|Year : 2019 | Volume
| Issue : 1 | Page : 11-15
Evaluation of two culture-based methods for the early detection of methicillin-resistant Staphylococcus aureus nasal carriage in pre-operative neurosurgical patients
Isabella Princess1, Siddhartha Ghosh2, S Elizabeth1
1 Department of Microbiology, Apollo Speciality Hospitals, Chennai, Tamil Nadu, India
2 Department of Neurosciences, Apollo Speciality Hospitals, Chennai, Tamil Nadu, India
|Date of Web Publication||13-Aug-2019|
Dr. Isabella Princess
Apollo Speciality Hospitals, Vanagaram, Chennai - 600 095, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Background: Pre-operative screening for nasal carriage of methicillin-resistant Staphylococcus aureus(MRSA) is practiced to reduce the risk of post-operative MRSA infections. Although controversies prevail on the necessity for screening, we perform MRSA screening in all pre-operative neurosurgical patients due to the benefits incurred.
Aim: The aim of this study was to evaluate two different culture-based methods for rapid screening of MRSA nasal carriage among pre-operative neurosurgical patients.
Methods: This cross-sectional, single-centre study was conducted in a tertiary healthcare facility in South India. All pre-operative neurosurgery patients were screened for nasal carriage of MRSA using two culture-based methods. Advantage of the newer screening method using chromogenic media over the conventional method was evaluated. A positive screening test was considered an indication for decolonisation using mupirocin and chlorhexidine prior to surgery. A repeat negative screening was ensured before the surgical procedure.
Results: MRSA colonisation rate among pre-operative neurosurgical patients in our study was 2.7%. Good correlation was observed between the two screening methods evaluated. Newer method using chromogenic media on comparison with conventional culture showed better turnaround time and shorter pre-operative stay of patients. Because the turnaround time is reduced, earlier contact isolation practice and treatment initiation was achieved for better care of MRSA carriers.
Conclusion: Chromogenic media usage for screening the nasal carriage of MRSA is beneficial to patients, surgeons and laboratory personnel. Decrease in turnaround time and processing time and early initiation of isolation along with major reduction in reagent usage are the benefits achieved.
Keywords: Chromogenic media, methicillin-resistant Staphylococcus aureus screening, nasal swab, neurosurgery, pre-operative
|How to cite this article:|
Princess I, Ghosh S, Elizabeth S. Evaluation of two culture-based methods for the early detection of methicillin-resistant Staphylococcus aureus nasal carriage in pre-operative neurosurgical patients. J Patient Saf Infect Control 2019;7:11-5
|How to cite this URL:|
Princess I, Ghosh S, Elizabeth S. Evaluation of two culture-based methods for the early detection of methicillin-resistant Staphylococcus aureus nasal carriage in pre-operative neurosurgical patients. J Patient Saf Infect Control [serial online] 2019 [cited 2022 Aug 10];7:11-5. Available from: https://www.jpsiconline.com/text.asp?2019/7/1/11/264395
| Introduction|| |
Methicillin-resistant Staphylococcus aureus (MRSA) colonisation poses a major threat to patients, more so if a patient colonised with MRSA undergoes a surgical procedure.
Once a patient is diagnosed to have MRSA colonisation, contact isolation and cohort nursing has to be followed to prevent the spread of MRSA from the colonised individual to other patients in close contact.
Another major intervention is the initiation of MRSA decolonisation therapy for the patient. The sooner this decolonisation is completed, the earlier the patient can be taken up for surgery., Thus, the average length of stay is prolonged for colonised individuals undergoing surgery when compared to non-colonised individuals. Controversial studies not supporting pre-operative screening do exist due to cost and feasibility. We intend to critically analyse the same and present our study findings.
| Methods|| |
This cross-sectional study was conducted at a tertiary care centre in Chennai, South India. Nasal swab screening is a part of neurosurgical package in our healthcare facility, wherein all pre-surgical patients are screened for MRSA and decolonised prior to surgery. This eliminates the risk of colonised patients developing post-surgical MRSA infections.
We conducted this analysis over a period of 1 year to compare the efficacy of a new chromogenic media for MRSA detection (chromID MRSA SMART, bioMerieux SA, France) with the conventional culture-based method.
A swab collected from the anterior nares of the patient was streaked onto blood agar plates and MRSA Smart (chromogenic media) in the microbiology laboratory. All samples were processed under strict aseptic condition in a biosafety cabinet under laminar flow. The testing protocol followed is depicted in [Figure 1].
Quality control was performed to test a new media called MRSA Smart for processing nasal swab cultures to screen for MRSA in pre-surgical patients. Standard control strains of methicillin-susceptible S. aureus, MRSA, coagulase-negative Staphylococci (CoNS) and methicillin-resistant CoNS were used. Once the internal quality control was satisfactory, it was proved that the new media can effectively detect all MRSA isolates from patient samples.
A parallel testing of the new media and conventional method was followed on patient samples for standardisation. One hundred samples were tested by both methods (old conventional method and new method).
All MRSA-positive screening tests were informed to the treating clinician. Patients were cohorted and placed on contact isolation. Decolonisation was done using local application of mupirocin and chlorhexidine bath for a period of 7 days. Once decolonisation was complete, those with a negative MRSA nasal swab culture were posted for the surgical procedure.
A retrospective analysis of post-operative cultures from patients with a positive MRSA screening was done.
| Results|| |
Among 657 pre-operative nasal swabs screened from January to December 2016, 18 (2.7%) patients tested positive for MRSA by both methods.
Validation of the media was first done using standard ATCC strains, and all types of colonies were cross-checked by both the methods. The results obtained during validation are detailed in [Table 1].
|Table 1: Results of conventional method and new method of methicillin-resistant Staphylococcus aureus screening|
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Among the 18 patients who had a positive MRSA screening, 3 of them required ventilator support post surgery (16.6%). Tracheal aspirates from two patients showed insignificant growth, whereas one patient had significant growth of MRSA from tracheal aspirate.
Root cause analysis was done, and it was found that the patient who had significant growth of MRSA was referred from another healthcare facility and taken up for surgery immediately after admission. Nasal swab sent on admission showed heavy growth of MRSA, and the patient was immediately started on decolonisation. Significant growth of MRSA in tracheal aspirate occurred on the 3rd day post initiation of decolonisation. Decolonisation for this patient was completed on day 7, and repeat nasal swab culture was negative.
Details on type of cultures sent postoperatively and the findings are detailed in [Table 2].
|Table 2: Post-operative cultures from methicillin-resistant Staphylococcus aureus carriers (n=18)|
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Post decolonisation, all the 18 patients were re-screened for MRSA, and 100% decolonisation was observed as all patients had a negative re-screening test for MRSA. The procedure and comparison between the two culture-based screening methods are elicited in [Table 3].
|Table 3: Methodology and comparison of two culture-based methods of methicillin-resistant Staphylococcus aureus screening|
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| Discussion|| |
MRSA is a notorious pathogen associated with many healthcare-associated infections. Although MRSA was exclusively considered as a hospital-acquired organism, it was strongly established as a community-acquired organism following the discovery of community-associated MRSA in the year 1981. When patients present to the hospital from a community, chances of either infection or colonisation with MRSA are likely high. It is wise to screen patients especially those undergoing invasive procedures as they could be asymptomatic carriers. The average percentage of MRSA carriers worldwide is estimated to be 2.7% with a much higher carriage rate of 5% among healthcare workers.
When colonised individuals are subjected to invasive procedures and surgeries, they have a one-step higher risk of developing post-operative infections with MRSA. Commonly occurring MRSA infections are among those undergoing orthopaedic and cardiac implant surgeries. Once this occurs, there is a huge impact on the patient's prognosis as most of them end up with implant failures and other morbidities, sometimes also leading to death.
Apart from these observations, studies from the West have shown high estimated cost of isolation for MRSA carriers and increased average length of stay., A positive correlation between MRSA carriage and development of infection in colonised individuals is well established. Usual indications for pre-operative screening are orthopaedic surgeries, neurosurgeries, cardiac surgeries and vascular surgeries.,,,
Although controversial studies not supporting pre-operative screening do exist, we strongly believe that screening should be mandatory as a positive correlation was evident amongst colonised individuals developing MRSA infections post surgery. In our study, however, the patient who developed post-operative ventilator-associated pneumonia with MRSA was on the decolonisation process. These are unavoidable circumstances where the patient required emergency craniotomy on the day of admission. Appropriate decolonisation for all MRSA carriers is completed prior to surgery in order to prevent post-operative MRSA infections.
Methods used for MRSA screening are conventional culture, chromogenic media, polymerase chain reaction (PCR), GeneXpert, etc., The turnaround time for conventional culture is 48 h, chromogenic media is 16–18 h, PCR is 27.6 h and GeneXpert is 21.4 h.
In our study, comparison of the two culture-based methods (old method: conventional culture and new method: chromogenic media) was done. We did not prefer PCR and GeneXpert due to high cost and non-availability of in-house molecular laboratory.
Advantages after implementation of the new screening method are as follows:
- There is a significant reduction in turnaround time by 30 h
- Reports of MRSA screening are available within 18 h using the new method, whereas the old method took 48–50 h
- We were able to achieve better infection control and barrier nursing practices for MRSA-positive patients by isolating them and initiating cohort/barrier nursing within 18 h (30 h earlier than the old method)
- Earlier detection helps to initiate decolonisation therapy 30 h earlier than usual. This ensures reduction in length of hospital stay of the patient
- Patients with negative MRSA screening test can be taken up for surgery earlier than the usual time of 48 h post admission, thereby decreasing the waiting time for surgery and hence length of stay
- There is elimination of the tedious procedure which was previously followed leading to better utilisation of technician's time
- Reagent and plastics have been significantly reduced.
Cost incurred for procuring the new media was lesser than the total cost used in the older conventional culture method.
Because there are many advantages and benefits for patients, clinicians and laboratory personnel and marked reduction in turnaround time and sample processing time, we continue to use the new MRSA Smart media for processing nasal swab cultures for pre-operative screening of neurosurgical patients [Table 4].
|Table 4: Key benefits of chromogenic media for screening methicillin-resistant Staphylococcus aureus nasal carriage|
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Repeat nasal swab for MRSA screening was done in our study as there have been reports of decolonisation failure. All our patients who underwent decolonisation had a negative repeat nasal swab screening. They underwent surgery post decolonisation.
| Conclusion|| |
Early detection of MRSA nasal carriage is the need of the hour among pre-operative patients. In an attempt to significantly reduce the turnaround time, we found that chromogenic media has more benefits compared to the conventional culture-based methods. Compared to molecular detection of MRSA from nasal swabs, it is cost-effective with lesser turnaround time. Therefore, chromogenic media (MRSA Smart) is a better alternative to various other methods of MRSA screening.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]