Staphylococcus argenteus (formerly S. aureus clonal complex 75) is an emerging species in the S. aureus complex (1). Several studies reported sporadic cases of S. argenteus infections mainly in Asia, Oceania, and the Pacific Islands (2) but rarely in Europe (3). We report the clinical characteristics of a community-acquired bone and joint infection with S. argenteus in a child living in France.

At the end of July 2017, a 9-year-old boy with no unusual medical history or previous local trauma was hospitalized because of acute signs of infection of the third finger on his right hand. He was first seen in a local hospital and given an initial diagnosis of cellulitis (arthritis). Two days later, he was admitted to the emergency pediatric ward of a tertiary care hospital where a surgical joint exploration was performed and confirmed the diagnosis of arthritis associated with an abscess of the extensor tendon sheath (Table).

Surgical microbiological samples cultured on blood agar plates (aerobic conditions at 37°C for 24 h) grew a strain that was identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (Microflex LT, Bruker, France) as having log scores ranging from 1.39 to 1.87 (corresponding to S. aureus, S. simiae, or S. epidermidis). These scores were lower than those required for reliable identification of species (2.3) or genus (2.1) levels. Antimicrobial drug susceptibility testing (Vitek2; bioMérieux, Marcy l’Etoile, France) identified resistance to penicillin G.

Because there was no initial reliable identification of this strain, we performed molecular tests. The strain was negative for nuc, lukS-PV, mecA, mecC, tst-1, and spa genes. The V3 region sequence of the gene coding for 16S rRNA showed 100% identity with that for S. aureus. Microarray analysis (S. aureus Genotyping Kit 2.0; Alere Technologies GmbH, Jena, Germany) assigned this strain to the clonal complex 2250/2277 of one of the main clusters of S. argenteus (2,4). The patient was discharged and received an oral antimicrobial regimen for 6 weeks; healing was closely monitored (Table).

Five weeks later, the patient was hospitalized because of recurrent signs of infection (Table). Magnetic resonance imaging of the right hand showed osteitis (Technical Appendix, panel A). A second surgical procedure was performed (Table). Cultures of surgical samples remained sterile after 10 days and a 16S rDNA PCR result was negative. Histologic analysis showed chronic osteitis (Technical Appendix Figure, panel B). An oral drug regimen, including clindamycin and ofloxacin for 6 weeks, was prescribed. Long-term outcome was good (Table), despite persistence of stiffness in the finger.

This rare case of osteomyelitis caused by S. argenteus highlights the difficulties in correctly identifying this species. As with S. schweitzeri, S. argenteus is an emergent species that has been described as part of the S. aureus species complex (5). S. argenteus was first described in 2002 as a CC75/sequence type T1223 clone of S. aureus in Aboriginal communities in Australia (6). This species was named S. argenteus in 2011 because of its lack of staphyloxanthin production (1). Most studies reported prevalence rates for S. argenteus among strain collections of 0.16%–18.6% according to geographic distribution, with a clear predominance in Asia and the West Pacific region (1,5–7) and a rare description in Europe (3).

In our case, no epidemiologic link to Asia or the West Pacific region was observed. The clinical spectrum of infections with S. argenteus remains poorly described, but varies from asymptomatic nasal carriage (8) to community-acquired infections, including skin and soft tissue infections (1,6), bacteremia (1,9), and foodborne illness (8). Apart from 2 cases of bacteremia reported by Dupieux et al. (9), clinical data for S. argenteus infections has been poorly detailed (Technical Appendix, Figure). To the best of our knowledge, only 1 case of osteomyelitis has been reported (7).

Previous cases and the case we report indicate that S. argenteus could be responsible for invasive infections that are difficult to manage. S. argenteus was initially considered to be less virulent than S. aureus on the basis of a study in Australia, which reported that this species was associated mainly with skin and soft tissue infections and rarely with bacteremia (3/220 cases) (1). However, a comparative study of 311 cases of S. argenteus and S. aureus sepsis in Thailand showed a similar outcome after 28 days (10). Moreover, virulence factors, such as Panton-Valentine leucocidin and enterotoxins, have been described in S. argenteus isolates (4,8–10). In contrast to reports from Aboriginal communities in Australia (6) and remote populations in the West Pacific region (Technical Appendix, Table), resistance to methicillin was not detected in strains from the case-patients in this study.

In contrast to S. aureus, the effect of carriage of S. argenteus has not been studied. For our case-patient, screening for S. argenteus nasal carriage was not performed. However, a recent study of foodborne illness outbreaks reported the ability of this bacterium to spread in the environment and colonize food handlers (8).

S. argenteus is an emerging species for which its clinical spectrum remains poorly described. Further studies are needed to better address the global prevalence and clinical role of this bacterium, including its potential effects in chronic human infections.

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