Over four semesters, nose and throat swabs were collected from 380 undergraduate nursing students to analyze Staphylococcus aureus and MRSA carriage rates. 48.9% of participants were found to carry S. aureus in their nose or throat. While most carriers had nasal carriage only, 16.8% had throat carriage exclusively. The overall MRSA carriage rate was low at 1.31%, suggesting clinical exposure has not increased rates. Continued monitoring of nursing students is needed to understand how carriage changes over time with increased clinical experience.

1. 0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
Spring 2013 Fall 2013 Spring 2014 Fall 2014
Penicillin
Cefoxitin
Erythromycin
Clindamycin
Tetracycline
A total of 380 individuals’ samples were collected from undergraduate nursing students over a four semester period, Spring 2013, Fall 2013,
Spring 2014 and Fall 2014. The intent of this study was to encourage previous participants to contribute throughout their undergraduate
nursing school career. Due to this, not all 380 samples collected were from different people. A total of 269 different individuals were
sampled, meaning that many students chose to participate in the study for two or more semesters. After consenting and filling out a brief
questionnaire (Table 1), sterile swabs were used to collect samples from participant’s nares and pharynx. Of the 380 participants, a total of
22 males and 358 females participated. In the group of 380 participants, the average age was 22.5 years with a minimum age of 18 years and
maximum age of 52 years.
Nose and Throat Carriage Rates for Staphylococcus aureus
in Undergraduate Nursing Students
Jaime F. Randise, Austin M. Martini, Lindsey A. DeSandre, Anna K. Fairfax, Matthew C. Mason, Robert M. Schilke, and Kevin B. Kiser
Department of Biology and Marine Biology, University of North Carolina Wilmington, 601 S. College Road, Wilmington, NC 28403
Methicillin-resistant Staphylococcus aureus (MRSA) carriage in patients is a risk factor for infections in hospitals. Approximately 30% of healthy individuals carry S. aureus in the nose; however, only a small percentage of those isolates are MRSA. Healthcare workers may serve as transient carriers of S. aureus on skin and clothing and may pose a
transmission risk to patients. Whether healthcare workers acquire nose and/or throat carriage when repeatedly exposed to MRSA patients has not been clearly determined. To examine the role of clinical exposure in MRSA carriage, UNCW nursing students were tested over the past three semesters for nose and throat carriage. After students
filled out consent forms and questionnaires, swab samples from their nose and throat were cultured on CHROMagar Staph aureus plates. Once isolated and identified, each S. aureus isolate was tested for antibiotic sensitivity by disk diffusion. MRSA was characterized by cefoxitin-resistance. Across three semesters, the S. aureus carriage rates
were 38% (21% nose/25% throat), 44% (26% nose/33% throat), and 62% (46% nose/35% throat). This study highlights the importance of testing the throat, as well as nose, for S. aureus colonization, where seventeen percent of subjects were exclusive throat carriers. Only five students (1%) tested positive for MRSA. This low rate may have
occurred because students were well informed about protecting themselves against MRSA or newly admitted nursing students had not yet been exposed to MRSA. A longitudinal study is currently underway to track students from the semester prior to starting the nursing program, through their clinical experience, until graduation.
Figure 5. Rates of S. aureus carriage in nursing students
across four semesters. Participants with no carriage consisted
of 51.3% of the total, while 48.9% of participants were
carriers of S. aureus either in their nose, throat or nose and
throat.
William Brock, Brandon Ludlum, Meghan Dalziel, Camry Wagner, Rheanna McKnight, Cortney Castine, Taylor Morrisette, Samuel Gmuca, Garrett Hutchings, Haleigh Nelson, and Erin DeYoung also
contributed to this study. We would like to thank the students and faculty of the UNCW School of Nursing for their overwhelming cooperation and support. Special thanks to Dr. Anne-Marie Goff,
the Association of Nursing Students advisor, for helping us to coordinate sample collections. This research was supported with intramural funds from UNCW including an Experiencing Transformative
Education through Applied Learning (ETEAL)-supported pedagogy initiative, Center for the Support of Undergraduate Research and Fellowships (CSURF) Research Supplies Awards and Travel Grants,
and applied learning funds from the Department of Biology and Marine Biology.
The infection rate of methicillin-resistant Staphylococcus aureus (MRSA) is dramatically higher in hospital environments than in other
community-acquired settings. Healthcare-associated infection (HAIs) account for 86% of invasive MRSA infections, while community acquired
MRSA accounts for the remaining 14% [1]. Nosocomial MRSA infections carry a mortality rate of 20-50% [2]. Research is being conducted on
how to limit the spread of MRSA in the hospital setting. Studies have indicated that 6.25% healthcare workers carry MRSA [3]. This statistic
has been based on tracking MRSA by swabbing the anterior nares. Emphasis is placed on the nose, as 80% of invasive nosocomial infections
originate from nasal carriers [4]. However, a 2007 study showed that 37.1% of tested individuals were nasal carriers, but 12.8% were solely
throat carriers, which emphasizes the importance of not only checking the nose but also checking the throat for carriage [4]. Healthcare
professionals who are carriers of MRSA have special “contact precautions” to make sure that they do not infect their patients. Unfortunately,
if a health care professional is asymptomatic, and if healthcare workers do not know they are MRSA carriers they unknowingly can be placing
their patients at risk. Some hospitals test their workers regularly for MRSA though this is not a common practice. The goal of our study is to
observe MRSA carriage in nursing students and determine if and when they become MRSA carriers. This is accomplished by collecting nose
and throat swabs of nursing students every semester. By continuously testing nursing students throughout their nursing school career, we
will be able to discern carriage rates of MRSA and observe whether S. aureus carriage changes over time.
1. Jernigan J., Kallen A. “Methicillin-Resistant Staphylococcus aureus (MRSA) Infections.” Centers for Disease Control and Prevention 2010:1.1-44
2. Hanberger, H. “Increased mortality associated with methicillin-resistant Staphylococcus aureus (MRSA) infection in the Intensive Care Unit." National Center for Biotechnology Information. U.S.
National Library of Medicine, 13 May 2011.
3. Mattieu E., Yolaine M. “Carriage of Methicillin-Resistant Staphylococcus aureus Among Hospital Employees: Prevalence, Duration, and Transmission to Households Infection Control.” National
Center for Biotechnology Information. U.S. National Library of Medicine, 25 Feb. 2004.
4. Dominik M., Reno F., Barbara J. “Throat Swabs Are Necessary to Reliably Detect Carriers of Staphylococcus aureus.” Clinical Infection Diseases, Aug.-Sept. 2007.
5. Lowy, F. D. "Antimicrobial Resistance: The Example of Staphylococcus aureus." Journal of Clinical Investigation 111.9 (2003): 1265-273.
Out of the 380 total individuals from the past four semesters, 48.9% of all participants were carriers for S. aureus in their nares and/or pharynx. Three
out of the four semesters showed more nose-only carriers than throat-only carriers. This finding is supported by previous studies [4]. However, testing for
throat carriers cannot be overlooked; out of the total carriers, 16.8% were specifically throat carriers, which is higher than shown in previous studies.
Therefore, the number of throat carriers is noteworthy compared to the number of nose carriers. Furthermore, penicillin resistance was lower than
expected with an average of 65.6% of isolates exhibiting resistance to the antibiotic. Studies have shown that over 80% of staphylococcal infections
displayed penicillin resistance [5]. Of the total participants from the past four semesters, 1.31% were MRSA carriers. To be considered a MRSA carrier, the
isolate had to be resistant to cefoxitin, which is a methicillin surrogate. This number is lower than expected from previous studies [3]. The data suggests
that clinical exposure does not increase MRSA carriage. However, there is potential for healthcare workers and nursing students to become passive
carriers, which is difficult to quantify with this study. The overall low percentage of carriers may be attributed to the increased awareness and education
of safe healthcare practices in the UNCW School of Nursing.
Figure 6. Rates of S. aureus carriers resistance to selected
antibiotics across four semesters. The clindamycin cohort
includes resistance and inducible clindamycin resistance.
Average resistance of S. aureus to the antibiotics were:
penicillin 65.6%, cefoxitin 2.2%, erythromycin 25.6%,
clindamycin 19.5%, tetracycline 11.5%. *This measurement
was not taken.
N=65 N=94 N=115 N=106
*
Figure 2. Each sample was then
spotted on CHROMagar™, a
medium which allows S. aureus to
exhibit a pink-to-red hue after a 24-
hour incubation period at 35˚C.
Samples that showed other colors
or no growth were not tested
further and were concluded to be
negative for S. aureus.
Figure 1. Nose and
throat swabs were
collected from each
participant and
placed in tubes of
tryptic soy broth
supplemented with
7.5% NaCl to
incubate for 24
hours at 35˚C.
Figure 3. Isolates
were confirmed as
S. aureus by testing
for coagulase, an
enzyme produced by
S. aureus. After a 24-
hour incubation
period in rabbit
plasma with EDTA at
35˚C, the samples
were observed for
coagulation.
Figure 4. Disk diffusion was used
to test for antibiotic resistance
among confirmed S. aureus
isolates. A suspension of bacteria
was spread across Mueller-Hinton
agar. Five antibiotic disks were
placed on the media. After
incubation for 24 hours at 35˚C,
zones of inhibition were
measured to distinguish between
sensitivity and resistance. A “D-
zone” indicated inducible-
clindamycin resistance.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Spring 2013 Fall 2013 Spring 2014 Fall 2014
None
Throat only
Nose and throat
Nose only
Spring 2013 Fall 2013 Spring 2014 Fall 2014
1. Previous
hospitalization
Yes 32.30%* 11.22% 5.30% 3.80%
No 66.10%* 88.77% 94.70% 96.20%
2. Previous staph/
MRSA infection
Yes 10.70% 4.10% 1.80% 3.80%
No 87.70% 95.90% 98.20% 96.20%
3. Frequency of
antibiotic use** ----
Never ---- 4.10% 1.80% 0%
Not in 12 months ---- 38.80% 46.90% 44.80%
Once in 12 months ---- 30.60% 30.0% 35.20%
More than once in the
past 12 months ---- 26.50% 21.20% 20.0%
4. Self-reported nose
picking
Yes 20.30% 43.60% 47.30% 53.33%
No 79.70% 56.40% 52.70% 46.66%
Table 1. Questionnaire data. 1) Percentage of
participants from each semester that have
been hospitalized in the past 12 months
(*Spring 2013 participants were asked “have
you ever been hospitalized.” This may explain
the higher percentage of positive responses
compared to the other semesters). 2)
Percentage of participants each semester that
have ever been diagnosed with a staph or
MRSA infection. 3) Frequency of antibiotic use
among the participants over given periods of
time (**Spring 2013 participants were only
asked if they were prescribed antibiotics in the
past 6 months: 37% yes, 61.5% no). 4)
Percentage of participants that self-reported
nose picking. This is being investigated as a
contributing factor to nursing students
becoming carriers of S. aureus.
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