Incidence and risk factors for surgical site infection in general surgeries 1

ABSTRACT Objective: to estimate the incidence of surgical site infection in general surgeries at a large Brazilian hospital while identifying risk factors and prevalent microorganisms. Method: non-concurrent cohort study with 16,882 information of patients undergoing general surgery from 2008 to 2011. Data were analyzed by descriptive, bivariate and multivariate analysis. Results: the incidence of surgical site infection was 3.4%. The risk factors associated with surgical site infection were: length of preoperative hospital stay more than 24 hours; duration of surgery in hours; wound class clean-contaminated, contaminated and dirty/infected; and ASA index classified into ASA II, III and IV/V. Staphyloccocus aureus and Escherichia coli were identified. Conclusion: the incidence was lower than that found in the national studies on general surgeries. These risk factors corroborate those presented by the National Nosocomial Infection Surveillance System Risk Index, by the addition of the length of preoperative hospital stay. The identification of the actual incidence of surgical site infection in general surgeries and associated risk factors may support the actions of the health team in order to minimize the complications caused by surgical site infection.

In the Brazilian literature, there is a lack of studies on general surgeries, which makes it difficult to estimate the SSI rates and the identification of risk factors associated with infection. Therefore this study arose from the need to identify risk factors for SSI in general surgeries, since the scientific production on this subject has privileged the survey in specific surgeries (4)(5)(6)(7)9) . This study aimed to estimate the incidence of Data extracted from SACIH software were entered into an EXCEL spreadsheet by the researchers, and then exported to STATA 12 software for statistical analysis (StataCorp, College Station, TX). Access to the SACIH database was authorized by the study hospital administration and by the coordination of the HICS.
As inclusion criterion, information was selected from patients submitted to general surgeries classified as NHSN and performed in patients older than 18 years. An NHSN procedure is defined as that performed in an operating room where the surgeon makes at least one incision, which is closed before leaving the operating room.
Initially, the database had information on 20,124 general surgical procedures. After applying the inclusion criteria, a population of 17,236 procedures was achieved. In analyzing the data consistency, the missing and/or inconsistent information identified in each database variable were excluded and data were analyzed in relation to the complete information in order to verify the occurrence or not of the differential loss.
It should be noted that study losses were classified as non-differential. Therefore, a final sample of 16,882 procedures was used ( Figure 1).
The presence or absence of SSI was considered as a dependent variable. The following independent variables were analyzed: gender (male and female); age (under and above 54 years old, according to the average, since the variable presents normal distribution); preoperative hospital stay (greater and less than 24 hours before the surgical procedure, as  Bivariate analysis showed an association between most of the independent variables with the dependent variable SSI (p<0.20), except for age and implant use (

Discussion
The overall SSI incidence of 3.4% found in this study was higher than studies carried out in developed countries, such as USA (2) , 1.9%; France, 1.0% (14) and Italy, 2.6% (15) . However, it was lower than in studies carried out in data reported from India and Turkey, which presented an SSI incidence of 5.0% (16) and 4.1% (17) , respectively. Two Brazilian studies involving SSI in general surgeries had higher rates than the identified incidence and compared to international researches, ranging from 6.4% (8) to 11.0% (3) .
The variation in incidence rates observed between the literature and the data from this study may be related However, it can be inferred that the low incidence of SSI found in this study may be related to the nonperformance of PDS. Data involving orthopedic patients (9) showed that the non-performance of PDS impacts on the actual SSI rate, which may be 3 times higher when performed only during the hospitalization of the patient.
The risk factors for SSI identified were: length of preoperative hospital stay, duration of surgery, ASA index and PCSW. In this study these risk factors were also identified in researches conducted with a larger number of patients and involving general surgeries (2,(14)(15)(16)(17) .
In specific surgeries, such as orthopedic surgeries (4,6) , factors such as ASA index, Wound class and duration of surgery were statistically associated with SSI, although in head and neck surgeries (5) (4,6,9) .

ANVISA (3) recommends a preoperative hospital stay
of less than 24 hours as an indicator of the process and structure for SSI prevention (3) . A preoperative hospital stay greater than 24 hours is related to a greater incidence of contamination of the patient during the hospitalization period (19) , facilitating the development of infectious processes (20) .
Another variable that showed a statistically significant association with SSI was the duration of surgery. In this study, for each hour of duration of surgery, there was a 34% increase in the chance of SSI development (p<0.001). The duration of surgery is associated with higher SSI rates (4,(13)(14)(15)(16)(17)21) . It is inferred that this may be related to a greater exposure of the incision site to pathogens (22) and/or a greater chance of breach of the aseptic technique in the procedure (23) .
It is worth mentioning that the duration of surgery correlates with other risk factors predisposing to SSI, such as the ASA index, suggesting that patients with higher ASA rates tend to have longer duration of surgery (18) .
In addition, increased duration of surgery is associated not only with increased SSI rates, but also with other clinical and post-surgical complications such as wound dehiscence, development of Urinary Tract Infection and even septic shock (21) . The search for a shorter duration of surgery can significantly improve the risk of SSI.
The variable PCSW was also statistically associated with SSI. Those surgeries as clean-contaminated, contaminated and dirty/infected showed an increase