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 Table of Contents  
ORIGINAL ARTICLE
Year : 2021  |  Volume : 18  |  Issue : 2  |  Page : 56-61

Can preoperative screening for methicillin-resistant staphylococcus aureus effectively predict surgical site infections in spine surgeries?


1 Department of Spine Surgery, Baby Memorial Hospital, Kozhikode, Kerala, India
2 Department of Microbiology, Baby Memorial Hospital, Kozhikode, Kerala, India

Date of Submission09-Nov-2021
Date of Acceptance07-Dec-2021
Date of Web Publication27-Jan-2022

Correspondence Address:
Suresh S Pillai
Senior Consultant Spine Surgeon, Department of Orthopaedics, Baby Memorial Hospital, Calicut, Kerala-673 004
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/joasis.joasis_32_21

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  Abstract 


Introduction: Hospital care-associated infections prolong hospital stay and thus increased financial burden, causes long-term disability and mortality in patients and can increase resistance of microorganisms to antimicrobials. Surgical site infections (SSIs) are the most frequent type of hospital care-associated infections in the developing countries. Staphylococcus is the most commonly isolated organism with methicillin-resistant Staphylococcus aureus (MRSA) posing a great threat. The most common human reservoir for S. aureus is the nares. We propose a study to evaluate the efficacy of preoperative screening of MRSA by nasal and throat culture by correlating it with postoperative SSI. Study Design: Prospective study. Purpose of the Study: 1. To determine the prevalence of MRSA colonization in a population of patients scheduled for elective spine surgery. 2. To determine whether preoperative nasal and throat swab cultures for MRSA are predictive of postoperative SSI in patients undergoing spine surgery. Materials and Methods: Two hundred and forty-eight patients who underwent spine surgery at Baby Memorial Hospital, Calicut, from December 2018 onward are included in this study. Patients who had spine surgeries for infections were excluded from the study. Patients who developed postoperative SSIs were cross-checked with preoperative data and analyzed whether the infecting organism is same as in the preoperative nasal and throat swab culture (if it is present). The significance of the correlation between preoperative nasal and throat swab culture and postoperative SSI are assessed statistically with Chi-square test. Discussion: Among the 248 patients in this study, preoperative nasal and throat swab culture yielded MRSA in 27 patients (nasal – 24, throat – 2, and both – 1). Out of 248 patients, 6 patients developed SSIs with MRSA, but none of them had MRSA in preoperative nasal or throat swab culture. Conclusion: Preoperative MRSA screening by throat and nasal swab is not routinely needed in spine surgery as it appears to carry no positive predictive value in postoperative SSIs.

Keywords: Methicillin-resistant Staphylococcus aureus, screening, spine surgery, surgical site infection


How to cite this article:
Pillai SS, Dennison P, Manikandan T, Sudarsana J. Can preoperative screening for methicillin-resistant staphylococcus aureus effectively predict surgical site infections in spine surgeries?. J Orthop Assoc South Indian States 2021;18:56-61

How to cite this URL:
Pillai SS, Dennison P, Manikandan T, Sudarsana J. Can preoperative screening for methicillin-resistant staphylococcus aureus effectively predict surgical site infections in spine surgeries?. J Orthop Assoc South Indian States [serial online] 2021 [cited 2022 May 26];18:56-61. Available from: https://www.joasis.org/text.asp?2021/18/2/56/336659




  Introduction Top


Staphylococcus aureus is the most common organism responsible for surgical site infection (SSI).[1] Methicillin-resistant S. aureus (MRSA) is a much severe problem in postoperative wound infection because of its drug resistance. MRSA is endemic worldwide in hospitals and prompt diagnosis can prevent serious infections such as necrotizing fasciitis, septicemia, and osteomyelitis. There is an upward trend in the S. aureus being methicillin-resistant in the isolates from patients in the intensive care units (ICUs) over the years. Compared to methicillin-sensitive S. aureus (MSSA), MRSA poses a greater threat as the length of hospitalization, mortality rate and hospital costs are higher.[2],[3],[4] A large multicentric study showed that 41% of the S. aureus isolated in India were MRSA.[5] Similar results were seen in the US with MRSA ICU infections as high as 53% of all S. aureus, whereas Canada showed lower prevalence.[6],[7] Bhattacharya et al. reported that 34.93% of SSIs were caused by S. aureus, among which 25.45% were due to MRSA.[8]

The 90-day mortality, as reported, increased significantly with MRSA (20.7%) compared to MSSA (6.7%).[9] MRSA carries the mecA gene, which is responsible for the methicillin resistance. mecA gene is located on a genomic island named the staphylococcal cassette chromosome mec (SCCmec) element, which itself has five distinct types. SCCmec is a mobile genetic element that is capable of exchange between different staphylococcal species, and cassette chromosome recombinase gene complex is responsible for the mobility.[10],[11] The antibiotic susceptibility pattern is the main difference between MRSA and MSSA cells. MRSA cells are resistant to all β-lactam antibiotics and can acquire resistance to other antibiotics easily, leading to the development of multiresistant strains. Multiple drug resistance might give a selective advantage for MRSA cells, under antibiotic pressure in hospital settings, making it more virulent than MSSA.[12],[13] Lack of proper antibiotic stewardship may lead to antibiotic resistance. Acquisition of mecA gene encoding for penicillin-binding protein decreases the affinity for β-lactam antibiotics which allow cell wall synthesis even in the presence of penicillins, cephalosporins, and carbapenems. In such situations, the choice of treatment of MRSA infections becomes limited significantly [Table 1] and [Table 2].
Table 1: All positive cases – Swab or Surgical Site Infection

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Table 2: Swab result vs Surgical Site Infection

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To reduce the suffering and economic burden due to MRSA, screening of patients for MRSA at the time of admission to hospitals was started. Screening is done in an effort to decolonize these patients before elective surgeries. However, it is uncertain whether this practice is evidence-based or not.

Many previous studies have come out with opposing evidence on the efficacy of the screening in positive predictive value on SSI. Luhman et al. did a screening study on pediatric spine surgeries and reported that 22.1% of patients screened showed MRSA or MSSA in nares swab. They used this data to adjust preoperative antibiotic regimens and to incorporate intraoperative SSI prevention measures in the study population.[14] Takkar et al. did a retrospective study on spine surgery cases and reported two out of five MRSA SSIs had a positive nasal swab culture of MRSA. Although a direct correlation was not made, they recommend preoperative screening with nares culture.[15] To the best of our knowledge, this is the first prospective study which was unbiased by preoperative swab test and proceeded to surgery with standard antibiotic policy.


  Materials and Methods Top


Study design

A prospective study was conducted from December 2018 to October 2021 in a single hospital. The study population included all patients undergoing spine surgery under a single surgeon. All the patients were screened for nasal and throat MRSA one day before surgery. Patients then went on to have the surgery done under the standard antibiotic protocol of the hospital. Swab culture results were collected postoperatively, but no change in the antibiotic policy was made unless the patient showed signs of infection. Standard antibiotic protocol of the institution, in orthopedics was injection cefuroxime 1.5 gm IV 30 min before surgery, and continued till 72 h postsurgery. The diagnosis of SSI was made according to the Center for Disease Control SSI criteria, which defines SSI as an infection occurring at the surgical wound site within 30 days postoperatively or within a year if an implant is used. All infections were treated with debridement and culture – aerobic, anaerobic, mycobacterial, and fungal, followed by culture-specific antibiotics. Patients who had spine surgeries for infections were excluded from the study [Figure 1], [Figure 2], [Figure 3].
Figure 1: Gender vs Throat Swab Result

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Figure 2: Nasal and Throat Swab positive cases by Age Group

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Figure 3: Swab Result vs Surgical Site Infection

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Statistical analysis

Statistical analysis was conducted using SPSS v 20.0 (IBM Corp. Released 2011. IBM SPSS Statistics for windows, Version 20.0. Armonk, NY: IBM Corp). Statistical significance was calculated by Chi-square test. Statistical significance was set at P < 0.05.


  Results Top


Prevalence

Total number of patients examined was 248. Out of which, 55 (22%) patients had positive culture, in either nasal (43 – 17.7%) or throat (11 – 4.8%) or both throat and nasal (1) swabs. Among the 55 swab-positive cases, only 22 (40% among swab-positive and 8.9% of total patients) yielded MRSA. Nineteen (7.7%) patients had nasal colonization alone, two (0.8%) had throat colonization alone, and one (0.4%) had simultaneous throat and nasal colonization of MRSA. Other organisms grown were 24 in nasal and 9 in throat swabs. Throat swab-specific organisms were Haemophilus influenzae (5 – 2%) and Streptococcus pneumoniae (2 – 0.8%). MSSA was the most common organism cultured among non-MRSA organisms (18 – 7.3%; 16 nasal and 2 in throat swab culture) followed by coagulase-negative Staphylococcus species (8 – 3.2%; methicillin-resistant 6 and methicillin-sensitive 2). Only one patient had two organisms cultured, MSSA and H. influenzae in throat swab.

We had 14 (5.6%) SSIs among which 6 (2.4%) were caused by MRSA and 8 (3.2%) were non-MRSA organisms. Non-MRSA organisms were MSSA (3 – 1.2%), methicillin-resistant coagulase-negative Staphylococcus species (3 – 1.2%), Pseudomonas aeruginosa (1 – 0.4%), and Acinetobacter baumanni (1 – 0.4%).

Demographical aspects

Gender

Out of the 248 patients screened, 126 were males and 122 were females. Among the 55 swab-positive cases, 31 (12.5% of total and 24.6% among men) were males and 24 (9.7% of total and 19.7% among women) were females. Male-to-female ratio was 1.3:1. MRSA positivity rates in cultures were 12 and 10 for men and women, respectively – 1.2:1.

We had a total of 14 SSIs of which 6 were in males and 8 in females. MRSA SSI rates were two in males and four in females, with a clear female preponderance (1:2).

Age

Our study population had a mean age of 47.58 years, with quarter of the cases done in 51 to 60 years age group (63 – 25.4%). Maximum number of infections were noted in the 41 – 50 years age group (5 – 35.7%). 2 each in 31 – 40 years, 51-60 years and 61 – 70 years (14.3%) and 1 infection in 71 – 80 years (7.1%).

No MRSA infections were noted in 51 – 60 years age group, where maximum number of cases was done. Four infections were in 41 to 50 age group (66.7%) and one each in 61 to 70 and 71 to 80 age groups (16.7%).

Relation between swab culture and surgical site infection

Among the swab-positive cases in our study, only two developed SSIs. One culture yielded MSSA, whereas the other was methicillin-resistant coagulase-negative Staphylococcus. One had MRSA infection, whereas the other was infected by Pseudomonas aeruginosa. Thus, even in cases with positive nasal or throat culture, where SSIs occurred, the infecting organisms were not the same as in swab culture. Chi-square test yielded 0.993 signifying no correlation between MRSA in nasal or throat swabs and SSIs.


  Discussion Top


The impact of hospital-acquired infections lies in prolonged hospital stay and additional financial burden for health systems and patients, long-term disability, increased resistance of microorganisms to antimicrobials, and unnecessary deaths.[3] SSI is the most frequent type of hospital-acquired infection in developing countries, and ranges from 1.2% to 23.6%. SSIs in our study were only 5.6%, which were comparable to developed countries (2%–3%), and lower than other studies conducted in the Indian subcontinent (15.51% and 17.8%).[1],[3],[8]

S. aureus comprised more than half of SSI in our study (9 – 64.3%) which was much higher than Bhattacharya et al. reported (34.93%) and comparable to Negi et al. (50.4%).[1],[8] Among the S. aureus, MRSA was 66.7%, which was also much higher than studies by Negi et al. (5.7%) and Bhattacharya et al. (25.45%), but comparable to study by Kaye et al. (58.2%).[1],[4],[8]

MRSA infections were noted in 6 patients (2.4% of total study) with a gender distribution of MRSA infection 2:1 in favor of women, which was in contrast to study by Bhattacharya et al. who observed male preponderance (1:1.67).[8]

Takkar et al. did a retrospective study of MRSA screening with postoperative SSIs in spine surgeries, and reported that MRSA SSI developed in 8% of the MRSA-positive group versus 0.61% in the MRSA-negative group.[15] Luhman et al. did a prospective study in pediatric spine surgeries and found no positive correlation between screening and postoperative MRSA SSI. This could be as a result of the latter study taking precautionary measures in the form of preoperative nasal decolonization with mupirocin ointment for 5 days, adjusting the preoperative antibiotic regime, and intraoperative preventive measures.[14]

Our study has a prospective design but was unbiased as no change in standard antibiotic policy (preoperative, intraoperative, or postoperative) nor attempt to decolonize the nares were done in any patients. Still we observed no positive correlation between nasal or throat swab cultures and SSIs.


  Conclusion Top


We cannot for sure say, nasal and throat swab screening completely excludes MRSA colonization. Or in other words, throat and nasal cavity alone may not be the colonization areas. It could be any skin fold or in the axilla or the groin. Hence, when throat and nasal swab cultures are negative, that does not mean the patient is not a carrier of MRSA elsewhere in the body. Meanwhile, when MRSA is present in nasal and throat swab cultures and wound infection occurs, it is not due to the MRSA harbored in the nasal or throat cavity. This reult undermines the significance of screening for MRSA with nasal and throat swabs.

This study does not test the efficacy of decolonization or effectiveness of screening programs. It tests whether MRSA isolated by nasal and throat swab cultures causes postoperative wound infection, if it occurs. In none of the cases in our study, there was a positive correlation.

Screening MRSA with nasal and throat swabs is cost-effective, but unfortunately, it did not correlate to SSIs. We conclude that preoperative MRSA screening by throat and nasal swabs is not routinely needed as it appears to have no way of predicting SSIs in elective spine surgeries.

Ethical clearance

Ethical Clearance have been obtained prior to study from Baby Memorial Hospital Ethical Clearance Group.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Negi V, Pal S, Juyal D, Sharma MK, Sharma N. Bacteriological Profile of Surgical Site Infections and Their Antibiogram: A Study From Resource Constrained Rural Setting of Uttarakhand State, India. J Clin Diagn Res 2015;9:DC17-20.  Back to cited text no. 1
    
2.
Lodise TP, McKinnon PS. Clinical and economic impact of methicillin resistance in patients with Staphylococcus aureus bacteremia. Diagn Microbiol Infect Dis 2005;52:113–22.  Back to cited text no. 2
    
3.
California Code, Health and Safety Code - HSC § 1288.55 [Internet]. Findlaw. [cited 2020 Nov 10]. Available from: https://codes.findlaw.com/ca/health-and-safety-code/hsc-sect-1288-55.html. [Last accessed on 2020 Nov 10].  Back to cited text no. 3
    
4.
Kaye KS, Anderson DJ, Sloane R, Chen LF, Choi Y, Link K, et al. The Impact of Surgical Site Infection on Older Operative Patients. J Am Geriatr Soc 2009;57:46–54.  Back to cited text no. 4
    
5.
Joshi S, Ray P, Manchanda V, Bajaj J, Chitnis DS, Gautam V, et al. Methicillin resistant Staphylococcus aureus (MRSA) in India: Prevalence & susceptibility pattern. Indian J Med Res 2013;137:363–9.  Back to cited text no. 5
    
6.
Kil EH, Heymann WR, Weinberg JM. Methicillin-resistant Staphylococcus aureus: an update for the dermatologist, Part 1: Epidemiology. Cutis 2008 ;81:227–33.  Back to cited text no. 6
    
7.
Pre-Operative Screening for Methicillin-Resistant Staphylococcus aureus (MRSA) Infection: A Review of the Clinical-Effectiveness and Guidelines. CADTH Technol Overv 2010;1:e0114.  Back to cited text no. 7
    
8.
Bhattacharya S, Pal K, Jain S, Chatterjee SS, Konar J. Surgical Site Infection by Methicillin Resistant Staphylococcus aureus– on Decline? J Clin Diagn Res. 2016;10:DC32–6.  Back to cited text no. 8
    
9.
Engemann JJ, Carmeli Y, Cosgrove SE, Fowler VG, Bronstein MZ, Trivette SL, et al. Adverse clinical and economic outcomes attributable to methicillin resistance among patients with Staphylococcus aureus surgical site infection. Clin Infect Dis 2003;36:592–8.  Back to cited text no. 9
    
10.
Katayama Y, Ito T, Hiramatsu K. A New Class of Genetic Element, Staphylococcus Cassette Chromosome mec, Encodes Methicillin Resistance in Staphylococcus aureus. Antimicrob Agents Chemother 2000;44:1549–55.  Back to cited text no. 10
    
11.
Ito T, Ma XX, Takeuchi F, Okuma K, Yuzawa H, Hiramatsu K. Novel Type V Staphylococcal Cassette Chromosome mec Driven by a Novel Cassette Chromosome Recombinase, ccrC. Antimicrob Agents Chemother 2004;48:2637–51.  Back to cited text no. 11
    
12.
Rozgonyi F, Kocsis E, Kristóf K, Nagy K. Is MRSA more virulent than MSSA? Clinical Microbiology and Infection 2007;13:843–5.  Back to cited text no. 12
    
13.
Vriens MR, Fluit AC, Troelstra A, Verhoef J, van der Werken C. Is methicillin-resistant Staphylococcus aureus more contagious than methicillin-susceptible S. aureus in a surgical intensive care unit? Infect Control Hosp Epidemiol 2002;23:491–4.  Back to cited text no. 13
    
14.
Luhmann SJ, Smith JC. Preoperative MRSA Screening in Pediatric Spine Surgery: A Helpful Tool or a Waste of Time and Money? Spine Deform 2016;4:272–6.  Back to cited text no. 14
    
15.
Thakkar V, Ghobrial GM, Maulucci CM, Singhal S, Prasad SK, Harrop JS, et al. Nasal MRSA colonization: impact on surgical site infection following spine surgery. Clin Neurol Neurosurg. 2014;125:94–7.  Back to cited text no. 15
    


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