and serum glucose for the CSF ratio; then dexamethasone and antibiotics within minutes, before any imaging. Never delay antibiotics or dexamethasone for CT or lumbar puncture.
• CT before lumbar puncture only for immunocompromise, prior CNS disease or a mass, a new seizure, papilledema, a focal neurologic deficit, or moderate to severe impairment of consciousness; when the exam shows only meningeal and infectious signs, lumbar puncture proceeds directly. Check platelets and coagulation first.
• Dexamethasone 0.15 mg/kg (about 10 mg) IV every 6 hours for 4 days, the first dose 10–20 minutes before or with the first antibiotic, continued only if pneumococcus is confirmed and stopped if another organism or a non-bacterial cause is identified; starting it after antibiotics is of uncertain value.
• Empiric antibiotics: ceftriaxone 2 g IV every 12 hours plus vancomycin 15–20 mg/kg IV every 8–12 hours (trough 15–20 mcg/mL or AUC-guided, kept until susceptibilities return to cover ceftriaxone-non-susceptible pneumococcus) for adults 18–50; add ampicillin 2 g IV every 4 hours for age over 50 or any Listeria risk factor. Severe beta-lactam allergy: moxifloxacin or meropenem in place of ceftriaxone and TMP-SMX in place of ampicillin (meropenem alone also covers Listeria). Post-neurosurgical meningitis: cefepime or meropenem plus vancomycin.
• CSF: opening pressure above 20 cm H2O, white cells above 1,000/mm³ and neutrophil-predominant, protein above 1 g/L, and glucose below 40 mg/dL or a CSF-to-serum ratio below 0.4 point to bacterial meningitis; the Gram stain is diagnostic in 60–90%. Send PCR if partially treated; add HSV PCR with empiric acyclovir when encephalitic features (seizures, personality change, temporal findings) dominate.
• Pathogen-directed therapy and duration: penicillin-susceptible pneumococcus — penicillin G or ceftriaxone for 10–14 days (continue vancomycin plus ceftriaxone, with or without rifampin, when the ceftriaxone MIC is 1 mcg/mL or above); meningococcus — ceftriaxone or penicillin G for 7 days; Listeria — ampicillin 2 g every 4 hours with or without gentamicin for at least 21 days (TMP-SMX if penicillin-allergic); Haemophilus — ceftriaxone for 7 days; aerobic gram-negative bacilli — cefepime or meropenem for 21 days.
• Supportive care: isotonic fluids, antipyretics, prompt seizure treatment (benzodiazepine plus levetiracetam, EEG for altered mentation out of proportion), head of bed at 30 degrees, avoidance of hypotonic fluids and hyponatremia. Droplet precautions until meningococcus is excluded or for the first 24 hours of effective therapy; notify infection control and public health.
• After the acute phase: hunt for a parameningeal source (sinus and mastoid imaging, otoscopy, dental assessment); echocardiography for pneumococcal or staphylococcal bacteremia or a murmur; evaluation for CSF leak, asplenia, or complement deficiency with recurrent or meningococcal disease; formal audiology before discharge because sensorineural hearing loss is the commonest sequela; pneumococcal vaccination when indicated.
• Chemoprophylaxis for close contacts of confirmed meningococcal disease (household, childcare, direct exposure to oral secretions, unprotected airway management): rifampin 600 mg orally twice daily for 2 days, ciprofloxacin 500 mg orally once, or ceftriaxone 250 mg IM once. None is needed for pneumococcal or Listeria meningitis.

Vertebral osteomyelitis and spinal epidural abscess

• Organisms: hematogenous vertebral osteomyelitis — S. aureus (MSSA more than MRSA), then coagulase-negative staphylococci, streptococci and enterococci, and gram-negatives such as E. coli from a urinary source. Contiguous diabetic-foot osteomyelitis — polymicrobial (S. aureus, streptococci, anaerobes, aerobic gram-negatives). Post-surgical or hardware infection — S. aureus, coagulase-negative staphylococci, Cutibacterium acnes, and gram-negatives. Consider tuberculosis, Brucella, and fungi with a subacute course or exposure.
• Workup: two sets of blood cultures (fungal and mycobacterial cultures if indolent); if S. aureus grows, transesophageal echocardiography and a search for other metastatic foci. Baseline ESR and CRP for trending, CBC, CMP, HbA1c, and a search for the hematogenous source (skin, urine, endovascular, dental). Add HIV testing, and Brucella serology or an interferon-gamma release assay with exposure.
• Hold antibiotics in the stable patient: when the patient is hemodynamically stable and neurologically intact, withhold empiric therapy until blood cultures and an image-guided biopsy of the disc space, endplate, or epidural collection (aerobic and anaerobic cultures, fungal, AFB, and histopathology) are obtained, because prior antibiotics markedly lower culture yield. If blood cultures are negative at 48–72 hours, proceed to CT-guided biopsy; if the first biopsy is also negative and the patient remains stable, repeat image-guided or open biopsy before committing to empiric therapy, and reconsider tuberculosis, Brucella, fungal infection, and malignancy.
• Start antibiotics immediately, before any biopsy, for sepsis or hemodynamic instability or any new or progressive neurologic deficit: vancomycin loaded at 20–25 mg/kg then AUC-guided (target 400–600), plus ceftriaxone 2 g IV every 24 hours, or cefepime 2 g IV every 8–12 hours with nosocomial or pseudomonal risk. Draw cultures first whenever possible.
• Spinal epidural abscess: a small collection without cord compression in a neurologically intact patient can be managed medically with neurologic checks every 4 hours (strength, sensory level, bowel and bladder function) and immediate neurosurgical co-management; aspiration of the collection, when feasible, is both diagnostic and partial source control. Urgent surgical decompression and drainage is indicated for any new or progressive motor weakness, sensory level, radicular deficit, or bowel or bladder dysfunction, for an enlarging collection or worsening pain and inflammatory markers despite therapy, and for progressive vertebral destruction, deformity, or instability.
• Pathogen-directed therapy: MSSA — nafcillin or oxacillin 2 g IV every 4 hours or cefazolin 2 g IV every 8 hours; MRSA — vancomycin (AUC-guided) or daptomycin 6–8 mg/kg IV every 24 hours; streptococci — ceftriaxone 2 g IV every 24 hours or penicillin G; Enterobacterales — ceftriaxone or a carbapenem per susceptibilities; Pseudomonas — cefepime or meropenem.
• Duration: 6 weeks of parenteral or highly bioavailable oral therapy from the start of effective treatment (counted from any debridement), extended to 8 weeks or longer for an undrained abscess, extensive bone destruction, or incomplete source control. Oral step-down with a highly bioavailable agent (levofloxacin plus rifampin, linezolid, or high-dose TMP-SMX) is reasonable after clinical and biochemical response in a susceptible organism; otherwise place a PICC and arrange outpatient parenteral therapy. Rifampin is never monotherapy and interacts with anticoagulants, statins, and antiretrovirals.
• Supportive care: multimodal analgesia, mobilization as tolerated with external bracing for significant pain or instability concern, VTE prophylaxis, glycemic control, and treatment of the source (endocarditis, infected catheters, diabetic foot).

Monitoring and disposition

• S. aureus bacteremia: daily vitals and fever curve, cardiac and neurologic exam, line site, and culture results; twice-weekly creatinine and CBC on cefazolin or nafcillin (interstitial nephritis, neutropenia, hepatitis), AUC-guided vancomycin levels, weekly CK on daptomycin. Discharge when afebrile, cultures sterile, the echo result known, no metastatic focus, access secured after clearance, and an outpatient parenteral plan with weekly labs in place; ID follow-up within 1–2 weeks and at the end of therapy.
• Meningitis: a monitored or step-down bed with neurologic checks every 2–4 hours for the first 24–48 hours; ICU for falling consciousness, seizures, shock, or airway protection. Daily CBC, BMP, renal function with vancomycin levels, sodium for SIADH, and capillary glucose on dexamethasone. Discharge when afebrile, at baseline mentation, on a defined regimen with a stop date, audiology completed, and neurology and ID follow-up arranged.
• Vertebral osteomyelitis: neurologic exams every 4 hours initially while an epidural abscess is managed medically; ESR and CRP at baseline and again around 4 weeks (CRP should fall by roughly half, and a rising value warrants re-evaluation rather than reflexive extension); no routine repeat MRI — image for clinical or biochemical worsening; weekly CBC, creatinine, and liver tests, vancomycin AUC, CK on daptomycin, platelets on prolonged linezolid. Discharge when afebrile with stable or improving pain, a stable neurologic exam, a defined pathogen-directed regimen and end date, secure access or an oral plan, and safe mobility; ID follow-up within 1–2 weeks and at the end of therapy, with instructions to return immediately for weakness, numbness, or urinary retention.

Escalate care if

• S. aureus bacteremia persists beyond 48–72 hours after line removal and effective beta-lactam therapy — declare complicated disease, obtain transesophageal echocardiography, hunt for a deep focus (spine MRI, duplex ultrasound for septic thrombophlebitis of the catheter vein, splenic or renal abscess), and extend to 4–6 weeks. Fever persisting beyond 72 hours with sterile cultures — look for an undrained focus, septic thrombophlebitis, or drug fever rather than broadening antibiotics.
• New or worsening heart failure, new conduction block, a large mobile vegetation with embolism, or persistent bacteremia beyond 5–7 days — urgent surgical evaluation.
• In meningitis, a falling GCS, a new focal deficit, or pupillary changes — immediate head CT and neurosurgery or ICU consultation for hydrocephalus, abscess, or raised intracranial pressure; hypotension, rising lactate, or purpura fulminans — septic shock management; no improvement at 48 hours, or pneumococcus with reduced cephalosporin susceptibility treated with dexamethasone — repeat lumbar puncture to confirm sterilization and image for subdural empyema or ventriculitis.
• In spinal infection, any new or progressive weakness, sensory level, radicular deficit, or bowel or bladder dysfunction — emergent MRI and urgent surgical decompression with broad empiric antibiotics started immediately; persistent fever or bacteremia beyond 48–72 hours — repeat cultures, echocardiography, and repeat MRI for an enlarging epidural, paravertebral, or psoas abscess.
• Hypotension, rising lactate, or new organ dysfunction in any of the three — sepsis resuscitation, immediate antibiotics if they were being held, and ICU-level care.

Duration

Uncomplicated S. aureus bacteremia: 14 days IV from the first negative culture. Complicated bacteremia and endocarditis: 4–6 weeks, typically 6 weeks for endocarditis. Meningitis: 7 days for meningococcus and Haemophilus, 10–14 days for pneumococcus, 21 days for gram-negative bacilli, and at least 21 days for Listeria. Vertebral osteomyelitis and epidural abscess: 6 weeks from effective therapy, 8 weeks or longer without complete source control. Uncomplicated gram-negative bacteremia, by contrast, needs 7 days.

Caveats

• Never substitute vancomycin for a beta-lactam in MSSA bacteremia for convenience — failure and mortality are higher. Cefazolin is usually tolerated in penicillin allergy because it shares no R1 side chain; with documented anaphylaxis to cephalosporins use vancomycin or daptomycin and pursue allergy evaluation or desensitization.
• Any implanted hardware (valve, graft, pacemaker, joint) automatically makes S. aureus bacteremia complicated. Daptomycin must not be used when pneumonia is a possible focus, and statins should be held or CK monitored closely while on it.
• Never delay antibiotics or dexamethasone in suspected meningitis for CT or lumbar puncture. Withholding antibiotics in suspected vertebral osteomyelitis is appropriate only while the patient is hemodynamically stable and neurologically intact.
• Vancomycin and ampicillin need renal dose adjustment, and vancomycin with piperacillin-tazobactam or contrast raises AKI risk; use AUC-guided dosing. Fluoroquinolone oral step-down in osteomyelitis requires documented susceptibility.
• The meningitis pathway assumes immunocompetence and no neurosurgical or head-trauma history; the spinal pathway assumes no prosthetic hardware, no injection drug use, and no instability or deformity on imaging — each of these broadens the empiric regimen or lowers the surgical threshold.

References

1. WHO launches first-ever guidelines on meningitis diagnosis, treatment and care. (2025) · Primary guideline
2. The bacterial spectrum of spinal infections based on blood and tissue cultures: a systematic review and meta-analysis. Scientific Reports. · Systematic review“Staphylococcus aureus demonstrates the highest detection rate across all diagnostic methods...empiric antibiotic therapy for SI—particularly in post-surgical or post-traumatic settings—should prioritize coverage against S. aureus and ensure activity against both methicillin-sensitive and methicillin-resistant strains.”
3. Severe community-acquired meningitis. Critical Care. (1999) · Narrative review“When the clinical examination only reveals meningeal and infectious signs (60-70% of cases) lumbar puncture is the first examination to perform. If, on the other hand, onset is progressive and there appears to be signs of deficiency without change in mental status, followed by signs of intracranial hypertension, a cerebral computed tomography (CT) scan must be urgently performed in order to exclude the presence of an expansion process.”