Staphylococcus epidermidis is a bacterium commonly found on human skin. While usually harmless, its presence in the bloodstream, known as bacteremia, is a significant and increasingly common healthcare-associated infection. This infection can pose serious health challenges, particularly for vulnerable individuals.
Understanding the Infection
Staphylococcus epidermidis typically resides on the surface of human skin and mucous membranes, forming part of the normal human microbiota. However, it can become an opportunistic pathogen, causing infection once it enters the body, especially when the immune system is compromised.
The bacterium commonly gains entry into the bloodstream through indwelling medical devices, such as intravenous catheters, prosthetic joints, cardiac devices, and other surgical implants. Once S. epidermidis colonizes these devices, it can produce a protective biofilm, a complex community of bacteria encased in an extracellular matrix that shields them from immune defenses and antibiotic treatments.
Risk factors for S. epidermidis bacteremia primarily involve healthcare settings, such as hospitalization, especially in intensive care units. Individuals with weakened immune systems or indwelling medical devices are at higher risk. S. epidermidis is recognized as a leading cause of catheter-related bloodstream infections, accounting for at least 22% of such infections in intensive care unit patients in the USA.
Recognizing the Signs
Symptoms of Staphylococcus epidermidis bacteremia often indicate a systemic response to the infection. Common signs include fever, chills, and general fatigue.
Localized indicators can appear around the site of a medical device insertion, including redness (erythema), swelling, tenderness, or pus.
Diagnosing S. epidermidis bacteremia primarily relies on blood cultures. For suspected catheter-related bloodstream infections, blood cultures are drawn from both a peripheral vein and the catheter site to increase diagnostic reliability. Since S. epidermidis is a common skin bacterium, it can sometimes contaminate blood culture samples. Therefore, guidelines suggest that two or more positive blood cultures within 48 hours, coupled with symptoms like fever or chills, increase the likelihood of a true infection.
Managing the Condition
Treatment for Staphylococcus epidermidis bacteremia primarily involves antibiotic therapy. However, a challenge arises from the high prevalence of antibiotic resistance in S. epidermidis strains, particularly methicillin-resistant S. epidermidis (MRSE), with over 80% of isolates displaying resistance to methicillin.
Given this high resistance rate, empiric treatment often begins with intravenous vancomycin, assuming methicillin resistance. If susceptibility testing later reveals that the bacterium is methicillin-susceptible, treatment can then be adjusted to beta-lactam antibiotics, such as nafcillin or oxacillin. The specific antibiotic regimen is guided by laboratory susceptibility testing results, ensuring the most effective treatment for the identified strain.
Management of S. epidermidis bacteremia, especially when associated with medical devices, often requires removal or replacement of the infected device. Biofilms on these devices are highly resistant to antibiotics, making eradication difficult without removing the source. The duration of antibiotic therapy varies, often requiring several weeks of intravenous antibiotics, particularly for complicated cases. Infectious disease specialists are often involved in guiding treatment plans, especially for complex or resistant infections.
Potential Health Impacts
Untreated Staphylococcus epidermidis bacteremia can lead to severe health complications. One serious outcome is sepsis, a life-threatening condition where the body’s response to infection causes widespread inflammation and potential organ damage. Catheter-related bloodstream infections, often caused by S. epidermidis, can progress to sepsis.
The infection can also result in infective endocarditis, an infection of the heart valves. This is particularly concerning for individuals with pre-existing heart conditions or prosthetic heart valves, where S. epidermidis is a common cause, accounting for up to 40% of prosthetic valve endocarditis cases. Biofilm formation on cardiac valves can lead to vegetations.
Other potential complications include osteomyelitis, an infection of the bone that can occur if bacteria spread from the bloodstream. Abscess formation, localized collections of pus, can also develop in various organs if the infection disseminates.
Reducing Risk
Preventing Staphylococcus epidermidis bacteremia, particularly in healthcare environments, relies on strict infection control measures. Hand hygiene protocols for healthcare professionals are important in reducing the spread of bacteria. This includes thorough handwashing or using alcohol-based hand rubs, especially before and after patient contact and before performing clean or aseptic procedures.
Proper aseptic technique is also important during the insertion and maintenance of medical devices, such as intravenous catheters and central lines. This involves meticulous skin preparation before procedures to minimize the introduction of skin bacteria into the bloodstream. Regular monitoring of medical devices for signs of infection, along with timely removal of unnecessary catheters and IV lines, helps reduce the risk of S. epidermidis colonization and subsequent bacteremia.