Background: Postoperative spinal wound infections are relatively common and are often associated with increased morbidity and poor long-term patient outcomes. The purposes of this study were to identify the common bacterial flora on the skin overlying the lumbar spine and evaluate the efficacy of readily available skin-preparation solutions in the elimination of bacterial pathogens from the surgical site following skin preparation.
Methods: A prospective randomized study was undertaken to evaluate 100 consecutive patients undergoing elective lumbar spine surgery. At the time of surgery, the patients were randomized to be treated with one of two widely used, and Food and Drug Administration (FDA)-approved, surgical skin-preparation solutions: ChloraPrep (2% chlorhexidine gluconate and 70% isopropyl alcohol) or DuraPrep (0.7% available iodine and 74% isopropyl alcohol). Specimens for aerobic and anaerobic cultures were obtained prior to skin preparation (pre-preparation), after skin preparation (post-preparation), and after wound closure (post-closure). A validated neutralization solution was used for each culture to ensure that the antimicrobial activity was stopped immediately after the sample was taken. Positive cultures and specific bacterial pathogens were recorded.
Results: Coagulase-negative Staphylococcus, Propionibacterium acnes, and Corynebacterium were the most commonly isolated organisms prior to skin preparation. The overall rate of positive cultures prior to skin preparation was 82%. The overall rate of positive cultures after skin preparation was 0% (zero of fifty) in the ChloraPrep group and 6% (three of fifty) in the DuraPrep group (p = 0.24, 95% confidence interval [CI] = 0.006 to 0.085). There was an increase in positive cultures after wound closure, but there was no difference between the ChloraPrep group (34%, seventeen of fifty) and the DuraPrep group (32%, sixteen of fifty) (p = 0.22, 95% CI = 0.284 to 0.483). Body mass index (BMI), duration of surgery, and estimated blood loss did not a show significant association with post-closure positive culture results.
Conclusions: ChloraPrep and DuraPrep are equally effective skin-preparation solutions for eradication of common bacterial pathogens on the skin overlying the lumbar spine.
Level of Evidence: Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.
1Departments of Orthopaedic Surgery (J.W.S., B.M.W., M.T.N., and M.H.H.) and Neurological Surgery (P.A.S., J.C.L., and J.K.S.), Northwestern University Feinberg School of Medicine, 676 North St. Clair Street, Suite 1350, Chicago, IL 60611
Infections following spine surgery can have disastrous consequences1-4. Unfortunately, postoperative spinal wound infections are relatively common and are often associated with considerable morbidity, increased costs, and poor long-term patient outcomes5. The type and severity of infection are often dictated by the complexity of the operation. In elective cases in which instrumentation had been utilized, the prevalence of postoperative infection has been reported to be 2.8% to 6%3,6-9. This rate increases to approximately 9.5% if the spinal surgery is performed to treat spinal injury9.
Several factors have been associated with an increased risk of developing postoperative wound infections, including smoking, obesity, diabetes, long-term corticosteroid use, alcohol abuse, malnutrition, history of infection, operative time, and increased blood loss3,10-12. Another potential risk factor is the amount of bacterial flora present at the operative site at the time of incision. The use of an effective antimicrobial skin preparation solution prior to surgery is essential for the prevention of contamination at the surgical site and, ultimately, in the surgical wound. The efficacy of various common skin preparations has been studied in foot and ankle as well as shoulder surgery13,14. However, the bacterial flora from these areas may be different from those on the lumbar spine; thus, the findings in the literature are not necessarily applicable to surgery involving the lumbar spine.
The purpose of this study was to identify the common bacterial flora on the skin overlying the lumbar spine and to evaluate the efficacy of two readily available skin-preparation solutions (ChloraPrep versus DuraPrep) in the elimination of bacterial pathogens from the surgical site following skin preparation.
Materials and Methods
This prospective randomized controlled trial included 100 consecutive patients undergoing elective lumbar spine surgery from February to August 2010. All procedures were performed at a single institution by one of four surgeons (M.H.H., M.T.N., J.C.L., and J.K.S.). Institutional review board approval (Northwestern University STU00008875) was obtained, and the trial was registered at ClinicalTrials.gov under registry number NCT01105195. All patients gave informed consent to participate in the study. Patients were excluded from the study if they had an open wound at the incision site, abrasion in the vicinity of the planned incision, an active infection at or near the surgical site, or an active infection elsewhere in the body. We had each patient fill out a brief questionnaire in an attempt to identify any confounding variables, such as diabetes and corticosteroid use. There was no specific cleansing or shaving protocol prior to surgery, and patients were instructed to adhere to their routine bathing practices. If necessary, the skin hair in the surgical area was removed with clippers in the operating room before surgery.
Perioperative antibiotics were given to all 100 patients. They received 1 or 2 g of cefazolin (based on weight) prior to surgery unless they had an allergy to penicillin, in which case they received 900 mg of clindamycin. Patients who required spinal instrumentation followed the same protocol with the addition of 1 g of vancomycin, as this was the current protocol at our institution for all cases in which spinal instrumentation was used or total joint replacement was performed. The same type of non-antimicrobial drape was used in all cases in an attempt to minimize confounding variables. All patients were closely monitored for postoperative wound complications for a minimum of six months.
Patients enrolled in the study were randomized at the time of surgery to be treated with one of two widely used, and Food and Drug Administration (FDA)-approved, surgical skin preparation solutions: ChloraPrep (2% chlorhexidine gluconate and 70% isopropyl alcohol; Enturia, El Paso, Texas) or DuraPrep (0.7% available iodine and 74% isopropyl alcohol; 3M Healthcare, St. Paul, Minnesota). The agent used for each patient was determined immediately prior to skin preparation by opening a sealed, randomly assigned envelope. The lumbar spine was then prepared according to the manufacturer’s instructions by the attending surgeon. Each preparation solution was allowed to adequately dry for approximately three to five minutes in order to minimize the recognized risk of fire associated with alcohol-based solutions. Fifty patients were included in each group.
Culture Analysis and Neutralization
All 100 patients had specimens obtained for aerobic and anaerobic cultures prior to skin preparation, after skin preparation, and immediately after skin closure. All culture specimens were obtained with premoistened, sterile rayon-tipped swabs. A validated neutralization agent was used for each culture to ensure that the antimicrobial activity of the skin preparation solution (ChloraPrep or DuraPrep) was stopped immediately after the sample was taken. The culture swabs were premoistened in the neutralization solution. Each swab was then used to sample a 2.5-cm size area of skin adjacent to the planned incision site. The swab was then placed in a sealed sterile transport container and was immediately brought to the microbiology laboratory at our institution. All cultures were monitored for seven days.
The ChloraPrep sampling (neutralizing) solution consisted of 0.04% monobasic potassium phosphate, 1.01% dibasic sodium phosphate, 0.1% Triton X-100, 1.0% polyoxyethylene sorbitan monooleate (Tween 80), 0.3% lecithin, and 1.0% Tamol. The DuraPrep sampling (neutralizing) solution consisted of 0.04% monobasic potassium phosphate, 1.01% dibasic sodium phosphate, 0.1% Triton X-100, and 0.2% sodium thiosulfate. The pH of each solution was adjusted to 7.9 ± 0.1 prior to dispensing into water dilution bottles and steam sterilizing for twenty minutes at 121°C. An independent contract laboratory (Microbiotest, Sterling, Virginia) formulated and tested the neutralization solutions and found that they were both effective and nontoxic.
Sample-size requirements were based on the findings of a prospective randomized study evaluating the rate of positive cultures of specimens from the shoulder following skin preparation14. On the basis of the assumption that a 20% difference in positive-culture rates would be clinically relevant, the number of patients required to achieve 80% power at alpha = 0.05 was fifty per group. Descriptive statistics were calculated for all variables of interest. Continuous measures were summarized with the use of means and standard deviations, whereas categorical data were summarized with the use of counts and percentages.
A two-tailed Student t test was used to compare demographic variables, such as age, body mass index (BMI), duration of surgery, and estimated blood loss, between the two groups. The Fisher exact test and chi-square analyses were used to analyze the effectiveness of the two skin preparation solutions (ChloraPrep versus DuraPrep). Finally, logistic regression analysis was used to determine whether age, BMI, duration of surgery, or estimated blood loss had a positive or negative effect on post-closure culture results. Significance was defined as p < 0.05.
Source of Funding
External funding of this study was obtained from 3M (St. Paul, Minnesota), the company that manufactures DuraPrep. This funding was exclusively used for microbiology expenses and the testing of the neutralization solutions. The company was not involved with the design of the study, organization, and/or analysis of the data.
One hundred patients participated in this study. The average age was 52.3 years (range, twenty-five to eighty-nine years), and the average BMI was 30 kg/m2 (range, 18.5 to 43.6 kg/m2). In the ChloraPrep group, three patients were heavy smokers (>1.5 packs per day), three had diabetes mellitus, three were taking corticosteroids at the time of surgery, four had a history of alcohol abuse, two were immunocompromised, and ten had undergone previous spine surgery. In the DuraPrep group, three patients were heavy smokers (>1.5 packs per day), four had diabetes mellitus, two were taking corticosteroids at the time of surgery, two had a history of methicillin-resistant Staphylococcus aureus (MRSA), two had a history of alcohol abuse, three were immunocompromised, and nine had undergone previous spine surgery.
A variety of procedures were performed during the study period. Forty-six patients underwent a microdiscectomy, forty-one had a posterior spinal fusion with or without an associated interbody fusion, twelve had a decompression alone, and one had a kyphoplasty. The average duration of surgery was 203.5 minutes (range, twenty-five to 680 minutes), and the estimated blood loss averaged 282 mL (range, 5 to 2000 mL). There were no significant differences between the groups with regard to age or BMI. The patients in the ChloraPrep group had a significantly higher average estimated blood loss and duration of surgery compared with those in the DuraPrep group (Table I).
Prior to surgical skin preparation, bacteria grew on culture of specimens from 84% of the patients. There was no difference in positive pre-preparation culture results between the ChloraPrep and DuraPrep groups (84% versus 80%; chi-square analysis, p = 0.60; 95% confidence interval [CI] = 0.731 to 0.890) (Table II). The most common organisms isolated overall were coagulase-negative Staphylococcus (seventy isolates), followed by Propionibacterium acnes (thirty-six isolates), Corynebacterium (twenty-one isolates), and Micrococcus (ten isolates) (Fig. 1). On the average, 1.4 different organisms were isolated from each culture site prior to surgical skin preparation. Furthermore, 27% of the patients had two bacterial isolates, and 19% had three.
The overall rate of positive cultures following skin preparation was 0% for the ChloraPrep group and 6% for the DuraPrep group. The Fisher exact test showed no significant difference in the rate of positive post-preparation cultures (p = 0.24, 95% CI = 0.006 to 0.085). The positive culture results in the DuraPrep group consisted of growth of Propionibacterium in one case and Peptostreptococcus in two.
There was a significant increase in positive culture results after wound closure compared with the rate following skin preparation (3% versus 33%, p < 0.0001), but there was no difference between the ChloraPrep (34%, seventeen of fifty) and DuraPrep (32%, sixteen of fifty) groups (chi-square analysis, p = 0.22; 95% CI = 0.284 to 0.483) with regard to post-closure results. The most common bacteria isolated after wound closure were Propionibacterium (fifteen isolates), followed by Micrococcus (seven isolates), coagulase-negative Staphylococcus (seven isolates), Peptostreptococcus (four isolates), and Corynebacterium (one isolate) (Fig. 1). BMI (adjusted odds ratio [OR] = 0.987, 95% CI = 0.929 to 1.048), duration of surgery (adjusted OR = 1.002, 95% CI = 0.998 to 1.001), and/or estimated blood loss (adjusted OR = 0.999, 95% CI = 0.291 to 1.680) did not show a significant association with positive post-closure culture results. Age was the only variable that was significant in that, with every one-year increase in age, the patient was 1.03 times more likely to have negative post-closure results (adjusted OR = 1.032, 95% CI = 1.001 to 1.064) (Table III). One patient in the ChloraPrep group had an area of superficial wound dehiscence. Otherwise, there were no deep and/or superficial infections at a minimum of six months postoperatively.
Postoperative spinal wound infections are relatively common, and are often associated with considerable morbidity, increased costs, and poor long-term patient outcomes5. Several factors have been associated with an increased risk of developing a postoperative wound infection3,10-12. Intuitively, a potential risk factor is the amount of bacterial flora present on the skin at the time of incision; however, to our knowledge, there are no definitive studies substantiating this hypothesis.
Over the past five years, several studies have evaluated the effectiveness of various skin preparation solutions13,14. Ostrander et al.13 assessed the efficacy of DuraPrep, ChloraPrep, and Techni-Care in foot and ankle surgery. Although ChloraPrep was the most effective skin preparation solution, the overall rate of positive culture results was still relatively high (approximately 21%). Saltzman et al.14 then evaluated the effectiveness of DuraPrep, ChloraPrep, and Betadine (povidone-iodine) in shoulder surgery and found that the overall positive-culture rate after skin preparation was 31% in the Betadine group, 19% in the DuraPrep group, and 7% in the ChloraPrep group (p < 0.001). In both of these studies, there were no significant differences among the preparation agents with regard to postoperative infection rates; however, the studies lacked power to enable the authors to comment on infection as a specific end point.
Two larger-scale studies have been performed to look specifically at the rates of postoperative infection after the use of different skin preparation solutions. Swenson et al.15 evaluated DuraPrep, ChloraPrep, and Betadine in 3209 general surgery operations. The lowest infection rate was seen in the DuraPrep group (3.9%), when compared with the Betadine (6.4%) and ChloraPrep (7.1%) groups (p = 0.02). In another study, Darouiche et al.16 demonstrated that ChloraPrep was superior to Betadine in preventing postoperative infections in 849 surgical patients (infection rates of 9.5% versus 16.1%; p = 0.004; adjusted relative risk = 0.59, 95% CI = 0.41 to 0.85). Since these results are controversial, it remains unclear whether using a specific preparation agent actually lowers the incidence of postoperative infection.
In the current study, ChloraPrep and DuraPrep were equally effective skin preparation solutions. Both were very effective in eradicating the skin bacterial flora after application and prior to skin incision (100% success rate in the ChloraPrep group and 94% in the DuraPrep group, p = 0.24). This study also illustrates that the bacterial flora overlying the lumbar spine is nearly identical to that overlying the shoulder. With that said, our results for each skin preparation solution are better than those from the aforementioned studies of the shoulder and foot13,14. The reason for these differences remains unclear. One possibility is that the preparation solutions can be more uniformly applied to the skin overlying the lumbar spine. Uniform application to the foot and/or shoulder may be more difficult as a result of the complex topographical anatomy of those regions, specifically between the toes and in the axilla. Another possible explanation is that the baseline bacterial load on the spine is lower than that on the shoulder and/or foot, allowing the preparation solutions to be more effective on the spine.
Our data show that there was a significant increase in the number of positive culture results following skin closure and removal of the non-antimicrobial incise drape. The predominant bacterium found was Propionibacterium (Fig. 1). This may represent recolonization during the procedure; however, we do not have the scientific evidence to support this. Removing the incise drape may cause a disruption of the natural skin flora that typically resides beneath the epidermis, resulting in an increased number of bacteria on the surface. Regardless, the high rate of positive culture results following skin closure did not seem to affect the prevalence of postoperative wound complications and/or infection.
There are several limitations to this study. First, we used qualitative culture rather than quantitative culture data. Therefore, it is unclear if certain patients had a higher bacterial load at baseline, and whether or not that would alter the effectiveness of the skin preparation solution and ultimately increase the risk of infection. Second, the manufacturer of one of the skin preparation solutions (DuraPrep) provided funding for this study. This funding was used exclusively for microbiology expenses and evaluation of the neutralization solutions, and the company was not involved with the organization or analysis of data. Finally, our study was not powered to detect differences in postoperative infection rates.
Despite these limitations, we were able to identify the native bacteria present on the skin overlying the lumbar spine. Furthermore, we demonstrated that both ChloraPrep and DuraPrep are extremely effective in eradicating this bacterial flora after skin preparation. Ultimately, these data add to the existing body of literature and suggest that there are multiple skin preparation solutions that are effective in eradicating bacteria prior to skin incision. Whether the use of a particular skin preparation solution lowers the rate of postoperative infection is still unclear. It is likely that the cause of postoperative infection is multifactorial, and the use of a specific skin preparation solution has little effect on the prevalence of postoperative spine infection. Therefore, surgeons can probably use one of many FDA-approved skin preparation solutions and may want to consider the one that is most cost-effective at their institution.
Investigation performed at the Departments of Orthopaedic Surgery and Neurological Surgery, Northwestern University Feinberg School of Medicine, Chicago, Illinois
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Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.Copyright 2012 by The Journal of Bone and Joint Surgery, Incorporated