The effect of increased bed numbers on MRSA transmission in acute medical wards.

An 18-month prospective survey was performed to examine the effect of adding a fifth bed to four-bedded bays in three acute medical wards on colonization by methicillin-resistant Staphylococcus aureus (MRSA). Screening procedures were in accordance with the UK national guidelines. All patients newly colonized with MRSA were visited, and their bed location determined. Data from the five-bedded bays were compared with those from four-bedded bays in similar wards. Potential routes of transmission were investigated by observational surveys. The relative risk of colonization in five-bedded medium dependency bays was 3.15 compared with that of similar four-bedded bays (P < 0.005), and in five-bedded low dependency bays was 3.16 (P < 0.005). Increasing the number of beds in a fixed area heightens the risk of cross-infection with MRSA.