132 Non-respiratory swabs have little role in the detection of methicillin resistant Staphylococcus aureus in cystic fibrosis

Abstract

Background: Chronic methicillin resistant Staphylococcus aureus (MRSA) infection in CF is associated with faster FEV1 decline and greater mortality. Screening for infection involves swabs from both upper respiratory (nose, throat) and peripheral sites (groin, axilla), as well as sputum culture. There are no data to indicate which is superior. Methods: Microbiology results of pts attending our adult tertiary care centre who have had any positive MRSA result between 01/01/09 and 01/08/2010 were reviewed. Patients were considered continuously infected between their earliest and last MRSA culture. Results: 17pts (5%) had at least 1 MRSA isolate: 6 known chronic MRSA; 3 intermittent; 6 detected on routine outpatient sputum culture; 2 detected on ward screening. 307 microbiology samples were taken during periods of MRSA positivity: 180 (59%) were swabs (throat = 71, nose = 35, groin = 59 and axilla = 15) and 127 sputa. Of these, 70 (55%) sputa were MRSA positive. Nose swabs grew MRSA in 24%, throat 23%, groin 19% and axilla 0% cases. 28 sets of concurrent samples from 12 pts were discordant. Nose swabs were positive in 17/28 (61%) of these, throat swabs in 8/14 (57%). Peripheral swabs grew MRSA in 5/27 (19%), all also positive in nose +/− sputum. Concurrent sputa were MRSA positive in 15/23 (65%). Discussion: Upper respiratory tract swabs constitute an important tool for MRSA surveillance. Little additional information however is derived from non-respiratory swabs, and their routine use could be discontinued in units with low MRSA prevalence. In those who expectorate easily, sputum is the most effective method of detecting MRSA. There is a considerable false negative rate for all sample methods.