# Deep sternal wound infection after cardiac surgery: A combination of 2 distinct infection types, deep incisional surgical-site infection and mediastinitis: Results of a retrospective study

Christian de Tymowski, Sophie Provenchère, Marylou Para, Xavier Duval, Nathalie Grall, Tarek Sahnoun, Bernard Iung, Solen Kernéis, Jean-Christophe Lucet, Philippe Montravers

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Christian de Tymowski, Sophie Provenchère, Marylou Para, Xavier Duval, Nathalie Grall, et al. Deep sternal wound infection after cardiac surgery: A combination of 2 distinct infection types, deep incisional surgical-site infection and mediastinitis: Results of a retrospective study. Surgery, 2025, 181, 10.1016/j.surg.2025.109255. hal-05119078

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https://u-paris.hal.science/hal-05119078v1

Submitted on 18 Jun 2025

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**Introduction**

After cardiac surgery, surgical-site infections are among the most serious infectious complications, with an incidence ranking behind postoperative infectious pneumonia and bloodstream infections.¹⁻³ Their incidence has remained constant in recent years and varies between 1% and 3% (extreme values 0.5%-10%), depending on the definitions used, associated patient risk factors, type of cardiac surgery, compliance with preventive measures, and perioperative monitoring.⁴⁻¹⁰ Surgical-site infections requiring surgical management are commonly referred to as deep sternal wound infections (DSWI).¹¹⁻¹³ This entity has been divided into 2 groups according to the US Centers for Disease Control and Prevention (CDC) definition: deep incisional surgical-site infection (diSSI), which involves only suprasternal tissues, and mediastinitis, which is an organ-space infection of the substernal area or the sternal bone.¹,¹⁰,¹⁴

In a previous study conducted between 2006 and 2012, we investigated the specific risk factors for DSWI according to clinical presentation.¹⁰ Our results were consistent with the conventional risk factors extensively described in the literature,⁵,⁶,⁹,¹⁵,¹⁶ including older age, obesity, diabetes mellitus, and coronary artery bypass grafting (CABG) as the main risk factors for DSWI. However, differences were found between mediastinitis and diSSI, suggesting a different pathophysiology. Mediastinitis was associated with a shorter time to diagnosis of DSWI and with more virulent pathogens such as *Staphylococcus aureus*, whereas diSSI was associated more often with commensal skin flora, bilateral mammary artery harvesting, female sex, and chronic kidney disease. These findings suggest that mediastinitis is associated with direct contamination of the wound during surgery or digestive translocation during the perioperative period, whereas diSSI may be associated with delayed wound healing. Although mediastinitis has been extensively studied and shows significant morbidity and mortality rates ranging from 3% to 20% depending on the length of follow-up,¹¹,¹⁷,¹⁸ specific data on the prognosis of diSSI are scarce and show conflicting results. The aim of this study was to describe the incidence and the perioperative and bacteriological characteristics of DSWIs according to their clinical presentation (mediastinitis and diSSI) and their association with 90-day mortality.

**Methods**

**Study design**

This monocentric retrospective study was conducted in a tertiary care teaching hospital that performs more than 1,000 cardiac surgical procedures with cardiopulmonary bypass (CPB) per year. All consecutive patients who underwent cardiac surgery with CPB between 2006 and 2019 were eligible. In our center, cardiac surgery without CPB is not a standard procedure and represents less than 1 operation per year. The second operation of patients who underwent 2 cardiac surgeries within the same year was excluded, as we considered that the postoperative course of the first surgery could influence the outcome of the second surgery.

**Definitions of surgical-site infection**

DSWI was defined as the need for reoperation for local or systemic infection involving the sternotomy scar¹⁰,¹⁴ within 90 days of surgery. The sternal scar was assessed daily after surgery. DSWIs were validated at regular meetings involving a cardiac surgeon, an intensive care physician, and a physician from the infection control team. The date of DSWI was the date of reoperation for surgical-site

infection, and only the first reoperation for suspected DSWI was included. Mediastinitis was defined according to CDC/National Healthcare Safety Network definitions and criteria as the need for reopening of the sternum with deep purulent discharge or destruction of the sternal bone/deep sternal osteomyelitis associated with isolation of micro-organisms in mediastinal drainage cultures or blood.¹⁴ DiSSI was defined as the association of a sternal wound requiring reoperation for debridement or drainage without the need to reopen the sternum, without sternal bone destruction, and with isolation of micro-organisms in intraoperative specimens or blood cultures.¹⁹ The group of patients without DSWI was termed "DSWI-free" and included patients with nonmicrobial sternal dehiscence.

**Outcomes and objectives**

The primary outcome was 90-day mortality. Secondary outcomes were 28-day mortality and 90-day mortality in a landmark analysis where all patients who died within the first 28 days were excluded from the analysis. This analysis accounted for a survival bias, as patients had to survive the initial period to develop a DSWI.²⁰ The secondary objective was to identify risk factors for 90-day mortality.

**Data collection**

Data were collected from 3 databases. The first registry, Cardiobase, prospectively includes all adult patients undergoing cardiac surgery with CPB. This database was approved by the Paris-Nord Biomedical Research Project Evaluation Committee (CERB, institutional review board no. 00006477), the Advisory Committee on Information Processing in Health Research (Paris, France), and the Commission Nationale Informatique et Liberté (CNIL, Paris, France). It is registered on ClinicalTrials.gov (NCT03393169). The registry collects demographic data, medical history, type of surgery, and perioperative data. Cardiobase information on DSWI was combined with that from a second database collected by the Infection Control Unit.¹⁰,²¹ Finally, survival data were extracted from French public data of the Institut National de la Statistique et des Etudes Economiques from 2006 to 2021, where the date of death was recorded.

**Patient management**

Intraoperative management of patients has been published previously.²² During the study period, cephalosporins were the first-line intraoperative antibiotic prophylaxis (cefamandole from 2006 to 2015 and cefazolin from 2016 to 2019), and the combination vancomycin/gentamicin was the second-line prophylaxis in cases of beta-lactam allergy (Supplementary Table S1). In our center, CABG is most commonly performed with bilateral mammary artery harvesting, with the use of vein grafts when mammary artery harvesting is difficult. After surgery, patients were systematically admitted to the intensive care unit (ICU) for at least 48 hours. Our protocol for patients with suspected DSWI was to initiate intravenous antibiotic therapy and perform urgent reoperation with surgical wound debridement as soon as the diagnosis was suspected (positive blood cultures with no other route of entry, significant purulent drainage from the sternotomy, positive Gram stain or positive culture from a sternal puncture). After surgical debridement, all patients benefited from the one-stage technique of closed suction drainage with 2 suprasternal drains for diSSI and 4 to 8 supra- and infrasternal drains for mediastinitis.¹²,¹³,²³
After surgical debridement and primary sternal closure, a vacuum-assisted closure (VAC) system was used for both mediastinitis and diSSI to treat delayed wound healing and/or tissue or sternal defect necrosis. VAC treatment included surgical revision, placement of a VAC device, and replacement of VAC sponges generally every 2 days.

## Statistical analysis

Continuous variables were expressed as medians with interquartile ranges and were compared using the Mann-Whitney U test or the Kruskal-Wallis test as appropriate. Categorical variables were expressed as counts and percentages and compared using the Fisher exact test or $\chi^2$ test as appropriate. For changes over time, patients were grouped into 2-year periods and proportions of patients over time were evaluated using the Cochran-Armitage test.

Time-to-event analyses were estimated using Kaplan-Meier analyses. To assess whether DSWI was an independent factor for death, multivariate analyses were performed using a Cox model. For all models, variables with nominal 2-tailed P-values less than .05 were included in the multivariate model, except for variables with apparent collinearity. Final models were selected using backward stepwise regression and assessed using AIC and Tjur's R2²² discrimination coefficient. A landmark analysis was planned to exclude patients who died before the 75th percentile of time to onset to diSSI (28 days).

All statistical analyses were performed using R software (R Core Team, 2014; R Foundation for Statistical Computing, Vienna, Austria). Figures were generated using the 'ggplot2' package, and statistics were generated using the 'stat' package. Missing values were not imputed. Statistical analysis was reported according to the STrengthening the Reporting of OBservational studies in Epidemiology recommendations for cohort studies²⁴ (see list in Supplementary Table S2).

## Results

### Homogeneity of the cohort

From 2006 to 2019, 14,850 (99%) of 14,960 patients fulfilled the inclusion criteria (Figure 1). The number of patients included remained constant throughout the study period (Supplementary Figure S1, A). Of these patients, 542 (3.6%) developed a DSWI during the postoperative period. The incidence of DSWI decreased over time (Supplementary Figure S1, B). Overall, 3,352 (9%) patients had died by day 90, with a decrease over time (Supplementary Figure S1, C), particularly in patients with DSWI (Supplementary Figure S1, D).

### Patient characteristics by occurrence of DSWI

Both types of DSWI were associated with typical risk factors for DSWI (Table 1). Patient-related risk factors were age, obesity, arterial hypertension, diabetes mellitus, dyslipidemia, ischemic heart disease, peripheral arterial disease (PAD), end-stage renal disease (ESRD), and chronic obstructive pulmonary disease. Procedure-related risk factors were CABG and CPB duration, with diSSI associated with shorter cardiopulmonary bypass duration. Overall, patients with DSWI had a more complicated postoperative course than patients without DSWI, with more catecholamine requirements, chest tube outputs, and longer ICU stays.

### Clinical and microbiological characteristics by type of DSWI

The time frame of DSWI occurrence differed according to clinical presentation: mediastinitis occurred earlier than diSSI, 14 days (10–21) versus 19 days (13–28) ($P < .001$) (Supplementary Figure S2). In addition, mediastinitis and diSSI had different bacterial characteristics. *Enterobacterales* and *S aureus* were more frequently cultured in mediastinitis than in

<figure><img src="image_2.png" /><figcaption>**Figure 1.** Flow chart of the study. diSSI, deep incisional surgical site infection; DSWI, deep sternal wound infection; INSEE, Institut National de la Statistique et des Etudes Economiques.</figcaption></figure>
<table><caption>**Table I**

Patient characteristics by occurrence of DSWI</caption><thead><tr><th></th><th>Overall,<br>(N = 14,850; 100%)</th><th>DSWI-free<br>(n = 14,310; 96%)</th><th>diSSI,<br>(n = 390; 2.6%)</th><th>Mediastinitis<br>(n = 152; 1%)</th><th>DSWI-free vs<br>diSSI P value</th><th>DSWI-free vs<br>mediastinitis<br>P value</th><th>diSSI vs<br>mediastinitis<br>P value</th></tr></thead><tbody><tr><td><strong>Demographics</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Male</td><td>10,279 (69)*</td><td>9,932 (69)</td><td>235 (60)</td><td>112 (74)</td><td>&lt;.001</td><td>.256</td><td>.003</td></tr><tr><td>Age, yr</td><td>66 [56–74]</td><td>66 [56–74]</td><td>68 [59–75]</td><td>70 [63–77]</td><td>&lt;.001</td><td>&lt;.001</td><td>.145</td></tr><tr><td>Obesity†</td><td>3,291 (22)</td><td>3,067 (22)</td><td>169 (44)</td><td>55 (36)</td><td>&lt;.001</td><td>&lt;.001</td><td>.098</td></tr><tr><td><strong>Medical history</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Smoking</td><td>5,322 (36)</td><td>5,125 (36)</td><td>130 (33)</td><td>67 (44)</td><td>.312</td><td>.035</td><td>.019</td></tr><tr><td>Arterial hypertension</td><td>8,696 (59)</td><td>8,278 (58)</td><td>304 (78)</td><td>114 (75)</td><td>&lt;.001</td><td>&lt;.001</td><td>.463</td></tr><tr><td>Diabetes mellitus</td><td>4,044 (27)</td><td>3,729 (26)</td><td>249 (64)</td><td>66 (43)</td><td>&lt;.001</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>Insulin-dependent</td><td>1,248 (8.4)</td><td>1,099 (7.7)</td><td>125 (32)</td><td>24 (16)</td><td>&lt;.001</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>Noninsulin-dependent diabetes</td><td>2,792 (19)</td><td>2,626 (18)</td><td>124 (32)</td><td>42 (28)</td><td>&lt;.001</td><td>.003</td><td>.345</td></tr><tr><td>Dyslipidemia</td><td>7,452 (50)</td><td>7,103 (50)</td><td>259 (66)</td><td>90 (59)</td><td>&lt;.001</td><td>.019</td><td>.116</td></tr><tr><td>PAD</td><td>1,804 (12)</td><td>1,661 (12)</td><td>103 (26)</td><td>40 (26)</td><td>&lt;.001</td><td>&lt;.001</td><td>.982</td></tr><tr><td>LVEF &lt;30%</td><td>683 (4.6)</td><td>644 (4.5)</td><td>22 (5.6)</td><td>17 (11)</td><td>.286</td><td>&lt;.001</td><td>.025</td></tr><tr><td>Ischemic heart disease</td><td>7,401 (50)</td><td>6,965 (49)</td><td>331 (85)</td><td>105 (69)</td><td>&lt;.001</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>ESRD</td><td>191 (1.3)</td><td>173 (1.2)</td><td>13 (3.3)</td><td>5 (3.3)</td><td>.001</td><td>.040</td><td>.980</td></tr><tr><td>COPD</td><td>1,216 (8.2)</td><td>1,142 (8.0)</td><td>45 (12)</td><td>29 (19)</td><td>.011</td><td>&lt;.001</td><td>.022</td></tr><tr><td><strong>Preoperative data</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Beta-blocker</td><td>8,700 (59)</td><td>8,316 (58)</td><td>290 (74)</td><td>94 (62)</td><td>&lt;.001</td><td>.355</td><td>.004</td></tr><tr><td>ACE inhibitor</td><td>7,264 (49)</td><td>6,943 (49)</td><td>236 (61)</td><td>85 (56)</td><td>&lt;.001</td><td>.070</td><td>.328</td></tr><tr><td>Statins</td><td>8,474 (57)</td><td>8,072 (57)</td><td>305 (78)</td><td>97 (64)</td><td>&lt;.001</td><td>.064</td><td>&lt;.001</td></tr><tr><td>Antiaggregant</td><td>8,510 (57)</td><td>8,086 (57)</td><td>315 (81)</td><td>109 (72)</td><td>&lt;.001</td><td>&lt;.001</td><td>.022</td></tr><tr><td>Surgical emergency</td><td>1,119 (7.5)</td><td>1,068 (7.5)</td><td>29 (7.4)</td><td>22 (14)</td><td>.983</td><td>.001</td><td>.012</td></tr><tr><td>Infective endocarditis†</td><td>761 (5.1)</td><td>753 (5.3)</td><td>4 (1.0)</td><td>4 (2.6)</td><td>&lt;.001</td><td>.147</td><td>.229</td></tr><tr><td>Previous cardiac surgery</td><td>1,358 (9.1)</td><td>1,326 (9.3)</td><td>19 (4.9)</td><td>13 (8.6)</td><td>.003</td><td>.762</td><td>.102</td></tr><tr><td>EuroSCORE 2</td><td>2 [1–5]</td><td>2 [1–5]</td><td>2 [1–4]</td><td>3 [2–6]</td><td>.643</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td><strong>Intraoperative data</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Vancomycin prophylaxis</td><td>1,774 (12)</td><td>1,720 (12)</td><td>33 (8.5)</td><td>21 (14)</td><td>.031</td><td>.495</td><td>.059</td></tr><tr><td>ACC time</td><td>47 [36–66]</td><td>47 [36–66]</td><td>40 [33–52]</td><td>47 [36–63]</td><td>&lt;.001</td><td>.920</td><td>&lt;.001</td></tr><tr><td>CPB time</td><td>59 [46–85]</td><td>60 [46–86]</td><td>49 [42–65]</td><td>59 [46–90]</td><td>&lt;.001</td><td>.690</td><td>&lt;.001</td></tr><tr><td>Isolated CABG</td><td>5,722 (39)</td><td>5,349 (37)</td><td>295 (76)</td><td>78 (51)</td><td>&lt;.001</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>BIMA bypass grafting</td><td>5,754 (39)</td><td>5,374 (38)</td><td>294 (75)</td><td>86 (57)</td><td>&lt;.001</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>CABG and valve surgery</td><td>1,383 (9.3)</td><td>1,322 (9.2)</td><td>34 (8.7)</td><td>27 (18)</td><td>.725</td><td>&lt;.001</td><td>.003</td></tr><tr><td>Isolated valve surgery</td><td>5,837 (39)</td><td>5,763 (40)</td><td>44 (11)</td><td>30 (20)</td><td>&lt;.001</td><td>&lt;.001</td><td>.010</td></tr><tr><td>Thoracic aortic surgery</td><td>1,519 (10)</td><td>1,497 (10)</td><td>15 (3.8)</td><td>7 (4.6)</td><td>&lt;.001</td><td>.019</td><td>.687</td></tr><tr><td>Cardiac transplantation</td><td>223 (1.5)</td><td>211 (1.5)</td><td>3 (0.8)</td><td>9 (5.9)</td><td>.251</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>Postbypass norepinephrine and dobutamine</td><td>1,229 (8.3)</td><td>1,168 (8.2)</td><td>48 (12)</td><td>13 (8.6)</td><td>.003</td><td>.862</td><td>.214</td></tr><tr><td><strong>Postoperative data</strong></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>MV duration, h</td><td>6 [5–10]</td><td>6 [5–10]</td><td>7 [5–12]</td><td>8 [6–26]</td><td>.016</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>Chest tube output at 24 h, mL</td><td>540 [380–750]</td><td>535 [380–740]</td><td>580 [428–790]</td><td>670 [480–1,000]</td><td>.004</td><td>&lt;.001</td><td>.003</td></tr><tr><td>ICU LOS, d</td><td>3 [2–5]</td><td>3 [2–5]</td><td>4 [2–8]</td><td>7 [3–23]</td><td>&lt;.001</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>Hospital LOS, d</td><td>11 [8–16]</td><td>11 [8–16]</td><td>30 [10–43]</td><td>38 [23–58]</td><td>&lt;.001</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>D-28 mortality</td><td>595 (4.0)</td><td>579 (4.0)</td><td>6 (1.5)</td><td>10 (6.6)</td><td>.012</td><td>.116</td><td>.004</td></tr><tr><td>D-90 mortality</td><td>809 (5.4)</td><td>757 (5.3)</td><td>25 (6.4)</td><td>27 (18)</td><td>.331</td><td>&lt;.001</td><td>&lt;.001</td></tr><tr><td>D-90 mortality in the landmark analysis†</td><td>214 (1.5)</td><td>178 (1.3)</td><td>19 (4.9)</td><td>17 (12)</td><td>&lt;.001</td><td>&lt;.001</td><td>.005</td></tr></tbody></table>

ACC, aortic crossclamp; ACE, angiotensin-converting enzyme; BIMA, bilateral internal mammary artery; CABG, coronary artery bypass graft; COPD, chronic obstructive pulmonary disease; CPB, cardiopulmonary bypass; diSSI, deep incisional surgical-site infection; DSWI, deep sternal wound infection; EuroSCORE, European System for Cardiac Operative Risk Evaluation; ICU, intensive care unit; LOS, length of stay; LVEF, left ventricular ejection fraction; MV, mechanical ventilation; PAD, peripheral arterial disease.

* Continuous variables are expressed as median and interquartile range (IQR) and compared using the Mann-Whitney U test. Categorical variables are expressed as n (%) and compared using the Fishes exact test.

† Obesity was defined as body mass index >30 kg/m². Infective endocarditis was defined as endocarditis treated with antibiotics at the time of surgery.

‡ D-90 mortality in the Landmark analysis: mortality at 90 d that excludes patients who died within the first 28 d.
<table><caption>**Table II**
Microbiological characteristics by type of DSWI</caption><thead><tr><th></th><th>All DSWI,<br>(N = 542; 100%)</th><th>diSSI,<br>(n = 390; 72%)</th><th>Mediastinitis<br>(n = 152; 28%)</th><th>P value</th></tr></thead><tbody><tr><td>Gram-negative bacteria</td><td>199 (37)</td><td>129 (33)</td><td>70 (46)</td><td>.005</td></tr><tr><td>Enterobacterales</td><td>177 (33)</td><td>114 (29)</td><td>63 (41)</td><td>.006</td></tr><tr><td>Escherichia coli</td><td>57 (11)</td><td>37 (9.5)</td><td>20 (13)</td><td>.211</td></tr><tr><td>Serratia spp.</td><td>17 (3.1)</td><td>11 (2.8)</td><td>6 (3.9)</td><td>.583</td></tr><tr><td>Enterobacter spp.</td><td>43 (7.9)</td><td>25 (6.4)</td><td>18 (12)</td><td>.036</td></tr><tr><td>Morganella spp.</td><td>14 (2.6)</td><td>10 (2.6)</td><td>4 (2.6)</td><td>&gt;.999</td></tr><tr><td>Citrobacter spp.</td><td>14 (2.6)</td><td>11 (2.8)</td><td>3 (2.0)</td><td>.767</td></tr><tr><td>Proteus spp.</td><td>21 (3.9)</td><td>17 (4.4)</td><td>4 (2.6)</td><td>.349</td></tr><tr><td>Klebsiella spp.</td><td>32 (5.9)</td><td>21 (5.4)</td><td>11 (7.2)</td><td>.411</td></tr><tr><td>Other Gram-negative bacteria</td><td>7 (1.3)</td><td>6 (1.5)</td><td>1 (0.7)</td><td>.679</td></tr><tr><td>Gram-positive bacteria</td><td>363 (67)</td><td>271 (69)</td><td>92 (61)</td><td>.046</td></tr><tr><td>Staphylococcus sp.</td><td>300 (55)</td><td>226 (58)</td><td>74 (49)</td><td>.051</td></tr><tr><td>S aureus</td><td>99 (18)</td><td>62 (16)</td><td>37 (24)</td><td>.022</td></tr><tr><td>MSSA</td><td>90 (17)</td><td>55 (14)</td><td>35 (23)</td><td>.012</td></tr><tr><td>MRSA</td><td>9 (1.7)</td><td>7 (1.8)</td><td>2 (1.3)</td><td>&gt;.999</td></tr><tr><td>CoNS</td><td>206 (38)</td><td>168 (43)</td><td>38 (25)</td><td>&lt;.001</td></tr><tr><td>Streptococcus spp</td><td>8 (1.5)</td><td>4 (1.0)</td><td>4 (2.6)</td><td>.229</td></tr><tr><td>Enterococcus spp</td><td>62 (11)</td><td>45 (12)</td><td>17 (11)</td><td>.907</td></tr><tr><td>Other Gram-positive bacteria</td><td>13 (2.4)</td><td>11 (2.8)</td><td>2 (1.3)</td><td>.532</td></tr><tr><td>Anaerobic bacteria</td><td>18 (3.3)</td><td>16 (4.1)</td><td>2 (1.3)</td><td>.104</td></tr><tr><td>Fungi</td><td>7 (1.3)</td><td>3 (0.8)</td><td>4 (2.6)</td><td>.101</td></tr><tr><td>Polymicrobial</td><td>102 (19)</td><td>76 (19)</td><td>26 (17)</td><td>.524</td></tr><tr><td>Associated bacteremia</td><td>133 (25)</td><td>63 (16)</td><td>70 (46)</td><td>&lt;.001</td></tr><tr><td>Enterobacterales</td><td>37 (6.8)</td><td>16 (4.1)</td><td>21 (14)</td><td>&lt;.001</td></tr><tr><td>Staphylococcus sp.</td><td>89 (16)</td><td>46 (12)</td><td>43 (28)</td><td>&lt;.001</td></tr><tr><td>S aureus</td><td>63 (12)</td><td>33 (8.5)</td><td>30 (20)</td><td>&lt;.001</td></tr><tr><td>CoNS</td><td>26 (4.8)</td><td>13 (3.3)</td><td>13 (8.6)</td><td>.011</td></tr><tr><td>Other Gram-positive bacteria</td><td>4 (0.7)</td><td>0 (0)</td><td>4 (2.6)</td><td>.006</td></tr></tbody></table>

CoNS, coagulase negative Staphylococci; diSSI, deep incisional surgical-site infection; DSWI, deep sternal wound infection; MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-sensitive Staphylococcus aureus.

diSSI (41% vs 29%, P = .006 and 24% vs 16%, P = .022, respectively), whereas coagulase-negative staphylococci were more common in diSSI (43% vs 25%, P < .001) (Table II).

Finally, associated bacteremia was present in 46% of mediastinitis cases compared with 16% of diSSI cases (P < .001). Staphylococci were the most common bacteria cultured from blood (67%), including S aureus, which represented 47% compared with 18% of all DSWIs (P < .001). Notably, 81% (30/37) of patients with S aureus mediastinitis were bacteriemic.

## Patient characteristics by 90-day mortality

Compared with 90-day survivors, patients who died were older, more likely to be female, and had greater rates of preoperative comorbidities, including insulin-dependent diabetes, PAD, ESRD, or heart failure (Table III). The underlying cardiac pathology was also different: surgical emergency, current infective endocarditis, and previous cardiac surgery were more common in deceased patients, whereas ischemic heart disease was less common. Regarding intraoperative data, deceased patients had longer CPB duration, more often underwent valve surgery, and more often required postbypass catecholamine support. Finally, deceased patients also had a more complicated postoperative course, with greater chest tube outputs, longer mechanical ventilation, catecholamine infusion, and more mediastinitis.

Deceased patients with mediastinitis and diSSI had similar risk factors for mortality and experienced a comparable time from onset of infection to death (15 days [5–29] vs 17 days [3–27], P = .467, Supplementary Figure S3). However, patients with diSSI who died were more likely to have ischemic heart disease and to have undergone bilateral internal mammary artery bypass grafting surgery (Supplementary Table S3).

## Relationship between mortality and DSWI subtype in the general population

Patients with mediastinitis had the worst survival compared with patients with diSSI and without DSWI (82% vs 94% vs 95%, respectively, both P < .001) (Figure 2). No significant difference was observed between patients without diSSI and without DSWI (P = .378). The lack of difference between patients without diSSI and without DSWI may be related to a better 28-day survival rate in patients with diSSI compared with patients without DSWI (98% vs 96%, respectively, P = .01). In multivariate analysis (Table IV), mediastinitis, in contrast to diSSI, was an independent risk factor for 90-day mortality (hazard ratio [HR], 2.16; 1.43–3.28; P < .001), together with age >56 years, insulin-dependent diabetes, PAD, history of neurovascular stroke, heart failure, ESRD, chronic obstructive pulmonary disease, cirrhosis, surgical emergency, active infective endocarditis, previous cardiac surgery, and CPB time (Table IV).

## Relationship between mortality and DSWI subtypes in the landmark analysis

Given the competitive mortality bias, a landmark analysis was performed excluding all patients who died in the first 28 days, the time required for 75% of diSSI to occur. In this analysis, patients with mediastinitis still had a lower 90-day survival rate than patients without diSSI and without DSWI (88% vs 95% and 99%, respectively, P = .004 and P < .001). Furthermore, in this analysis, patients with diSSI also had a decreased survival rate compared with patients without DSWI (P < .001) (Figure 3 and Supplementary Table S4). In multivariate analysis (Table IV), mediastinitis and diSSI were risk factors for 90-day mortality
<table><caption>**Table III**

Patient characteristics by 90-d mortality</caption><thead><tr><th></th><th>Overall<br>(N = 14,850, 100%)</th><th>Missing<br>value</th><th>Survivors<br>(n = 14,041, 95%)<br>2.6%)</th><th>Deaths at 90 d<br>(n = 809, 5.4%)</th><th>P value</th></tr></thead><tbody><tr><td><strong>Demographics</strong></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Male</td><td>10,279 (69)*</td><td>0</td><td>9,755 (69)</td><td>524 (65)</td><td>.005</td></tr><tr><td>Age, yr</td><td>66 [56, 74]</td><td></td><td>65 [56, 74]</td><td>70 [60, 78]</td><td>&lt;.001</td></tr><tr><td>Obesity</td><td>3,291 (22)</td><td>0</td><td>3,123 (22)</td><td>168 (22)</td><td>.593</td></tr><tr><td><strong>Medical history</strong></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Smoking</td><td>5,322 (36)</td><td>0</td><td>5,046 (36)</td><td>276 (34)</td><td>.293</td></tr><tr><td>Diabetes mellitus</td><td>4,044 (27)</td><td>0</td><td>3,817 (27)</td><td>227 (28)</td><td>.587</td></tr><tr><td>Insulin-dependent diabetes</td><td>1,248 (8.4)</td><td>0</td><td>1,155 (8.2)</td><td>93 (11)</td><td>.001</td></tr><tr><td>Noninsulin-dependent diabetes</td><td>2,792 (19)</td><td>0</td><td>2,659 (19)</td><td>133 (16)</td><td>.077</td></tr><tr><td>Dyslipidemia</td><td>7,452 (50)</td><td>0</td><td>7,116 (51)</td><td>336 (42)</td><td>&lt;.001</td></tr><tr><td>PAD</td><td>1,804 (12)</td><td>0</td><td>1,671 (12)</td><td>133 (16)</td><td>&lt;.001</td></tr><tr><td>Neurovascular stroke</td><td>1,339 (9.0)</td><td>0</td><td>1,221 (8.7)</td><td>118 (15)</td><td>&lt;.001</td></tr><tr><td>LVEF&lt;30%</td><td>683 (4.6)</td><td>0</td><td>590 (4.2)</td><td>93 (11)</td><td>&lt;.001</td></tr><tr><td>Ischemic heart disease</td><td>7,401 (50)</td><td>0</td><td>7,100 (51)</td><td>301 (37)</td><td>&lt;.001</td></tr><tr><td>ESRD</td><td>191 (1.3)</td><td>0</td><td>151 (1.1)</td><td>40 (4.9)</td><td>&lt;.001</td></tr><tr><td>COPD</td><td>1,216 (8.2)</td><td>0</td><td>1,100 (7.8)</td><td>116 (14)</td><td>&lt;.001</td></tr><tr><td>Cirrhosis</td><td>148 (1.0)</td><td>0</td><td>122 (0.9)</td><td>26 (3.2)</td><td>&lt;.001</td></tr><tr><td><strong>Preoperative data</strong></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Beta-blocker</td><td>8,700 (59)</td><td>0</td><td>8,327 (59)</td><td>373 (46)</td><td>&lt;.001</td></tr><tr><td>ACE inhibitor</td><td>7,264 (49)</td><td>0</td><td>6,950 (49)</td><td>314 (39)</td><td>&lt;.001</td></tr><tr><td>Statins</td><td>8,474 (57)</td><td>0</td><td>8,141 (58)</td><td>333 (42)</td><td>&lt;.001</td></tr><tr><td>Antiaggregant</td><td>8,510 (57)</td><td>0</td><td>8,156 (58)</td><td>354 (44)</td><td>&lt;.001</td></tr><tr><td>Surgical emergency</td><td>1,119 (7.5)</td><td>0</td><td>917 (6.5)</td><td>202 (25)</td><td>&lt;.001</td></tr><tr><td>Infective endocarditis†</td><td>761 (5.1)</td><td>0</td><td>614 (4.4)</td><td>147 (18)</td><td>&lt;.001</td></tr><tr><td>Previous cardiac surgery</td><td>1,358 (9.1)</td><td>0</td><td>1,150 (8.2)</td><td>208 (26)</td><td>&lt;.001</td></tr><tr><td>EuroSCORE 2</td><td>2.2 [1.1, 4.6]</td><td>55</td><td>2 [1, 4]</td><td>8 [3, 17]</td><td>&lt;.001</td></tr><tr><td><strong>Intraoperative data</strong></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Vancomycin prophylaxis</td><td>1,774 (12)</td><td>80</td><td>1,596 (11)</td><td>178 (22)</td><td>&lt;.001</td></tr><tr><td>ACC time</td><td>47 [36, 66]</td><td>466</td><td>46 [36, 65]</td><td>64 [44, 101]</td><td>&lt;.001</td></tr><tr><td>CPB time</td><td>59 [46, 85]</td><td>420</td><td>58 [46, 83]</td><td>94 [62, 152]</td><td>&lt;.001</td></tr><tr><td>Isolated CABG</td><td>5,715 (39)</td><td>0</td><td>5,561 (40)</td><td>154 (19)</td><td>&lt;.001</td></tr><tr><td>BIMA bypass grafting</td><td>5,754 (39)</td><td>0</td><td>5,576 (40)</td><td>178 (22)</td><td>&lt;.001</td></tr><tr><td>CABG and valve surgery</td><td>1,380 (9.3)</td><td>0</td><td>1,265 (9.1)</td><td>115 (14)</td><td>&lt;.001</td></tr><tr><td>Isolated valve surgery</td><td>5,794 (39)</td><td>0</td><td>5,449 (39)</td><td>345 (43)</td><td>.024</td></tr><tr><td>Thoracic aortic surgery</td><td>1,508 (10)</td><td>0</td><td>1,367 (9.8)</td><td>141 (18)</td><td>&lt;.001</td></tr><tr><td>Cardiac transplantation</td><td>223 (1.5)</td><td>0</td><td>190 (1.4)</td><td>33 (4.1)</td><td>&lt;.001</td></tr><tr><td>Postbypass norepinephrine and dobutamine</td><td>1,229 (8.3)</td><td>0</td><td>1,048 (7.5)</td><td>181 (22)</td><td>&lt;.001</td></tr><tr><td><strong>Postoperative data</strong></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>MV duration, h</td><td>6 [5, 10]</td><td>973</td><td>6 [5, 9]</td><td>44 [9, 196]</td><td>&lt;.001</td></tr><tr><td>Chest tube output at 24 h, mL</td><td>540 [380, 750]</td><td>3,874</td><td>535 [380, 740]</td><td>660 [440, 1,100]</td><td>&lt;.001</td></tr><tr><td>Postoperative surgery</td><td>905 (6.1)</td><td>0</td><td>833 (5.9)</td><td>72 (8.9)</td><td>&lt;.001</td></tr><tr><td>diSSI</td><td>389 (2.6)</td><td>0</td><td>364 (2.6)</td><td>25 (3.1)</td><td>.389</td></tr><tr><td>Mediastinitis</td><td>151 (1.0)</td><td>0</td><td>125 (0.9)</td><td>26 (3.2)</td><td>&lt;.001</td></tr><tr><td>ICU LOS, d</td><td>3.0 [2.0, 5.0]</td><td>814</td><td>3 [2, 5]</td><td>8 [3, 20]</td><td>&lt;.001</td></tr><tr><td>Hospital LOS, d</td><td>11 [8, 16]</td><td>281</td><td>11 [8, 16]</td><td>12 [5, 25]</td><td>.533</td></tr></tbody></table>

ACC, aortic crossclamp; ACE, angiotensin-converting enzyme; BIMA, bilateral internal mammary artery; CABG, coronary artery bypass graft; COPD, chronic obstructive pulmonary disease; CPB, cardiopulmonary bypass; diSSI, deep incisional surgical site infection; DSWI, deep sternal wound infection; ESRD, end-stage renal disease; EuroSCORE, European System for Cardiac Operative Risk Evaluation; ICU, intensive care unit; LOS, length of stay; LVEF, left ventricular ejection fraction; MV, mechanical ventilation; PAD, peripheral arterial disease.

* Continuous variables are expressed as median and interquartile range [IQR] and compared using the Mann-Whitney U test. Categorical variables are expressed as n (%) and compared using the Fisher exact test.

† Infective endocarditis was defined as endocarditis treated with antibiotics at the time of surgery.

(HR, 6.57; 3.90–11.06, and HR, 4.20; 2.52–6.99, respectively, both P < .001).

## Discussion

### Summary of main results

In our retrospective single-center study, we observed that mediastinitis and diSSI were associated with different pathogens and had very different prognoses, whereas many studies have grouped these 2 entities under the terms DSWI¹⁸,²⁵,²⁶ or mediastinitis.¹¹⁻¹³ Mediastinitis occurred earlier than diSSI and was associated with virulent pathogens (*S aureus*, Enterobacterales) and bacteraemia, whereas almost 50% of diSSI were attributable to

coagulase-negative staphylococci. In addition, mediastinitis was associated with a worse outcome than diSSI and was an independent predictor of 90-day mortality. However, in our landmark analysis, which excluded patients who died within 28 days, diSSI was also an independent risk factor for 90-day mortality.

### Significance of the study

Our study therefore supports our hypothesis that diSSI is a distinct infectious entity from mediastinitis. In clinical research, these 2 entities should be carefully grouped under the term DSWI. Furthermore, diSSI should not be overlooked because of its association with 90-day mortality. As the median time from onset of diSSI to mortality is 15 days—and exceeded 29 days in 25% of
<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /><figcaption>**Figure 2.** 90-day survival rate according to DSWI occurrence. (A) DSWI considered as a single group. (B) DSWI subdivided into DiSSI and Mediastinitis. *diSSI*, deep incisional surgical-site infection; *DSWI*, deep sternal wound infection.</figcaption></figure>

<table><caption>**Table IV**
Cox analysis for 90-d mortality</caption><thead><tr><th rowspan="2">Predictors</th><th colspan="3">Cox analysis in the overall population</th><th colspan="3">Cox analysis in the landmark analysis</th></tr><tr><th>Estimates</th><th>CI</th><th>P value</th><th>Estimates</th><th>CI</th><th>P value</th></tr></thead><tbody><tr><td>Age group, yr</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>First quartile &lt;56 yr</td><td>ref</td><td>ref</td><td>—</td><td>ref</td><td>ref</td><td>—</td></tr><tr><td>Second quartile [56, 65] yr</td><td>1.50</td><td>1.19–1.90</td><td>.001*</td><td>2.50</td><td>1.55–4.03</td><td>&lt;.001*</td></tr><tr><td>Third quartile [66–74] yr</td><td>2.05</td><td>1.63–2.58</td><td>&lt;.001*</td><td>2.83</td><td>1.76–4.57</td><td>&lt;.001*</td></tr><tr><td>Fourth quartile [74–94] yr</td><td>4.01</td><td>3.22–5.01</td><td>&lt;.001*</td><td>5.51</td><td>3.46–8.77</td><td>&lt;.001*</td></tr><tr><td>Insulin-dependent diabetes</td><td>1.57</td><td>1.24–1.99</td><td>&lt;.001*</td><td>1.77</td><td>1.17–2.67</td><td>.007*</td></tr><tr><td>Peripheral arterial insufficiency</td><td>1.38</td><td>1.12–1.70</td><td>.002*</td><td>—</td><td>—</td><td>—</td></tr><tr><td>History of neurovascular stroke</td><td>1.23</td><td>1.00–1.51</td><td>.047*</td><td>—</td><td>—</td><td>—</td></tr><tr><td>LVEF &lt;30%</td><td>2.50</td><td>1.95–3.19</td><td>&lt;.001*</td><td>1.94</td><td>1.66–2.27</td><td>&lt;.001*</td></tr><tr><td>ESRD</td><td>2.66</td><td>1.88–3.76</td><td>&lt;.001*</td><td>2.03</td><td>1.55–2.66</td><td>&lt;.001*</td></tr><tr><td>COPB</td><td>1.68</td><td>1.37–2.07</td><td>&lt;.001*</td><td>1.36</td><td>1.21–1.53</td><td>&lt;.001*</td></tr><tr><td>Cirrhosis</td><td>2.19</td><td>1.42–3.38</td><td>&lt;.001*</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Beta-blocker</td><td>—</td><td>—</td><td>—</td><td>1.79</td><td>1.31–2.46</td><td>&lt;.001*</td></tr><tr><td>ACE inhibitor</td><td>0.79</td><td>0.67–0.92</td><td>.003*</td><td>1.24</td><td>1.07–1.45</td><td>.005*</td></tr><tr><td>Statins</td><td>0.77</td><td>0.64–0.93</td><td>.007*</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Antiaggregant</td><td>0.84</td><td>0.69–1.02</td><td>.075</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Surgical emergency</td><td>2.24</td><td>1.85–2.72</td><td>&lt;.001*</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Aortic stenosis</td><td>0.68</td><td>0.55–0.85</td><td>.001*</td><td>0.67</td><td>0.46–0.97</td><td>.035*</td></tr><tr><td>Infective endocarditis</td><td>1.86</td><td>1.49–2.33</td><td>&lt;.001*</td><td>2.09</td><td>1.37–3.19</td><td>.001*</td></tr><tr><td>Previous cardiac surgery</td><td>1.43</td><td>1.17–1.76</td><td>.001*</td><td>1.75</td><td>1.20–2.57</td><td>.004*</td></tr><tr><td>CPB time (/10 min)</td><td>1.11</td><td>1.10–1.12</td><td>&lt;.001*</td><td>1.11</td><td>1.08–1.14</td><td>&lt;.001*</td></tr><tr><td>Valvular surgery</td><td>1.23</td><td>0.99–1.53</td><td>.061</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Thoracic aortic surgery</td><td>—</td><td>—</td><td>—</td><td>0.44</td><td>0.26–0.74</td><td>.002*</td></tr><tr><td>CABG</td><td>1.22</td><td>0.99–1.50</td><td>.068</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Post-bypass norepinephrine and dobutamine</td><td>—</td><td>—</td><td>—</td><td>1.38</td><td>0.94–2.02</td><td>.101</td></tr><tr><td>DSWI subtypes</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>DSWI-free</td><td>ref</td><td>ref</td><td>—</td><td>ref</td><td>ref</td><td>—</td></tr><tr><td>DiSSI</td><td>1.47</td><td>0.97–2.22</td><td>.072</td><td>4.20</td><td>2.52–6.99</td><td>&lt;.001*</td></tr><tr><td>Mediastinitis</td><td>2.16</td><td>1.43–3.28</td><td>&lt;.001*</td><td>6.57</td><td>3.90–11.06</td><td>&lt;.001*</td></tr><tr><td>Number of patients</td><td>14,902</td><td></td><td></td><td>13,545</td><td></td><td></td></tr><tr><td>R<sup>2</sup>Tjur</td><td>0.171</td><td></td><td></td><td>0.128</td><td></td><td></td></tr></tbody></table>

CABG, coronary artery bypass graft; CI, confidence interval; COPD, chronic obstructive pulmonary disease; CPB, cardiopulmonary bypass; diSSI, deep incisional surgical site infection; DSWI, deep sternal wound infection; ESRD, end-stage renal disease; LOS, length of stay; LVEF, left ventricular ejection fraction.

* Statistically significant.
<figure><img src="image_5.png" /><figcaption>**Figure 3.** 90-day survival rate according to DSWI occurrence in the landmark analysis. diSSI, deep incisional surgical-site infection; DSWI, deep sternal wound infection.</figcaption></figure>

patients with diSSI who died—our results suggest that patients with diSSI should be closely monitored for at least 1 month after presentation, as this population remains at high risk of death.

## Surgical management of DSWI

Sternal wound infection after cardiac surgery has been described since 1957.²⁷ Initial management was determined by antimicrobial treatment and reoperation for surgical debridement followed by open wound drainage²⁸ and antibiotic irrigation.²⁹,³⁰ In 1989, Durandy et al²³ presented a technique of surgical debridement combined with chest tube suction drainage using multiperforated rigid catheters to drain all infected areas. Later, in 2003, VAC therapy after surgical debridement was proposed, with positive long-term results reported.¹¹,³¹,³² However, these improvements in surgical management were minimally associated with a reduction in mortality rates, which remained at approximately 10–25%³³,³⁴ and are consistent with our findings. During the study period, surgeons at our center used these 2 strategies with surgical debridement and primary chest tube drainage and/or VAC therapy in cases of mediastinitis with extensive tissue or sternal necrosis.

## Heterogeneity of DSWI definitions

The different definitions of DSWI may explain the high variability in mortality rates reported in the literature. Several articles used the term mediastinitis, even though they included patients without retrosternal space infection,¹¹⁻¹³ whereas others referred only to mediastinal space infection.³¹,³² To the best of our knowledge, no other study has examined the mortality rates of DSWI according to the CDC definition. Several articles used the CDC classification ¹,³⁵ to present risk factors for diSSI and mediastinitis, but diSSI and mediastinitis were combined into a single entity for mortality analysis. In the study by Gelijns et al¹ on the prognosis of all types of serious infections after cardiac surgery, a 65-day mortality rate of 5% was found in infected patients. Ridderstolpe et al³⁵ pooled mediastinitis and diSSI and found a 1-year mortality rate of 7.2% for DSWI. To promote homogeneity between studies, 2

classifications on the basis of depth of infection have been proposed, but with limited success.³⁶,³⁷ In the study by Jones et al,³⁶ in which a 6-stage classification was proposed, a mortality rate of 9% at 30 days was observed for mediastinitis, whereas the mortality rate was zero for patients with suprasternal infection only. These results are similar to our observations, although this study did not use a time limit between surgery and the onset of infection.

## Variability by time of infection

In contrast to the CDC classification, several studies did not use a time frame between surgery and DSWI.¹²,¹³,²⁵,³²⁻³⁵ However, time to infection appears to be an important criterion for severity. In 1996, El Oakley and Wright³⁸ proposed a classification on the basis of the delay in onset of DSWI and the presence of risk factors: type I infections occurring within 2 weeks of surgery, type II infections occurring between 2 and 6 weeks after surgery, and type III infections occurring more than 6 weeks after surgery. In 2011, Dessap et al¹³ used this classification to highlight a significant difference in mortality according to delay after surgery. Early DSWI (type I) had a 1-year mortality rate of 35% compared with 19% for late DSWI (mix of type II and type III). These results are in line with ours, as in our study mediastinitis had a median onset of 14 days compared with 19 days for diSSI.

## Variability by time of death

Finally, the last source of heterogeneity that limits comparison between studies is the variability in the time of reported mortality. This is particularly evident when mortality is reported without any precision³⁹ or when ICU¹¹,³¹ and hospital mortality³² are reported without a defined time cut-off. Other studies report mortality at different fixed intervals, such as 30-day,¹²,¹³,¹⁷,³⁶ 90-day,²⁵,⁴⁰ or 1-year mortality.¹³,¹⁷

## Pathophysiologic hypotheses to explain the differences in mortality between mediastinitis and diSSI

Two other studies have suggested that diSSI have a better prognosis than mediastinitis.¹³,³⁶ Three hypotheses may explain this finding. First, mediastinitis is associated with more virulent pathogens, including *S aureus* and *Enterobacterales*. In line with these observations, mediastinitis was associated with more bacteraemia in our study. Second, the patients' conditions differ between these 2 entities. In our study, patients with mediastinitis had more comorbidities, such as older age, complex surgery such as heart transplantation, previous cardiac surgery, and urgent surgery. Therefore, they had a greater European System for Cardiac Operative Risk Evaluation 2 and a longer bypass time. Third, mediastinal infection may favor several specific complications such as bleeding, prosthetic valve endocarditis and heart failure.¹³,³¹

## Strengths and limitations

Finally, our study has several limitations. First, it was a single-center study with a specific antibiotic prophylaxis protocol. However, the incidence of DSWI in our study is consistent with the range reported in previously published studies.³⁵,³⁹,⁴¹,⁴² Unfortunately, the effect of the dose of antibiotic prophylaxis could not be studied because this information was not recorded. In addition, the effect of the type of antibiotic prophylaxis was not analyzed, as this has already been investigated in a previous article. That study found that the combination of vancomycin and gentamicin was associated with an increased risk of diSSI in CABG surgery.⁴³
Second, our cohort spans 16 years, which may introduce a temporal bias. However, in our center, the definition of DSWI remained consistent over time, its incidence appeared to be homogeneous, and the same surgical approach was employed throughout the study period.

Third, in our study we considered the date of surgery to be the date of onset of DSWI. This approximation is supported by the fact that our center has implemented a therapeutic strategy to promptly evaluate patients presenting with symptoms suggestive of DSWI. Consequently, the time between surgery and symptom onset is typically less than 48 hours in our center.

Lastly, there is a potential limitation related to changes in antimicrobial treatment, with the introduction of new antibiotics such as cefepime and daptomycin. However, this bias is likely to be minimal, as both mediastinitis and diSSI appear to benefit equally from these newer antibiotics.

In conclusion, in our large cohort of patients, diSSI and mediastinitis showed different incidence, bacterial characteristics, and prognosis, with mediastinitis being particularly associated with a poor prognosis. Therefore, diSSI and mediastinitis should be carefully regrouped under the entity of DSWI. Furthermore, when considering the risk of competing mortality, diSSI also emerged as an independent factor for 90-day mortality. Our findings suggest that aggressive therapeutic strategies are required to effectively manage both infections. Therefore, further studies are warranted to assess whether increased and prolonged surveillance or alternative therapeutic approaches can reduce mortality, particularly in high-risk patients.

## Funding/Support

The authors declare that no external funding was received for this study.

## Conflict of Interest/Disclosure

The authors declare no conflicts of interest in association with the present study.

## Data availability statement

Data available on request.

## Supplementary Materials

Supplementary material associated with this article can be found, in the online version, at [https://doi.org/10.1016/j.surg.2025.109255](https://doi.org/10.1016/j.surg.2025.109255).

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