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Staphylococcal Infection

Staphylococcal Infection is an infection caused by bacteria of the genus Staphylococcus. The most clinically important species is Staphylococcus aureus, which can cause infections ranging from localized skin disease to life-threatening bacteremia, endocarditis,pneumonia, osteomyelitis, and sepsis.

Also called

Staph infection

ICD-10

A49.0

Specialty

Infectious

Onset

Acute

Reviewed

August 2026
On This Page

Overview

–Staphylococcal Infection can affect almost any body system.

–S. aureus commonly colonizes the skin and anterior nares without causing disease, but it can enter damaged tissue or the bloodstream and produce invasive infection.

–Common clinical manifestations include:

  • Skin and soft-tissue infections
  • Abscesses
  • Wound infections
  • Bacteremia
  • Endocarditis
  • Osteomyelitis
  • Septic arthritis
  • Pneumonia
  • Toxic shock syndrome
  • Food poisoning

Etiology & Risk Factors

-Etiology

–Staphylococcal Infection is most commonly caused by Staphylococcus aureus, a Gram-positive, catalase-positive, coagulase-positive coccus that commonly forms clusters.

Transmission occurs through:

  • Direct skin-to-skin contact
  • Contact with contaminated surfaces
  • Autoinoculation from colonized skin or mucosa

 

-Risk Factors

  • Skin breaks or wounds
  • Recent surgery or hospitalization
  • Indwelling catheters or medical devices
  • Diabetes mellitus
  • Immunosuppression

Pathophysiology

Colonization → disruption of skin or mucosal barrier → bacterial invasion → local inflammation and tissue destruction → abscess or invasive infection → bloodstream dissemination → sepsis and metastatic infection

Clinical Presentation

-Symptoms:

Presentation depends on the site of infection.

Skin and Soft Tissue

  • Painful skin lesion
  • Redness
  • Swelling
  • Warmth
  • Pus or drainage
  • Fever

Invasive Infection

  • Fever
  • Chills
  • Malaise
  • Hypotension
  • Altered mental status
  • Shortness of breath

Endocarditis

  • Persistent fever
  • Fatigue
  • New or changing heart murmur
  • Embolic manifestations

-Signs:

  • Erythematous, warm, tender skin lesion
  • Fluctuant abscess
  • Purulent drainage
  • Fever
  • Tachycardia
  • Hypotension in severe infection
Staphylococcal Infection Overview
Staphylococcal Infection Overview

Bacterial Classification

Staphylococci · Classification

Coagulase-Positive
Main human pathogen
S. aureus — clinically important coagulase-positive Staph
Coagulase test positive → plasma clot
Coagulase-Negative (CoNS)
Important species
S. epidermidis — prosthetic/device infections
S. saprophyticus — UTI in young women
S. lugdunensis — unusually virulent CoNS
1
S. aureus
Coagulase-positive
GramGram-positive cocci in clusters
TestsCatalase +, coagulase +, DNase +
KeyGolden pigment, β-haemolytic, mannitol +
DiseasesSkin abscesses, pneumonia, endocarditis, osteomyelitis, TSS, SSSS, food poisoning
2
S. epidermidis
CoNS · device pathogen
TestsCoagulase −, catalase +, novobiocin sensitive
CultureNon-haemolytic, no pigment
KeyNormal skin flora; forms biofilm
DiseasesProsthetic valve, catheter, joint and other device infections
3
S. saprophyticus
CoNS · UTI pathogen
TestsCoagulase −, catalase +, novobiocin resistant
CultureNon-haemolytic
KeyDistinguished from S. epidermidis by novobiocin resistance
DiseaseUTI in young sexually active women
S. aureus — High-Yield Virulence Factors & Toxins
FactorKey mechanismExam association
Protein ABinds Fc of IgG → blocks opsonisationImmune evasion
CoagulaseFibrin formation around bacteriaCoagulase-positive Staph
Exfoliative toxinCleaves desmoglein-1SSSS + bullous impetigo
TSST-1Superantigen → cytokine releaseToxic Shock Syndrome
EnterotoxinPreformed, heat-stable toxinFood poisoning — rapid vomiting
PVLLeukocyte lysisNecrotising skin infection / pneumonia
Exam hook: Exfoliative → SSSS · TSST-1 → TSS · Enterotoxin → food poisoning · PVL → necrotising infection.
MRSA — Essential Facts
Resistance
• mecA gene → PBP2a
• Low affinity for β-lactams
• = methicillin-resistant S. aureus
Clinical
• HA-MRSA → healthcare-associated
• CA-MRSA → community-associated; often skin abscesses
• Severe infection: vancomycin is a classic treatment option
Most tested distinction: S. aureus = coagulase + · S. epidermidis = novobiocin sensitive · S. saprophyticus = novobiocin resistant.

History Taking

-Ask about:

  • Onset and progression of symptoms
  • Skin wounds or abscesses
  • Recent surgery
  • Recent hospitalization
  • Intravenous catheter or other medical devices
  • Previous MRSA infection
  • Antibiotic exposure
  • Diabetes or immunosuppression
  • Intravenous drug use
  • Joint or bone pain

Physical Examination

-General Examination

  • Temperature
  • Heart rate and blood pressure
  • General appearance
  • Signs of sepsis or shock

 

-System-Specific Examination:

  • Inspect skin for abscesses and wounds
  • Examine joints for swelling and restricted movement
  • Examine bones for localized tenderness
  • Cardiac examination for murmurs
  • Respiratory examination for pneumonia
  • Examine catheter and surgical sites

Investigations

-Complete Blood Count

Useful for assessing systemic infection and inflammatory response.

 

-Biochemistry / Specific Tests

  • Blood cultures for suspected bacteremia or systemic infection

  • Culture and antimicrobial susceptibility testing from purulent material

  • Serum creatinine and other organ-function tests in systemic infection

  • Inflammatory markers when useful for monitoring

 

-Imaging

Imaging depends on the suspected site:

  • Ultrasound for suspected abscess

  • Echocardiography when endocarditis is suspected

  • X-ray or Magnetic Resonance Imaging (MRI) for suspected bone or joint infection

  • Chest imaging for suspected pneumonia

 

-Special / Confirmatory Tests

Bacterial Culture

Culture confirms the organism and allows antimicrobial susceptibility testing.

Testing is particularly important for distinguishing:

  • MSSA (Methicillin-susceptible Staphylococcus aureus)

  • MRSA (Methicillin-resistant Staphylococcus aureus)

 

Important Investigation Note

Blood cultures are essential in suspected invasive Staphylococcus aureus infection, while purulent collections should be cultured whenever possible.

Diagnosis

Staphylococcal Infection is diagnosed by:

Compatible clinical syndrome → appropriate specimen collection → bacterial culture → identification of Staphylococcus species → antimicrobial susceptibility testing.

For suspected bacteremia, blood cultures are essential. The infection source should then be identified and assessed for metastatic spread.

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Management

Staphylococcal Infections · Treatment by Condition

MSSA — Methicillin-Sensitive S. aureus
Condition1st LineAlternativeDuration
Skin & soft tissue
Cellulitis, furunculosis, abscess		 Flucloxacillin 500 mg QDS PO
Abscess: incision & drainage — antibiotics only if surrounding cellulitis		 Co-amoxiclav PO
Cefalexin 500 mg QDS PO		 5–7 days
Impetigo
Bullous (S. aureus) or non-bullous		 Topical mupirocin — mild/localised
Flucloxacillin PO — extensive		 Cefalexin PO 5–7 days
Pneumonia
Community / post-influenza		 Flucloxacillin 1–2g IV q6h Cefazolin 2g IV q8h
Clindamycin if penicillin allergy		 7–14 days
Bacteraemia / Endocarditis Flucloxacillin 2g IV q4h — gold standard for MSSA endocarditis Cefazolin 2g IV q8h — non-inferior, less CNS penetration 4–6 weeks (endocarditis)
14 days (bacteraemia)
Osteomyelitis / Septic arthritis Flucloxacillin 2g IV q6h → step-down to PO when improving Cefalexin or Clindamycin PO (step-down) 4–6 weeks (osteo)
3–4 weeks (septic arthritis)
Toxic Shock Syndrome (TSS) Flucloxacillin 2g IV q4h + Clindamycin 900 mg IV q8h — clindamycin suppresses toxin production IV immunoglobulin (IVIG) — adjunct for refractory TSS 10–14 days
Scalded Skin Syndrome (SSSS) Flucloxacillin IV → PO
Supportive: fluid/electrolyte replacement, wound care		 Cefalexin PO (mild) 7–10 days
Food poisoning
Preformed enterotoxin		 Supportive only — oral rehydration. Antibiotics NOT indicated (preformed toxin — no live bacteria to treat) Self-limiting 24–48h
MRSA — Methicillin-Resistant S. aureus
Condition1st LineAlternativeDuration
Skin & soft tissue (mild)
CA-MRSA, abscess, cellulitis		 Co-trimoxazole (TMP-SMX) PO — CA-MRSA 1st line
Doxycycline 100 mg BD PO		 Clindamycin PO — check D-zone test for inducible resistance
Abscess: I&D alone often sufficient		 5–7 days
Skin & soft tissue (severe)
Necrotising fasciitis, severe cellulitis		 Vancomycin IV — target trough 15–20 mg/L or AUC/MIC 400–600
+ Clindamycin — anti-toxin effect (PVL)		 Linezolid 600 mg BD IV/PO 7–14 days
Pneumonia
Necrotising / cavitating		 Linezolid 600 mg BD IV — preferred over vancomycin (better lung penetration)
+ Clindamycin — suppresses PVL toxin		 Vancomycin IV — if linezolid not available 7–21 days
Bacteraemia Vancomycin IV — gold standard
Echocardiogram to exclude endocarditis		 Daptomycin 6–10 mg/kg IV OD — non-inferior; good for persistent bacteraemia 14 days minimum (longer if endocarditis)
Endocarditis Vancomycin IV — 6 weeks native valve; 6 weeks + rifampicin + gentamicin for prosthetic Daptomycin 8–10 mg/kg IV — left-sided endocarditis alternative 6 weeks
Osteomyelitis / Septic arthritis Vancomycin IV → step-down to PO agent when sensitive
Step-down: TMP-SMX or Linezolid PO		 Daptomycin IV — alternative to vancomycin
+ Rifampicin — adjunct for biofilm penetration		 4–6 weeks (osteo)
Meningitis / CNS Linezolid IV — best CNS penetration
Vancomycin IV — standard; adjust dose for CSF levels		 TMP-SMX IV — adequate CNS penetration 14–21 days
Decolonisation
Pre-op / carriers		 Mupirocin 2% nasal ointment BD × 5 days
Chlorhexidine 4% body wash daily × 5 days		 Octenidine — if mupirocin resistance
Add oral antibiotics only if systemic carriage		 5 days
Key MRSA rules:   Vancomycin = IV only (not oral — not absorbed)  |  Daptomycin = NOT for pneumonia (inactivated by surfactant)  |  Linezolid = oral bioavailability ~100% — can switch IV→PO safely  |  Always add Rifampicin for prosthetic device infections  |  Clindamycin + anti-toxin agents for toxin-mediated disease (TSS, PVL)
S. epidermidis — Device / Prosthetic Infections
ConditionTreatmentNotes
Prosthetic valve endocarditis Vancomycin IV + Rifampicin + Gentamicin (first 2 weeks) Often requires valve replacement surgery
Central line / catheter infection Vancomycin IV — remove line if possible
Line salvage: vancomycin lock therapy		 Remove device whenever feasible — biofilm = antibiotic failure
Joint prosthesis infection Vancomycin IV + Rifampicin
Step-down: Rifampicin + TMP-SMX or doxycycline PO		 Debridement + implant retention (DAIR) or two-stage revision
CSF shunt infection Vancomycin IV ± intrathecal vancomycin
Shunt removal + external drainage		 Shunt removal essential for cure — antibiotics alone fail
Rifampicin rule: Always add rifampicin for biofilm-associated (prosthetic) infections — penetrates biofilm, prevents resistance when used with another agent. Never use rifampicin alone (rapid resistance emerges).

Complications

  • Abscess formation
  • Bacteremia
  • Sepsis
  • Septic shock
  • Endocarditis
  • Pneumonia
  • Osteomyelitis
  • Septic arthritis
  • Metastatic abscesses
  • Toxic shock syndrome
  • Multiorgan failure

Prognosis

The prognosis varies widely according to the site and severity of infection. Localized skin infections generally have a good outcome with appropriate treatment and source control. Bacteremia, endocarditis, pneumonia, and other invasive infections carry substantially greater morbidity and mortality, particularly when treatment or source control is delayed.

Key Points / Clinical Pearls

  • Staphylococcal Infection is most commonly caused by Staphylococcus aureus.
  • S. aureus commonly colonizes the skin and nose.
  • It can cause both localized and invasive disease.
  • Skin and soft-tissue infections are common manifestations.
  • Abscesses commonly require incision and drainage.
  • MSSA and MRSA require different antibiotic considerations.
  • Culture and susceptibility testing guide definitive antibiotic therapy.
  • Blood cultures are essential when bacteremia is suspected.
  • S. aureus bacteremia requires evaluation for a deep infection source.
  • Endocarditis is an important complication of bacteremia.
  • Osteomyelitis and septic arthritis can occur through hematogenous spread.
  • Infected medical devices may require removal.
  • Source control is a key component of treatment.
  • Centers for Disease Control and Prevention (CDC). Staphylococcus aureus and Staph Infections .
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  • Murray CJ, et al. Global Burden of Bacterial Antimicrobial Resistance in 2019: A Systematic Analysis. Lancet. 2022;399(10325):629-655. PubMed .
  • Stevens DL, Bisno AL, Chambers HF, et al. Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections. Clin Infect Dis. 2014;59(2):e10-e52. Clinical Infectious Diseases .
  • Liu C, Bayer A, Cosgrove SE, et al. Clinical Practice Guidelines by the Infectious Diseases Society of America for the Treatment of Methicillin-Resistant Staphylococcus aureus Infections in Adults and Children. Clin Infect Dis. 2011;52(3):e18-e55. PubMed .
  • National Library of Medicine (NIH). Staphylococcus aureus Infection . StatPearls.