The study, led by Renato Pascale and Sara Tedeschi of the University of Bologna together with colleagues at the IRCCS Istituto Ortopedico Rizzoli and Maria Cecilia Hospital, followed 161 adults diagnosed with deep surgical-site infections following spinal instrumentation between January 2018 and June 2022. These infections, abbreviated DSII, involve tissues beneath the fascia surrounding implanted hardware, and their management is uniquely difficult. The implants themselves provide a surface on which bacteria can form biofilms, those resilient, glue-like microbial communities that shield pathogens from both antibiotics and immune cells. Standard care therefore combines surgical debridement, the physical removal of infected tissue, with prolonged antibiotic therapy, and the choice between retaining, replacing, or removing the hardware is individualized according to spinal stability and the severity of infection.

The patient population reflected the demanding reality of complex spine surgery. Participants had a median age of 62 years, a median Charlson comorbidity index of 3, and more than half were men. Degenerative disease and scoliosis each accounted for about 29 percent of the original operations, but a striking 19.3 percent had undergone instrumentation because of cancer. Infections typically declared themselves early: 70.2 percent were diagnosed within the first three months after surgery, with a median interval of 27 days between the primary operation and the diagnosis of infection. Wound dehiscence, the reopening of the surgical incision, was the most common warning sign, occurring in 59 percent of cases. Polymicrobial infections, in which several bacterial species are present at once, made up just over a quarter of the cohort.

Despite meticulous care at two referral centers for bone and joint infection, treatment failure was common. Fifty-one patients, or 31.7 percent, ultimately failed treatment, an outcome defined by wound reopening, the appearance or recurrence of a fistula, new pain or functional decline after apparent resolution, or death attributable to the infection. Among the failures, wound reopening dominated, occurring in nearly two-thirds of cases, while 11 patients developed fistulas and three died. The figures are a sobering reminder that even in high-volume centers with dedicated infectious disease consultants, roughly one in three patients with an infected spinal construct will not be cured by the first combined medical and surgical assault.

When the researchers dug into what separated the failures from the cures, one microbial distinction stood out with statistical force. Gram-positive bacteria, the traditional culprits in implant infections, caused 60.3 percent of cases, but the 33.8 percent of infections driven by Gram-negative rods, including Pseudomonas aeruginosa and Escherichia coli, were disproportionately linked to bad outcomes. Gram-negative etiology proved to be an independent risk factor for treatment failure in two separate multivariable analyses: the odds of failure were roughly four times higher for these infections whether the treatment window was framed as eight weeks (odds ratio 4.20) or twelve weeks (odds ratio 4.46). This aligns with a growing body of evidence from prosthetic joint infections suggesting that Gram-negative pathogens are inherently harder to eradicate from foreign material, a fact that current understanding of spinal implant infections, still surprisingly thin, has only begun to absorb.

The second headline finding concerns quinolones, the antibiotic class that includes ciprofloxacin and levofloxacin. Patients whose regimens included a quinolone had dramatically lower odds of treatment failure, with odds ratios of 0.11 in both the eight-week and twelve-week analyses, meaning the odds of failure were reduced by nearly 90 percent in this observational dataset. The biological rationale is plausible: quinolones penetrate bone well, are active against many Gram-negative rods, and can be administered orally for months. Yet the investigators themselves urge caution. Because quinolones were likely reserved for patients with susceptible pathogens and optimized targeted therapy, the association may reflect careful antimicrobial selection within a higher-risk subgroup rather than a genuine causal benefit. Residual confounding, they acknowledge, cannot be excluded in a retrospective design.

Perhaps the most consequential result is the one that did not appear. When the team compared treatment schedules of eight versus twelve weeks, excluding patients who failed early during therapy to isolate the effect of a completed course, they found no significant association between duration and outcome. To guard against a subtle statistical trap known as immortal time bias, in which patients must survive long enough to complete a long regimen before being counted as such, the researchers also performed prespecified landmark sensitivity analyses at eight and twelve weeks, restricting comparisons to patients still at risk at each time point. Those analyses, conducted on 90 and 75 patients respectively, confirmed the primary result: longer was not demonstrably better. The median treatment duration in the cohort was 82 days, and the question of whether some patients could safely stop earlier remains, as the authors stress, unresolved rather than settled.

The study’s methodology reveals both its strengths and its limits. The investigators applied a rigorous Delphi consensus definition of postoperative spine infection, using hierarchical criteria spanning microbiology, imaging, laboratory values, intraoperative findings, and histology, and a dedicated infectious disease team made every diagnosis. Firth penalized logistic regression was used to temper the small-sample bias that arises when only 51 events are distributed across multiple covariates. Yet the same constraints shape the conclusions. The study spans two hospitals in the same Italian region, limiting generalizability; treatment duration was chosen by individual physicians rather than randomized, inviting confounding by indication; the rate of culture-negative infections exceeded that reported in prior literature; and detailed surgical variables such as the number of instrumented levels were not consistently available for adjustment. The authors explicitly label their duration findings exploratory.

What emerges is a reframing of the clinical conversation around one of orthopedic surgery’s costliest complications. Rather than asking only how long to treat, the DeFEndO study suggests clinicians should ask what they are treating. Cancer patients, whose immunosuppression, chemotherapy-induced mucosal damage, and malnutrition impair infection control, fared worse, and so did those harboring Gram-negative rods. Rifampin, long championed for biofilm infections of prosthetic joints, showed no protective signal here, echoing the mixed results of randomized trials elsewhere. The authors call for prospective studies, particularly to define optimal therapy for Gram-negative spinal infections, where evidence remains scarcest. Until then, the message for surgeons and infectious disease physicians is quiet but profound: the calendar may matter less than the microbe, and curing a spine seeded with infection begins with knowing exactly which organism is hiding on the hardware.

Subject of Research: Risk factors for treatment failure of deep surgical-site infections following spinal instrumentation

Article Title: Risk factors for treatment failure of surgical site deep infections following spinal instrumentation: multicentre observational study (DeFEndO study)

Article References: Pascale, R., Gallo, M., Regge Gianas, N., Fornaro, G., Grassi, I., Zagarrigo, M., Grechi, A., Zuppiroli, A., Santoro, D., Tenti, E., Boriani, L., Zamparini, E., Gasbarrini, A., Viale, P., Giannella, M., Curti, S., & Tedeschi, S. (2026). Risk factors for treatment failure of surgical site deep infections following spinal instrumentation: multicentre observational study (DeFEndO study). Journal of Bone and Joint Infection, 11(5), 601-611. https://doi.org/10.5194/jbji-11-601-2026

Image Credits: AI Generated

DOI: 10.5194/jbji-11-601-2026

Keywords: spinal instrumentation, surgical site infection, deep infection, treatment failure, antibiotic duration, quinolones, Gram-negative bacteria, biofilm, rifampin, spine surgery, multicentre observational study, infectious diseases

The ubiquity of the contamination was striking. Three compounds in particular, trimethoprim, chlortetracycline, and sulfamethoxazole, were detected in 100 percent of the samples analyzed, meaning that no single site in the entire river system was free of antibiotic residues. Concentrations of individual antibiotics ranged widely, from as little as 2.8 nanograms per liter for lomefloxacin to a maximum of 1235.8 nanograms per liter for erythromycin, a macrolide antibiotic commonly used in both human medicine and livestock production. While such concentrations are measured in parts per trillion and are far below therapeutic doses, chronic exposure at these levels is precisely the condition that scientists worry can drive the evolution and spread of antibiotic resistance genes in aquatic microbial communities.

Spatial patterns in the data told a clear story about how the pollution moves through the watershed. Antibiotic concentrations followed the order of midstream greater than downstream greater than upstream, suggesting that the middle reaches of the river system, where urban development and population density are highest, act as a major loading zone. Equally telling was the comparison between the main river channel and its tributaries: levels in the tributaries were generally higher than in the mainstream, indicating that the main stem of the Beiyun River is strongly influenced by inflows from the smaller streams draining its sub-catchments. In effect, the tributaries function as conveyor belts, collecting antibiotic residues from neighborhoods, hospitals, livestock facilities, and industrial sites, and delivering them into the larger river.

To move beyond simple detection and identify where the antibiotics actually come from, the research team employed a quantitative source-apportionment method known as principal component analysis with multiple linear regression, or PCA-MLR. This technique, originally developed for tracing air pollution sources, works by reducing a large dataset of measured pollutant concentrations into a small number of underlying statistical factors, each of which corresponds to a characteristic pollution signature. Regression analysis then estimates how much each factor contributes to the observed concentrations of individual compounds. In this study, the model resolved the antibiotic load in the Beiyun River system into six identifiable pollution sources plus one unknown source, providing a quantitative breakdown that single-source monitoring cannot achieve.

The results of the apportionment pointed to two dominant contributors. Mixed pollution source inputs, a category that aggregates diffuse urban runoff, agricultural activity, and other combined pathways, explained 35.4 percent of the variance in the data, making it the single largest source. Wastewater treatment plant discharges ranked a close second, accounting for 31.1 percent of the variance. The chemical fingerprints of these two sources were distinct. The mixed source contributed most heavily to the quinolone antibiotics difloxacin and ciprofloxacin, accounting for 72.1 percent and 71.4 percent of their respective loads. The wastewater treatment plant source, by contrast, dominated the sulfonamide class, contributing 74.8 percent of sulfacetamide, 73.9 percent of sulfachloropyridazine, 73.3 percent of sulfadimethoxine, and 70.9 percent of sulfadiazine.

The prominence of wastewater treatment plants as a source is a recurring theme in urban water pollution research, and the Beiyun findings add Beijing to a long list of cities where conventional treatment infrastructure falls short of removing pharmaceutical micropollutants. Standard activated-sludge treatment processes are designed to strip out organic matter, nitrogen, and phosphorus, but many antibiotics are either poorly biodegraded or are re-released back into the water column as parent compounds or metabolites during sludge handling. Sulfonamides in particular are known to pass through treatment barriers with relatively high efficiency, which is consistent with the strong association between these compounds and treatment plant discharges found in the new study. Upgrading plants with advanced oxidation processes, ozonation, or activated carbon polishing has been shown elsewhere to substantially reduce pharmaceutical loads, and the source apportionment here suggests such upgrades would deliver measurable benefits in this watershed.

On the question of ecological risk, the study’s multi-level assessment delivered a nuanced verdict. Overall, the ecological risks posed by antibiotics across the Beiyun River system remained at acceptable levels, a conclusion that may surprise readers given the universal detection of the compounds. Risk quotients, calculated by comparing measured environmental concentrations with predicted no-effect concentrations for sensitive aquatic species, stayed within thresholds regarded as tolerable for the system as a whole. However, the assessment flagged specific exceptions. Tetracyclines showed relatively high risk quotients, reflecting the combination of their persistent detection and the known sensitivity of algae and other primary producers to this drug class. Clarithromycin, a macrolide, exhibited low but non-negligible risks to certain aquatic species, consistent with prior toxicological work showing that macrolides can affect photosynthesis and growth in freshwater organisms at environmentally relevant concentrations.

The significance of these findings extends well beyond the boundaries of a single watershed. Antibiotic residues in surface water are widely recognized as a key driver of antimicrobial resistance, one of the most serious public health threats of the coming decades. When bacteria in rivers are exposed to sub-inhibitory concentrations of antibiotics over long periods, strains carrying resistance genes gain a selective advantage, and those genes can then move between species and environments through horizontal gene transfer. Urban rivers like the Beiyun, which flow through neighborhoods where millions of people live, work, and recreate, represent critical nodes in this process, linking clinical and agricultural antibiotic use to the broader environmental resistome. Understanding exactly which sources contribute which compounds is therefore a prerequisite for designing effective interventions.

The study also highlights the value of source apportionment as a policy tool. Knowing that mixed diffuse inputs and treatment plant effluents together account for roughly two-thirds of the antibiotic burden allows regulators to prioritize interventions, whether through upgrading treatment technology, controlling runoff from livestock and aquaculture operations, tightening prescription and disposal practices, or managing the hydrological connections between tributaries and the main stem. The finding that tributaries consistently carry higher concentrations than the mainstream suggests that targeted action on sub-catchment scale pollution could yield disproportionate benefits for the entire river system.

For Beijing, a megacity of more than twenty million people whose rivers have undergone decades of engineering and restoration, the new data provide a baseline against which future management efforts can be measured. The research was funded by the Natural Science Foundation of Jiangxi Province, the Jiangxi Provincial Department of Science and Technology, and the National Natural Science Foundation of China, and was conducted by a team led from Jiangxi Agricultural University together with collaborators in Beijing. As antibiotic use continues to grow worldwide and urbanization intensifies across Asia, Africa, and Latin America, the Beiyun River system offers a case study in what complete pharmaceutical contamination of an urban watershed looks like, and a demonstration that with careful chemical detective work, the sources of that contamination can be named, ranked, and ultimately addressed.

Subject of Research: Antibiotic contamination, sources, and ecological risks in an urbanized Beijing watershed

Article Title: Occurrence, source apportionment, and risk assessment of antibiotics in the Beiyun River system: a highly urbanized watershed in Beijing, China

Article References: Lou, Q., Zhao, X., Zhang, X., Liang, L., Han, L., Tu, W., & Chen, M. (2026). Occurrence, source apportionment, and risk assessment of antibiotics in the Beiyun River system: a highly urbanized watershed in Beijing, China. Environmental Monitoring and Assessment, 198(10), Article 1125. https://doi.org/10.1007/s10661-026-15933-7

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15933-7

Keywords: antibiotics, Beiyun River, Beijing, water pollution, source apportionment, PCA-MLR, ecological risk, wastewater treatment, sulfonamides, tetracyclines, macrolides, quinolones