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 ProfessionsAssociate 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):94-101.

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 thoughtsSON 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 positive

Coagulase positiveCoagulase negative

Coagulase negative

Grape-likeclusters ofStaphylococci

Gram positive

Spider bites?

Folliculitis“staph infection?”

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: LA County Health Department

Source: Mark Grubb, MD

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 Methods1) Streak nasal swab on Mannitol Salt Agar (screen) and Chromagar (confirmatory).

Laboratory Methods2) Incubate Mannitol Salt Agar (MSA) plates for 24-48 hours.

-Selective and Differential media

Staphylococcus spp. S. aureus

Laboratory Methods3) Perform Catalase test and Latex Agglutination test (Staphytect).

Laboratory Methods4) Correlate MSA with Chromoagar plate.

BBL™ CHROMagar™Family of ProductsA Lean Approach to Testing

BBL™ CHROMagar™ MRSA, supplemented with chromogens and inhibitory agents, is used for the qualitative direct detectionof nasal colonization by MRSA.

*mauve-colored colonies = 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 swabBy infection type and wave

Wave 1

Wave 2

Wave 3

Wave 1 to Wave 2 Wave 1 to Wave 3Percent Change

Z Percent Change

Z

MRSA 1.15% 0.0% 0.0% NA NA 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 < .001Note: 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 activitiesBy variable and wave

Wave 1 Wave 2 Wave 3Exposure 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 with MRSA

8.0% 16.8% 60.1%

Involvement in gym/sports activities

32.1% 81.9% 79.4%

*** = p < .001Note: 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 infectionBy infection type

S. aureus S. otherOdds Ratio Z Odds Ratio Z

Exposure to healthcare settingsAs a patient 0.80 -0.68 1.15 0.41As a worker/volunteer 1.42 1.06 2.72** 2.95

Contact with person diagnosed with MRSA0.86 -0.49 0.77 -0.77

Involvement in gym/sports activities 1.45 1.13 4.98*** 4.43

Control variablesAge 0.99 -0.25 1.01 0.31Male 1.13 0.19 1.40 0.66White 1.25 0.43 1.08 0.20Had boil/skin infection since last interview

2.43* 2.14 1.76 1.12

Number of observations 233 233Number of subjects 83 83Model Wald (Chi-square) 8.08 41.75***

* = p < .05** = p < .01*** = p < .001

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/~rr33rrohde@txstate.edu