Fracture-related infection often brings microbiology into focus at exactly the point where interpretation becomes most consequential. When a culture result or dataset reports CoNS, the immediate question is usually whether this identifies a clinically meaningful pathogen category. The more useful question is narrower: what does this label actually preserve, and what does it leave unresolved in the setting of fracture-related infection?
Summary
CoNS refers to coagulase-negative staphylococci, a laboratory grouping rather than a single organism.
Multiple staphylococcal species fall within this category.
In fracture-related infection, microbiological confirmation depends on reproducible recovery from separate deep tissue or implant specimens.
A single positive deep culture is suggestive rather than confirmatory within current FRI criteria.
Reporting organisms only as CoNS retains less species-level detail than species-level reporting.
Why This Matters
Fracture-related infection remains a relevant clinical burden. In Germany, 1.23% of all fractures treated as inpatients resulted in FRI in 2018, and administrative incidence increased between 2008 and 2018. Within that setting, microbiological results help shape diagnostic interpretation, but not every label used in reporting carries the same level of meaning. (Rupp, 2024)
The issue is especially relevant because coagulase-negative staphylococci are common in musculoskeletal infection microbiology, yet the label itself is broad. In a Leuven cohort of 194 fracture-related infections, Staphylococcus aureus was the most commonly isolated pathogen at 31.4%, followed by Staphylococcus epidermidis at 25.8% and non-epidermidis/non-lugdunensis CoNS at 14.9%. That distribution already shows that CoNS is not one organism and that reporting at different levels of species resolution can change what a microbiology table allows the reader to see. (Depypere, 2022)
What CoNS Actually Means in Fracture-Related Infection
What CoNS refers to
CoNS refers to coagulase-negative staphylococci, a broad group of Gram-positive cocci united by the absence of coagulase rather than by one shared clinical behaviour. Many species belong to this group, and the literature has historically focused far more heavily on Staphylococcus aureus than on these organisms. The grouping remains practical in daily microbiology, but practical reporting convenience is not the same as diagnostic precision. (Michels, 2021)
Which organisms are commonly included
Commonly encountered members of the CoNS grouping include:
Staphylococcus epidermidis
Staphylococcus haemolyticus
Staphylococcus hominis
Staphylococcus capitis
Staphylococcus lugdunensis
These species were among the more frequently speciated coagulase-negative staphylococci in a large Australian cohort of bloodstream infection episodes, in which Staphylococcus epidermidis was by far the most common, followed by Staphylococcus haemolyticus, Staphylococcus hominis, Staphylococcus capitis, and Staphylococcus lugdunensis. Stating them explicitly is useful because many readers recognise the umbrella term CoNS without having a concrete sense of which organisms may sit inside it. (Keogh, 2025)
Why the category is broader than it sounds
The CoNS category is broader than it sounds because it compresses species with different ecological niches, virulence traits, and clinical associations into one reporting label. CoNS is a heterogeneous group, yet many studies still compile all CoNS into one category despite substantial interspecies differences. That matters because the key clinical question is rarely whether an organism is simply coagulase-negative. It is whether the specific organism recovered behaves like a contaminant in that sampling context, or like a plausible pathogen in that clinical setting. (Michels, 2021)
Species-level data support that concern. In a cohort of 4046 CoNS bloodstream infection episodes, 27% of isolates were not assigned to species, and meaningful differences were observed across species in age distribution, onset classification, comorbidities, and flucloxacillin resistance. Staphylococcus lugdunensis also showed a distinct profile compared with several other CoNS species. Although bloodstream infection is not the same disease model as fracture-related infection, these findings support the narrower interpretive point relevant here: species-level reporting can preserve distinctions that grouped CoNS reporting does not. (Keogh, 2025)
What matters in fracture-related infection interpretation
Within fracture-related infection, diagnostic weight is assigned by the FRI framework to reproducibility across deep samples rather than to the shorthand label itself. Current consensus criteria state that phenotypically indistinguishable pathogens identified by culture from at least two separate deep tissue or implant specimens are confirmatory. By contrast, a pathogenic organism identified from a single deep tissue or implant specimen is only suggestive. This distinction is central to how CoNS should be read in practice. The term itself does not confirm infection. Reproducible recovery across separate deep specimens does much of that interpretive work. (Rupp, 2024)
This becomes especially important because CoNS species are also common skin commensals. They are often classified as contaminants rather than causative agents, yet the distinction between contamination and infection remains difficult, and universally applicable markers for making that distinction are lacking. For fracture-related infection, that uncertainty is not resolved by the CoNS label. It is narrowed, if at all, by specimen quality, sampling reproducibility, and the surrounding clinical picture. (Michels, 2021)
What can be lost when results are reported only as CoNS
Grouped reporting can retain less species-level detail than species-level reporting. In a cohort of fracture-related infections, Staphylococcus epidermidis was kept separate from non-epidermidis/non-lugdunensis CoNS, which already signals that not all coagulase-negative staphylococci were treated as an interchangeable block. Polymicrobial fracture-related infections were present in 25.3% of cases, and within polymicrobial infections non-epidermidis CoNS and Staphylococcus epidermidis both appeared frequently. Once species-level distinctions begin to matter within a dataset, collapsing them back into a single CoNS category can make the microbiological picture less precise. (Depypere, 2022)
This does not mean that every clinical decision in fracture-related infection requires exhaustive speciation, nor that every report using the term CoNS is inherently uninformative. It does mean that the reader should notice what level of detail has been retained. A table reporting Staphylococcus epidermidis, Staphylococcus lugdunensis, and non-epidermidis CoNS is showing something different from a table reporting only CoNS. The two are not equivalent forms of microbiological reporting, even when both are technically accurate. (Depypere, 2022; Keogh, 2025)
Practical Implications for Clinical Decision-Making
The term CoNS should not be read as a diagnosis in itself. In current fracture-related infection criteria, confirmatory microbiology depends on phenotypically indistinguishable organisms being recovered from at least two separate deep tissue or implant specimens. (Rupp, 2024)
A single deep positive culture remains an interpretive signal rather than confirmatory proof. That matters particularly for CoNS because these organisms also inhabit skin and can enter samples through contamination. (Rupp, 2024; Michels, 2021)
Species-level reporting can preserve clinically relevant information. CoNS species differ in virulence, epidemiology, and resistance patterns, and grouped reporting may compress those differences. (Michels, 2021; Keogh, 2025)
The way samples are obtained and reproduced across deep specimens remains part of how the result should be interpreted. Deep tissue or implant specimens interpreted within a structured fracture-related infection framework do not carry the same meaning as a loosely contextualised culture label. (Rupp, 2024)
Published microbiology tables should be read with attention to reporting resolution. CoNS may be a valid category, but it is a broader and less resolved one than species-level identification. (Depypere, 2022; Keogh, 2025)
Common Pitfalls
Mistaking CoNS for a single pathogen entity. CoNS is a heterogeneous grouping containing many species rather than one clinically uniform organism class. (Michels, 2021)
Assuming the label itself confirms fracture-related infection. Current fracture-related infection criteria place confirmatory weight on reproducible recovery across separate deep samples, not on the word CoNS. (Rupp, 2024)
Treating all CoNS species as interchangeable. Available evidence shows interspecies differences in clinical profile and resistance patterns. (Michels, 2021; Keogh, 2025)
Reading grouped and species-level reporting as equivalent. Both may be technically correct, but they do not preserve the same amount of microbiological information. (Depypere, 2022; Keogh, 2025)
Closing Note
CoNS remains a useful laboratory shorthand, but in fracture-related infection the label alone does not determine diagnostic meaning. What matters is whether the result is reproducible across deep samples, how much species-level detail is retained, and how the finding sits within the broader clinical context.
References
Rupp M, Spiegl UJA, Alt V. Fracture-Related Infection-Epidemiology, Etiology, Diagnosis, Prevention, and Treatment. Dtsch Arztebl Int. 2024;121:145-152. PMID: 37970721.
Depypere M, Kuehl R, Senneville E, et al. The Microbiological Etiology of Fracture-Related Infection. Front Cell Infect Microbiol. 2022;12:934074. PMID: 35873162.
Michels R, Last K, Becker SL, Papan C. Update on Coagulase-Negative Staphylococci-What the Clinician Should Know. Microorganisms. 2021;9(4):830. PMID: 33919781.
Keogh S, Larsen EN, Edwards F, et al. Speciation of coagulase-negative staphylococci: A cohort study on clinical relevance and outcomes. Infect Dis Health. 2025;30(4):307-315. PMID: 40335430.