Introduction
Surgical site infection, a major public health problem, is the second most frequently reported health care associated infections worldwide.1 Center of Disease Control (CDC), US redefined the ‘wound infection’ in 1992 and renamed as ‘Surgical site infections’. It is defined as infections that develop at the surgical site within one month after a surgical operation or three months after implant surgery, breast, cardiac and joint surgeries.2 According to CDC, SSIs are classified as superficial incisional, deep incisional and organ/space SSIs.3 In India Incidence of SSIs is reported between 3.6 % to 22.5%.4 The risk of SSIs can significantly be influenced by factors such as old age, poor nutritional status, obesity, preexisting comorbidities (diabetes Mellitus, hypertension), poor surgical technique, prolonged duration of surgery, inadequate antimicrobial prophylaxis etc.5 Surgical site Infections (SSIs) are usually caused by exogenous and endogenous micro-organisms infecting the wound during the surgery. Pathogenic drug resistant bacteria are emerging due to inappropriate choice of antibiotics. Although Gram positive organisms, especially Staphylococcus spp, are the common causative agents of SSIs, multi drug resistant (MDR) gram negative organisms are taking upper-hand day by day.1 Therefore, the identification of bacterial pathogens causing surgical site infections along with their antibiogram is utmost important in a hospital setting to reduce incidence of health care associated infections, post-operative hospital stay and cost and to implement antimicrobial stewardship appropriately.6 The study was aimed to find out bacteriological profile of surgical site infections along with their antibiogram in a tertiary care hospital in Kolkata.
Materials and Methods
A cross sectional and observational study was conducted after Institutional Ethical Committee clearance in the Department of Microbiology of Nil Ratan Sircar Medical College in Kolkata for a period of 12 months from September 2020 to August 2021. A total 6582 surgeries were performed within this one-year time period in the Institute. Pus or discharge collected from 220 (3.34%) clinically suspected SSI cases by swab sticks in duplicate from various surgical wards and sent immediately to Microbiology Laboratory for further processing.
Inclusion criteria
All patients irrespective of age and gender, having post-operative wound infections were included in this study.
Exclusion criteria
Infection at surgical site after 30 days’ post-operative are excluded from the study except breast, implant, and joint surgeries. Infections in episiotomy wounds or wounds with cellulitis were also not considered.
Detailed clinical history
A detailed clinical history from every case regarding age, gender, type of wound, risk factors and associated comorbidities, use of prophylactic antimicrobial, was obtained.
Processing in microbiology lab
All samples collected are subjected to gram stain for provisional diagnosis. Another swab was inoculated on MacConkey agar (MAC) and 5% sheep blood agar (BA) and plates and incubated at 37°C overnight. No growth after incubation for 48 hours were reported as sterile. Growth on culture plates was identified by its colony morphology followed by battery of standard biochemical tests 7, 8. Vitek®2 compact system (BIOMERIEUX) was used for further identification and antimicrobial susceptibility testing. All gram negative isolates were stocked in glycerol broth at (-) 80°C for further testing of antimicrobial resistant mechanisms. All dehydrated media and reagents were purchased from Hi Media Laboratories Pvt. Ltd., Mumbai, India. Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 were used as control.
SSI rate calculation
Surgical site infection (SSI) rate was calculated using the following formula.9
Total number of culture positive specimens x100
SSI Rate = Total number of surgeries performed
Detection of antimicrobial resistance
All Gram negative pathogens resistant to 3rd generation cephalosporins were screened for extended spectrum β lactamases (ESBLs) including Amp C detection phenotypically by disc diffusion method followed by confirmatory test as per CLSI guideline 10. Carbapenemase production was detected from carbapenem resistant gram-negative isolates phenotypically by Carba NP test as per CLSI guideline 10.
Results
In the present study, 6582 surgeries were performed during the study period in the Institute, out of which 220 (3.34%) cases were suspected clinically for SSI. Significant growth was detected in 186 (2.83%) cases [Table 1], out of which 137 (62.27%) showed mono-microbial growth and 49 (22.28%) growth was poly-microbial. No growth was noted after 48 hours of incubation in 34 (15.45%) cases [Table 2]
Table 1
Showing number of suspected SSI, confirmed SSI and rate of infection
|
Total surgeries performed |
6582 (100%) |
|
No of symptomatic SSI |
220 (3.34%) |
|
No of culture positive Samples |
186 (2.83%) |
|
Infection rate in SSI |
2.83% |
Table 2
Showing number of isolates from clinical specimens
|
Single growth |
137 (62.27%) |
|
Multiple growth |
49 (22.28%) |
|
No growth |
34 (15.45%) |
|
Total |
220 (100%) |
In the present study,161 (73.18%) cases were male and 59 (26.82%) cases were female, with male: female ratio being 2.73:1. The peak of incidence of SSI was observed in age group of >60 years (44.55%) followed by in 51-60 years’ age group (16.82%) [Figure 1]. Superficial SSI was detected in 123 (66.13%) cases, whereas 63 (33.87%) cases showed features of deep SSI. Presence of Diabetes mellitus, obesity and using prophylactic antibiotic >2 hours prior to surgery were found to be significantly associated [Table 3].
Table 3
Showing risk factors associated with SSI (n=220)
Infection rate was observed to be maximum in Plastic Surgery Department (4.8%), followed by Pediatric Surgery Department (4.6%) and General Surgery Department (3.2%) [Table 4].
Table 4
Showing rate of infection of SSI in various departments
Bacteriological profile
Total 218 microbial pathogens were isolated. Out of these, 84 (38.53%) were gram positive cocci, 128 (58.72%) as gram negative bacilli and 6 (2.75%) as Candida spp. Out of 84-gram positive organisms, MRSA (Methicillin resistant Staphylococcus aureus) was the predominant isolates (39.29%) followed by CONS (Coagulase Negative Staphylococcus spp) (22.62%) and Enterococcus spp (20.24%). Gram negative bacilli were found to be predominant pathogen of SSI. Escherichia coli (35.94%) was the most frequent isolate (35.94%) among them, followed by Klebsiella pneumoniae (20.31%) and Pseudomonas aeruginosa (17.97%) [Table 5].
Table 5
Characterization of various isolates obtained from patients with surgical site infection
Antimicrobial susceptibity pattern
In the present study, gram positive organisms showed highest susceptibility to Linezolid (100%) and Vancomycin (97.62%) and least susceptibility to penicillin (4.76%) [Table 6]. Gram negative organisms showed more resistant pattern. Ampicillin, Cephalosporin or Ciprofloxacin were found to be least susceptible, whereas Polymyxin B, Meropenem or Cephalosporin –Sulbactum were found to be more effective antimicrobial agents [Table 7].
Table 6
Showing antimicrobial susceptibility pattern of gram positive isolates
Table 7
Showing antimicrobial resistant pattern of gram negative isolates
Among the gram negative isolates, ESBL (extended spectrum β lactamases) (67.97%) was the commonest resistance exhibited, followed by MBL (metallo β lactamases) (31.25%) and AmpC (4.69%) [Figure 2].
Discussion
Post-operative surgical site infections are considered as a significant burden to health care centers in terms of extended hospital stay, substantial associated morbidity and mortality, and increased hospital cost.11 It has been reported as one of the major causes of health care associated infections in spite of technological advances and wound management. 11 It has been estimated that infection rate of SSI in India varies between 2.5% to 41.9%. 12, 13 In the present study, infection rate was found to be 2.83%. It was reported to be 2.69% in the study of Kokate et al, 14 3.43% in Khan et al, 9 4.3% in Kamath et al15 & 5.5% in Karan et al 16. In the present study, rate of infection was predominant in male patient (73.18%) with male: female 2.73:1. This finding was concordant with the study of Negi V et al1 (2.93:1), Naz R17 (2.11:1). Chakraborty SP et al18 and Malik S et al19 also showed male preponderance in their study. The incidence of surgical site infection increases with advancing age due to low immunity, low wound healing, increased catabolism and presence of co-morbidities.1 In the present study, maximum affected age group was found to be >60 years (44.55%) followed by 51-60 years of age group (16.82%). Similar findings were noted in Negi V et al,1 Mangram J et al,3 and Naveen K et al.20 Diabetes mellitus and obesity were found to be significant risk factors associated with SSI. Use of prophylactic antibiotic within 60 minutes before surgery was another significant factor found to be associated. Leela Rani Kasukurthy, 2020 showed in her study that anemia, diabetes mellitus and hypertension were the most important risk factors, diabetes being the most frequent one.6 Similar findings were also noted in Negi V et al1 and Khan AKA et al.21 Maximum rate of infection was observed in plastic surgery (4.8%) followed by paediatric surgery (4.6%) and general surgery (3.2%). Rate of infection was found to be maximum in orthopedics in Khan AS et al,9 whereas it is maximum in general surgery in Nirupa et al.22
Out of 220 cases of clinically suspected SSIs, 186 (84.55%) cases were culture positive. Dhote et al23 showed 92% growth, where as 52% growth was detected in Khan AS et al,9 60.5% in Kaur et al23 and 49.5% in Kokate et al.14 Growth was mono microbial in 62.27% cases in the present study, whereas in 22.28% cases multiple growth was detected. Growth was sterile in 15.45% cases. Predominant mono microbial growth was observed in the study of mama et al (91.6%),24 Shreeram et al. (80.4%),25 Negi V et al. (94.7%),1 Mundhada et al. (50%),26 Benebdeslam et al. (76.8%),27 and Insan et al. (60%).28 Gram negative bacilli (58.72%) were predominantly detected in our study followed by gram positive cocci (38.53%) and yeasts (2.75%). Out of gram negative bacilli, E. coli was the predominant isolate (35.94%) followed by Klebsiella (20.31%). Out of gram positive cocci, Staphylococcus aureus was the predominant isolate (57.14%) followed by CONS (22.62%). Similar findings were also demonstrated in Pradeep MSS et al, 29 Goswami et al,30 Khan AS et al,9 Amare et al, 31 Mama et al 24, Dhote et al 23, Kokate et al14 and Shreeram et al. 25
Antimicrobial susceptibility testing revealed high degree of resistance to majority of isolates. Among gram positive organisms, Methicillin resistant Staphylococcus aureus (MRSA) was found in 39.29% cases. Higher incidence of MRSA was detected in Pradeep MSS et al (44.8%)29, Patnaik N et al (52.3%)32 and Jain K et al (48.78%).33 On the contrary, Aggarwal et al34 showed incidence of MRSA 10% only and Negi V et al1 showed it 15.7%. Vancomycin and Linezolid was found to be most effective antimicrobials, irrespective of methicillin resistance. This finding was also noted in Verma U et al,35 Negi V et al,1 Patnaik N et al32 and Shreeram et al.25 Gram negative organisms showed higher degree of resistance and Polymyxin B and Meropenem were found to be most effective antimicrobials. Better susceptibility to carbapenems was noted in Verma U et al,35 Negi V et al, 1 Kamath et al15, Khan et al9 and Kaur et al. 23 Patnaik N et al32 showed highest susceptibility of Polymyxin B to non-fermenters.32 Among the gram negative isolates, ESBL (extended spectrum β lactamases) was produced in 67.97% cases, MBL (metallo β lactamases) in 31.25% cases and AmpC in 4.69% cases. ESBL was detected as the commonest mechanism of resistance in Kasukurthy LR6 also.
Conclusion
Surgical site infections still remain a great concern to physicians and surgeons in health care facilities in spite of rapid improvement of technologies and knowledge. 1 Rapidly increasing resistance to majority of existing antimicrobials also makes the problems more challenging. As a result, it has become more evident to understand the microbial etiology of SSIs of every health care facility to establish improved antimicrobial policy and implement appropriate antimicrobial stewardship. 1
