Methicillin Resistant Staphylococcus
aureus (MRSA): Carriage and
Conversion Rates in Nursing Students –
An Interim Report
PI – Rodney E. Rohde, PhD, MS, SV, SM(ASCP)CMMBCM
Associate Dean for Research, College of Health Professions
Associate Professor, Clinical Laboratory Science
Cheryl Rowder, PhD, RN, CCRC (Seton Hospital now)
Thomas L. Patterson, MS, BS, MT (ASCP)
Gerald D. Redwine, M.ED., MT(ASCP)
Bob Vásquez, PhD
Emilio Carranco, M.D.
1
The information/data within this
PPT has been published.
• Please see the following article for complete
information & citation for credit:
• Rohde, R.E., Rowder, C., Patterson, T., Redwine,
G., Vásquez, B., & Carranco, E. Methicillin
Resistant Staphylococcus aureus (MRSA): An
Interim Report of Carriage and Conversion Rates
in Nursing Students. Clin Lab Sci, 2012 ;25(2):94101.
Study Support
• 2010 TSAHP Research Grant Award
• THANK YOU!
• Texas State University, College of Health
Professions, Dean’s Office, CLS Program,
School of Nursing (SON)
• Texas State University Research
Enhancement Grant (Gerald Redwine, CLS
Dr. Cheryl Rowder, Seton Hospital, & Dr.
Barbara Covington, SON – Round Rock)
Objectives - Overview
• Microbiology & epidemiology of Staphylococcus
aureus & MRSA background
• Purpose / Goals of study
• Methodology / Preparation
• Analysis
• Interim results
• Discussion / Implications
• Final thoughts
SON Director Marla Erbin-Roesemann, PhD,
RN & CHP Dean Ruth Welborn, PhD, RN
What is Staphylococcus aureus?
•
•
•
•
Gram-positive cocci in clusters.
Multiple infection sites: skin, bones, lungs, or blood.
Transmission (infection versus colonization)
Methicillin resistant Staphylococcus aureus (MRSA)- resistant to
the broad-spectrum antibiotics commonly used to treat it
– 1st reported in U.K. in 1961 (Jevons, 1961); Seven years later, after
the resistant strain had become widespread in Japan, Europe, and
Australia, the first case of MRSA in the U.S. was reported in 1968
at a Boston hospital (Barrett, McGehee, & Finland, 1968).
• Worldwide, an estimated two billion people carry some form of S.
aureus; of these, up to 53 million (2.7% of carriers) are thought to
carry MRSA. In the U.S., 95 million carry S. aureus in their noses; of
these, two and a half million (2.6% of carriers) carry MRSA (Graham,
Lin, & Larson, 2006).
Staphylococcus aureus
Staphylococcus epidermidis
Coagulase negative
Coagulase negative
Coagulase positive
Coagulase positive
Grape-like
clusters of
Staphylococci
Gram positive
“staph infection?”
Spider bites?
Folliculitis
MRSA!
Healthcare associated infections (HAIs) have become one of
the most costly and deadly growing public health threats of
our time.
The CDC estimates that MRSA has surpassed HIV as the
leading cause of morbidity and mortality in the U.S. (CDC,
2010)
“not your Grandma’s bug anymore”
Risk Factors
•
•
•
•
•
Hospital Associated
(HA-MRSA)
Hospitalization
Long-term care
facilities
Invasive devices
Recent antibiotic use
Weakened immune
system
Risk Factors
Community Associated
(CA-MRSA)
• Age?
•
•
•
•
•
Contact sports
Sharing
Weakened immune system
1, 2-3, >4 Abx & drug class
Crowded or unsanitary
conditions
Epidemiology
• SA a colonizer of healthy mucous membranes and skin of
humans and many other animals.
• Other than shedding by humans, the environment appears to
play a negligible role in the ecology of this organism.
• In humans it demonstrates a niche preference for the
anterior nares, especially of adults.
• Three patterns in healthy people:
 Persistent carriers (~20%)
 Intermittent carriers (~ 60%)
 Never colonized (20%)
What is the usual clinical expression of
MRSA infection?
•
•
•
•
•
Spider bite
Turf burn
Impetigo
Boil
Abscess
Source: Mark Grubb, MD
Source: LA County Health Department
Source: CDC
Source: CDC
Source: CDC
Spectrum of Disease
• Fever, PAIN!
• >80% skin and soft tissue infection (SSTI)
– Abscesses
– Furuncles
– Carbuncles
– Cellulitis
• Local swelling, redness, heat
• Painful lesion or pimple with or without
drainage
• Misdiagnosed as spider bites
Source: CDC
Spectrum of Disease
• Severe / invasive infection sites:
– Lungs
– Bloodstream
– Bone
– Joints
– Surgical sites
• Complications of preceding SSTIs
• Or viral respiratory tract infections
(especially flu)
Source: CDC
Purpose & goals of this study*
• (1) Assess initial prevalence or acquisition of S. aureus & MRSA in
a cohort of nursing students over five semesters (~ two years) of
clinical care experiences in a variety of settings,
• (2) to examine the antibiotic sensitivity of MRSA isolates by
microbiological susceptibility testing, and
• (3) to conduct an univariate analysis for identify of risk factors
significantly associated with nasal carriage of S. aureus & MRSA in
a population of nursing students at a four year public university.
• (4) The purpose of this project seeks to add to the knowledge of risk
for acquisition and length of time to colonization of MRSA for
healthcare workers (HCWs). First documented study!
*Study is at ½ way point – study will be complete in May 2012
Study Methodology / Preparation
• A longevity (time-series) prospective cohort design will be
applied to determine the rate of S. aureus and MRSA carriage
in a cohort of nursing students at Texas State and to describe
exposures (risk factors) associated with carriage.
• IRB approval from Texas State University – San Marcos
(#2010F5693).
• Data collection and analysis will be continuous from
September 2010 through May 2012.
• Eligible participants were all Texas State University students
over the age of eighteen. (N = 87)
• Purposive sampling strategy
• Questionnaire for demographics & risk factors
Study Methodology / Preparation
• Informed consent (Nursing & CLS faculty)
• Questionnaire (CLS)
–
–
–
–
–
–
–
–
–
–
–
Age
Gender
Ethnicity
Possible MRSA exposure
Knowledge of MRSA
Hospital admission and work
Intravenous drug use
Dorm living status
Jail
Athletic involvement
Clinical care experiences (contact isolation, area of work, etc.)
• Nasal Swab (Self-administered with CLS supervision)
Study Methodology / Preparation
Study Methodology / Preparation
• A positive MRSA swab will represent an end point for a
participant.
• Medical intervention will be recommended by Dr.
Carranco (Student Health Center).
• Post treatment tests will verify a negative nasal swab.
Laboratory Methods
1) Streak nasal swab on Mannitol Salt Agar (screen) and Chromagar
(confirmatory).
Laboratory Methods
2) Incubate Mannitol Salt Agar (MSA) plates for 24-48 hours.
-Selective and Differential media
Staphylococcus spp.
S. aureus
Laboratory Methods
3) Perform Catalase test and Latex Agglutination test (Staphytect).
Laboratory Methods
4) Correlate MSA with Chromoagar plate.
*mauve-colored colonies = MRSA
BBL™ CHROMagar™
Family of Products
A Lean Approach to Testing
BBL™ CHROMagar™ MRSA,
supplemented with chromogens and
inhibitory agents, is used for the
qualitative direct detection
of nasal colonization by MRSA.
Analysis
• Statistical analysis will be performed using:
– Stata, version 12
• Descriptive, demographics
• Generalized estimating equations (GEE) to obtain
population-averaged panel logistic regression
models
• Allow for AR(1) error process
• Data screened for missing and/or out of
range values, sparse cell frequency counts,
and the sample size to number of cells ratio
Results – baseline
• Enrollment = 87/96 participants (90.6%)
• Demographics (August 2010)
– Ages 20 to 58 years (mean 24.5; median 23; mode 20)
– Age group of 20-24 (68.9%) was greatest; 25-29
(16.1%); 30-34 (10.1%); 35-39 (2.2%); 40+ (2.2%)
– Gender: Male to female ratio
• 11 (12.6%) to 76 (87.4%)
– Ethnically, Caucasians (74.7%) and Hispanics (12.6%)
made up the majority of the population.
• AA (3.4%), Asian (8%), other (1.1%)
Results - 3rd wave
• Enrollment = 70/86 participants (~81%)
• Demographics (May 2011)
– We found that with respect to sex and race however,
attrition had not affected sample composition in any
meaningful way.
– Furthermore, because this study will continue, we will
expect to recover participants in the next wave of data
collection.
Table 1.
Percent of sample with positive nasal swab
By infection type and wave
Wave 1 to Wave 2
Percent
Z
Wave Wave Wave
Change
1
2
3
MRSA
1.15% 0.0% 0.0%
NA
NA
Wave 1 to Wave 3
Percent
Z
Change
NA
NA
S. aureus
20.7% 26.4% 20.0%
5.7
0.89
-0.7
-0.11
S. other
9.2% 68.9% 80.0%
59.7***
8.97
70.8***
8.97
*** = p < .001
Note: We suggest viewing these from a descriptive statistics perspective since the
alpha error rate increases with multiple comparisons.
Table 2.
Percent of sample with exposure to healthcare setting, people with MRSA, and
gym/sports activities
By variable and wave
Wave 1
Wave 2
Wave 3
Exposure to healthcare settings
As a patient
32.1%
39.2%
23.1%
As a worker/volunteer
27.5%
78.5%
98.5%
Contact with person diagnosed
8.0%
16.8%
60.1%
with MRSA
Involvement in gym/sports
32.1%
81.9%
79.4%
activities
*** = p < .001
Note: We suggest viewing these from a descriptive statistics perspective since
the alpha error rate increases with multiple comparisons.
Table 3.
Logistic regression models explaining positive infection
By infection type
S. aureus
Odds Ratio
Z
Exposure to healthcare settings
As a patient
0.80
-0.68
As a worker/volunteer
1.42
1.06
Contact with person diagnosed with
0.86
-0.49
MRSA
Involvement in gym/sports activities
1.45
1.13
Control variables
Age
Male
White
Had boil/skin infection since last
interview
Number of observations
Number of subjects
Model Wald (Chi-square)
* = p < .05
** = p < .01
*** = p < .001
S. other
Odds Ratio
Z
1.15
2.72**
0.41
2.95
0.77
-0.77
4.98***
4.43
0.99
1.13
1.25
-0.25
0.19
0.43
1.01
1.40
1.08
0.31
0.66
0.20
2.43*
2.14
1.76
1.12
233
83
8.08
233
83
41.75***
Discussion
• The prevalence of S. aureus in our cohort of nursing
students was not similar to previously reported studies of
19% to 37% as reported by Bischoff, et al. (2004).
• Also, age, gender, chronic sinusitis, medical student status,
and hospitalization were associated with carrier status for S.
aureus (Bischoff et al., 2004, p. 485) but not our study.
• Equally, this study found diametrically opposed findings
from those of Rohde, et al. (2009) in that hospitalization
was not related to carrier risk but did replicate the results of
previous studies that time spent in the hospital setting as
either a volunteer or healthcare worker increased this risk.
Discussion
• MRSA colonization in our nursing student cohort did not
increase in this interim report of a longitudinal study.
• S. aureus colonization remained stable as predicted in most
point prevalence studies (25-30%).
• Species colonization other than S. aureus (e.g. S.
epidermidis, S. haemolyticus) increased to significant levels
which may play an important role in nosocomial
transmission understanding.
Implications
• Few studies have examined conversion of populations
• Cross-sectional studies may provide point prevalence but do not
fully explain progression from one form to another
• S. aureus is a known risk factor for conversion to MRSA, but little
is known of conversion from S. spp. to S. aureus.
• Our study to date found a statistically significant rise in rates of S.
spp. associated with time spent as either a volunteer or worker in
healthcare
– indicates a potential risk for healthcare providers for conversion to positive
status and for potential risk to patient safety.
• While (most) healthcare providers are not screened for MRSA or
any staphylococci, yet they are expected to care for patients who
are positive with use of contact isolation. Is this enough?
Points to Ponder
• This project offers a powerful, collaborative and synergistic
research opportunity between two College of Health Professions
units – CLS and Nursing.
• Students in both units will be able to apply real-world clinical
experience in the teaching and research realm
• All investigators will strengthen the bridge between the
classroom and research arena
• A strong research foundation at TX State – CHP is growing,
specifically in the realm of MRSA prevalence, understanding,
and knowledge
• A strong hybrid translational research focus is being developed
across education and public health/clinical domains
Closing comments
• Control Prevention
– Wash your hands and/or use gels!
– Education – demand a culture &
antibiogram!
– Don’t share fomites!
– Use antibiotics appropriately!
– Be aware of risk factors & environment!
• KPC (the new MRSA?), VRE, C. diff
At work!
PI Background
•
Rohde, R.E. Denham, R., & Brannon, A. (Summer, 2009). Methicillin
Resistant Staphylococcus aureus: Nasal Carriage Rate and Characterization
in a Texas University Setting. Clinical Laboratory Science, 22(3): 176-184.
 60/203 (29.6%) colonized with S. aureus & 15/203 (7.4%) with MRSA. There were 108 (53.2%) dorm
students that participated in this study. Of those, 34 (31.5%) were positive for S. aureus colonization, and
seven (6.5%) were positive for MRSA colonization. Risk for hospitalization & boil/skin infection.
•
Felkner, Marilyn, R. E. Rohde, Ana Maria Valle-Rivera, Tamara Baldwin,
and L.P. (Sky) Newsome. Methicillin Resistant Staphylococcus aureus
Nasal Carriage Rate in Texas County Jail Inmates. Journal of Correctional
Health Care, 2007;13(4): 289-295. [Top Ten most cited article JCHC]
 28.5% S. aureus & 4.5% MRSA in TX jail (N = 403); Risk for any incarceration, healthcare, & boil/skin.
•
Dissertation Topic: Methicillin Resistant Staphylococcus aureus (MRSA):
Knowledge, Learning, and Adaptation.
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Acknowledgements
• Thanks to
– Nursing cohort participants, Texas State University
– Clinical Laboratory Science (CLS) students, Texas State, Classes
of 2011 & 2012
– Dr. Carmen Adams, CLS, Texas State
– Dave Falleur, CLS Chair
– Dr. Ruth Welborn, Dean, CHP, Texas State
– Dr. Marla Erbin-Roesemann, Dr. Barbara Covington & Rita
Zapata Mokarzel, School of Nursing, TX State
– CTMC San Marcos (Microbiology Abx susceptibility work!)
– TX State SHC
Questions?!?
www.txstate.edu/~rr33
rrohde@txstate.edu