These bacteria are spread by having direct contact with an infected person, by using a contaminated object, or by inhaling infected droplets dispersed by sneezing or coughing.
Skin infections are common, but the bacteria can spread through the bloodstream and infect distant organs.
Skin infections may cause blisters, abscesses, and redness and swelling in the infected area.
The diagnosis is based on the appearance of the skin or identification of the bacteria in a sample of the infected material.
Antibiotics are chosen based on whether they are likely to be effective against the strain causing the infection.
Thoroughly washing the hands can help prevent spread of infection.
(See also Overview of Bacteria Overview of Bacteria Bacteria are microscopic, single-celled organisms. They are among the earliest known life forms on earth. There are thousands of different kinds of bacteria, and they live in every conceivable... read more .)
Staphylococcus aureus is present in the nose (usually temporarily) of about 30% of healthy adults and on the skin of about 20%. The percentages are higher for people who are patients in a hospital or who work there.
The bacteria can spread from person to person by direct contact, through contaminated objects (such as gym equipment, telephones, door knobs, television remote controls, or elevator buttons), or, less often, by inhalation of infected droplets dispersed by sneezing or coughing.
Carriers are people who have the bacteria but do not have any symptoms caused by the bacteria. Carriers can move the bacteria from their nose to other body parts with their hands, sometimes leading to infection. People who are hospitalized or work in a hospital are more likely to be carriers.
Types of staph infections
Staphylococcus aureus infections range from mild to life threatening.
The most common staphylococcal infections are
However, the bacteria can travel through the bloodstream (called bacteremia Bacteremia Bacteremia is the presence of bacteria in the bloodstream. Bacteremia may result from ordinary activities (such as vigorous toothbrushing), dental or medical procedures, or from infections ... read more ) and infect almost any site in the body, particularly heart valves (endocarditis Infective Endocarditis Infective endocarditis is an infection of the lining of the heart (endocardium) and usually also of the heart valves. Infective endocarditis occurs when bacteria enter the bloodstream and travel... read more ) and bones (osteomyelitis Osteomyelitis Osteomyelitis is a bone infection usually caused by bacteria, mycobacteria, or fungi. Bacteria, mycobacteria, or fungi can infect bones by spreading through the bloodstream or, more often, by... read more ).
The bacteria also tend to accumulate on medical devices in the body, such as artificial heart valves or joints, heart pacemakers, and catheters inserted through the skin into blood vessels.
Certain staphylococcal infections are more likely in certain situations:
Bloodstream infections: When a catheter that is inserted in a vein has remained in place for a long time
Endocarditis: When people inject illicit drugs or have an artificial heart valve or when a catheter inserted in a vein is infected
Osteomyelitis: When Staphylococcus aureus spreads to the bone from an infection in the bloodstream or from an infection in nearby soft tissue, as may occur in people with deep pressure sores or foot sores due to diabetes
Lung infection (pneumonia Overview of Pneumonia Pneumonia is an infection of the small air sacs of the lungs (alveoli) and the tissues around them. Pneumonia is one of the most common causes of death worldwide. The most common symptom of... read more ): When people have had influenza (particularly) or a bloodstream infection, when people are taking corticosteroids or medications that suppress the immune system (immunosuppressants), or when they are hospitalized because they need tracheal intubation and mechanical ventilation (called hospital-acquired pneumonia Hospital-Acquired Pneumonia Hospital-acquired pneumonia is lung infection that develops in people who have been hospitalized, typically after about 2 days or more of hospitalization. Many bacteria, viruses, and even fungi... read more )
There are many strains of Staphylococcus aureus. Some strains produce toxins that can cause staphylococcal food poisoning Staphylococcal Food Poisoning Staphylococcal food poisoning results from eating food contaminated with toxins produced by certain types of staphylococci, resulting in diarrhea and vomiting. This disorder can be caused by... read more , toxic shock syndrome Toxic Shock Syndrome Toxic shock syndrome is a group of rapidly progressive and severe symptoms that include fever, rash, dangerously low blood pressure, and failure of several organs. It is caused by toxins produced... read more , or scalded skin syndrome Staphylococcal Scalded Skin Syndrome Staphylococcal scalded skin syndrome is a complication of a staphylococcal skin infection in which the skin blisters and peels off as though burned. In addition to the blistered, peeling skin... read more .
Toxic shock syndrome Toxic Shock Syndrome Toxic shock syndrome is a group of rapidly progressive and severe symptoms that include fever, rash, dangerously low blood pressure, and failure of several organs. It is caused by toxins produced... read more is also caused by toxins produced by some streptococci Streptococcal Infections Streptococcal infections are caused by any one of several species of Streptococcus. These gram-positive, sphere-shaped (coccal) bacteria (see figure ) cause many disorders, including... read more . This syndrome causes rapidly progressive and severe symptoms that include fever, rash, dangerously low blood pressure, and failure of several organs.
Risk factors for staph infections
Certain conditions increase the risk of getting a staphylococcal infection:
Chronic lung disorders (such as cystic fibrosis Cystic Fibrosis (CF) Cystic fibrosis is a hereditary disease that causes certain glands to produce abnormally thick secretions, resulting in tissue and organ damage, especially in the lungs and the digestive tract... read more or emphysema Chronic Obstructive Pulmonary Disease (COPD) )
A transplanted organ Overview of Transplantation Transplantation is the removal of living, functioning cells, tissues, or organs from the body and then their transfer back into the same body or into a different body. The most common type of... read more , an implanted medical device (such as artificial heart valves Repairing or replacing a heart valve Heart valves regulate the flow of blood through the heart's four chambers—two small, round upper chambers (atria) and two larger, cone-shaped lower chambers (ventricles). Each ventricle has... read more , joints Hip replacement Hip fractures may occur in the round upper end (head) of the thighbone, in the narrow part of the thighbone just below the head (neck), or in the bumps in the broader area just below the neck... read more , or heart pacemakers Artificial Pacemakers There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more ), or a catheter inserted into a vein for a long time
An open wound or sore
Chronic skin disorders
Medications, such as corticosteroids, that suppress the immune system (immunosuppressants), or cancer chemotherapy
Injection of illicit drugs
Newborns and breastfeeding mothers
Resistance to antibiotics
Many strains have developed resistance Antibiotic resistance Bacteria are microscopic, single-celled organisms. They are among the earliest known life forms on earth. There are thousands of different kinds of bacteria, and they live in every conceivable... read more to the effects of antibiotics. If carriers take antibiotics, the antibiotics kill the strains that are not resistant, leaving mainly the resistant strains. These bacteria may then multiply, and if they cause infection, the infection is more difficult to treat.
Whether the bacteria are resistant and which antibiotics they resist often depend on where people got the infection: in a hospital or other health care facility or outside of such a facility (in the community).
Methicillin-resistant Staphylococcus aureus (MRSA)
Because antibiotics are widely used in hospitals, hospital staff members commonly carry resistant strains. When people are infected in a health care facility, the bacteria are usually resistant to several types of antibiotics, including almost all antibiotics that are related to penicillin (called beta-lactam antibiotics Penicillins Penicillins are a subclass of antibiotics called beta-lactam antibiotics (antibiotics that have a chemical structure called a beta-lactam ring). Carbapenems, cephalosporins, and monobactams... read more ). Strains of bacteria that are resistant to almost all beta-lactam antibiotics are called methicillin-resistant Staphylococcus aureus (MRSA). Methicillin is a type of penicillin.
MRSA strains are common when infection is acquired in a health care facility (called hospital-acquired infection). Some strains of MRSA cause infections that are acquired outside of a health care facility (called community-acquired infection), including mild abscesses and skin infections. The number of these community-acquired infections is increasing.
Did You Know...
Symptoms of Staph Infections
Skin infections due to Staphylococcus aureus can include the following:
Folliculitis Folliculitis and Skin Abscesses Folliculitis and skin abscesses are pus-filled pockets in the skin resulting from bacterial infection. They may be superficial or deep, affecting just hair follicles or deeper structures within... read more is the least serious. A hair root (follicle) is infected, causing a slightly painful, tiny pimple at the base of a hair.
Impetigo Impetigo and Ecthyma Impetigo is a superficial skin infection that leads to the formation of scabby, yellow-crusted sores and, sometimes, small blisters filled with yellow fluid. It is caused by Staphylococcus... read more consists of shallow, fluid-filled blisters that rupture, leaving honey-colored crusts. Impetigo may itch or hurt.
Abscesses Skin Abscesses Folliculitis and skin abscesses are pus-filled pockets in the skin resulting from bacterial infection. They may be superficial or deep, affecting just hair follicles or deeper structures within... read more (boils or furuncles) are warm, painful collections of pus just below the skin.
Cellulitis Cellulitis Cellulitis is a spreading bacterial infection of the skin and the tissues immediately beneath the skin. This infection is most often caused by streptococci or staphylococci. Redness, pain, and... read more is infection of skin and the tissue just under it. Cellulitis spreads, causing pain and redness.
Toxic epidermal necrolysis Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN) Stevens-Johnson syndrome and toxic epidermal necrolysis are two forms of the same life-threatening skin disorder that cause rash, skin peeling, and sores on the mucous membranes. (See also Overview... read more and, in newborns, scalded skin syndrome are serious infections. Both lead to large-scale peeling of skin.
All staphylococcal skin infections are very contagious.
Breast infections (mastitis Mastitis A breast infection ( mastitis) can occur after delivery ( postpartum infection), usually during the first 6 weeks and almost always in women who are breastfeeding. If the baby is not positioned... read more ), which may include cellulitis and abscesses, can develop 1 to 4 weeks after delivery. The area around the nipple is red and painful. Abscesses often release large numbers of bacteria into the mother’s milk. The bacteria may then infect the nursing infant.
Pneumonia often causes a high fever, shortness of breath, and a cough with sputum that may be tinged with blood. Lung abscesses Abscess in the Lungs A lung abscess is a pus-filled cavity in the lung surrounded by inflamed tissue and caused by an infection. A lung abscess is usually caused by bacteria that normally live in the mouth and are... read more may develop. They sometimes enlarge and involve the membranes around the lungs and sometimes cause pus to collect (called an empyema Types of fluid ). These problems make breathing even more difficult.
Bloodstream infection is a common cause of death in people with severe burns. Symptoms typically include a persistent high fever and sometimes shock.
Endocarditis can quickly damage heart valves, leading to heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more (with difficulty breathing) and possibly death.
Osteomyelitis causes chills, fever, and bone pain. The skin and soft tissues over the infected bone become red and swollen, and fluid may accumulate in nearby joints.
Diagnosis of Staph Infections
For skin infections, a doctor's evaluation
For other infections, culture of blood or infected body fluids
Staphylococcal skin infections are usually diagnosed based on their appearance.
Other infections require samples of blood or infected fluids, which are sent to a laboratory to grow (culture), identify, and test the bacteria. Laboratory results confirm the diagnosis and determine which antibiotics can kill the staphylococci (called susceptibility testing Testing a Microorganism's Susceptibility and Sensitivity to Antimicrobial Drugs Infectious diseases are caused by microorganisms, such as bacteria, viruses, fungi, and parasites. Doctors suspect an infection based on the person's symptoms, physical examination results,... read more ).
If a doctor suspects osteomyelitis, x-rays, computed tomography (CT), magnetic resonance imaging (MRI), radionuclide bone scanning Radionuclide Scanning Radionuclide scanning is a type of medical imaging that produces images by detecting radiation after a radioactive material is administered. During a radionuclide scan, a small amount of a radionuclide... read more , or a combination is also done. These tests can show where the damage is and help determine how severe it is.
Bone biopsy is done to obtain a sample for testing. The sample may be removed with a needle or during surgery.
Treatment of Staph Infections
Sometimes surgical removal of infected bone and/or foreign material
Infections due to Staphylococcus aureus are treated with antibiotics. Doctors try to determine whether the bacteria are resistant to antibiotics and, if so, to which antibiotics.
Infection that is acquired in a hospital is treated with antibiotics that are effective against MRSA. They include vancomycin, linezolid, tedizolid, quinupristin plus dalfopristin, ceftaroline, telavancin, daptomycin, and other antibiotics. If results of testing later indicate that the strain is susceptible to methicillin and the person is not allergic to penicillin, a drug related to methicillin, such as nafcillin or oxacillin, is used. Depending on how severe the infection is, antibiotics may be given for weeks.
MRSA infection can be acquired outside of a health care facility. The community-acquired MRSA strains are usually susceptible to other antibiotics, such as trimethoprim/sulfamethoxazole, clindamycin, minocycline, or doxycycline, as well as to the antibiotics used to treat MRSA infections acquired in the hospital.
Mild skin infections due to MRSA, such as folliculitis, are usually treated with an ointment, such as one that contains bacitracin, neomycin, and polymyxin B (available without a prescription) or mupirocin (available by prescription only). If more than an ointment is required, antibiotics effective against MRSA are given by mouth or intravenously. Which antibiotic is used depends on the severity of the infection and the results of susceptibility testing.
If an infection involves bone or foreign material in the body (such as heart pacemakers, artificial heart valves and joints, and blood vessel grafts), rifampin and possibly another antibiotic are sometimes added to the antibiotic regimen. Usually, infected bone and foreign material has to be removed surgically to cure the infection.
Abscesses, if present, are usually drained.
Prevention of Staph Infections
People can help prevent the spread of these bacteria by always thoroughly washing their hands with soap and water or applying an alcohol-based hand sanitizer.
Some doctors recommend applying the antibiotic mupirocin inside the nostrils to eliminate staphylococci from the nose. However, because overusing mupirocin can lead to mupirocin resistance, this antibiotic is used only when people are likely to get an infection. For example, it is given to people before certain operations or to people who live in a household in which the skin infection is spreading.
If carriers of staphylococci need to have certain types of surgery, they are often treated with an antibiotic before the surgery.
People with a staphylococcal skin infection should not handle food.
In some health care facilities, people are routinely screened for MRSA when they are admitted. Some facilities screen only people who are at increased risk of getting a MRSA infection, such as those who are about to have certain operations. Screening involves testing a sample taken from the nose with a cotton swab. If MRSA strains are detected, people are isolated to prevent spread of the bacteria.
Other Staphylococcal Infections
Staphylococcus aureus produces an enzyme called coagulase. Other species of staphylococci do not and thus are called coagulase-negative staphylococci. These bacteria normally reside on the skin of all healthy people.
These bacteria, although less dangerous than Staphylococcus aureus, can cause serious infections, usually when acquired in a hospital. The bacteria may infect catheters inserted through the skin into a blood vessel or implanted medical devices (such as heart pacemakers or artificial heart valves and joints).
These bacteria are often resistant to many antibiotics. Vancomycin, which is effective against many resistant bacteria, is used, sometimes with rifampin. Medical devices, if infected, often must be removed.