Methicillin-resistant Staphylococcus aureus Colonization in the Long-term Care Setting: Characteristics of Nasal Carriage and Transmission 公开

Stone, Nimalie D (2009)

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Abstract


Methicillin-resistant Staphylococcus aureus Colonization in the Long-term Care Setting:
Characteristics of Nasal Carriage and Transmission
By Nimalie D. Stone, M.D.
Methicillin-resistant Staphylococcus aureus (MRSA) is highly prevalent in long-term
care facilities (LTCFs) but its transmission dynamics are not well defined in this setting. Over a
6-month period we classified MRSA nasal carriage into 3 groups: persistent (all cultures positive),
intermittent (at least one, but not all cultures positive), and non-carrier (no cultures positive). We
plated each nasal swab on MRSA selective media for culture and graded growth on a semi-
quantitative scale from 0 (no growth) to 6 (heavy growth).We calculated a growth score for each
subject by averaging the growth from all cultures obtained to estimate burden of carriage. We
defined MRSA acquisition as an initial negative culture followed by >1 positive culture with no
subsequent negative cultures. We collected epidemiologic data for risk factor analysis and typed
MRSA isolates by pulsed-field gel electrophoresis (PFGE). Among 412 residents at 3 LTCFs,
MRSA prevalence was 59% with distributions of carriage similar at all three facilities: 20%
persistent, 39% intermittent, 41% non-carriers. Multivariate analysis showed MRSA carriage was
associated with prior history of MRSA culture (OR 3.5, p<0.0001), device use (OR 1.8, p=0.03),
and receipt of systemic antibiotics (OR 1.7, p=0.04). The mean growth score of MRSA differed
significantly between the persistent and intermittent positive carriers (3.4 vs. 1.2, p<0.0001). Of
254 residents with an initial negative swab, 25 (10%) acquired MRSA over the 6 months; rates
were similar at all three LTCFs. Multivariate analysis demonstrated receipt of systemic
antibiotics during the study was the only significant risk factor for MRSA acquisition (OR 7.8,
p=0.002). MRSA strains from acquisitions were related to those from a roommate by PFGE in
9/25 (36%) cases; 6 of these 9 roommates had persistent carriage. MRSA colonization prevalence
was high across three separate VA LTCFs. MRSA acquisition was strongly associated with
antibiotic exposure in the LTCF. Roommate sources were often persistent carriers but
transmission from roommates accounted for less than half of all MRSA acquisitions.

Table of Contents

TABLE OF CONTENTS

Section









Pages

Introduction.................................................................................................1

Background..................................................................................................2

Methods......................................................................................................4

Null
Hypothesis.................................................................................4
Cohort
Design.......................................................................................4
Patient
Selection...................................................................................4
Statistical
Analysis.....................................................................................5

Results.......................................................................................................7

Cohort
Characteristics.............................................................................7
Univariate/Multivariable
Models........................................................................................7

Molecular typing analysis.................................................................9

Discussion and Conclusions.............................................................................10

References...................................................................................................13

Tables.........................................................................................................15

Table 1. Characteristics of residents within each of the three VA long-term care facilities
enrolled in the study...............................................................................15

Table 2. Distribution of MRSA carrier cohorts by long-term care facility.............16

Table 3. Univariate analysis of risk factors for MRSA carriage during the study....17
Table 4A. Multivariable analysis of risk factors predictive of MRSA carriage am.ong
long-term care facility residents (n=412)......................................................18
Table 4B. Multivariable analysis of risk factors predictive of MRSA carriage among
long-term care facility residents (n=412) .....................................................19
Table 5. Comparison of mean growth scores between intermittent and persistent MRSA
carrier cohorts among three long-term care facilities.......................................20

Table 6. Univariate analysis of risk factors for MRSA acquisition during the study...21
Table 7. Multivariable analysis of risk factors predictive of MRSA acquisition among
long-term care facility residents (n=195)...................................................... 22



Figure ..........................................................................................................23

Figure 1. Pulse-field gel electrophoresis (PFGE) image demonstrating relatedness of
MRSA strains............................................................................................23


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