Staphylococcus aureus infection

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at September 1, 2016
StartDiseasesStaphylococcus aureus infection

There are over 30 different species of Staphylococcus found on the human body. The most common form found is Staphylococcus aureus. It is a part of the normal flora of the skin and lives mostly in the nose, respiratory tract, and reproductive areas of a female. Staphylococcus aureus infection is a type of staphylococcal infection (staph infection) and is one of the top five most commonly hospital-acquired infections and affects approximately 500,000 patients each year in the United States.

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Definition & Facts

Staphylooccus aureus (also known as Staph aureus) is a gram-positive bacteria. It was discovered in 1880 by Sir Alexander Ogston. Its name comes from the Greek and means a bunch of grapes or berries. This is also what Staph aureus looks like under the microscope.

Staph aureus lives on the body and is typically harmless. However, if it enters the body, it can cause an infection by producing powerful toxins that can spread throughout the bloodstream. Staph aureus infections are types of bacterial infections.

Symptoms & Complaints

A Staph aureus infection often presents as a skin infection. One type of infection is an abscess, which is a pus-filled pocket under the skin. The surrounding skin is usually red and warm to the touch.

Another type of infection is cellulitis. This can occur after bacteria enters through an abrasion or laceration of the skin. Cellulitis causes redness, swelling, and pain at the site of the infection.

Staph aureus can also cause a skin infection called impetigo. This condition causes a painful rash and can result in the skin forming oozing blisters.

Staph aureus can also produce an infection called staphylococcal scalded skin syndrome in children and infants. The toxins cause a fever and a rash which sometimes blisters. After the blisters open, the top layer of skin falls off, and the underlying skin is red and raw, resembling a burn

Staph aureus is also the most common form of bacteria found in food poisoning. The symptoms can come on very quickly, usually within hours of eating the contaminated food. The symptoms do not include a fever, but do include nausea, vomiting, diarrhea, and dehydration.

In addition to skin infections, Staphylococcus aureus can cause more serious conditions. This includes bacteremia, a staph infection that enters into the blood. The infection can travel to different organs in the body, or it can settle into the muscles and bones.

Staph aureus can cause endocarditis if it settles in the heart (infective endocarditis) or pneumonia if it settles in the lungs. In women, staph aureus can also cause toxic shock syndrome, a condition associated with wearing tampons during menstruation. In this condition, the bacteria produces a toxin that spreads into the bloodstream very quickly. Staph aureus infections can also cause osteomyelitis.

Causes 

Staph aureus can live on the body and cause no problems or infections. However, Staph aureus is contagious. The most common form of transmission is from an individual who has an active Staph aureus infection. The bacteria can spread into an open wound or into the mucous membranes of another individual.

Individuals more at risk for transmission are patients who are imunocompromised, have recently had surgery or people who have a device like an artificial cardiac pacemaker implanted in their body.

Staph aureus is very hardy, and it is possible for it to live on objects or linens used by an infected individual. If these items are used by others, the infection could be shared. Transmission is also more prevalent in locations where a large number of people come in contact with the same equipment like a daycare, a gym, or a hospital. Staph aureus can also be acquired through eating contaminated food. 

Diagnosis & Tests

Diagnosis of skin infections are performed either by assessment of the affected site during a physical examination or testing of the pus that is removed from a skin infection. If the infection has spread into the bloodstream, a blood culture can be performed. If the culture tests positive for a Staph aureus infection, the laboratory technician can test the sample to determine which antibiotic constitutes the most effective treatment.

Treatment & Therapy

In some instances, the skin infection caused by Staph aureus will resolve without treatment. These infections usually heal in a couple of weeks. However, other infections may require drainage of the wound and a course of antibiotics. If the infection is the result of a device implanted in the body, the device may need to be removed.

If food poisoning caused the infection, it usually clears up without intervention in a day or two. The more severe infections like toxic shock syndrome, endocarditis, and pneumonia can cause an individual to need to be hospitalized for supportive treatment and intravenous antibiotics. 

The primary antibiotic used to treat Staph aureus infections has been from the penicillin family. Occasionally gentamicin will also be administered in conjunction with penicillin for more serious infections like endocarditis.

Some strains of Staph aureus have evolved and have become resistant to the methicillin line of antibiotics. These bacteria are called Methicillin-resistant Staph aureus (MRSA).

Vancomycin is used to treat infections that do not respond to the traditional antibiotics. Depending on the severity of the infection, the antibiotics can be administered orally or intravenously. However, strains of vancomycin-resistant Staphylococcus aureus have emerged as well, contributing to the problem of 'superbugs'.

Prevention & Prophylaxis

The easiest way to prevent Staph aureus infections is thorough hand washing. Hands should be washed for 15 to 30 seconds. If the hands are not visibly soiled, a hand sanitizer can also be effective.

Additionally, keeping wounds and injuries clean and using a dry, sterile dressing until healed can prevent an infection. If the wound does have drainage, keeping it covered will prevent the spread of the infection.

Another way to prevent the spread of the infection is to launder clothing and linens at a high temperature, especially if they have been handled by an individual with an active infection.

Toxic shock syndrome can be prevented by frequently changing tampons, alternating between a sanitary napkin and a tampon and keeping the area very clean. Food poisoning can be prevented by handling food properly, washing hands frequently and making sure meat is fully cooked.