Antimicrobial Stewardship & Fever Workup
From the FUO buckets to the neutropenic-fever emergency and C. diff
Stewardship and antibiotic selection
Goal. Antimicrobial stewardship means the narrowest effective agent, at the correct dose, for the shortest effective duration: curing the infection while limiting resistance, C. difficile, toxicity and cost.
- Culture firstblood and site cultures, without delaying urgent therapy
- Empiric coveragematched to the likely source, organism and local resistance
- De-escalatenarrow to the tightest agent once cultures and susceptibilities return
- IV to oralswitch once the patient is stable and can absorb a well-absorbed drug
- Stop dateshortest evidence-based duration; stop when infection is excluded, with procalcitonin supporting the decision
Match spectrum to the likely bug. Below the diaphragm, cover anaerobes (metronidazole, piperacillin-tazobactam); in pneumonia, cover atypicals (azithromycin, doxycycline or a fluoroquinolone); for hospital-acquired gram-negative infection, use an antipseudomonal β-lactam.
| Target | Agents | Pitfalls |
|---|---|---|
| MRSA | Vancomycin, linezolid, daptomycin, ceftaroline | Daptomycin is inactivated by surfactant, so never use it for pneumonia; ceftaroline is the classic anti-MRSA cephalosporin |
| Pseudomonas | Cefepime, ceftazidime, piperacillin-tazobactam, meropenem or imipenem, ciprofloxacin, aminoglycosides | Ceftriaxone and ertapenem do not cover Pseudomonas |
| Anaerobes | Metronidazole, piperacillin-tazobactam, carbapenems | Needed for intra-abdominal and pelvic sources |
| Atypicals | Azithromycin, doxycycline, fluoroquinolones | β-lactams miss them |
Penicillin allergy
Take the history. Many patients carry a penicillin-allergy label, but most tolerate penicillin when formally tested. A remote mild rash usually does not preclude β-lactams. A severe delayed reaction such as SJS/TEN or DRESS means avoiding all β-lactams. True IgE-mediated anaphylaxis means avoiding penicillins, but aztreonam and cephalosporins with dissimilar side chains (such as cefazolin) are usually usable; otherwise choose a non-β-lactam such as vancomycin for a serious infection, or involve an allergist for testing or desensitization.
Cefazolin has a unique side chain and is often tolerated even in penicillin-allergic patients. Aztreonam does not cross-react with penicillins.
Fever of unknown origin
Definition. Classic FUO is a temperature above 38.3 °C (101 °F) on several occasions, lasting more than 3 weeks, and undiagnosed after an appropriate evaluation. The causes fall into four buckets:
- Infection: occult abscess, endocarditis, extrapulmonary TB, osteomyelitis.
- Malignancy: lymphoma, renal cell carcinoma, leukemia.
- Autoimmune or connective tissue disease: adult-onset Still disease in the young, giant cell arteritis in the old, SLE.
- Miscellaneous: drug fever, venous thromboembolism, factitious fever.
Evaluation. The workup is driven by the history (travel, animals, drugs, exposures) and a repeated exam: repeat blood cultures, HIV and TB testing, inflammatory markers, cross-sectional imaging, and stopping culprit drugs, since drug fever usually settles within days. Avoid empiric antibiotics in the stable patient, because they obscure culture data.
Neutropenic fever
Definition. A single oral temperature ≥38.3 °C (101 °F), or ≥38.0 °C (100.4 °F) sustained for 1 hour, with an absolute neutrophil count below 500/μL (or below 1,000 and expected to fall below 500). It is a medical emergency: treat before the workup is complete. Inflammatory signs are blunted, so pneumonia may lack an infiltrate and urinary infection may lack pyuria.
- ANC below 500 + feveremergency; blood cultures from a vein and any central line now
- Empiric antipseudomonal monotherapycefepime, piperacillin-tazobactam, or meropenem/imipenem within an hour
- Add vancomycin only ifhypotension, catheter or skin infection, pneumonia, mucositis, known MRSA
- Reassess at 48–72 hoursde-escalate to cultures; persistent fever after 4–7 days prompts empiric antifungal therapy
Do not delay the first dose for cultures or imaging, do not add vancomycin routinely, and remember that ertapenem does not cover Pseudomonas.
Clostridioides difficile
Risk and testing. C. difficile follows antibiotics (clindamycin classically, plus fluoroquinolones and cephalosporins), PPIs and hospitalization. Test only patients with ≥3 unformed stools in 24 hours, using NAAT (PCR) plus toxin EIA. Never test formed stool or asymptomatic carriers, and do not retest as a test of cure.
| Situation | Features | Treatment |
|---|---|---|
| Initial episode | Diarrhea; severe if WBC ≥15,000 or creatinine >1.5 mg/dL | Oral fidaxomicin (preferred by IDSA/SHEA 2021) or oral vancomycin (equally acceptable per ACG 2021); metronidazole only if neither is available |
| Fulminant | Hypotension, ileus, toxic megacolon | Oral or NG vancomycin 500 mg four times daily plus IV metronidazole; rectal vancomycin if ileus; colectomy if refractory or perforated |
| Recurrent | Return within 8 weeks | Fidaxomicin or a vancomycin taper; bezlotoxumab (anti-toxin B) lowers recurrence; fecal microbiota transplant for multiple recurrences |
Always. Stop the offending antibiotic, avoid antimotility agents, use contact precautions, and wash hands with soap and water, because alcohol gel does not kill spores. IV vancomycin does not reach the gut lumen and is useless here.
Adult immunizations
- Influenza: every adult, every year.
- Tdap: once, then Td or Tdap every 10 years, plus Tdap in every pregnancy.
- Recombinant zoster (Shingrix): 2 doses from age 50 (from 19 if immunocompromised); it is not live and has replaced the live vaccine.
- Pneumococcal: PCV20 or PCV21, or PCV15 followed by PPSV23, for all adults 50 or older (ACIP 2024; previously 65) and for younger adults at high risk.
- Asplenia: pneumococcal, meningococcal and Hib vaccines against encapsulated organisms.
- Others: hepatitis B for all adults 19 to 59 and for adults 60 or older with risk factors or who request it, and HPV through age 26.
Live vaccines (MMR, varicella, live zoster, intranasal influenza, yellow fever) are contraindicated in pregnancy and significant immunosuppression, such as HIV with CD4 below 200.