S. lugdunensis Native-Joint Septic Arthritis: Case Report and Review of the Literature

Staphylococcus lugdunensis is a skin commensal classified as a coagulase-negative Staphylococcus (CoNS). Though CoNS is typically associated with less aggressive clinical disease than Staphylococcus aureus, there is growing awareness that S. lugdunensis may be as virulent as S. aureus. The association between S. lugdunensis and infective endocarditis is well known, but few reports of native-joint disease with this organism exist. We report a case a 28-year-old male with no prior medical problems presenting with native-joint septic arthritis. Cultures grew S. lugdunensis. To our knowledge, this is the fifth case reported in the literature.


Introduction
S. lugdunensis was rst described in 1988 [1]. It remains a rare pathogen, but it has since been associated with a wide variety of clinical infectious syndromes, including cardiovascular, soft-tissue, bone, and prosthetic joint infections. S. lugdunensis has been associated with higher severity and mortality than other coagulase-negative Staphylococcus (CONS) species, presenting with features more similar to disease caused by S. aureus. A case series with native valve infective endocarditis (IE) caused by S. lugdunensis reported mortality as high as 42% and surgical needs for more than 51% of cases [2][3][4][5]. For prosthetic valve IE, mortality exceeded 78%. Soft-tissue infections and pyogenic disease involving S. lugdunensis have also been reported and may be more common than once thought in community-acquired infections [6]. S. lugdunensis and S. aureus can infect joints via direct inoculation or hematogenous spread. e association between S. lugdunensis and prosthetic joint disease is well established, with reports of infections ranging between 6 weeks and 4 years after implantation [4,7,8].
ere is a paucity of reports on infections involving native joints.

Case Presentation
A 28-year-old male with no past medical history presented to the emergency room with two weeks of right knee pain. He denied any recent sexually transmitted diseases, illicit drug use, or prior episodes of knee pain. He reports no trauma to the knee. Over-the-counter pain medications did not relieve his pain, which progressed and eventually limited his ability to use his joint.
On examination, the patient was afebrile. His right knee was erythematous, warm, swollen, and with reduced range of motion. A moderate e usion was noticed. He was unable to bare weight on the a ected leg. Laboratory analysis revealed leukocytosis, with white blood cell counts of 12,100 per microliter (mcL). Imaging revealed mild softtissue swelling and a moderate e usion. A diagnostic arthrocentesis was performed, and uid analysis revealed 28,875 white blood cells per mcL, predominantly neutrophilic. Gram stain revealed Gram-positive cocci in clusters at 1 day of growth. At 48 hours, cultures grew S. lugdunensis. Magnetic resonance imaging (MRI) revealed di use soft-tissue edema, most prominent in the popliteal fossa around the knee and a large knee joint e usion with synovitis ( Figure 1). Six synovial uid samples grew S. lugdunensis. Susceptibilities were obtained via bioMerieux VITEK 2 antimicrobial susceptibility testing, showing resistance only to oxacillin. e patient underwent washout by orthopedic surgery on day one and day three. Vancomycin was given for four days and subsequently changed to clindamycin. e patient completed seven days of parenteral antibiotics and transitioned to oral clindamycin for the remainder of a four-week course. He had full clinical resolution at his third week of therapy.

Discussion and Literature Review
Native-joint septic arthritis caused by S. lugdunensis is rare. Our review of the English literature found only four cases [7,[9][10][11]. One case did not have prior joint disease or chronic medical conditions, while all other cases had rheumatoid arthritis (RA) [7,[9][10][11]. Preexisting joint disease is a known risk factor for bacterial arthritis [12]. One prospective study of bacterial arthritis reported preexisting joint disease in 40% of cases, most commonly RA [13]. e most common pathogen associated with bacterial arthritis is S aureus [12]. However, the incidence of CoNS has risen in the past two decades and is more common with prosthetic joints. An observational study with 7275 total hip and knee arthroplasties over 38 years found 75 cases of prosthetic joint infections, with CoNS causing 18 infections, 3 of which were S. lugdunensis [14]. e incidence of CoNS increased from 10 to 21% during period [15].
S. lugdunensis is classi ed as a CoNS. It nevertheless retains partial coagulase activity and has many similarities with S. aureus [4,8]. Agglutination tests are typically used to distinguish CoNS from S. aureus, but performance characteristics of these tests for S. lugdunensis are variable and can lead to false identi cation of S. aureus [4,16]. us, the true burden of S. lugdunensis may be underappreciated. Samples may be reported as S. aureus, and both pathogens cause similar disease. Both organisms are skin commensals and are associated with soft-tissue infections, bacteremia, and infective endocarditis. Like S aureus, S. lugdunensis can cause severe disease. Infective endocarditis by S. lugdunensis can present with complications such as valvular perforation, myocardial abscesses, embolic stroke, and death [2,4,11]. Soft-tissue infections can be purulent and may progress to bacteremia and infective endocarditis [10,11].

Conclusion
e present case contributes to a small but growing list of cases of native-joint septic arthritis by S. lugdunensis.  Clinicians must be aware of the association between S. lugdunensis and severe clinical disease. Lincomycin-based therapy was a successful treatment option for our case. Further studies are needed to compare di erent therapeutic options.