Differentials
Insect or spider bite
SIGNS / SYMPTOMS
Spider bites may show puncture marks or be witnessed.
Less likely to have central ulceration with surrounding erythema or pain.
More likely to respond to penicillins or cephalosporins.
Risk factors for MRSA infection may not be present.
INVESTIGATIONS
Culture and antibiotic susceptibilities of the wound or abscess negative for MRSA.
Gram stain is appropriate for initial classification of the possible pathogen.
Cellulitis
SIGNS / SYMPTOMS
Cellulitis is less likely to present as erythematous lesions or pustules, in single or multiple forms. It is less likely to be mistaken for an insect bite or folliculitis.
Risk factors for MRSA infection may not be present.
INVESTIGATIONS
Culture and antibiotic susceptibilities of exudate present negative for MRSA.
Folliculitis
SIGNS / SYMPTOMS
Patients often present with single or multiple skin lesions or pustules, which may be difficult to differentiate from community-associated MRSA infection.
Risk factors for MRSA infection may not be present.
INVESTIGATIONS
Culture and antibiotic susceptibilities of drainage negative for MRSA.
Pneumonia, not due to MRSA
SIGNS / SYMPTOMS
Presentation may be similar to that of patients with MRSA pneumonia.
Patients present with fever, chills, cough, and shortness of breath, and are often severely ill.
Risk factors for MRSA infection may not be present.
INVESTIGATIONS
Blood culture, sputum culture negative for MRSA.
MRSA pneumonia may have multilobar infiltrates that cavitate on chest x-ray.
Bacteremia, not due to MRSA
SIGNS / SYMPTOMS
Presentation may be similar to that of patients with MRSA bacteremia.
Risk factors for MRSA infection may not be present.
INVESTIGATIONS
Blood culture negative for MRSA.
Urinary tract infections, not due to MRSA infection
SIGNS / SYMPTOMS
Patients may present with painful urination, hematuria, fever, altered mental status, chills, or urinary retention.
Presentation may be similar to that of patients with MRSA urinary tract infection.
Risk factors for MRSA infection may not be present.
INVESTIGATIONS
Urine culture negative for MRSA.
Infective endocarditis, not due to MRSA infection
SIGNS / SYMPTOMS
Presentation may be similar to patients with MRSA endocarditis.
Risk factors for MRSA infection may not be present.
INVESTIGATIONS
Blood culture negative for MRSA.
Joint infections, not due to MRSA infection
SIGNS / SYMPTOMS
Presentation may be similar to that of patients with MRSA joint infection.
Risk factors for MRSA infection may not be present.
INVESTIGATIONS
Joint aspirate culture negative for MRSA.
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