Estimation of methicillin-resistant Staphylococcus aureus transmission by considering colonization pressure at the time of hospital admission
Introduction
Hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) has been an increasing problem worldwide since the initial reports 35 years ago.1 Colonized and infected patients are the major institutional reservoir, and transient carriage on the hands of hospital personnel is the most common mechanism of patient-to-patient transmission.2
MRSA surveillance in hospitals is universally recommended.3, 4 To assess colonization and infection rates over time or to compare them with those of other hospitals, infection control personnel must use rates adjusted for the major risk factors.5, 6, 7 For MRSA, infection and/or colonization rates more accurately reflect the risk of acquisition when they are adjusted for the length of stay. Therefore, the most common indicator is the number of MRSA cases/1000 patient-days. To estimate MRSA transmission in a hospital or a ward, only cases of MRSA acquired in the setting are considered. However, this value does not take into account the duration of exposure to the imported MRSA reservoir (length of stay of patients infected or colonized at the time of admission). This has been identified as an independent risk factor of MRSA acquisition in a recent study conducted in a French intensive care unit (ICU).8
Our objective was to evaluate the usefulness of an indicator taking the imported MRSA reservoir into account.
Section snippets
Methods
Data were collected from January to December 2002, in a 600-bed public teaching hospital that provides a comprehensive range of departments including two ICUs, two surgical wards, a maternity unit, a psychiatric ward, a paediatric department, two internal medicine wards and a 120-bed long-term care facility for the elderly. Any patient admitted to an acute ward was included in the study (the long-term care facility was excluded). An MRSA carrier was defined as a patient from whom MRSA was
Results
During the study period, 14 202 patients were admitted to acute wards in our hospital, and 1128 (7.9%) of them were screened for MRSA. In 2002, no screening samples were taken from maternity, paediatric and psychiatry patients because none presented known risk factors for MRSA carriage at the time of admission. Samples were taken at admission from 17.0% (1128/6652) of the other patients. When assessed in three successive four-month periods, the percentage was lowest during the third period (
Discussion
CP is an indicator for the risk of MRSA transmission. Each additional MRSA carrier substantially increases the MRSA acquisition risk for other patients. In their study conducted in an ICU, Merrer et al. defined CP as the number of imported+hospital-acquired MRSA/patient-days in the week/total number of patient-days.8 We chose to consider only imported MRSA pateint-days because this parameter reflects the true unavoidable MRSA pressure.
In our study, the incidence of acquired MRSA/100
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Studying the transmission dynamics of meticillin-resistant Staphylococcus aureus in Hong Kong using spa typing
2011, Journal of Hospital InfectionCitation Excerpt :The source of transmission was considered to be undetermined if the spa type of the acquired MRSA did not match that of an imported MRSA within the same ward. The colonisation pressure per 1000 patient-days was defined as the ratio of imported MRSA plus acquired MRSA patient-days to the total number of patient-days during the study period, as described previously.17 The incidence density of nosocomial MRSA transmission per 1000 colonisation-days with respect to different spa types was measured.