Diagnosing Staphylococcal Infections

To diagnose a staphylococcal, or staph, infection, your NYU Langone doctor takes a medical history and performs a physical exam. During the exam, your doctor looks for skin lesions and other signs of infection. He or she may also use other methods to determine whether you have an infection.

Blood Test

Your doctor may draw blood to find out if your white blood cells are elevated. High levels can be a sign that the immune system is fighting an infection. 

A test can also be used to determine whether you’re infected with methicillin-resistant Staphylococcus aureus (MRSA), a type of staph that’s resistant to common antibiotics. Like other staph infections, MRSA can spread to bones, joints, blood, and organs, causing serious damage. 

Tissue Culture

A doctor may take a sample of pus from a wound or tissue from the infected area and send it to a lab for testing. To obtain a pus sample, the doctor usually wipes a cotton swab across the surface of an infected wound. For a deeper infection, a doctor numbs the wound, then surgically opens it to drain the pus and takes a tissue sample. 

The doctor sends the sample to a lab, where a technician places it in a Petri dish, a round, shallow container with nutrients that encourage bacteria to grow over 24 to 48 hours. A test is used to tell the doctor which medications the organism is resistant to and which antibiotics would be most effective. It can help your doctor choose the medication best able to fight the staph infection.