The Ability of Rapid PCR Based Methods to Identify Surgical Patients Colonised With Methicillin Resistant Staphylococcus Auerus

Katie Hardie, HPA

Hardy KJ, Gossain S, McMurray C, Shabir S , Williams A, Athamneh N, Hawkey PM

Health Protection Agency, Heartlands Hospital, Birmingham; Dept of Infection and Immunity, Birmingham University, Birmingham

 

Objectives: To determine the ability of the rapid IDI MRSA PCR based assay to identify surgical patients colonised with MRSA compared to conventional culture methods.

Methods: During a 9 month period all patients admitted to 4 surgical wards had nasal swabs taken for detection of MRSA on admission and every 4 days subsequently. Each swab was plated directly onto MRSA ID agar and then tested using the IDI MRSA assay.

Results: A total of 7545 nasal samples were examined from 3769 patients. Seven hundred and fifty six samples were positive by the IDI MRSA assay, of which MRSA was isolated on direct culture from 374 (49.5%). Of the 382 samples that were negative on direct culture, MRSA was isolated on broth enrichment from 138 samples, and MSSA from 42 samples. Overall the IDI MRSA assay has a sensitivity of 97%, a specificity of 96.1%, NPV of 99.7% and a PPV of 71%.

Conclusion: The IDI MRSA assay provides a rapid and sensitive way of screening surgical patients for MRSA, with a very high negative predictive value. The increased number of patients identified as colonised with MRSA using the IDI MRSA assay compared to conventional culture, may be due to the increased sensitivity of PCR compared to culture. Rapid and sensitive identification of surgical patients colonised with MRSA aids in the prompt decolonisation and isolation of patients.

Emergence and eradication of two distinct epidemic methicillin resistant Staphylococcus aureus strains with high level mupirocin resistance.

Hardy KJ, McMurray C, Shabir S, Gossain S, Hawkey PM.

Health Protection Agency, Heart of England NHS Foundation Trust, Birmingham.

Background: Methicillin resistant Staphylococcus aureus (MRSA) is a major cause of hospital acquired infection. Decolonisation of patients colonised with MRSA is predominantly with mupirocin, but resistance does occur and has been associated with treatment failures.

Methods: All patients admitted to 7 surgical wards had a nasal screen for MRSA on admission and every 4 days for the duration of their stay over an eighteen month period. If a patient was found to be colonised with MRSA that had high level resistance to mupirocin all contacts within the bay were screened, naseptin was used for decolonisation and the patients were nursed in a side room.

Results: A total of 1068 / 11,714 (9.1%) patients were colonised with MRSA. 70 patients (6.5%) were colonised with an MRSA strain that had high level resistance to mupirocin. All of these strains belonged to two SIRU profiles, one of which is a subtype of EMRSA-16 and the other a subtype of EMRSA-15. 62 patients were colonised with the EMRSA-16 strain. The average length of stay before acquisition was 23 days, and the transmission occurred predominantly on 3 of the surgical wards. Transmission of the EMRSA-15 strain occurred between 8 patients on one surgical ward, the average length of time to acquisition was 11 days.

Discussion: This study demonstrates that by using active screening, isolation of patients and a change in decolonisation treatment highly transmissible high level mupirocin resistant strains can be eradicated.