Staph Infections

Staph Infections

Also called: Staphylococcal Infections, Staphylococcus Aureus Infections

Reviewed By:
David Slotnick, M.D.


Staph infections are caused by Staphylococcus (staph) bacteria and can result in a wide variety of conditions and diseases. Staph bacteria are commonly found on the skin and in the nasal cavities without causing an infection. Disease may result when the bacteria are able to invade the body because there are breaks in the skin or the immune system is suppressed.

Most staph infections cause only minor skin problems, such as pimples and boils. More serious conditions that may be caused by staph bacteria include:

  • Skin diseases such as impetigo and cellulitis
  • Pneumonia
  • Osteomyelitis (bone infection)
  • Endocarditis (heart infection)
  • Toxic shock syndrome
  • Food poisoning

Staph bacteria may be transmitted through the air, via contaminated objects or surfaces, and from person to person. Staph infections frequently occur during medical procedures and hospital stays, but outbreaks can also occur in schools and other places.

Staph infections may be treated with antibiotics, although some staph bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), have developed resistance to many medications. MRSA first appeared in healthcare facilities but is being increasingly found in communities. About 94,000 Americans developed a serious MRSA infection in 2005, with more than 18,000 deaths, according to the Centers for Disease Control and Prevention (CDC).

However, most staph infections, including MRSA, are much less serious. The majority involve local skin infections and symptoms such as boils. Minor staph infections may not require antibiotics at all, just professional drainage and cleaning.

Staph infections can often be prevented with proper personal hygiene, including frequent hand washing and not sharing towels or razors, and proper wound care. It is also important not to misuse antibiotics. Recent research of an experimental vaccine successfully provided short-term protection against certain types of MRSA among some subjects.

About staph infections

Staph infections are caused by Staphylococcus (staph) bacteria, which can affect many bodily systems. In the human body, these bacteria can infect the skin, lungs, bones and blood. Infections can range from relatively minor (e.g., pimples and boils on the skin) to debilitating or life-threatening (e.g., bacteremia, endocarditis). Staph infections can also cause pneumonia, which could be life-threatening to people with weakened immune systems.

Staphylococcal bacteria are named after the Greek words for a cluster of grapes (staphyle) and berry (kokkus). A staph bacterium was thus referred to as a “cluster-forming berry” because, as the round bacteria reproduce, they form grapelike clusters of microbes.

The bacteria can be found on the bodies of humans, animals and in the environment (e.g., in dust particles). They are present on the skin (including areas around the groin and anus) or mucous membranes of the nose and mouth of up to 30 percent of healthy people, according to the Centers for Disease Control and Prevention (CDC). In these cases, people carry the bacteria without developing an infection.

A healthy immune system typically prevents staph bacteria from causing infection. However, these bacteria may cause infection in people with immunosuppression (a weakened immune system). Staph bacteria usually enter the body through a break in the skin (e.g., due to a cut or scrape), or tear of the mucous membranes, the moist tissue lining cavities and passageways of the body, such as inside the nose or mouth. Bacteria can also enter the bloodstream during certain dental or medical procedures. Though staph infections typically begin in one area, they may spread through the bloodstream to other parts of the body.

After staph has entered the body, the bacteria use a variety of defenses to protect themselves from the immune system. Some types of staph bacteria use enzymes to stick to tissues, foreign bodies and each other to reduce the surface area exposed to antibodies produced by the immune system to fight infection. The bacteria may also produce a layer of slime called biofilm around clumps of bacteria that reduces the effectiveness of the antibodies. Successfully resisting the immune system enables the bacterial infection to cause symptoms.

In some cases, the body may develop more serious symptoms when the staph bacteria release toxins. This can occur when staph bacteria cause more serious conditions such as food poisoning, toxic shock syndrome or scalded skin syndrome, an infection that causes skin to be easily shed.

Staph bacteria themselves are also resilient. They can withstand high temperatures, high salt concentrations and a lack of moisture. This can make it difficult to kill the bacteria (e.g., when on objects, surfaces or in food).

Staph infections most frequently occur in hospitals and other healthcare facilities (e.g., nursing homes), where many people have weakened immune systems. Hospital-acquired staph infections include surgical wound infections, bloodstream infections (bacteremia), urinary tract infections and pneumonia. Staph infections are one of the most common causes of patients developing conditions secondary to the condition for which they were originally admitted (nosocomial infections).

Community-acquired staph infections are those obtained outside of hospitals or healthcare facilities, and among people who have not been recently hospitalized. Staph bacteria are a leading cause of community-acquired infections. They can infect the body through an injury or because of a weakened immune system. Community-acquired staph infections typically involve disorders of the skin, bones or joints.

A growing resistance to antibiotics

Some staph bacteria have developed a resistance to many medications. The best-known example is methicillin-resistant Staphylococcus aureus (MRSA, often pronounced “mursa.”) MRSA, sometimes described as a “superbug,” is resistant to certain antibiotics including penicillin, oxacillin, amoxicillin and methicillin (which is no longer commercially available in the United States), and sometimes to vancomycin.

An estimated 94,360 Americans developed a serious MRSA infection in 2005, with 18,650 related fatalities, more than the number of deaths from AIDS, the Centers for Disease Control and Prevention (CDC) reported in 2007. About 85 percent of the invasive MRSA cases involved transmission at a healthcare facility, and most of these developed later outside the facility.

After several outbreaks occurred in 2007, CDC officials described MRSA as an epidemic in some areas of the United States. However, most of these infections are minor and go away without treatment. People can help prevent MRSA and other staph infections by practicing good hygiene and not misusing antibiotics.

Types and differences of staph infections

There are more than 20 species of Staphylococci bacteria, although only three are responsible for most cases of human infection. The most common is Staphylococcus aureus (S. aureus). S. aureus are typically more harmful and more likely to cause disease than other types of staph bacteria. S. aureus are a common cause of serious hospital-acquired staph infections such as pneumonia and bloodstream infections (bacteremia). Methicillin-resistant Staphylococcus aureus (MRSA) is a well-known variation of this species.

Staphylococcus epidermidis (S. epidermis) is the type of staph bacteria that commonly colonize the skin of people without causing infection. Infection by these bacteria is most likely to occur after skin injury or among immunosuppressed people.

Staphylococcus saprophyticus (S. saprophyticus) is believed to cause 10 percent of urinary tract infections in otherwise healthy young women.

Additional staph bacteria that less commonly affect humans include S. haemolyticus, S. hominis, S. warnerii, S. sacharolyticus and S. cohnii.

Conditions caused by staph infections

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.

Risk factors and causes of staph infections

Staph bacteria are often present on the skin or within the nose of healthy people. The bacteria are most often spread through direct skin-to-skin contact with a bacteria carrier. This can occur if someone touches an area of the body with the bacteria then touches another person. Staph bacteria may also be transmitted via contaminated objects or surfaces (e.g., shared towels, eating utensils) or through the air (e.g., when a person carrying the bacteria sneezes or coughs). By late childhood, most people develop some immunity against infection because the body develops antibodies as a result of repeat exposure to the bacteria.

Many cases of staph infections result from medical procedures or stays in hospitals or other healthcare facilities. These hospital-acquired (nosocomial) infections may result from an immunosuppressed patient being exposed to the bacteria of healthcare workers or other patients. The bacteria may also invade the body during certain dental or surgical procedures.

Factors that may increase a person’s risk of developing a staph infection include:

  • Immunosuppression (e.g., due to certain illnesses or disease, or due to use of certain medications such as antibiotics or corticosteroids)

  • Open wounds (e.g., cuts, burns)

  • Existing skin conditions or disease

  • Implantation of foreign objects (e.g., shunt, intravascular catheter, dialysis graft) into the body

  • Being in close physical proximity to others (e.g., daycare, college dormitories)

  • Newborns and nursing mothers

  • Heart conditions such as heart murmurs or mitral valve prolapse

People at greater risk for serious cases of methicillin-resistant Staphylococcus aureus (MRSA) include those who are male, black or older than 65, according to the U.S. Centers for Disease Control and Prevention.

Additional risk factors for various conditions caused by staph infections may vary, depending on the condition. These include:

InfectionRisk Factor
FolliculitisPoor general health Diabetes Wearing tight clothing
ImpetigoWarm, humid weather Crowded conditions
CellulitisRecent surgery Alcoholism Diabetes Intravenous drug use
Scalded skin syndromeYoung children (5 years old or younger)
BacteremiaRecent dental or medical procedures Intravenous drug use People undergoing dialysis
PneumoniaRecent dental or medical procedures Intravenous drug use People undergoing dialysis
Infectious arthritisTraumatic injury Joint surgery Rheumatoid arthritis
EndocarditisExisting heart conditions or diseases Adults over 60 Recent dental or medical procedures Intravenous drug use
Toxic shock syndromeProlonged use of tampons Use of barrier contraceptive devices (e.g., diaphragm, sponge) Recent childbirth Recent surgical procedures Past diagnosis of toxic shock syndrome

Signs and symptoms of staph infections

The signs and symptoms of staph infections may vary, based on the condition caused and its severity. Staph infections frequently involve minor skin problems, such as pimples or boils.  

Staph infections of the skin may involve symptoms such as rash, blisters, boils and sores that deepen and become ulcers. Patients with scalded skin syndrome may experience skin peeling off in large sheets.

Most staph infections, both of the skin and other systems may also include fever. Other common symptoms of infection include chills, shaking, fatigue, weakness, nausea and vomiting. Each body system produces characteristic symptom, such as diarrhea for food poisoning or coughing for pneumonia.

Some of the most serious symptoms may occur when staph infects the bloodstream or heart. There, it may produce fever, chills, rapid heart rate and breathing, and eventually shock.

Diagnosis methods for staph infections

In many cases, staph infections may be initially suspected based on the patient’s symptoms. A physician will perform a complete physical examination and compile a thorough medical history to make a diagnosis.

A probable diagnosis may be confirmed by taking staph bacteria from a sample of material from the site of the infection. The bacteria may be confirmed by their appearance when viewed under a microscope. In addition, bacteria may be cultured by isolating and growing the bacteria and observing its response to a variety of chemicals. This can help identify what type of medication, if any, may be necessary to treat it. However, because staph bacteria may be present on the body without causing illness, multiple cultures may be required to rule out other potential causes of a patient’s symptoms. Staph cultures may take several days to complete.

Sites from which samples may be taken include:

InfectionSample Site
Folliculitis or impetigoSkin lesion
Scalded skin syndromeSkin and throat
SinusitisNasal cavities
PneumoniaBlood or respiratory tract
Infectious arthritisJoint fluid
Toxic shock syndromeBlood, vagina, throat
Foodborne illnessStool, suspected food source (usually tested when outbreaks occur)

In addition to culturing the bacteria, other tests may be necessary to confirm a diagnosis of a staph infection. These methods include:

  • Blood tests. A complete blood count (CBC) is a routine blood test that measures the composition of cells within the blood. This may reveal an elevated level of white blood cells, which indicates the presence of infection. Other types of blood tests may also be performed.

  • Imaging tests. To view possible abnormal changes to internal tissues, x-rays, an MRI (magnetic resonance imaging), echocardiogram or CAT scan (computed axial tomography) may be used. These imaging tests are often able to show any damage to the bones, muscles or joints caused by a staph infection.

Treatment options for staph infections

Treatment of a staph infection depends on the type of staph bacteria involved, the illness caused, its location and severity. Antibiotics may be used to kill bacteria, although some bacteria are more sensitive to antibiotic treatment than others. The usefulness of certain types of antibiotics is limited by antibiotic resistance developed by some staph bacteria.

To slow the development of germ resistance, antibiotics may not be prescribed for minor staph infections such as pimples and boils. Warm compresses on affected areas may help pus to be released and the infection to clear. Boils should never be squeezed because this can spread infection. Abscesses are likely to be drained by a physician and allowed to heal. Without proper measures, draining abscesses can spread the bacteria, so it is recommended that the procedure be performed only by a health professional.

Cases of foodborne illness (food poisoning) usually resolve on their own, without treatment, within a day or two. Patients with weakened immune systems or those who become severely dehydrated may require intravenous fluids administered in a hospital.

More serious cases of staph infection may require treatment with oral or intravenous antibiotics. Patients should follow physician instructions regarding their medications. It is especially important to complete the full course of antibiotics prescribed, even if that means continuing to take the medication after a patient’s condition improves. Patients with serious staph infections may need to be hospitalized.

Without treatment, the infection may spread and, in some cases, death can result. In addition to antibiotics, patients who were infected during the installation of a foreign object into the body (e.g., heart valves, prosthetic joints) may require its removal for treatment of the staph infection to be effective.

At one time, drug-resistant staph bacteria were seldom a problem outside of hospitals. In recent years, drug-resistant staph bacteria have been community-acquired as well. Most staph bacteria now produce an enzyme called penicillinase, which makes them resistant to many forms of penicillin and related drugs. Because of this, new antibiotics have been developed and prescribed, but the bacteria are showing increased resistance to these medications as well. This includes methicillin-resistant Staphylococcus aureus (MRSA) and strains of staph bacteria resistant to the antibiotic vancomycin.

A patient’s progress will be monitored during treatment. If no sign of improvement is seen, a physician may conclude the bacteria are resistant to the antibiotics being used, and other types of antibiotics may be prescribed. If the infection was contracted in a hospital setting, patients with a drug-resistant staph infection may be isolated to prevent the spread of infection. In addition, some staph infections may recur and require additional antibiotic treatment.

Patients with toxic shock syndrome and foodborne illness may also require intravenous fluid replacement to combat dehydration and help prevent shock.

Prevention methods for staph infections

Despite the prevalence of staph bacteria on the human body and in the environment, serious staph infections are still relatively uncommon. The majority of staph infections result in minor skin infections such as pimples and boils.

There are certain steps people can take to help prevent contracting a staph infection. Proper care of wounds, including cleaning them with soap and water and covering them with sterile material, helps reduce the risk of infection. Over-the-counter antibiotic ointment may also be used. It is also important to avoid contact with other people’s wounds or material contaminated by the wounds of others, such as bandages.

Wearing loose clothing can help prevent chafing, which can cause a break in the skin and provide entry for staph bacteria.

Not sharing personal hygiene materials (e.g., towels, razors) also helps reduce the spread of bacterial infection. In addition, hand washing with soap and water or alcohol-based lotions helps kill the bacteria before they can gain entry into the body.

In community settings, outbreaks of staph infections such as methicillin-resistant Staphylococcus aureus (MRSA) are more likely in crowded areas such as schools, daycare centers, dormitories, locker rooms, military barracks and prisons. It is seldom necessary to close a school or other facility for cleaning, but in some cases school and health officials may decide to do so. Inanimate objects that may have been in contact with MRSA-infected skin can be disinfected with detergents or with disinfectants approved by the Environmental Protection Agency.

The spread of staph bacteria that can cause foodborne illness may be prevented by washing hands (including under the fingernails) and kitchen utensils before and after preparing food. In addition, leftover prepared food, especially dairy products and meat, should be promptly refrigerated. Foods left at room temperature can foster bacterial growth. If food must be left out for any length of time, hot foods should be kept hot, and cold foods should be kept cold.

Patients with certain medical conditions or implanted devices are at greater risk of developing staph infections. These include patients with heart murmurs, mitral valve prolapse, artificial limbs or implanted devices. Such patients are often advised by their physician to take prophylactic (preventive) antibiotics before dental examinations, dental procedures or other invasive medical procedures.

Staph infections are often associated with medical procedures or stays in hospitals. To reduce the risks of these infections, a physician may recommend prophylactic antibiotics for patients before admission. Carriers in healthcare facilities may also be given antibiotics to reduce their risk of transmitting the bacteria to others. Frequent and thorough hand washing among healthcare staff is also a key preventive measure against hospital-acquired staph infections. This includes washing hands before and after interacting with each patient.

Ongoing research regarding staph infections

According to the National Institutes of Health, recent tests involving a vaccine against Staphylococcus aureus bacteria (S. aureus) have successfully protected certain subjects for a short time. These tests were conducted among patients with kidney disease who were receiving dialysis treatment and were thus were at high risk of contracting a staph infection. The vaccine provided protection against two strains of S. aureus.

Booster shots are being tested to determine whether the length of immunity provided by the experimental vaccine can be extended to provide protection for longer periods of time. In addition, research continues into making the vaccine effective against other strains of staph bacteria.

This research is a product of decades-long study into developing vaccines to protect infants and young children against Haemophilus influenzae type B (Hib).

Questions for your doctor on staph infections

Preparing questions in advance can help patients have more meaningful discussions with healthcare professionals regarding their conditions. Patients may wish to ask their doctor the following questions about staph infections:

  1. What symptoms indicate I may have a staph infection?

  2. How do you think I was exposed to the staph bacteria?

  3. Is there a way to identify what type of staph bacteria are causing my infection?

  4. Do you recommend this diagnostic test for me? Why or why not?

  5. How serious is my staph infection? What possible health conditions can it cause?

  6. How will you treat my staph infection? What risks are associated with this treatment?

  7. Are the staph bacteria causing my infection resistance to certain types of medications? How will I be treated if this is the case?

  8. How long will it take my infection to completely go away?

  9. Am I contagious? Should my family or other household members be tested for the presence of a staph infection?

  10. How concerned should I be about MRSA? What can I do to avoid, or keep from spreading, MRSA and other staph infections?

  11. What should I expect if there’s a MRSA or other staph outbreak in my child’s school or a relative’s nursing home?

  12. How can I find out if I am an asymptomatic carrier of staph bacteria? Do you recommend that I do this? Why or why not?
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