A 77-year-old man with hypertension and sick sinus syndrome status post pacemaker implantation was evaluated in the outside hospital for four month history of chills. Review of systems was negative for other symptoms. The pacemaker’s battery was changed two years ago. He denied intravenous drug use. His vital signs were stable and physical examination revealed no cardiac murmurs. The pacemaker insertion site was well healed without associated skin changes. His complete blood count (CBC) and comprehensive metabolic panel (CMP) were unremarkable. Blood cultures grew Staphylococcus epidermidis in 4/4 bottles. This was believed to be a contaminant and patient was discharged home.
Two months later, patient was evaluated again for ongoing chills. Blood cultures again grew Staphylococcus epidermidis from 2/2 bottles. Given the absence of clinical findings and unremarkable physical examination, patient was managed symptomatically and discharged home without antibiotic therapy.
One month after his second hospitalization, patient was seen at our facility for severe disabling chills. CBC and CMP were unremarkable. C-reactive protein was elevated. A trans-esophageal echocardiogram (TEE) showed 1.6cm x 1.4 cm mobile mass attached to ventricular pacemaker lead, consistent with a vegetation. Blood cultures showed growth of Staphylococcus epidermidis from 4/4 bottles. The infected pacemaker lead was extracted. The patient received a prolonged course of IV antibiotics for chronic pacemaker lead infection. On follow-up, he was asymptomatic and blood cultures were negative.
Coagulase-negative Staphylococcus (CoNS) is a major constituent of human skin commensal flora. Often considered a contaminant, it also recognized as a cause of clinically significant infection in patients with prosthetic devices, pacemakers and intravenous catheters.
The differentiation of a contaminant from a pathogen causing true infection is based on clinical and microbiological factors. A true infection should be considered in a patient with fever, leukocytosis or hypotension. Microbiologic factors that favor a true infection include growth of CoNS in culture within 48 hours of inoculation, growth in both aerobic and anaerobic bottles, and multiple cultures positive for the same organism with identical antibiograms.
Cardiac device infection is rare, and can be categorized into pocket infection and deeper infection. Deeper infections are difficult to diagnose, and manifest as lead vegetation and right-sided endocarditis. When chronic, symptoms can be subtle with chills as one of the most common presenting symptom. Diagnosis of pacemaker infection is established on the basis of positive blood cultures and the presence of a vegetation on trans-esophageal echocardiography. Treatment involves removal of infected hardware and a prolonged course of antibiotics.
Blood cultures positive for coagulase-negative Staphylococcus pose a significant diagnostic challenge in the hospital setting. True bacteremia should be differentiated from pseudo-bacteremia on the basis of clinical findings and microbiologic factors. A true infection should be considered in patients with a cardiac device and repeatedly positive blood cultures. Hospitalists should have a low threshold to initiate a further work up with a TEE to look for underlying device infection.
To cite this abstract:Kataria KK, Grover S, Kumar J. Coagulase-Negative Staphylococcus: Contaminant or Pathogen?. Abstract published at Hospital Medicine 2016, March 6-9, San Diego, Calif. Abstract 601. Journal of Hospital Medicine. 2016; 11 (suppl 1). https://www.shmabstracts.com/abstract/coagulase-negative-staphylococcus-contaminant-or-pathogen/. Accessed December 13, 2019.