Signs and Symptoms of MRSA Infection in a Wound Bed
MRSA wound infections present with classic signs of purulent infection—purulent drainage or exudate, erythema extending beyond the wound margins, warmth, tenderness, and induration—often accompanied by systemic signs including fever >38°C, tachycardia, and elevated white blood cell count in severe cases. 1
Local Wound Bed Signs
Purulent Features (Most Specific for MRSA)
- Purulent drainage or exudate from the wound is the most reliable local indicator suggesting possible MRSA involvement, particularly in patients with risk factors 1, 2
- Thick, opaque, or creamy discharge that may be yellow, white, or blood-tinged 1
- Fluctuance suggesting abscess formation beneath the wound bed, which requires incision and drainage as primary treatment 1
Inflammatory Changes
- Erythema (redness) extending >5 cm from the wound edge with associated induration (firmness) 1
- Warmth to palpation over and surrounding the wound 1
- Tenderness or pain that may be out of proportion to examination findings (concerning for deeper infection) 1, 2
- Edema and swelling of surrounding tissues 1
Wound Bed Characteristics
- Necrotic tissue or slough within the wound bed 1
- Delayed wound healing despite appropriate wound care 1
- Foul odor (though this is more common with anaerobic infections) 1
Systemic Signs (Indicating Severe Infection)
SIRS Criteria (Systemic Inflammatory Response Syndrome)
- Temperature >38°C or <36°C 1, 2
- Heart rate >90 beats per minute 1
- Respiratory rate >24 breaths per minute 1
- White blood cell count >12,000 or <4,000 cells/μL 1
Severe Infection Warning Signs
- Hypotension or hemodynamic instability 1, 2
- Altered mental status or confusion 1, 2
- Rapid progression of erythema or necrosis over hours 1, 2
- Bullous changes or skin sloughing (concerning for necrotizing infection) 1, 2
Critical Risk Factors That Increase MRSA Suspicion
Patient-Specific Risk Factors
- Previous history of MRSA infection or colonization within the past year (most reliable predictor) 1
- Recent hospitalization or residence in long-term care facility 1
- Prior long-term or inappropriate antibiotic use 1
- Nasal carriage of MRSA 1
- Injection drug use 1, 2
- Penetrating trauma to the wound 1, 2
Wound-Specific Risk Factors
- Long duration of the wound (chronic wounds) 1
- Presence of osteomyelitis underlying the wound 1
- Diabetic foot wounds (MRSA prevalence 5-30% in diabetic foot infections) 1
- Failure to respond to beta-lactam antibiotic therapy within 48-72 hours 2
Common Pitfalls to Avoid
Do not assume MRSA based solely on:
- Residual erythema after several days of appropriate antibiotics—some inflammation persists even after bacterial eradication 1
- Non-purulent cellulitis without specific risk factors—MRSA is actually an uncommon cause of typical cellulitis, even in high-prevalence settings 1, 3, 2
- Colonization alone—isolating MRSA from a wound culture does not automatically indicate infection; clinical signs must be present 1
Critical distinction: Purulent drainage mandates consideration of MRSA and potential need for drainage procedures, whereas non-purulent inflammation typically represents streptococcal infection requiring only beta-lactam antibiotics 1, 2
When to Obtain Cultures
- Obtain wound cultures when purulent drainage is present 1
- Culture deep tissue or bone specimens when osteomyelitis is suspected, rather than superficial swabs 1
- Blood cultures are indicated in patients with severe systemic features, malignancy, neutropenia, or severe immunodeficiency 3
The presence of purulent drainage combined with any MRSA risk factors (previous MRSA, recent hospitalization, injection drug use, or treatment failure) should prompt empiric MRSA-active antibiotic therapy while awaiting culture results. 1, 2