Epidemiological Characteristics and Predisposing Factors for Surgical Site Infections Caused by Bacterial Pathogens Exhibiting Multidrug-Resistant Patterns

Background: Surgical site infection is the most common kind of nosocomial infection in developed and developing countries. Objectives: Our aim was to identify the prevalence of factors predisposing to multidrug resistance and the antimicrobial susceptibility profile of pathogens. Method: This retrospective study enrolled 10,878 patients who underwent operations in 2018–2020. Pathogens were identified using eosin methylene blue agar. Mueller–Hinton agar was used to assess antimicrobial sensitivity and resistance. In total, 382 patients with confirmed surgical site infection (SSI), whose culture showed growth, were included in the study. Results: The prevalence of SSI in the current study was 3.5%. Escherichia coli was the predominant pathogen (35.8%), followed by Staphylococcus aureus (21.8%). Antibiotic use, chronic renal failure, diabetes, and emergency operations were found to increase the likelihood of multidrug resistance (OR = 6.23, CI = 1.443–26.881, p = 0.014; OR = 5.67, CI = 1.837–19.64, p = 0.02; OR = 2.54, CI = 1.46–7.35, p = 0.03; OR = 1.885, CI = 1.067–3.332, p = 0.002, respectively). The pathogens showed different levels of antimicrobial resistance against ceftriaxone (72.7%), ciprofloxacin (46.6%), and gentamicin (34%). Antimicrobial resistance of about 1–3.4% was exhibited by linezolid, tigecycline, and teicoplanin. Conclusion: The study presented significantly increased multidrug-resistant (MDR) Enterobacteriaceae pathogens isolated from surgical sites. They involve significant morbidity and mortality rates and increased health-related costs.


Introduction
Surgical site infections (SSIs) are postoperative infections occurring within 30 days of surgery. They involve significant morbidity and mortality rates and increased health-related costs [1,2]. SSI is the most common form of nosocomial infection in both developed and developing countries. The most common causative pathogens are Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Klebsiella pneumoniae (K. pneumoniae), and Enterococcus spp. [3].
The prevalence of surgical site infections varies between 1 and 18% in some developing countries [4]. To date, there have been no studies regarding SSI reported from Somalia.
The increasing number of multidrug-resistant (MDR) microorganisms isolated from surgical sites is an increasing health threat and a public health issue. A multidrug-resistant microorganism is a pathogen that is resistant to 2 or more of the 40 antimicrobial agents. One of the most common reasons for widespread antimicrobial resistance is the poorly controlled use of wide-spectrum antibiotics [4]. Patients with MDR pathogens are resistant to most first-line antimicrobial classes. This resistance necessitates the handling of these patients with a prolonged hospital stay. It involves increased healthcare costs and admissions to intensive care units and significant morbidity and mortality.
The patient-related risk factors for SSI include advanced age, obesity, current infection, diabetes mellitus, low albumin, and smoking. Surgery-related risk factors include prolonged and emergency operations, inadequate surgical scrubbing and skin preparation, abdominal surgeries, and contamination of the contents. Trauma, shock at the time of admission, the requirement of blood transfusions, hypothermia, hypoxia, and elevated blood glucose levels are physiological conditions that enhance the risk of SSIs [5].
In addition to addressing the increasing rate of SSIs due to multidrug-resistant pathogens, the importance of this study is its identification of the factors determining the widespread distribution of MDR pathogens and its evaluation of prevalence, the most common etiological pathogens, and the antimicrobial susceptibility pattern.

Methods
This study enrolled 10,878 patients who underwent operations at Mogadishu Somali Turkey Reccep Tayyip Erdogan Training and Research Hospital whose medical records were retrospectively reviewed between 2018 and 2020. The applied definition of SSI was described by the Centers for Disease Control and Prevention (CDC). In total, 382 patients with confirmed surgical site infection whose cultures showed growth were included in the study.

Inclusion and Exclusion Criteria
All patients who underwent surgeries that developed SSI less than 30 days after the operation were included in the study. All wounds not related to operations or abscesses were excluded from the study.

Sample and Culture
Surgical site drainage cultures and antibiograms were performed by the laboratory and microbiology unit of the hospital via standard laboratory protocols, and the findings of these tests were used for the study. After the surgical site drainage cultures were obtained, identifying the bacterial pathogens was achieved by a combination of BD BBL crystal identification system, as well as biochemical tests, including oxidase and citrate test, coagulase test, and catalase test according to the system of the Clinical and Laboratory Standards Institute (CLSI). Subsequently, antimicrobial sensitivity tests were performed using the standard Kirby-Bauer disk diffusion method and commercial disks (Oxoid discs). The ESBL were identified from positive cultures using cephalosporins (cefuroxime + ceftriaxone) and amoxicillin-clavulanic acid as the identifying disc to differentiate the patterns of growth between antibiotics with lactamase inhibitor and those without. Enterococcus antimicrobial sensitivity and resistance were assessed using blood agar. Cefoxitin-resistant Staphylococcus aureus was assessed in the same way as methicillinresistant Staphylococcus aureus (MRSA).

Sample Size
In total, 382 patients with confirmed SSIs whose cultures showed growth were included in the study. The patients were grouped into five age categories: newborn to 18 years, 19-39 y, 40-58 y, 59-76 y and >77 y.

Predisposing Factors for Multidrug Resistance
The study assessed factors affecting the incidence of multidrug resistance of microorganisms, divided into two groups: The patient-related factors included the age and gender of the patient, antimicrobial use, and coexisting conditions (diabetes, chronic renal failure, and obesity). The surgery-related factors included the type of surgeries (emergency and elective operations), the site of admission (non-ICU patients and ICU patients), type of patient (trauma or non-trauma), and intraoperative and postoperative blood transfusions.

Statistical Analysis
Descriptive and inferential measures were employed for the data analysis. As regards the categorical variables, the frequencies and proportions were presented as point estimates. As regards quantitative variables, the mean (±SD) was employed wherever necessary. The confidence interval (95%) was used to derive an interval estimate of the mean for the population. Binary analyses were performed to assess the association between independent and dependent variables. The odds ratios (ORs) and their 95% confidence intervals (CIs) were calculated. A p value of <0.05 was considered statistically significant. Variables that showed statistical significance under the bivariate analysis were included in the multivariate logistic regression model to determine factors that contribute to multidrug resistance. The adjusted ORs with their 95% CIs were computed to determine the association. All statistical analyses were performed using the Statistical Package for Social Sciences (SPSS -IBM) for Windows version 23.

Results
Of 10,878 patients, 382 patients displayed confirmed surgical site infections and cultures showing growth. These patients comprised the study population. The prevalence of surgical site infection in the current study was 3.5%. Almost all patients had experienced an open approach to their various types of surgery. All patients received cephalosporin antimicrobial prophylaxis before the operation. The mean age of the patients was 34.5 ± 20.6 years.
Antibiotic use, chronic renal failure (CRF) and diabetes were found to increase the chance of multidrug resistance (OR = 6.23, CI = 1.  (Table 1). The gender distribution of surgical site infections was 65.4% male (250 patients) and 34.6% female (182 patients), which shows a twofold increased predominance of SSIs in males. In total, 81.4% of the patients had a single isolate, and the remaining 18.6 cases showed polymicrobial pathogens. In our study, as illustrated in Table 2  We also assessed the presence of extended-spectrum beta-lactamases (ESBL)-producing pathogens. ESBL-producing pathogens were found in 15% of the cases (57 patients). E. coli was the most common pathogen, arising in 31 patients (54.5%). Concerning the overall E. coli isolates, 22.6% of the E. coli found produced the extended-spectrum beta-lactamases (ESBL), which was a significant increase. Klebsiella pneumonia was identified to be the second most common pathogen producing ESBL. It appeared in 19 patients (33.3%), followed by Proteus mirabilis in 3 patients (5.2%).
The prevalence and the pattern of methicillin-resistant Staphylococcus aureus (MRSA)producing species were evaluated throughout the study. The prevalence of MRSA was 3.1% (12 patients). In total, 9/83 S. aureus isolates produced MRSA (10.8%). The three remaining kinds of MRSA were produced by Staphylococcus epidermidis, Staphylococcus saprophyticus, and Staphylococcus hominis.
The antibiotic sensitivity and resistance of the pathogens were assessed, and the antimicrobial profiles are comprehensively depicted in Table 3. Table 3. Distribution of antibiotic resistance and antimicrobial profiles of specific pathogens.
In our study, antimicrobial resistance levels of about 1-3.4% were revealed by linezolid, tigecycline, and teicoplanin, respectively. Vancomycin and daptomycin did not show any antimicrobial resistance, including methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus. Carbapenems revealed a high sensitivity rate against pathogens of about 85.9% (86.8% to imipenem, 86.6% to ertapenem, and 82.9% to meropenem).
The spectrum of resistance to carbapenems was assessed; pseudomonas revealed the highest resistance to carbapenems at 13%, followed by Acinetobacter at 11.3% and Klebsiella at 8.8%.
Of 382 patients, 81.7% showed a multidrug resistance pattern, while 14.9% of the patients showed extensive drug resistance (XDR). Acinetobacter baumannii revealed the highest MDR and XDR spectra (100%), followed by E. coli at 96.4% and Klebsiella pneumonia at 73.5%.

Discussion
Multidrug-resistant (MDR) pathogens isolated from surgical sites have increased in number. They are a major health threat and public health issue. A systematic review and meta-analysis performed by Martin et al. suggests that diabetes is a significant risk factor for SSIs, potentially due to the vascular changes and leukocyte dysfunction it induces beyond its role in causing hyperglycemia [6]. A large cohort study of 4690 patients who underwent general surgical procedures concluded that emergency surgery, prolonged operating times, surgical site, prolonged preoperative hospital stay, higher ASA score, dirty/infected wound class, the presence of surgical drains, and intraoperative transfusion were independent risk factors for SSI (Isik O et al. p 0.05) [7]. The four independent parameters that increase the risk of SSI, reported by the Study on Efficacy of Nosocomial Infection Control (SENIC) trial, were abdominal operations, prolonged operations (>2 h), a contaminated or dirty procedure, and the presence of more than three diagnoses at the time of discharge [5].
Besides the increasing rate of SSIs due to MDR pathogens and the scarcity of literature regarding factors predisposing patients with SSIs to MDR, this study intended to identify factors determining the widespread distribution of MDR microorganisms. Our study revealed that antibiotic use, emergency operations, diabetes, and chronic renal failure are significantly related to multidrug resistance. The antimicrobial treatment of chronic renal failure patients with surgical site infections is challenging. The use of antibiotics should be adjusted according to renal function, the appropriate empirical therapy, and the culture test results once available to minimize the worsening of preexisting antimicrobial resistance. Age, obesity, trauma, and intraoperative blood transfusion are significantly associated with SSIs. However, the current study revealed they were not associated with multidrug resistance patterns against microorganisms [5,7]. Preoperative antibiotic prophylaxis, antiseptic skin preparation, hair removal, the avoidance of hypothermia, and perioperative glycemic control compose the bundle approach aimed at reducing SSIs to improve safety.
The constant assessment of the changing trends, besides pathogens and their antibiotic sensitivity and resistance patterns, is particularly crucial in developing countries where SSI prevalence and morbidity and mortality rates are high [8]. To date, there have been no studies into SSIs performed in Somalia. The prevalence of surgical site infection in our study was 3.5%, and a similar prevalence rate was found in other studies [5,9].
The pattern of antimicrobial sensitivity and resistance differed in the different classes of antibiotics and in the pathogens isolated from the culture. E. coli was the predominant pathogen for all age groups in our study and topped the table (35.8%), which coheres with other studies [6,10,11]. Research performed by S Elgoharia and associates reported that significantly increased Enterobacteriaceae pathogens cause SSIs. Another notable finding in our study is that Staphylococcus aureus was related to a significant reduction (21.8%) compared to E. coli, which agrees with the results of S Elgoharia and colleagues reporting similarly [10]. A review article by Lindsey M. and associates discussed the pattern of antimicrobial resistance toward pathogens and revealed E. coli to be the predominant pathogen in their study [12]. There is variation in the spectrum of pathogens causing SSIs. A prospective cohort study from Rwanda by Marie Josée and partners reported on the common pathogens in surgical site infection and identified that Klebsiella was the predominant pathogen, followed by E. coli [4].
Males were more vulnerable to surgical site infection in our study by nearly double (65.4%). The mean age of patients in our study was 34.5 years, which contrasts with other studies [13,14].
Second-and third-generation cephalosporins are the most common antibiotic classes prescribed for antimicrobial prophylaxis, prescribed in most admitted patients. However, they have the highest resistance rate against pathogens. Correlations between early culture and antibiotic results are necessary for deteriorating patients once culture results are available [4].
The current study reviewed the spectrum of ESBL cases (15%). In total, 23% of E. coli isolates (31/137) produced extended-spectrum beta-lactamases, which mirrors national surveillance data (23%) reported from Japan by Yoshio Takesue and associates [3]. E. coli was the highest in terms of ESBL, followed by Klebsiella.
Carbapenem-resistant Enterobacteriaceae (CRE) isolates have increased in number in recent years. This is a healthcare challenge due to the associated morbidity and mortality requiring complex management because of the extensive drug resistance pattern [16,17]. Carbapenems revealed a high sensitivity rate against pathogens (about 85.9%) in the current study.
John A. and collaborators reported on the causative pathogens and outcomes related to surgical site infection; the authors identified a significant increase (20.6%) in methicillinresistant S. aureus (MRSA), which is related to increased mortality and health-related costs [2]. National surveillance data reported from Japan by Yoshio Takesue and colleagues showed a significant reduction in methicillin-resistant S. aureus, from 72.5% to 53.8% [3]. Methicillin-resistant S. aureus (MRSA) was less prevalent in our study compared to the above studies. MRSA-producing Staphylococcus aureus was found in 10.8% of the cases, but all cases were sensitive to vancomycin. Vancomycin and daptomycin did not show any antimicrobial resistance, including methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus.
The limitations of our study include that it used a retrospective design that missed some variables influencing the multidrug resistance pattern, including intraoperative abdominal contaminations. Second, the study was single-center-based. This is the first and only study from Somalia. Further prospective studies are needed to afford detailed insight into the variables affecting the multidrug resistance and extensive drug resistance spectra.

Conclusions
The study results showed significantly increased multidrug-resistant (MDR) Enterobacteriaceae pathogens isolated from surgical sites, and they involve significant morbidity and mortality rates and increased health-related costs. Acinetobacter baumannii revealed the highest multidrug resistance and extensive drug resistance spectrum; tigecycline has shown a higher sensitivity rate against the pathogen. Antibiotic use, emergency operations, diabetes, and chronic renal failure are significantly related to multidrug resistance patterns.
Antimicrobial prophylaxis, appropriate skin preparation and hair removal, avoidance of hypothermia, and perioperative glycemic control are part of the bundle approach to reduce SSIs to improve safety.