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Time-Series Analysis of the Impact of Bed Occupancy Rates on the Incidence of Methicillin-Resistant Staphylococcus aureus Infection in Overcrowded General Wards

Published online by Cambridge University Press:  02 January 2015

Michael A. Borg ,
David Suda  and
Elizabeth Scicluna
Michael A. Borg*
Affiliation:
Infection Control Unit, Mater Dei Hospital, Msida, Malta
David Suda
Affiliation:
Department of Statistics & Operations Research, University of Malta, Msida, Malta
Elizabeth Scicluna
Affiliation:
Infection Control Unit, Mater Dei Hospital, Msida, Malta
*
Infection Control Unit, Mater Dei Hospital, Msida, Malta ([email protected])
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Abstract

Objective.

We investigated the impact of bed occupancy, particularly overcrowding, on the incidence of methicillin-resistant Staphylococcus aureus (MRSA) infection in general ward settings.

Methods.

We performed a time-series and mixed-model analysis of variance of monthly incidence of MRSA infection and corresponding bed occupancy rates, over 65 months, in the medicine and surgical wards within St. Luke's Hospital, a 900-bed tertiary care facility in Malta.

Results.

In the medicine wards, significant periodic fluctuations in bed demand were evident during the study period, with peaks of occupancy greater than 120% during the winter months. Cross-correlation analysis between the rate of bed occupancy and the rate of MRSA infection displayed an oscillatory configuration, with a periodicity of 12, similar to the periodicity evident in the autocorrelation bed-occupancy pattern. Further statistical analysis by means of analysis of variance confirmed that the months with excessive overcrowding tended to coincide with a significant increase in the rate of MRSA infection, occurring after a lag of approximately 2 months. Identical analysis of equivalent data from the surgical wards also revealed significant fluctuation in the rate of bed occupancy; however, occupancy never exceeded 100%. No cross-correlational relationship with MRSA infection incidence was present.

Conclusion.

The study data suggest that, in our setting, simple fluctuations in the rate of bed occupancy did not have a direct impact on the incidence of MRSA infection as long as the rate of bed occupancy was within designated levels. Rather, it was episodes of significant overcrowding, with occupancy levels in excess of designated numbers, that triggered increases in infection incidence rates.

Type
Original Articles
Information
Infection Control & Hospital Epidemiology , Volume 29 , Issue 6 , June 2008 , pp. 496 - 502
Copyright
Copyright © The Society for Healthcare Epidemiology of America 2008

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