Staphylococcal Bacteraemia

Staphylococcal bacteraemia is a serious bloodstream infection caused by Staphylococcus aureus bacteria, with a 30-day mortality rate of around 20%. This condition can lead to life-threatening complications affecting the heart, bones, lungs, and other vital organs throughout the body.

Table of contents

• What is staphylococcal bacteraemia?
• The bacteria behind the infection
• Types of staphylococcal bacteraemia
• Who is at higher risk?
• Signs and symptoms
• Possible complications
• How is it diagnosed?
• Treatment approaches

What is staphylococcal bacteraemia?

Staphylococcal bacteraemia (also called SAB) is a serious bloodstream infection caused by Staphylococcus aureus bacteria. This condition occurs when these bacteria enter the bloodstream and spread throughout the body^[1].

Your blood is normally sterile, meaning it does not contain any bacteria or other germs. When bacteria enter the bloodstream, they can cause serious health problems^[12]. Staphylococcal bacteraemia is associated with significant illness and death, with about 20% of patients dying within 30 days of diagnosis^[1].

This is a major cause of both community-acquired and healthcare-associated bloodstream infections. In the United States, the incidence ranges from 20 to 50 cases per 100,000 people, while other industrialized countries report 10 to 30 cases per 100,000 people^[1].

The bacteria behind the infection

Staphylococcus aureus (often called “staph”) is a type of bacteria commonly found on the skin and in the nose of about 30% of people^[3]. Most of the time, these bacteria do not cause any problems. However, if they enter the body through a cut, wound, or medical procedure, they can cause serious infections.

There are two main types of Staphylococcus aureus infections based on their response to antibiotics:

• Methicillin-resistant Staphylococcus aureus (MRSA): These bacteria are resistant to many common antibiotics, making them harder to treat^[4].
• Methicillin-susceptible Staphylococcus aureus (MSSA): These bacteria can usually be treated with standard antibiotics^[4].

In the United States, rates of healthcare-associated MRSA decreased by 17.1% between 2005 and 2012, though this decline slowed between 2013 and 2016. Meanwhile, community-acquired MSSA infections have slightly increased from 2012 to 2017^[1].

Types of staphylococcal bacteraemia

Staphylococcal bacteraemia is classified into three categories based on where and how the infection was acquired^[1]:

Community-acquired SAB generally affects people who have had no previous contact with the healthcare system. This group includes people who inject drugs and those who develop spontaneous bone and joint infections such as vertebral osteomyelitis or epidural abscess. These patients are more likely to have multiple complications at once, such as endocarditis with acute renal failure, shock, acute respiratory distress, or problems with blood clotting^[1].

Healthcare-associated, community-onset SAB includes people who have regular contact with the healthcare system. This includes individuals who were hospitalized in the past 90 days, those receiving intravenous therapy, wound care, or skilled nursing care at home, residents of long-term care facilities or nursing homes, and those receiving dialysis or chemotherapy^[1].

Healthcare-associated, hospital-onset SAB refers to infections that develop while a person is already in the hospital.

Who is at higher risk?

Anyone can develop staphylococcal bacteraemia, but certain people are more likely to get this infection. People at higher risk include those with chronic conditions such as diabetes, cancer, vascular disease, eczema, and lung disease^[5].

Other important risk factors include having a weakened immune system from HIV, organ transplant medications, or chemotherapy. Recent surgery, being in the hospital, or having medical devices such as catheters, breathing tubes, feeding tubes, pacemakers, artificial joints, or heart valves also increase risk^[4][5].

People with severe burns, especially deep burns or those covering a large area of the body, those on dialysis, and people who inject illegal drugs are also at increased risk^[5]. Additionally, participation in contact sports can increase risk due to skin-to-skin contact or sharing equipment^[5].

Signs and symptoms

Staphylococcal bacteraemia often starts as an infection in another part of the body, commonly the skin. Once the bacteria enter the bloodstream, symptoms typically become more severe^[4].

Common symptoms include abnormal body temperature that is either higher or lower than normal, signs of infection elsewhere in the body, mental changes such as sleepiness, confusion, or difficulty waking up, and feeling extremely ill with severe pain, discomfort, or shortness of breath^[4].

Additional symptoms may include chills, fast heartbeat, low blood pressure, abdominal pain, nausea and vomiting, diarrhea, and rapid breathing^[12].

Possible complications

Staphylococcal bacteraemia can lead to serious complications affecting various parts of the body. These include deep-seated infections such as infective endocarditis (infection of the heart valves), infections of medical devices, bone and joint infections, lung involvement, and recurrent infection^[1].

Without treatment, bacteraemia can spread to other areas of the body and cause conditions including cellulitis (skin infection), endocarditis, meningitis (infection of the protective membranes around the brain and spinal cord), osteomyelitis (bone infection), peritonitis (infection of the abdominal lining), and pneumonia^[12].

The most serious complication is sepsis, a life-threatening immune response to infection that can cause organ failure and death^[5][12].

How is it diagnosed?

A healthcare provider can diagnose staphylococcal bacteraemia through a physical examination and by asking about your symptoms, including how long you have had them^[12].

The main test used to diagnose bacteraemia is a blood culture, also called a bacterial culture. During this test, a provider withdraws a small amount of blood, usually from a vein in your arm, using a thin needle. The blood sample is then sent to a laboratory where it is tested for the presence of bacteria^[5][12].

Depending on your symptoms, your provider may also order additional tests such as cultures from other body fluids (sputum, urine, or wound samples), X-rays, CT scans, or ultrasound to determine where the infection started and whether it has spread to other parts of your body^[5][12].

Treatment approaches

Treatment for staphylococcal bacteraemia requires antibiotics. The choice of antibiotic depends on whether the bacteria are resistant to certain medications (MRSA or MSSA) and how severe the infection is^[5].

Antibiotics may be given as a cream or ointment for minor infections, as pills to swallow for moderate infections, or through an intravenous (IV) line directly into the bloodstream for serious infections^[5].

If you have an infected wound, your provider might need to drain it. In some cases, surgery may be necessary, especially for bone infections. If the infection is in or near a medical device such as a catheter, pacemaker, or artificial joint, the device may need to be removed^[2][5].

Early consultation with infectious disease specialists has been shown to improve outcomes and optimize therapy for patients with staphylococcal bacteraemia^[1].