Differential Diagnosis for Gram + Cocci in Clusters

• Single Most Likely Diagnosis
  • Staphylococcus aureus: This is the most common cause of gram-positive cocci in clusters. It is a common skin flora but can cause a range of infections from mild skin infections to life-threatening conditions like bacteremia and endocarditis.
• Other Likely Diagnoses
  • Staphylococcus epidermidis: Another common skin flora that can cause infections, particularly in immunocompromised patients or those with medical devices like catheters or prosthetics.
  • Staphylococcus saprophyticus: Often associated with urinary tract infections, especially in young, sexually active women.
• Do Not Miss Diagnoses
  • MRSA (Methicillin-resistant Staphylococcus aureus): Although it appears similar to Staphylococcus aureus under the microscope, MRSA is resistant to many antibiotics, making it crucial to identify for appropriate treatment.
  • Vancomycin-resistant Staphylococcus aureus (VRSA): Though rare, VRSA is highly resistant to antibiotics, including vancomycin, which is often a last resort for treating MRSA.
• Rare Diagnoses
  • Micrococcus species: These are less commonly pathogenic but can cause infections in certain contexts, such as in immunocompromised patients.
  • Staphylococcus lugdunensis: Known to cause more severe infections compared to other coagulase-negative staphylococci, including endocarditis and osteomyelitis.