Surgical Infections

An infection is the proliferation of microorganisms within tissues, body cavities, or spaces, which induces an immune response and overwhelms the body’s natural defenses. In surgical patients, these infections are frequently caused by the translocation of commensal organisms into deeper tissues, combined with the impairment of host defenses due to surgical injury or stress. Infections commonly identified in patients after surgery include surgical site infections, catheter-associated infections, and ventilator-associated infections. Infection subtypes can be prevented, diagnosed, or treated using several strategies. The mainstays of treatment in surgical patients involve local control of the infection as well as targeted antibiotic therapy.

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Overview

Definition

Surgical infection is a clinical disorder that manifests when the virulence factors of a microorganism introduced during surgical procedures overcome the innate and adaptive immune responses of the host.

Types of surgical infections

  • Ventilator-associated pneumonia
  • Catheter-associated urinary tract infections
  • Central line-associated infections
  • Surgical site infections (develop within 30 days of the procedure or within 90 days after a prosthetic material is implanted):
    • Superficial: skin and superficial soft-tissue infections around incision sites
    • Deep: infection involving fascia or deep spaces (e.g., abdominal or pelvic abscess)

Risk factors

  • Patient factors:
    • Diabetes mellitus
    • Obesity
    • Malnutrition
    • Peripheral vascular disease
    • Prior radiation to the area
    • Extremes of age
    • Hypothermia
    • Corticosteroid therapy
  • Treatment-related factors:
    • Long-term catheter use
    • Poor disinfection and sterile techniques for invasive procedures or catheter care
    • Drains
    • Emergent procedures
    • Absent or inadequate antibiotic prophylaxis
    • Prolonged hospitalization
    • Prolonged operative time

Etiology and Pathophysiology

Etiology

Several factors make patients who have undergone surgery particularly susceptible to nosocomial infections:

  • Incisions made during surgical procedures can serve as a direct site of entry.
  • Surgical illness creates a state of immunosuppression.
  • Periods of mechanical ventilation during and after surgery:
    • Risk for pneumonia
    • Increased aspiration risk

Pathophysiology

Presence of bacteria may or may not be associated with clinically significant infection.

  • Colonization: Bacteria are present but do not stimulate an immune response with corresponding signs and symptoms of local or systemic disease. 
  • Infection: Proliferation of microorganisms in tissues, organs, or cavities stimulates an immune response that leads to local and/or systemic disease. 
  • Sepsis: life-threatening organ dysfunction caused by excessive and disproportionate host response to infections

Pathogenesis of infection

  • Once microbes enter, host defenses (i.e., tissue barriers, iron-sequestering lactoferrin and transferrin, fibrinogen) act to control and/or eliminate pathogens:
    • In the peritoneal cavity, a diaphragm motion extracts the microorganism-containing peritoneal fluid from the abdominal cavity into the lymphatic circulation.
    • Macrophages, low levels of complement (C) proteins, and immunoglobulins are embedded in the vast majority of tissues to aid in host defense.
  • Macrophages secrete cytokines (tumor necrosis factor (TNF)-α; IL-1β, 6, and 8; and interferon (IFN)-γ) to recruit and activate inflammatory cells.
  • Potential outcomes:
    • The microorganism is eradicated.
    • Containment in the parenchyma (i.e., abscess)
    • Localized infection, displaying local symptoms (i.e., cellulitis)
    • Systemic infection (bacteremia or fungemia) with associated symptoms (i.e., fever, tachycardia)
Sites of bacterial colonization

Sites of bacterial colonization and common colonizers

Image by Lecturio. License: CC BY-NC-SA 4.0

Clinical Presentation

Timeline of infection

  • Early postoperative (1‒3 days):
    • Always consider a preexisting community-acquired infection.
    • Early surgical site infection:
      • Group A Streptococcus
      • Clostridium perfringens
    • Pneumonia: peak incidence at postoperative day 2
    • Urinary tract infection: should be considered in any patient with a catheter in place
  • Late postoperative (> 3 days):
    • Surgical site infection is the most common cause.
    • Catheter-related infections
    • Antibiotic-associated infections: C. difficile

Physical examination

Signs of systemic inflammation (SIRS):

  • Temperature > 38ºC (100.4ºF) or < 35ºC (95ºF)
  • HR > 90/min
  • RR > 20/min or PaCO2 < 35 mm Hg
  • WBC > 12,000 (leukocytosis) or < 4,000 (leukopenia)

Specific findings related to surgical infections:

  • Tenderness at or around the surgical wound
  • Redness (erythema) of the surgical incision
  • Purulent drainage from the surgical wound
  • Rebound tenderness
  • Guarding
  • Peritonitis

Signs of shock:

  • Hypotension
  • Pallor
  • Diaphoresis
  • Rigors
  • Altered mental status

Quick sepsis-related organ failure assessment (qSOFA):

  • Identifies patients at the greatest risk of poor outcomes outside of an ICU
  • Based on 3 parameters:
    • RR ≥ 22/min
    • Altered mentation
    • Systolic BP ≤ 100 mm Hg

Diagnosis

Laboratory values

  • WBC > 10,000
  • ↑ Serum creatinine
  • ↑ BUN
  • ↑ CRP, erythrocyte sedimentation rate
  • Lactic acid
  • Urinalysis
  • Microbiology:
    • Urine culture
    • Sputum culture
    • Gram staining and culture of wound or collection
    • Blood cultures

Imaging

  • X-ray: 
    • 1st-line imaging modality in the majority of cases
    • Chest: assess for infiltrates or consolidation if > concern for pneumonia
    • Abdomen: upright to assess for free air
  • CT:
    • 2nd-line imaging modality in the majority of cases if the patient is stable
    • More sensitive than X-ray for detecting consolidation, infiltrates, and effusion
    • Abdominal CT identifies free air, free fluid, and bowel inflammation.
    • Soft-tissue infections can be identified with stranding, or if gas in the tissue is concerning for a necrotizing infection.
  • MRI:
    • Rarely the 1st-line modality except in children and pregnant individuals
    • Magnetic resonance cholangiopancreatography to image the biliary system
  • Ultrasound

Prevention

Prevention of surgical infections depends largely on sterile technique, hand hygiene, and the administration of prophylactic antibiotics.

Hand hygiene

  • The WHO’s 5 steps of hand hygiene:
    • Before touching a patient
    • Before a clean/aseptic procedure
    • After the risk of body-fluid exposure
    • After touching a patient
    • After touching a patient’s surroundings
  • Soap and water, or alcohol-based disinfectants are both acceptable (exception: for C. difficile, where soap and water must be used, as alcohol does not kill bacterial spores).

Preoperative MRSA screening

  • Can reduce MRSA transmission in wards
  • Contact precautions are initiated for patients with known MRSA infections or colonization:
    • Gown, mask, and gloves upon entering the patient’s room
    • Hand hygiene
  • Positive results are followed by decolonization therapy and antibiotic prophylaxis prior to the procedure.

Sterile technique

A term used to describe steps taken by the surgical team before and during a surgical procedure to prevent the development of postoperative infections, which includes:

  • Handwashing: 
    • Before every procedure, using an aqueous antiseptic surgical solution chosen by the institution
    • At least 3 minutes of washing time
  • PPE:
    • Sterile gowns
    • Gloves
    • Surgical cap 
    • Face shield
  • Prepping of the surgical site:
    • Chlorhexidine prep 
    • Betadine
  • Properly sterilized or single-use surgical instruments

Antibiotic prophylaxis

  • Antibiotic coverage to further prevent the proliferation of commensal microorganisms
  • Selection depends on:
    • Procedure to be performed 
    • Expected pathogens
    • Local patterns of resistance
    • Disease severity
    • Age of the patient
    • Immunosuppression 
    • Organ dysfunction
    • Allergies
    • Institutional guidelines
  • Single doses are used as they are as effective as multidose courses.
  • Attention must be paid to the timing of administration so that adequate serum concentrations are achieved prior to the start of the surgical procedure.
  • Cardiac, vascular, and orthopedic cases: 
    • Cefazolin or cefuroxime 
    • Vancomycin
  • GI procedures:
    • Oral:
      • Neomycin and erythromycin
      • Metronidazole
    • IV: 
      • Cefoxitin/cefotetan 
      • Ertapenem
      • Ampicillin-sulbactam
      • Cefazolin with metronidazole
  • Gynecological procedures:
    • Cefazolin, cefoxitin, cefotetan, or cefuroxime
    • Ampicillin-sulbactam

Management

The management of surgical infections is described using the term “source control,” which implies the combination of surgical management (if indicated) with the administration of antibiotics.

Antibiotic policy

  • Avoid antibiotics in self-limiting infections to avoid the development of resistance.
  • Identification and sensitivities of organisms guide antibiotic selection.
  • Empiric therapy can be started based on clinical suspicion, but should be narrowed to fit sensitivities of the identified organisms.
  • Each antibiotic has specific dosing and time intervals based on its pharmacokinetics.
  • Be aware of potential side effects and monitor accordingly.
Table: Suggestions for direct antibiotic therapy in surgery
Organism1st choiceAlternative
MSSACefazolinClarithromycin
MRSAVancomycin
  • Linezolid
  • Daptomycin
Coagulase-negative staphylococciVancomycin
  • Linezolid
  • Daptomycin
Streptococcus pneumoniaeBenzylpenicillinClarithromycin
S. pyogenes (group A β-hemolytic Streptococcus)
  • Benzylpenicillin
  • Clindamycin
Clarithromycin
EnterococciAmoxicillinVancomycin
Bacteroides spp.Metronidazole
  • Amoxicillin
  • Clavulanate
Escherichia coli
  • Piperacillin-tazobactam
  • Trimethoprim (urinary tract infections)
Meropenem
Haemophilus influenzaeCeftriazone
  • Amoxicillin
  • Clavulanate
Klebsiella spp.
  • Amoxicillin
  • Clavulanate
Meropenem
Proteus spp.
  • Amoxicillin
  • Clavulanate
Meropenem
Pseudomonas aeruginosaPiperacillin-tazobactamMeropenem
Clostridium spp.BenzylpenicillinMetronidazole
C. difficileMetronidazole
  • Vancomycin
  • Fidaxomicin

Surgical management

Abscess:

  • Most often needs to be drained
  • Technique depends on the type of abscess:
    • Incision and drainage for superficial skin/soft-tissue abscess
    • Percutaneous needle aspiration with/without catheter placement:
      • Abdominal/pelvic or deep soft-tissue abscesses
      • Ultrasound or CT guidance is used.
    • Open surgery: may be needed if percutaneous drainage is not feasible

Necrotizing fasciitis and diabetic foot infections:

  • Urgent surgical debridement of all necrotic tissue
  • Often require repeated/serial debridements

References

  1. Gossain, S., Hawkey, P.M. (2018). Infections and antibiotics. In Garden, O.J., et al. (Eds.), Principles and Practice of Surgery. pp. 48–59. https://www.clinicalkey.com/#!/content/3-s2.0-B9780702068591000042
  2. Quick, C.R.G., et al. (2020). Immunity, inflammation and infection. In Quick, C.R.G., et al. (Eds.), Essential surgery: Problems, Diagnosis and Management. pp. 31–49. https://www.clinicalkey.com/#!/content/3-s2.0-B9780702076312000031
  3. Anderwon, D.J. (2020). Infection prevention: Precautions for preventing transmission of infection. In Mitty, J. (Ed.), UpToDate. Retrieved June 1, 2021, from https://www.uptodate.com/contents/infection-prevention-precautions-for-preventing-transmission-of-infection
  4. Anderson, D.J., Sexton, D.J. (2019). Antimicrobial prophylaxis for prevention of surgical site infection in adults. In Mitty, J. (Ed.), UpToDate. Retrieved June 3, 2021, from https://www.uptodate.com/contents/antimicrobial-prophylaxis-for-prevention-of-surgical-site-infection-in-adults
  5. Hooton, T.M., Gupta, K. (2021). Acute simple cystitis in women. In Bloon, A. (Ed.), UpToDate. Retrieved June 1, 2021, from https://www.uptodate.com/contents/acute-simple-cystitis-in-women
  6. Weed, H.G., Baddour, L.M., Ho, V.P. (2020). Fever in the surgical patient. In Collins, K.A. (Ed.), UpToDate. Retrieved June 3, 2021. https://www.uptodate.com/contents/fever-in-the-surgical-patient

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