Sepsis & Bloodstream Infections
A Step 2 CK–focused sepsis lesson covering Sepsis-3 definitions, the Hour-1 bundle, and exposure-driven organism/treatment reasoning, anchored by neutropenic-fever and septic-shock next-best-step vignettes. Emphasizes cultures-before-antibiotics, norepinephrine-first pressor management, and classic buzzwords (asplenia/OPSI, Vibrio, meningococcemia, toxic shock).
Definitions & Presentation (Sepsis-3)
Sepsis = life-threatening organ dysfunction from a dysregulated host response to infection (Sepsis-3, 2016). Operationally, organ dysfunction means an acute rise in the SOFA score ≥2. Septic shock is a subset: persistent hypotension needing vasopressors to keep MAP ≥65 mmHg and lactate >2 mmol/L despite adequate fluid resuscitation — mortality >40%.
At the bedside, qSOFA (≥2 of: RR ≥22, altered mentation, SBP ≤100) flags high-risk infected patients, though the 2021 Surviving Sepsis Campaign recommends against qSOFA as a single screening tool and favors more sensitive screens (SIRS/NEWS/MEWS). On Step 2 CK, remember that fever + tachycardia alone is not sepsis — you need infection PLUS organ dysfunction: hypotension, ↑lactate, ↑creatinine, ↓urine output, altered mental status, or thrombocytopenia. Gram-positives (S. aureus, Streptococcus, Enterococcus) and gram-negatives (E. coli — the top single gram-negative, often urosepsis) predominate. Early recognition plus the Hour-1 bundle drives survival.
Bundle elements are started together within the first hour — only two true ordering rules: cultures before antibiotics, and fluids before pressors.
- Measure lactate; remeasure in 2–4 h if initially >2 mmol/L (track clearance)
- Draw 2 sets of blood cultures BEFORE antibiotics — but never delay abx >45 min to get them
- Broad-spectrum antibiotics within 1 hour of recognition
- ≥30 mL/kg IV balanced crystalloid (e.g., LR) for hypotension or lactate ≥4
- Norepinephrine = first-line vasopressor if MAP <65 during/after fluids
- Lactate ≥4 mmol/L signals tissue hypoperfusion and poor prognosis even if BP looks normal
- Add vasopressin, then IV hydrocortisone, for shock refractory to escalating norepinephrine
- Source control (drain the abscess, remove the infected line) is essential — antibiotics alone fail without it
Exposure Clue → Organism → Treatment
| Clue / Vignette | Organism | Treatment / Key point |
|---|---|---|
| Asplenia or sickle cell, fulminant | Encapsulated (S. pneumoniae, H. flu, N. meningitidis) | Ceftriaxone now; OPSI; vaccinate + prophylaxis |
| Neutropenic fever (post-chemo) | Pseudomonas aeruginosa | Cefepime or pip-tazo; ecthyma gangrenosum |
| IV drug use, tricuspid vegetation | S. aureus | Vancomycin; right-sided endocarditis |
| Central venous catheter | Coag-neg staph, S. aureus, Candida | Remove line; vancomycin |
| Raw oysters/seawater + cirrhosis | Vibrio vulnificus | Doxycycline + ceftriaxone; hemorrhagic bullae |
| Petechiae/purpura, dorm/military | N. meningitidis | Ceftriaxone; Waterhouse-Friderichsen |
| Urosepsis, elderly | E. coli | Ceftriaxone; #1 gram-negative |
| Pregnant/elderly, deli meat/soft cheese | Listeria | Add ampicillin (cephalosporins miss it) |
Asplenic and functionally asplenic (sickle cell) patients can't opsonize/clear encapsulated bacteria → overwhelming post-splenectomy infection (OPSI).
"Please SHiNE my SKiS" — encapsulated organisms:
- P — Pseudomonas aeruginosa
- S — Streptococcus pneumoniae (#1 OPSI cause)
- H — Haemophilus influenzae type b
- N — Neisseria meningitidis
- E — Escherichia coli
- S — Salmonella (esp. Typhi)
- K — Klebsiella pneumoniae
- S — group B Streptococcus (S. agalactiae)
Prevent with vaccination (pneumococcal, Hib, meningococcal) ± penicillin prophylaxis in select patients. Exam trigger: fever in an asplenic patient = emergency → empiric ceftriaxone immediately. (Dog bite in an asplenic patient? Think Capnocytophaga canimorsus.)
A 58-year-old woman 7 days after induction chemotherapy for AML has a single T 38.6°C spike. ANC 300/µL. BP 118/74, HR 96. Exam is unremarkable with no localizing source.
- Diagnosis: Febrile neutropenia (ANC <500 + single temp ≥38.3°C, or ≥38.0°C sustained 1 h) — a medical emergency.
- Next best step: Draw blood cultures (peripheral and line) and immediately start empiric antipseudomonal monotherapy — cefepime, pip-tazo, or a carbapenem. Do not wait for a fever source or for culture results.
- Add vancomycin only for specific triggers: suspected catheter/line infection, skin or soft-tissue infection, hemodynamic instability, pneumonia, or known MRSA colonization. Otherwise, empiric vancomycin is not routine and should be stopped if cultures are negative at 48 h.
A 70-year-old man with dysuria is hypotensive (BP 82/50), HR 118, T 39.1°C, and confused. Lactate 5.2 mmol/L. He receives blood cultures, ceftriaxone, and a 30 mL/kg LR bolus. Repeat BP is 84/52.
- Diagnosis: Septic shock, likely urosepsis (→ E. coli).
- Next best step: Start norepinephrine targeting MAP ≥65 mmHg — vasopressors are indicated for fluid-refractory hypotension. Do not keep giving open-ended fluid boluses (risks pulmonary edema).
- If MAP stays low despite escalating norepinephrine, add vasopressin, then IV hydrocortisone for refractory shock. Reassess perfusion by lactate clearance and urine output, and pursue source control (obstructing stone → decompression).
- Default broad regimen: Vancomycin (MRSA) + an antipseudomonal β-lactam (pip-tazo, cefepime, or meropenem)
- Blood cultures before antibiotics, but never delay abx to obtain them in septic shock
- De-escalate/narrow once cultures and sensitivities return
- Add ampicillin when Listeria is a concern (neonates, pregnant, elderly, immunocompromised, unpasteurized foods)
- Add clindamycin for toxin suppression in toxic shock / necrotizing fasciitis (Strep/Staph)
- Echinocandin (e.g., micafungin) if Candida bloodstream infection is suspected (TPN, prolonged central line, broad-spectrum abx)
- Procalcitonin can support stopping antibiotics but should not delay starting them
Comparison: Staphylococcal vs Streptococcal TSS
| Feature | Staphylococcal TSS | Streptococcal TSS |
|---|---|---|
| Organism / toxin | S. aureus (TSST-1 superantigen) | Group A Strep (S. pyogenes); pyrogenic exotoxin (SpeA/SpeC) superantigen |
| Exposure | Tampons, nasal packing, surgical wound | Skin/soft-tissue, necrotizing fasciitis, varicella |
| Blood cultures | Usually negative | Often positive |
| Skin | Diffuse macular rash → palm/sole desquamation | Less rash; severe soft-tissue pain out of proportion |
| Treatment | Remove source + vancomycin + clindamycin | Surgical debridement + penicillin + clindamycin ± IVIG |
Practice Infectious Disease now
Board-style questions, spaced-repetition flashcards, and a Socratic AI tutor — free to start.