An investigation of an outbreak: Methicillin resistant Staphylococcus aureus colonization in an intensive care cardiac unit.

Abstract

Background: Colonization in the nares with Methicillin Resistant Staphylococcus aureus (MRSA) has been described as a risk factor for eventual MRSA infection. The objective of this report is to describe the outbreak investigation, to identify the risk factors involved, and to evaluate and recommend control measures.

Methods: This study was a retrospective observational outbreak study carried out in the Intensive Care and Cardiac Unit. Percentages of patients with positive conversions were graphically plotted out and were used to determine expected percentage of conversions versus observed. The case definition was determined to be a patient with a positive culture for MRSA from a nasal swab upon discharge or transfer from the ICCU whose initial swab on admission was negative.

Results: The expected number of conversions was 2% per month and the newly observed number of conversions was 6%, which was >3 standard deviations from the mean. Repetitive sequence-based PCR (rep-PCR) was performed for the microbial DNA typing, which discovered genetically identical strains.

Discussion: The main finding in this outbreak investigation was that the common room which housed four of these patients was contaminated with MRSA. A limitation was that some patients who would have been included in the study did not get screened at discharge and their conversion status could not be ascertained and environment cultures were not performed. Active surveillance allowed for the detection of an outbreak of MRSA colonization which led to early intervention that prevented more patients from becoming colonized. Prevention of colonization should be one of the primary goal in the prevention of MRSA.