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Staph infections can cause or lead to a wide range of health problems. Staph bacteria are often present on the human body, but usually are able to cause infection only through a break in the skin or mucous membranes (the moist lining of body cavities and passageways). The majority of staph infections cause minor skin problems, such as pimples or boils and occur in otherwise healthy people.

Additional skin infections that may be caused by staph bacteria include:

• Folliculitis. The staph bacteria may infect hair follicles and cause a tiny white pimple to form at the base of the hair shaft, which may develop into an abscess. The most common form of abscess is a boil, a reddish bump that fills with pus that can be painful and warm to the touch. They range from a half inch in diameter to the size of a golf ball. Though boils may occur anywhere on the body, they are most frequently found on the face, neck, chest, buttocks and thighs. Usually within two weeks, the tip will become yellow or white before the boil ruptures and drains. Larger boils may leave scars. When a small boil occurs at the base of eyelashes, it is commonly called a stye. Styes usually resolve on their own within days.
  
  
• Impetigo. This highly contagious skin condition is common and usually occurs among children between 2 and 6 years old. In addition to being caused by staph bacteria, it may also be caused by Streptococcus pyogenes. In cases of impetigo, bacteria enter the outer layer of skin (epidermis) and form pus-filled lesions that ooze. The pus may spread the infection to other parts of the body or to other people, which can lead to outbreaks of the disease in group settings such as daycare centers. Impetigo is seldom serious and lesions typically clear up, without treatment, within a few weeks. If left untreated, impetigo can progress to scalded skin syndrome, an infection that causes skin to be easily shed.
  
  
• Cellulitis. Whereas impetigo affects the top layer of skin, cellulitis is a staph infection of the two deepest layers (dermis and subcutaneous tissue). This disease can affect any area of skin, causing it to become red, hot and painful. In children, symptoms are usually seen in the face and neck, and in adults they often occur in the extremities. Without treatment, the infection can spread to other parts of the body and may cause severe complications. Cellulitis is less common than impetigo and is not as contagious.
  
  
• Scalded skin syndrome. This rare disease tends to affect children younger than 5 years of age but may also occur in adults with immunosuppression or kidney failure. It results from a toxin produced by staph bacteria that causes the skin to redden and loosen. The skin may then rub off in large sheets. The raw area that is left will dry out and a crust will form over it.

Staph bacteria are sometimes able to move from the skin to deeper tissues. Blood infection frequently is the first step, a condition known as bacteremia. The organisms are then able to move throughout the body.

The respiratory system can become infected by staph bacteria through multiple routes. Bacteria living uneventfully within the nasal cavities can cause infection when a person’s immune system becomes suppressed or if the bacteria enter the respiratory system from the bloodstream through a tear or cut in the mucous membrane lining the inside of the nose.

Infections of the respiratory system and other nearby structures that may be caused by staph bacteria include:

• Sinusitis. Staph infection of the sinuses may cause inflammation of the mucous membranes. Among its many symptoms, sinusitis can lead to congestion of the sinuses and pain, especially headaches.
  
  
• Pneumonia. When staph bacteria reach the lungs, they may cause pneumonia. This is most common in infants and young children and is a possible complication of the flu. In addition to the flu, cases of staph-related pneumonia may follow head injuries that allow the bacteria living within the nasal cavities to move deeper into the respiratory system.
  
  
• Otitis media. Also known as a middle ear infection, otitis media is a common childhood illness, and staph bacteria are among the many possible causes. In cases of otitis media, the internal tube leading from the ear to the nose and throat (eustachian tube) becomes blocked, leading to pus accumulation. This can cause pain, redness of the eardrum and fever.

The skeletal system, including the bones, muscles and joints, may also be impacted by staph infections. This may result from a progressive skin or wound infection.

Staph infections that may involve the skeletal system include:

• Osteomyelitis (bone infection). Most cases occur in children, especially males. The disease most frequently follows fractures, penetrating wounds and blunt trauma injuries. The infection may also spread to the joints, causing arthritis.
  
  
• Infectious arthritis. Staph bacteria may infect a joint and cause inflammation. This infection tends to result from either the spread of bacteria through the blood or a puncture wound of the joint.

Staph bacteria may also infect the heart and cause an inflammatory condition called endocarditis. This infection of the innermost layer of the heart’s chambers and valves is uncommon but dangerous. Bacteria have difficulty adhering to some body surfaces. However, any irregularity can provide bacteria with an easy perch. For example, some people have heart murmurs, which may be caused by abnormalities in the movement of heart valves. Such abnormalities may shift the valve flaps out of position, allowing bacteria to collect on the flap. The bacteria may grow in clumps (vegetations) within the heart or on the valves. If the clumps break off, they may block blood vessels and prevent blood from reaching tissues on the other side of the blockage. This condition is usually caused when bacteria enter the body during dental or medical procedures.

Bacterial meningitis (inflammation of the membrane surrounding the brain and spinal cord) may sometimes result from a staph infection. This typically affects newborns or infants who have recently undergone surgery.

Toxic shock syndrome is another rare, but life-threatening disease caused by toxins released by staph bacteria. Though it is often associated with the use of tampons, it can also be triggered by other events such as childbirth, surgery, injuries and certain illnesses. Symptoms develop suddenly and without treatment, organ failure, shock or death may occur.

Toxins produced by staph bacteria may also cause foodborne illness, a gastrointestinal infection that is commonly called food poisoning. Food is most often contaminated when handled by someone who is a carrier of the bacteria. Foods most likely to be contaminated are those prepared by hand and that require no cooking. Once present, the bacteria are able to grow in some foods (e.g., dairy products, fish and processed meats) and begin to produce toxins. Patients who ingest the bacteria or their toxins may begin to show symptoms within hours of consuming contaminated foods. Treatment with antibiotics is not usually necessary (the toxins are not affected by antibiotics), and a full recovery usually occurs within 48 hours. Patients with foodborne illness due to staph bacteria are not contagious.