The objective of this study is to answer three main questions: What is the risk of wound infection for patients undergoing hip arthroplasty? What are the main etiologicagents of surgical site infection (SSI)? What are the risk factors most associated with surgical site infection? Method: This was a multicentric, retrospective cohort study which analyzed data collected in five general hospitals in Belo Horizonte, Brazil, between the period of January 2009 and December 2013. The continuous parameters studied were age, length of hospital stay before surgery, duration of surgery, number of professionals at surgery and number of hospital admissions. Categorical variables were surgical wound classification (clean, clean contaminated, contaminated, dirty/infected), American Society of Anesthesiologists (ASA) score (I, II, III, IV, V), type of surgery (elective, emergency), general anesthesia (yes, no), prophylactic antibiotic (yes, no), trauma surgery (yes, no) and Nosocomial Infections Surveillance (NNIS) risk index (IRIC = 0, 1, 2, 3). Results: Estimated SSI risk was 3.2% (95% C.I. = 2.6% to 4.1%) and risk of osteomyelitis was 0.6% (95% C.I. = 0.4% to 1.1%). ASA score > 2, general anesthesia, length of hospital stay before surgery higher than four days, more than two professionals at surgical field and duration of surgery higher than five hours were risk factors for SSI after hip prosthesis ( p < 0.05). The final multiple logistic regression analysis indicated that the modified NNIS risk was independently associated with surgical site infection after arthroplasty of hip. Conclusion: Despite the modified NNIS index being a risk factor for SSI, none of its independent variables was statistically significantly in the logistic model ( p > 0.100). Each modified NNIS risk category increased the chance of a patient being infected by almost three times, when compared with the previous category (OR = 2.82; p = 0.011).
Total hip arthroplasty (THA) is one of the most common orthopedic interventions [
There are several types of hip arthroplasty, and the choice of which one to use is dependent on patients’ needs and on the experience of the professionals. It is not the objective of this paper to explore the different procedures involved in THA. A meta-analysis published in 2014 showed that most evidence indicated no difference for post-surgery scores for functional and clinical measures between the different types of THA, even though the study was impaired due to missing data and poor reporting [
The number of THAs is steadily increasing and it is projected that by 2020, it will exceed 500,000 procedures per year [
Some factors are known to increase the risk of infection after surgery. Patient-related factors include (but are not limited to) age, gender, obesity and American Society of Anesthesiologists (ASA) score, while surgery-re- lated factors include duration of surgery, antibiotic prophylaxis, type of anesthesia and NNIS Index score [
This multicentric retrospective cohort study assessed SSI risk factors in patients undergoing total hip replacement during the period of January, 2009 to December, 2013 in five general hospitals in Belo Horizonte, Brazil.
The Hospital Infection Control Committees (HICC) of these hospitals gathered all the data used in our analysis during their routine procedures for surgical site infection surveillance following standard methods defined by the National Healthcare Safety Network (NHSN). The outcome variables were surgical site infection and osteomyelitis. The preoperative and operative parameters were divided into continuous and categorical variables. The former includes age, duration of hospital stay before surgery, duration of surgery, number of professionals involved in surgery and number of hospital admissions. The latter were surgical wound classification, the American Society of Anesthesiologists (ASA) preoperative assessment score, type of surgery (elective, emergency), general anesthesia (yes, no), prophylactic antibiotics (yes, no), trauma surgery (yes, no) and Nosocomial Infections Surveillance―NNIS risk index (0, 1, 2, 3).
Risk and protection factors for infection were identified by bilateral statistical hypothesis testing; the significance level was 5% (α = 0.05).Student’s t test or non-parametric tests were applied to assess continuous variables. The chi-square or Fisher’s exact test were used to analyze categorical variables, when necessary.
Analysis of each factor yielded a point estimate at a 95% confidence interval (C.I.―95%) for relative risk. A multivariate analysis with logistic regression was applied in the last phase of the study. Variables tested in the logistic model were selected when the univariate analysis generated a p-value ≤ 0.25.
A total of 2,161 patients undergoing hip arthroplasty in five Brazilian general hospitals during January, 2009 to December, 2013 were enrolled in our study. Surgical site infections were diagnosed in 70 of those patients while osteomyelitis were identified in 14 patients. The estimated SSI risk was 3.2% (C.I. 95% = [2.6% - 4.1%]) and the risk of osteomyelitis was 0.6% [C.I. 95% = [0.4% - 1.1%]).
The etiology of SSIs was identified in 70% of the cases and 65 different microorganisms were found in 49 SSIs: 27 Staphylococcus aureus (44%), 7 Acinetobacter baumannii (11%), 6 Escherichia coli (10%), 5 Pseudomonas aeruginosa (8%), and 19 were other microorganisms. The main etiologic agent in osteomyelitis was Staphylococcus aureus―61% of cases, followed by Escherichia coli (2), Acinetobacter baumannii (2), and Staphylococcus epidermidis (1).
The results of our univariate analysis of the continuous variables are shown in
The Modified NNIS risk index values range from 0 to 4 points and are defined by four independent and equally weighted variables. One point is given for each of the following factors: ASA score higher than two, wound classification as either contaminated or dirty/infected, duration of surgery over two hours (75th percentile for duration of hip replacement), and the need for general anesthesia.
The risk of surgical site infection, as aforementioned, is estimated to be between 0.2% to 1.1% [
Native microorganisms of the skin are the most associated with SSI [
Variable | SSI | Mean | Median | Standard Deviation | p-value |
---|---|---|---|---|---|
Age (Years) | Yes | 62.3 | 64 | 20.5 | 0.29 |
No | 65 | 67 | 16.4 | ||
Length of Hospital Stay Before Surgery (Days) | Yes | 3.2 | 1 | 6.8 | <0.001* |
No | 1.6 | 0 | 5.4 | ||
Durationof Surgery (Hours) | Yes | 2.7 | 2.5 | 1.2 | 0.158 |
No | 2.5 | 2.3 | 1 | ||
Number of Professionals at Surgery | Yes | 1.8 | 1 | 1 | 0.080* |
No | 1.9 | 2 | 0.7 | ||
Numberof Hospital Admissions | Yes | 1.4 | 1 | 0.8 | 0.216 |
No | 1.3 | 1 | 0.7 |
*Mann-Whitney/Wilcoxon Two-Sample Test. Other p-values calculated by student T-test.
Variable | Categories | n | SSI | SSI Risk (%) | RR | [C.I. 95% R.R.] | p-value |
---|---|---|---|---|---|---|---|
Surgical Wound Classification | Contaminatedordirty/infected | 29 | 2.00 | 6.9% | 2.63 | [0.67; 10.35] | 0.183 |
Clean or clean-contaminated | 1602 | 42.00 | 2.6% | ||||
American Society of Anesthesiologists (ASA) | >2 | 321 | 16.00 | 5.0% | 2.29 | [1.25; 4.18] | 0.011 |
≤2 | 1286 | 28.00 | 2.2% | ||||
Type of Surgery | Emergency | 83 | 4.00 | 4.8% | 1.96 | [0.71; 5.36] | 0.164 |
Elective | 1501 | 37.00 | 2.5% | ||||
General Anesthesia | Yes | 697 | 29.00 | 4.2% | 1.88 | [1.09; 3.24] | 0.029 |
No | 993 | 22.00 | 2.2% | ||||
Prophylactic Antibiotic | Yes | 772 | 39.00 | 5.1% | 0.41 | [0.18; 0.93] | 0.045 |
No | 49 | 6.00 | 12.2% | ||||
Trauma Surgery | Yes | 136 | 4.00 | 2.9% | 1.27 | [0.46; 3.52] | 0.558 |
No | 1422 | 33.00 | 2.3% | ||||
NNIS Risk Index | 0 | 1017 | 13.00 | 1.3% | - | - | <0.001 |
1 | 329 | 15.00 | 4.6% | ||||
2 | 20 | 3.00 | 15.0% | ||||
Length of Hospital Stay Before Surgery (Days) | >4 | 187 | 12.00 | 6.4% | 2.18 | [1.19; 3.99] | 0.016 |
≤4 | 1974 | 58.00 | 2.9% | ||||
Number of Professionals at Surgery | >2 | 234 | 14.00 | 6.0% | 2.73 | [1.51; 4.93] | 0.003 |
≤2 | 1822 | 40.00 | 2.2% | ||||
First Hospital Admission | Yes | 1750 | 53.00 | 3.0% | 0.73 | [0.43; 1.25] | 0.277 |
No | 411 | 17.00 | 4.1% | ||||
Age (Years) | >60 | 1377 | 43.00 | 3.1% | 0.91 | [0.56; 1.46] | 0.705 |
≤60 | 784 | 27.00 | 3.4% | ||||
Duration of Surgery (Hours) | >2 | 1003 | 33.00 | 3.3% | 1.14 | [0.64; 2.0] | 0.770 |
≤2 | 621 | 18.00 | 2.9% |
Variable | Coefficient | Standard Error | p-value | OddsRatio | [C.I. 95%] |
---|---|---|---|---|---|
ASA >2 | −0.54 | 0.65 | 0.408 | 0.58 | [0.16; 2.09] |
DurationofSurgery >2 hours | −0.39 | 0.42 | 0.362 | 0.68 | [0.30; 1.56] |
Surgical Wound Classification: Contaminated or dirty/infected | −0.17 | 0.98 | 0.866 | 0.85 | [0.12; 5.81] |
NNIS Risk Index | 0.55 | 0.71 | 0.444 | 1.73 | [0.43; 7.00] |
Modified NNIS Risk Index | 1.04 | 0.41 | 0.011 | 2.82 | [1.27; 6.26] |
Constant | −4.63 | 0.42 | 0 | 0.01 | 0 |
44%. Despite the advances in antibiotic prophylaxis, skin preparation remains as an important factor in reducing the risk of SSI [
The only preoperative risk factor suggested by our study was the ASA score. All the other risk factors indicated were operative factors. The ASA score is an indicator of the impact of comorbidities in the patient’s general health. A score equal to or greater than 3 is associated with increased risk of infection after surgery by some authors [
Although none of our references studied the number of professionals at surgery, [
The length of hospital stay before surgery was also indicated as risk factor for SSI after THA in our study and not explored in our references. Seriated genotyping evaluations are necessary to better determine the period after which the skin is colonized by hospital microorganisms. Duration of surgery, on the other hand, is associated with increased risk of SSI [
Some authors [
Antibiotic prophylaxis is a well-established method to prevent post-surgery infection [
Surgical site infection is one of the most common complications after THA. Our study estimates a rate of SSI in five Brazilian general hospitals that are almost three times higher than international studies. Identifying risk factors and addressing them prior to the procedure is key in preventing SSI.
Our analysis points that an ASA score higher than 2, the use of general anesthesia, and the number of professionals at surgery higher than 2 are risk factors for the development of SSI after THA. In our multivariate analysis, only the Modified NNIS risk index is pointed as a risk factor for SSI. Antibiotic prophylaxis is suggested to be a protective measure against SSI.
As a retrospective analysis, this study has several limitations. Nonetheless, it suggests important opportunities to improve the quality of care and to prevent SSI in hip arthroplasty, such as avoiding general anesthesia, keeping the operative staff to a minimum and diminishing traffic in the operating room. Elaboration of new pre-surgery protocols or reviewing the current ones and adherence to them, as well as proper collection of data for future analysis may be important measures to decrease the risk of infection in the studied hospitals.
We would like to thank FAPEMIG (Fundação de Amparo à Pesquisa do Estado de Minas Gerais) for their continuing effort in supporting and stimulating scientific projects and technologic innovation in Brazil.
Gabriel B.Tofani,Gustavo P.Irffi,Lucas F.Silva,Cynthia C. M.da Silva,Bráulio R. G. M.Couto,Gilberto D.Miranda,Carlos E. F.Starling, (2016) Risk Factors for Surgical Site Infection after Hip Arthroplasty: A Multicentric Study. Surgical Science,07,58-64. doi: 10.4236/ss.2016.72008
THA―Total Hip Arthroplasty
SSI―Surgical Site Infection
NNIS―National Nosocomial Infections Surveillance
HICC―Hospital Infection Control Committee
NHSN―National Healthcare Safety Network
ASA―American Society of Anesthesiologists
C.I.―Confidence Interval