Staphylococcus aureus causes a wide range of infections, from minor skin problems like boils and impetigo to life-threatening conditions like bloodstream infections, heart valve infections, and bone infections. About 20% of people permanently carry this bacterium in their nose, and another 30% carry it on and off, often without any symptoms at all. Problems arise when the bacteria breach the skin or enter the bloodstream.
Skin and Soft Tissue Infections
Skin infections are the most common problems caused by S. aureus. These range from mild to serious and include boils (painful, pus-filled lumps under the skin), carbuncles (clusters of connected boils), impetigo (crusty, oozing sores common in children), cellulitis (spreading redness and swelling of deeper skin layers), and wound infections. Many of these start at a small break in the skin, a cut, a scrape, or even an ingrown hair.
When an abscess forms, draining the pus is the single most important step for healing. Antibiotics on top of drainage are typically recommended when the abscess is larger than about 2 centimeters, when the infection is spreading rapidly, when you have a weakened immune system or conditions like diabetes, or when the abscess sits in a sensitive area like the face, hands, or genitals.
Food Poisoning
S. aureus is one of the fastest-acting causes of food poisoning. The bacteria produce toxins in food before you eat it, so symptoms hit quickly, usually within 30 minutes to 8 hours. You’ll experience sudden nausea, vomiting, stomach cramps, and diarrhea. The good news: it’s short-lived, typically resolving within 24 hours without medical treatment.
The riskiest foods are those handled after cooking and then not reheated, including sliced deli meats, puddings, pastries, and sandwiches. The toxin itself is heat-stable, meaning reheating contaminated food won’t always make it safe.
Bloodstream Infections
When S. aureus enters the bloodstream, it causes bacteremia, one of the most dangerous staph infections. The bacteria can seed virtually any organ, spreading from an initial skin wound, a surgical site, or an IV line to the heart, bones, joints, or lungs. A large study of over 7,500 adults with S. aureus bloodstream infections found that roughly 27 to 29% of patients died within 30 days, making this one of the more lethal bacterial infections treated in hospitals.
Symptoms include high fever, chills, sweats, and a rapid decline in overall well-being. Because the bacteria can lodge in distant organs, bloodstream infections often trigger secondary infections elsewhere in the body.
Heart Valve Infections
S. aureus is a leading cause of infective endocarditis, an infection of the heart’s inner lining and valves. Unlike endocarditis caused by other bacteria, staph endocarditis can attack completely healthy valves, not just ones that were already damaged. It runs an aggressive course, with high fever, new or changing heart murmurs, and embolic events where clumps of bacteria break off and travel to other organs. Complications can include pericarditis (inflammation around the heart), abscesses near the valve, electrical conduction problems in the heart, and ultimately heart failure from valve destruction.
Bone and Joint Infections
S. aureus is the most common cause of osteomyelitis (bone infection) and septic arthritis (joint infection). In bone infections, symptoms include fever, chills, and localized pain over the affected bone, followed by redness and swelling of the overlying skin. In children, vertebral osteomyelitis often shows up as back pain; toddlers may simply refuse to walk or develop a limp. X-ray changes can lag behind the actual infection by 10 to 14 days, so MRI or bone scans are often needed for earlier detection.
Septic arthritis causes a swollen, warm, painful joint with reduced range of motion, often alongside fever. Joints can become infected through the bloodstream, from a neighboring bone infection, after trauma, or following joint surgery. Prosthetic joints are especially vulnerable. In infants, the hip is the most commonly affected joint, and the usual signs of infection can be subtle or absent, with pain showing up mainly when the hip is moved (for example, during a diaper change).
Toxin-Driven Syndromes
Some of the most dramatic illnesses caused by S. aureus aren’t from the bacteria invading tissue directly but from toxins they release.
Toxic Shock Syndrome
This rare but severe condition is caused by a toxin called TSST-1, which acts as a “superantigen.” It massively over-activates the immune system, triggering a flood of inflammatory signals (sometimes called a cytokine storm) that can cause dangerously low blood pressure, high fever, a sunburn-like rash, and organ failure. While historically linked to tampon use, toxic shock syndrome can follow any staph infection, including wound infections and surgical sites.
Scalded Skin Syndrome
Staphylococcal scalded skin syndrome primarily affects newborns and young children. The bacteria produce toxins that break apart the proteins holding skin layers together, causing widespread blistering and peeling that resembles a burn. The skin becomes extremely fragile and painful to the touch. With prompt treatment, most children recover fully.
Pneumonia
S. aureus pneumonia is less common than pneumonia caused by other bacteria, but it tends to be more severe. It frequently develops as a secondary infection after influenza or other viral respiratory illnesses, when the virus has already damaged the airway lining. One particularly aggressive form, necrotizing pneumonia, destroys lung tissue rapidly and is strongly associated with strains that produce a toxin called Panton-Valentine leukocidin (PVL). This toxin kills white blood cells by punching holes in their membranes, disabling the immune cells that would normally clear the infection.
Why S. Aureus Is So Effective at Causing Disease
S. aureus carries an unusually large toolkit of weapons. It produces toxins that punch holes in cell membranes, enzymes that break down tissues, and proteins that hijack or disable immune cells. PVL, for example, locks onto receptors on white blood cells and forms pores that cause the cells to burst. At low concentrations it triggers a controlled cell death; at higher levels it causes the cells to rupture violently, releasing inflammatory chemicals that damage surrounding tissue.
The bacterium also coats itself in proteins that help it stick to human tissues, evade antibodies, and form biofilms, slimy protective layers that make infections on medical devices and implants especially stubborn to treat.
MRSA and Antibiotic Resistance
A significant portion of S. aureus infections are caused by methicillin-resistant strains (MRSA), which resist many standard antibiotics. Globally, about 32% of S. aureus bloodstream infections are methicillin-resistant, according to 2023 WHO surveillance data. The rates vary enormously by country: around 5% in Germany, 10% in the United Kingdom, 18% in Canada, 32% in Japan, and over 50% in India.
For infections caused by non-resistant (MSSA) strains, first-generation antibiotics in the penicillin family remain effective. MRSA infections require different antibiotic classes. Mild skin infections can often be treated with oral antibiotics, while serious or invasive MRSA infections generally require intravenous treatment in a hospital setting. The distinction between MSSA and MRSA matters because using the right antibiotic class early significantly improves outcomes.