A study on Surgical Site Infections ( SSI ) and associated factors in a government tertiary care teaching hospital in Mysore , Karnataka

Surgical site infections (SSI) frequently cause morbidity and mortality among inpatients of hospitals. They account for a considerable proportion of nosocomial infections among hospital inpatients. Hence they can act as surrogate markers for nosocomial infections. For surgical patients, SSIs are the most common nosocomial infection and they have been shown to be the leading cause of operation-related adverse events.[1,2] Several studies have demonstrated an increased length of hospitalization and the associated fi nancial implications for patients with SSI compared with non infected patients having similar surgical procedures.[3-5] The prevalence varies from hospital to hospital and across different countries.[6-8] When surgical patients with nosocomial SSI died, 77% of the deaths were reported as related to the infection and the majority (93%) were serious infections involving organs or spaces accessed during the operation.[9] An estimate showed that if a hospital with an annual surgical volume of 10000 operations could reduce their SSIs by half; this would result in an average annual cost savings of approximately $450,000.[10]


INTRODUCTION
Surgical site infections (SSI) frequently cause morbidity and mortality among inpatients of hospitals.They account for a considerable proportion of nosocomial infections among hospital inpatients.Hence they can act as surrogate markers for nosocomial infections.For surgical patients, SSIs are the most common nosocomial infection and they have been shown to be the leading cause of operation-related adverse events. [1,2][8] When surgical patients with nosocomial SSI died, 77% of the deaths were reported as related to the infection and the majority (93%) were serious infections involving organs or spaces accessed during the operation. [9]An estimate showed that if a hospital with an annual surgical volume of 10000 operations could reduce their SSIs by half; this would result in an average annual cost savings of approximately $450,000.

AIM AND OBJECTIVES
1. To study the incidence of Surgical Site Infections in the surgical wards of K.R.Hospital, Mysore.2. To identify the risk factors for the development of SSIs. 3. To prepare an antibiogram to evaluate sensitivity pattern of organisms causing SSIs.

Study subjects
One hundred and eighty patients who underwent various surgeries in the General Surgery department of K.R. Hospital Mysore were studied.

Study period
July-August 2007

Inclusion criteria
• Elective surgeries • Those who stayed for at least seven days post-operatively.

Exclusion criteria
• Grossly contaminated or infected wounds/procedures Following the surgical procedure, surgical sites were examined on postoperative day 3 and every 3 days thereafter.Wounds were graded on the following scale: grade 1= normal healing; grade 2 = suture line erythema < 1cm; grade 3 = suture line erythema > 1cm; grade 4 = frank, purulent drainage. [11]Four surgeons did the grading for all the subjects.Cultures were obtained on all wounds determined to be infected or as otherwise clinically indicated.Grade 3 or 4 wounds were considered infected.Wounds from which a positive culture was obtained in the setting of physical signs of infection (i.e., fever, infl ammation) were also considered infected.Antibiogram was prepared from culture sensitivity reports to evaluate the sensitivity pattern of organisms.
Demographic characteristics like age and sex were noted.Variables like BMI, co-morbid conditions, prophylactic antibiotic use, blood transfusion, and preoperative waiting period were compared in the infected and non-infected groups.
Statistical analysis was done using Microsoft Excel, SPSS 13 software.
Those risk factors that were univariately signifi cant using chi-square analysis at p < 0.05 were entered into binary logistic regression equation to evaluate the risk of each factor when adjusted for other factors.

RESULTS
During the study period 180 patients underwent various surgeries in the general surgery department of K.R. Hospital, Mysore.Among them abdominal surgeries constituted majority (76.11%) followed by limb surgeries.Others category included thyroid surgeries, lipoma and other tumor excisions [  2].
Anemia, hypertension and diabetes mellitus were the three comorbid conditions studied.Hemoglobin of 13 and 12 gm% were considered as the cut off points for the diagnosis of anemia in men and women respectively.Those with less than 10gm% were considered severely anemic and these were the ones who received maximum blood transfusions.Among 37 anaemic patients who underwent surgery 23 (62.16) developed SSI.
The study subjects who knew their diabetic and hypertensive status before admission and those diagnosed after admission were considered diabetics and hypertensive respectively.
Majority of them knew their status before admission and majority were not taking medication regularly.This was one of the factors for increasing their preoperative waiting period.It was also found that majority had both conditions.Twenty (83.33%)patients of the 24 diabetics and 17(73.91%) of the 23 hypertensives respectively developed SSIs [Table 2].
Among the 180 study subjects 41(22.78%)patients received blood transfusions.Per operative transfusions accounted for major share of these transfusions.Eight (5.7%) patients who did not receive any transfusion developed SSI.Four patients  2].
Among the 39 SSIs, 36 showed growth of colonies.Staphylococcus aureus was the predominant organism isolated from the surgical sites followed by Pseudomonas and Klebsiella.Some surgical sites had mixed infections involving multiple organisms [Table 3].
Organisms isolated from the SSIs showed resistance to all groups of antibiotics used in the surgery department of our hospital.Tetracycline encountered majority of the resistance followed by erythromycin and ampicillin.However these three antibiotics are not regularly used in our hospital.The commonly used antibiotics like Amikacin, Cephalexin and Cefotaxime also encountered resistance and this is a matter of concern [Table 4].
Once a SSI developed the surgeons order for culture and sensitivity tests and the antibiotics are changed accordingly.Co-morbid conditions like diabetes and hypertension were also monitored strictly.Despite these measures only 26(66.66%)SSIs were completely healed at the time of discharge.11(28.21%)patients went home with SSI still persisting.One patient had to be operated again to control SSI and one elderly patient succumbed to septicemia.

DISCUSSION
Post-operative wound infection still remains one of the most important causes of morbidity and is the most common nosocomial infection [2,12] in surgically treated patients.The present study was carried out among 180 elective surgery cases in the government tertiary care teaching hospital at Mysore, Karnataka state.Majority of the surgeries were abdominal followed by limb, thyroid surgeries, lipoma and other tumor excisions.
The rate of SSI varies greatly worldwide and from hospital to hospital.][8][9] The incidence of SSI in the present study is 21.66% even though high, is in agreement with the various studies.
The rate of SSI increases with the increase in age.In the current study a higher proportion of SSI was found among the subjects older than 50 years.][14][15] This is due to poor immune response, existing co morbidities in old patients and reduced compliance with treatment. [8] the present study a signifi cant proportion of males developed SSI compared to females.In another study in Pune, there was a marginal preponderance of male patients developing SSI (7.4%) over female patients with SSI (5.1%). [16]In Aligarh, females (27%) showed preponderance of SSI than males (18%). [17]However according to Berard F and Gandon J sex is not a pre determinant of the risk of SSI. [18] the present study, both underweight (BMI <18.5) and overweight (BMI>25.0)have been found to signifi cantly infl uence the onset of SSI.Similar results were found by Ashby etal. [15]In a study, by Xue etal., and Giles etal., higher BMI was a signifi cant predictor of SSI. [14,19] morbid conditions like anemia, diabetes and hypertension were the signifi cant risk factors for SSI.Diabetes remained signifi cant predictor in multivariate anlaysis.National Academy of Science also reported higher rate of infection in patients with Diabetes mellitus which is similar to our study. [13]Comparable results were found in various studies involving different surgical procedures. [14,19]dose-response relationship was noted in the association between blood transfusion and SSIs in the current study.Majority of the transfusions were intra or per operative.In a study by Tang et al., blood transfusion was found to be an important risk factor in determining SSI [20] which is similar to the present study.Allogeneic blood transfusion induces immunosuppression and predisposes to postoperative infection. [20]prolonged pre operative hospital stay with exposure to hospital environment has been shown to increase the risk of SSI. [6]omparable fi ndings were found in the present study.Anvikar A.R. and Lilani S.P. also reported higher rate of SSI in patients with prolonged preoperative hospital stay. [6,7]Prolonged preoperative hospital stay leads to colonization with antimicrobial resistant micro organisms and itself directly affects patient's susceptibility to infection either by lowering host resistance or by providing increased opportunity for ultimate bacterial colonization. [8]e-operative antibiotics are known to decrease incidence of SSI cases. [7,18,21]Prophylactic antibiotic usage was not a routine in the studied hospital.Only selected patients who had some infection or other risk factor received antibiotic prophylaxis.When it was not used a large proportion (24%) developed SSI compared to the situations where such prophylaxis was given.
Staphylococcus aureus was the predominant organism isolated from the surgical sites followed by Pseudomonas and Klebsiella in the present study.E.coli, citrobacter and proteus were the other organisms isolated from SSIs.Lilani et al., and Mahesh et al., also found pre-ponderance of Staphylococcus aureus and Pseudomonas in SSIs in their studies. [6,22]Many studies have reported Staphylococcus aureus as the commonest isolate from the postoperative wound infection. [9,23,24]Other organisms have shown varied preponderance in different studies.Staphylococcus aureus forms the bulk of the normal fl ora of skin and nails. [25]Hence; it is the commonest organism found in most of the SSIs.The high incidence of gram-negative organisms in the postoperative wound infections can be attributed to be acquired from patient's normal endogenous micro fl ora. [24] [10] International Journal of Medicine and Public Health | Apr-Jun 2014 | Vol 4 | Issue 2

Table 1
The age of study subjects ranged between 18 years to 67 years.Majority (64.44%) of them belonged to 18-30 years group.Out of 116 patients in this group 11 (9.5%) got infected.19patients were more than 50 years and among them 12(63%) developed surgical site infection.It was found that the frequency of SSI increased with age and this was statistically signifi cant [Table

Table 1 : Distribution of surgeries according to site
International Journal of Medicine and Public Health | Apr-Jun 2014 | Vol 4 | Issue 2received more than 3 units of blood and all of them developed infections [Table2].The parameters which had univariate statistical signifi cance were; Age, gender, BMI, Co morbid conditions: Anemia, Hypertentsion and Diabetes mellitus, Blood transfusion, pre operative waiting and prophylactic antibiotic usage.These were entered into multivariate analysis.Gender, Extreme BMI, Diabetes mellitus and Blood transfusion remained independent predictors of surgical site infection in multivariate analysis.Anemia, Hypertension and Prophylactic antibiotic usage did not show statistical signifi cance [Table

Table 2 : Factors associated with SSI
*Some SSIs were associated with multiple co-morbid conditions International Journal of Medicine and Public Health | Apr-Jun 2014 | Vol 4 | Issue 2

Table 3 : Organisms associated with SSI
Some SSIs were associated with multiple organisms, # of the 39 SSI only 36 showed the growth. *

Table 4 : Antibiogram
*Some organisms are resistant to more than one antibiotic, #of the 39 SSI only 36 showed the growth