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Staphylococcus epidermidis Infection
Introduction
Staphylococcus epidermidis is a coagulase-negative, gram-positive cocci bacteria that form clusters. It is also a catalase-positive and facultative anaerobe. They are the most common coagulase-negative Staphylococcus species that live on the human skin. In its natural environments such as the human skin or mucosa, they are usually harmless.[1] Many times, these coagulase-negative staph species invade the human body via prosthetic devices, at which point a small number of microbes travel down the prosthetic device to the bloodstream. The bacteria, then, can produce biofilms that help to protect them from host defense or antimicrobials.[2]
The belief is that Staphylococcus epidermidis is one of the most common causes of nosocomial infection, with infection rates as high as those of Staphylococcus aureus.[3]
Etiology
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Etiology
Staphylococcus epidermidis is usually a symbiont that is harmless in its natural environment.[4] However, it is an opportunistic pathogen that can cause virulence once it invades the human body via medical and prosthetic devices. Bacteremia from the Staphylococcus epidermidis and other coagulase-negative staphylococcus species arise most commonly by indwelling medical device contamination.[5] When placing a prosthetic device in a human body, the bacteria from the human skin can colonize the medical devices and enter the bloodstream.
Epidemiology
Staphylococcus epidermidis is among the most common causes of nosocomial blood infections.[5] Patients with prosthetic valves, cardiac devices, central lines, catheters, and IV drug use are at most risk of being infected with these species. It is also highly prevalent among neonates.[6]
Pathophysiology
One of the crucial factors allowing coagulase-negative species to survive in a harsh environment is the production of the biofilm. Biofilm formation occurs with initial adhesion to a foreign surface or endothelium, which leads to accumulation into multicellular structures.[4] Once formed, biofilm protects against innate host defense via protective exopolymers called poly-y-glutamic acid.[4] Other exotoxins and endotoxins also appear to cause immune reaction and virulence inside the host, one of which is a PSM peptide toxin that encodes methicillin-resistant island.[7]
History and Physical
Staphylococcus epidermidis can manifest in many ways once inside the human host, including localized and systemic infections. Below are some of the most common diseases.
Intravascular Catheter Infections
Staphylococcus epidermidis and other coagulase-negative staphs are one of the leading causes of catheter-related bloodstream infection. The infection largely occurs as the bacteria migrate from the patient’s skin to the surface of the catheter, but they also can migrate via luminal surfaces.[8] For patients with catheter infection, they may present with localized symptoms such as inflammation, erythema, or purulence around the insertion of the catheter. They also can present with systemic signs such as fever, hypotension, and other signs concerning sepsis.
Infectious Endocarditis
Staphylococcus epidermidis ranks as one of the most common species to cause infective endocarditis in both the prosthetic valve and the native valve. Up to 40% of cases of prosthetic valve endocarditis (PVE) are due to coagulase-negative staph.[9] Once the bacteria produce biofilm within the cardiac valves, it can accumulate and form vegetations.[10][11] Patients with endocarditis can present with fever, chills, malaise, night sweats, and dyspnea.[12] On physical exam, the patient can present with cardiac murmurs along with petechiae and/or splinter hemorrhages. Uncommonly, other clinical manifestations include Janeway lesions, Osler nodes, and Roth spots.
Cardiac Devices, Prosthetic Joints, and CNS Shunt Infection
Staphylococcus epidermidis can cause infections from implantation of medical devices such as cardiac devices, orthopedic devices, and CNS shunt. Up to 20% of patients with cardiac devices can become infected and can show signs of erythema, pain, purulence around the site of the infection, and sepsis.[8] For patients with prosthetic joint infection, they can present with pain and purulence around the site of the insertion of the prosthesis.
Shunt infection may present without symptoms, but can also cause headache, dizziness, nausea, vomiting, and altered mental status.
Evaluation
For patients suspected of having catheter-related bloodstream infections, blood cultures are necessary before starting antibiotics. The recommendation is to draw cultures from both the peripheral vein and the catheter site for the most reliable results.[13][14][15] Given that coagulase-negative staphs are frequently encountered as contaminants in blood cultures, having two bottles of blood culture positive with these species will increase the positive predictive value[16].
Patients suspected of having endocarditis based on a clinical picture will also require blood cultures and echocardiogram. At least three blood culture sets are recommended from separate venipuncture sites.[17]
An echocardiogram is imperative in the diagnosis of endocarditis. A transthoracic echocardiogram (TTE) is the initial step, which has a high sensitivity to 75% and specificity of about 100%.[18] If TTE is inconclusive and there is high clinical suspicion for endocarditis, then a transesophageal echocardiogram (TEE) can be done for further workup.
Treatment / Management
Treatment for Staphylococcus epidermidis infection largely depends on the type and severity of the infection. Patients with systemic infection warrant parenteral therapy. Resistance to methicillin is present in more than 80% of the coagulase-negative staph isolates.[19] The choice of empiric therapy for staphylococcus epidermidis infection would be IV vancomycin, as methicillin resistance should be assumed. If the pathogen is methicillin-susceptible, then treatment can be narrowed to beta-lactam antibiotics such as nafcillin and oxacillin. The duration of the therapy depends on the clinical presentation. Usually, prosthetic and medical devices require removal to control the source of the infection.(B3)
Differential Diagnosis
Bacteremia secondary to:
- Staphylococcus aureus
- Other coagulase-negative staph
- Gram-negative bacteria
- Streptococcal species
- Septic thrombophlebitis
- Viral infection
- Osteomyelitis
- Culture negative endocarditis
Prognosis
The prognosis depends on the type of infection and the patient’s comorbidities at the time of infection. In neonates with low birth weight, mortality due to S. epidermidis sepsis was as high as 4.8% and 9.4%.[20] For those with coagulase-negative staph endocarditis, the mortality rate can be high as 36%.[8]
Complications
Sepsis and septic shock are complications with high mortality that can arise with catheter-related infections. The mortality rate for septic shock can up to 20 to 30%.[21] Prosthetic valve endocarditis or native valve endocarditis can lead to complications, including septic emboli, mycotic aneurysm, perivalvular abscess, and heart failure.[8]
Deterrence and Patient Education
Patients who are undergoing procedures or surgery that requires implantation of prosthetic or medical devices should receive education about the possibility of the infection with Staphylococcus epidermidis. If patients are knowledgeable about common signs and symptoms of the infection, then it will lead to faster evaluation and treatment, which will overall lead to reduced mortality and complications.
Enhancing Healthcare Team Outcomes
Staphylococcus epidermidis, a common bacterium found on the human flora, are innocuous species that can become virulent once inside the host. This species of bacteria can have different consequences in an infected individual, and it requires a great deal of coordination between various medical staff to treat the infection.
Early consult with the infectious disease team will aid in starting the patient on the initial treatment. If the clinical picture is concerning for endocarditis, a cardiologist can provide a further evaluation with imaging such as TTE or TEE. Also, it is useful to have a pharmacist specializing in infectious disease to overlook the type and dosage of the medication based on the patient’s comorbidities.
Because one of the main methods of invasion for Staphylococcus epidermidis is through prosthetic and medical devices, following strict aseptic techniques during a procedure is necessary. A systemic review showed that an effective infection control team requires a multi-disciplinary team consisting of nurses, physicians trained in infection control, microbiologist, and data manager. For an institution to implement an efficacious protocol and system, it requires constant training in frontline staff with education, surveillance, and feedback.[22] [Level 2]
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