Abstract
Previous studies have been unable to identify patient or staff reservoirs for the majority of the nosocomial S. aureus acquisitions which occur in the presence of good infection control practice. We set out to establish the extent to which undetected pre-existing carriage explains apparent nosocomial S. aureus acquisition. Over two years elective cardiothoracic admissions were screened for S. aureus carriage before and during hospital admission. Routine screening (nose/groin/wound sampling), was supplemented by sampling additional body sites (axilla/throat/rectum) and culture-based methods optimised to detect fastidious phenotypes (small colony variants, cell wall deficient variants) and molecular identification by PCR. 35% of participants (53/151) were S. aureus carriers according to routine pre-healthcare screening; increasing to 42% (63/151) when additional body sites and enhanced cultures were employed. 71% (5/7) of apparent acquisitions were explained by pre-existing carriage using augmented measures. Enhanced culture identified a minority of colonised individuals (3/151 including 1 MRSA carrier) who were undetected by routine and additional screening cultures. 4/14 (29%) participants who became culture-negative during admission had S. aureus genomic material detected at discharge. Conventional sampling under-estimates carriage of S. aureus and this explains the majority of apparent S. aureus acquisitions among elective cardiothoracic patients.
Highlights
Pre-healthcare Post-operative Weekly Discharge Routine Nose x x Groin xWound x xClinical samples∗ Additional
10 instances of S. aureus carriage prior to admission which were missed by routine screening including one of MRSA carriage: eight by additional site sampling and two by enhanced culture methods
14 of 89 participants screened throughout admission met our culture-based definition of S. aureus carriage loss and, of these, four had molecular evidence of S. aureus identified at discharge
Summary
Previous studies have been unable to identify patient or staff reservoirs for the majority of the nosocomial S. aureus acquisitions which occur in the presence of good infection control practice. We set out to establish the extent to which undetected pre-existing carriage explains apparent nosocomial S. aureus acquisition
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