• Users Online: 83
  • Print this page
  • Email this page

 Table of Contents  
Year : 2022  |  Volume : 1  |  Issue : 2  |  Page : 62-66

A counterculture movement: Characterizing the prognostic utility of obtaining wound cultures for incisional surgical site infections

1 Department of Surgery, Western Michigan University Homer Stryker MD School of Medicine, Michigan, USA
2 Department of Surgery, Western Michigan University Homer Stryker MD School of Medicine, Michigan; Department of Plastic and Maxillofacial Surgery, University of Virginia, Virginia, USA

Date of Submission24-Dec-2022
Date of Decision04-Jan-2023
Date of Acceptance06-Jan-2023
Date of Web Publication15-Feb-2023

Correspondence Address:
Robert G Sawyer
1000 Oakland Drive Kalamazoo, MI 49008
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/wjsi.wjsi_16_22

Rights and Permissions

Background: Surgical site infections (SSIs) account for 15% of all healthcare-associated infections, yet, the utility of cultures remains controversial. We hypothesized that obtaining cultures would not affect outcomes from incisional SSI.
Methods: All incisional SSI from general surgery patients treated as inpatients at a single institution between 1997 and 2017 were included. Patient variables were compared by Student's t-test and Chi-square analysis. Predictors of in-hospital mortality, duration of therapy, and hospital length of stay, including the acquisition of wound cultures, were determined by multivariate (MV) logistic regression analysis.
Results: In total, 2054 SSIs were identified: 1077 (52.4%) with cultures and 977 (47.6%) without. Obtaining cultures were associated with higher severity of illness/Acute Physiology and Chronic Health Evaluation (APACHE-II) score (12.4 ± 0.2 vs. 8.8 ± 0.2; P < 0.0001) and multiple comorbidities, as well as a longer antimicrobial course (13.8 ± 0.3 days vs. 9.1 ± 0.2 days; P < 0.0001), length of stay (17.4 ± 0.8 days vs. 9.7 ± 0.5 days; P < 0.0001), and mortality (8.6% vs. 4.2%; P < 0.0001). Factors independently predicting mortality included age in years (odds ratio [OR] 1.03 [95% confidence interval [CI] 1.02–1.05], P < 0.0001), APACHE-II (OR 1.17 [95% CI 1.14–1.21], P < 0.0001), days from operation to diagnosis (OR 1.01 [95% CI 1.01–1.02], P < 0.0001), and diagnosis of SSI after discharge (OR 4.98 [95% CI 2.18–11.35], P < 0.0001). Obtaining cultures (OR 1.04 [95% CI 0.65–1.64], P = 0.88) were not associated with mortality. Acquisition of cultures was independently associated with longer antimicrobial duration and length of stay.
Conclusion: Routinely obtaining cultures from infected surgical incisions does not change the overall outcome and should be reserved for special circumstances, such as critical illness.

Keywords: Culture, surgical site infection, wound

How to cite this article:
McLaren G, Chou J, Sawyer RG. A counterculture movement: Characterizing the prognostic utility of obtaining wound cultures for incisional surgical site infections. World J Surg Infect 2022;1:62-6

How to cite this URL:
McLaren G, Chou J, Sawyer RG. A counterculture movement: Characterizing the prognostic utility of obtaining wound cultures for incisional surgical site infections. World J Surg Infect [serial online] 2022 [cited 2023 Mar 30];1:62-6. Available from: https://www.worldsurginfect.com/text.asp?2022/1/2/62/369707

  Introduction Top

Surgical site infections (SSIs) make up a significant portion of healthcare-associated infections. Previous studies report that 14%–38% of all nosocomial infections are SSIs.[1],[2],[3],[4],[5] It is also estimated that at least 1%–2% of all operations are complicated by an SSI.[2] The most commonly applied definition of an SSI is an infection of the surgical site (including incisional and organ space) within 30 days of the procedure or up to 1 year if an implant is present.[1] The most likely causative organisms of SSI are native flora of the patient's skin including aerobic Gram-positive cocci such as Staphylococcus species,[6] but are often polymicrobial.[7] Infections involving flora from colonized organs such as the gastrointestinal tract are also important. After a skin incision interrupts epithelial integrity, the subcutaneous tissue is then exposed to pathogens. Infection occurs due to an imbalance between the number and virulence of bacteria and host defense mechanisms.[8] A wound infection is suspected in the setting of erythematous and edematous skin that may be accompanied by a fever, purulent discharge, malodor, or other signs.[9]

Conventional treatment of SSIs may involve obtaining a culture of the wound, antimicrobial therapy, and local wound care. However, clinical signs of inflammation are not objective or definitive in diagnosing surgical incision wound infection. Wound cultures may be sensitive but not accurate for distinguishing between colonization and acute infection. In addition, it remains poorly understood whether incisions suspected of being infected should be sampled and whether this would yield meaningful data that alters clinical treatment.

The major argument against culturing incisions is that when wounds are opened and appropriate wound care is applied, the causative pathogens are predictable and antimicrobials can be chosen without culture data. In fact, culture results often return after a very brief course of antimicrobials (0 to 72 h) have been completed. We hypothesized that the acquisition of wound cultures does not improve outcomes in general surgery patients diagnosed with SSI.

  Methods Top

A prospectively collected dataset was analyzed to identify all incisional SSIs at a single institution for a 20-year period between 1997 and 2017. Subjects included those managed on the general surgery services, including those diagnosed during the hospitalization for their index operation or readmitted after discharge for the management of SSI diagnosed as an outpatient. Patients with SSIs treated exclusively on an outpatient basis were not included because of the difficulty identifying these patients as well as unreliable treatment data. Superficial and deep incisional SSIs were included, but organ space infections were excluded due to different source control and antimicrobial treatment paradigms. All SSIs identified were then divided into two groups: those with cultures and those without cultures.

Demographics and outcomes were compared by univariate analysis using Student's t-test and Chi-square analysis. Results are presented either as mean ± standard error of the mean or as a percentage of the total referent group. Independent predictors of mortality, prolonged hospital length of stay (>7 days after diagnosis of SSI), and prolonged antimicrobial treatment course (>10 days of therapy) were determined by multivariate (MV) logistic regression analysis, with the variable of wound culture added. Hosmer and Lemeshow testing was used for calibration and the receiver operating characteristic (ROC) curve C-statistic was calculated to evaluate precision.

  Results Top

In total, 2054 SSIs were identified: 977 (47.6%) with cultures and 1077 (52.4%) without. Demographics are shown in [Table 1]. Notably, obtaining cultures was associated with a higher severity of illness/APACHE-II score, black race, and multiple comorbidities. Obtaining cultures was less common among subjects with malignancy.
Table 1: Baseline demographics and clinical characteristics*

Click here to view

The most common pathogens isolated were Staphylococcus aureus (158, 16.2%) including 82 methicillin-resistant isolates, Enterococcus faecalis (122, 12.5%), Candida albicans (109, 11.2%),  Escherichia More Details coli (106, 10.8%), Pseudomonas aeruginosa (102, 10.4%), Enterococcus faecium (80, 8.2%) including 56 vancomycin-resistant isolates, and Streptococcus species (60, 6.1%). Overall, Gram-positive isolates were slightly more common than Gram-negative isolates: 562 versus 516 subjects.

By univariate analysis, obtaining cultures was associated with the rate of antimicrobial use, longer antimicrobial course, greater length of stay after diagnosis, and increased crude mortality [Table 2]. A greater percentage of patients who had cultures had a duration of antimicrobial therapy of more than 10 days (594/977 = 60.8% vs. 366/1077 = 34.0%, P < 0.0001) and a hospital length of stay after diagnosis of more than 7 days (542/977 = 55.5% vs. 346/1077 = 32.1%, P < 0.0001)
Table 2: Outcomes*

Click here to view

Three logistic regression models were constructed to evaluate factors independently associated with all-cause, in-hospital mortality, prolonged duration of antimicrobial therapy of more than 10 days, and prolonged hospital length of stay of more than 7 days after diagnosis of SSI. Variables included were age in years, sex, APACHE-II score at the time of diagnosis of SSI, days from index operation to the diagnosis of SSI, the presence of chronic immunosuppression (including solid organ transplantation), diagnosis after discharge from hospitalization including the index operation, and availability of wound cultures. Variables associated with mortality are given in [Table 3] and included increasing age, APACHE-II score, days from operation to diagnosis, and initial diagnosis of SSI after discharge from index operation; the acquisition of wound cultures was not independently associated with mortality (OR 1.04, 95% CI 0.65–1.64, P = 0.88).
Table 3: Multivariate analysis for in-hospital mortality, all surgical site infection

Click here to view

Prolonged antimicrobial duration was independently associated with younger age (OR 0.98, 95% CI 0.98–0.99, P < 0.001), APACHE-II score (OR 1.04, 95% CI 1.02–1.06, P < 0.001), and acquisition of wound cultures (OR 2.55, 95% CI 2.09–3.11, P < 0.001). Calibration was acceptable with a Hosmer–Lemeshow test P of 0.68 and precision was fair with a ROC area under the curve C-statistic of 0.67. Prolonged length of hospital stay after diagnosis of SSI was independently associated with younger age (OR 0.99, 95% CI 0.98–0.99, P < 0.012), APACHE-II score (OR 1.15, 95% CI 1.12–1.17, P < 0.001), diagnosis after discharge after index procedure (OR 4.15, 95% CI 3.23–5.33, P < 0.001), and acquisition of wound cultures (OR 2.23, 95% CI 1.78–2.79, P < 0.001). Model performance characteristics included Hosmer–Lemeshow test P = 0.06 and C-statistic = 0.80.

  Discussion Top

This study presents an analysis of postoperative SSIs based upon wound culture and its effect on surgical outcomes. A trend toward wound sampling was observed with patients that were more critically ill as indicated by APACHE-II scores, multiple medical comorbidities, prior blood transfusion, and management in the intensive care unit. These relationships are certainly related to the association between the acquisition of cultures and higher in-hospital mortality, longer antimicrobial duration, and longer hospital stay. Bernard et al. queried the National Surgical Quality Improvement Program, a national database of mixed nontrauma, noncardiothoracic surgical outcomes, and found that transfusion of even 1 U-packed red blood cell was associated with increased postoperative morbidity including SSI and sepsis.[10] Transfusion of blood products can be an essential intervention in surgical patients but also induces an inflammatory response that can alter immunity and increase the risk of infection.[11],[12] Transfusion of blood products alone has been associated with not only increased morbidity but increased length of hospital stay.[13]

Previous studies in other surgical disciplines have found no clinical benefit to obtaining postoperative surgical site cultures.[14] Part of the difficulty lies in the fact that there is no consensus method of sampling and analyzing surgical wounds.[15],[16],[17],[18],[19] Upon MV analysis of our institution's data, obtaining SSI cultures did not have a significant effect on patient mortality, and was independently associated with a longer treatment course and hospital stay. These data suggest that obtaining a wound culture may not improve clinical outcomes under normal circumstances. One potential explanation is that local wound management in the care of SSI, including opening the wound and wound care, may minimize the role of antimicrobials other than in the presence of invasive fascial infection.

Our study can be seen in the context of several limitations. First, as an observational study without randomization, it is not surprising that the patients with cultures had several characteristics suggesting they were more ill than patients without cultures (APACHE-II score, immunosuppression status, etc.). Second, at least half of SSI are diagnosed as outpatients, and since we only included patients treated as inpatients, we cannot comment on those managed outside the hospital. Third, in-hospital mortality is a crude outcome measure, and the role of SSI in the deaths of those subjects was not assessed and may have been minor. Fourth, even within one institution, there may be surgeon-to-surgeon variability in terms of which wounds get sampled and the sampling technique in the context of dressings, the incision itself, and timing with antimicrobial therapy.

  Conclusion Top

We found no evidence that the availability of cultures altered mortality or other relevant surgical outcomes following the treatment of SSIs. Although we attempted to control for variables affecting outcomes, only a randomized study of culture versus no culture will clearly answer the question of culture utility. Our findings suggest cultures are generally not necessary when treating SSI. Routinely obtaining cultures from infected surgical incisions seems unnecessary and should be reserved for special circumstances, such as significant prior antimicrobial exposure, unusually invasive infection, or critical illness.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Owens CD, Stoessel K. Surgical site infections: Epidemiology, microbiology and prevention. J Hosp Infect 2008;70 Suppl 2:3-10.  Back to cited text no. 1
de Lissovoy G, Fraeman K, Hutchins V, Murphy D, Song D, Vaughn BB. Surgical site infection: Incidence and impact on hospital utilization and treatment costs. Am J Infect Control 2009;37:387-97.  Back to cited text no. 2
Smyth ET, Emmerson AM. Surgical site infection surveillance. J Hosp Infect 2000;45:173-84.  Back to cited text no. 3
Malone DL, Genuit T, Tracy JK, Gannon C, Napolitano LM. Surgical site infections: Reanalysis of risk factors. J Surg Res 2002;103:89-95.  Back to cited text no. 4
Leaper D, Burman-Roy S, Palanca A, Cullen K, Worster D, Gautam-Aitken E, et al. Prevention and treatment of surgical site infection: Summary of NICE guidance. BMJ 2008;337:a1924.  Back to cited text no. 5
Altemeier WA, Culbertson WR, Hummel RP. Surgical considerations of endogenous infections – Sources, types, and methods of control. Surg Clin North Am 1968;48:227-40.  Back to cited text no. 6
Bowler PG, Duerden BI, Armstrong DG. Wound microbiology and associated approaches to wound management. Clin Microbiol Rev 2001;14:244-69.  Back to cited text no. 7
Pollock AV. Surgical wound sepsis. Lancet 1979;1:1283-6.  Back to cited text no. 8
Nagle SM, Stevens KA, Wilbraham SC. Wound Assessment. Treasure Island (FL): StatPearls Publishing; 2022. Available from: https://www.ncbi.nlm.nih.gov/books/NBK482198/?report=classic. [Last accessed on 2023 Jan 25].  Back to cited text no. 9
Bernard AC, Davenport DL, Chang PK, Vaughan TB, Zwischenberger JB. Intraoperative transfusion of 1 U to 2 U packed red blood cells is associated with increased 30-day mortality, surgical-site infection, pneumonia, and sepsis in general surgery patients. J Am Coll Surg 2009;208:931-7, 937.e1-2.  Back to cited text no. 10
Aubron C, Flint AW, Bailey M, Pilcher D, Cheng AC, Hegarty C, et al. Is platelet transfusion associated with hospital-acquired infections in critically ill patients? Crit Care 2017;21:2.  Back to cited text no. 11
Vamvakas EC. Platelet transfusion and postoperative infection in cardiac surgery. Transfusion 2007;47:352-4.  Back to cited text no. 12
Scott BH, Seifert FC, Grimson R. Blood transfusion is associated with increased resource utilisation, morbidity and mortality in cardiac surgery. Ann Card Anaesth 2008;11:15-9.  Back to cited text no. 13
[PUBMED]  [Full text]  
Kemp MA, Martina K, Collins CL, Salmon LJ, Gooden BR, Lyons MC. The use of routine postoperative microscopy and culture screening following elective hip and knee arthroplasty: An unnecessary cost with no effect on clinical management? J Arthroplasty 2017;32:1128-31.  Back to cited text no. 14
Levine NS, Lindberg RB, Mason AD Jr., Pruitt BA Jr. The quantitative swab culture and smear: A quick, simple method for determining the number of viable aerobic bacteria on open wounds. J Trauma 1976;16:89-94.  Back to cited text no. 15
Mutluoglu M, Uzun G, Turhan V, Gorenek L, Ay H, Lipsky BA. How reliable are cultures of specimens from superficial swabs compared with those of deep tissue in patients with diabetic foot ulcers? J Diabetes Complications 2012;26:225-9.  Back to cited text no. 16
Sapico FL, Ginunas VJ, Thornhill-Joynes M, Canawati HN, Capen DA, Klein NE, et al. Quantitative microbiology of pressure sores in different stages of healing. Diagn Microbiol Infect Dis 1986;5:31-8.  Back to cited text no. 17
Bonham PA. Swab cultures for diagnosing wound infections: A literature review and clinical guideline. J Wound Ostomy Continence Nurs 2009;36:389-95.  Back to cited text no. 18
Uppal SK, Ram S, Kwatra B, Garg S, Gupta R. Comparative evaluation of surface swab and quantitative full thickness wound biopsy culture in burn patients. Burns 2007;33:460-3.  Back to cited text no. 19


  [Table 1], [Table 2], [Table 3]


Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
Access Statistics
Email Alert *
Add to My List *
* Registration required (free)

  In this article
Article Tables

 Article Access Statistics
    PDF Downloaded29    
    Comments [Add]    

Recommend this journal