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Chapter 1: Background
In the early 1990s, methicillin-resistant Staphylococcus aureus (MRSA)
infections began to occur in the community in persons who had had no contact with
healthcare institutions or with anyone who had recently received healthcare [1, 2].
Community-acquired MRSA (CA-MRSA) is now present in hospitals and has caused
nosocomial outbreaks, particularly in children [3, 4]. There is increasing evidence that
CA-MRSA is spreading in communities among children with no known predisposing risk
[5-10].
Studies indicate that hospital-acquired MRSA (HA-MRSA) may be spread from
colonized healthcare workers to their family members, and that children carrying CAMRSA may spread it to their parents [7, 11-13]. Given this bidirectional transmission of
HA-MRSA and CA-MRSA, it is not surprising that a recent publication noted that 18%28% of patients with healthcare-related risk factors (HRFs) had a community-associated
strain, primarily USA300, and 26% of patients without HRFs had a healthcare-associated
strain, usually USA100 [14].
Now that it is well established that CA-MRSA spreads among children in the
community and that MRSA carried by healthcare workers spreads to family members, it
could be hypothesized that MRSA (CA-MRSA and HA-MRSA) are prevalent and being
transmitted among children in day care centers [5, 11]. There are only 3 publications on
the prevalence and epidemiology of MRSA in day care centers [13, 15, 16]. With the
rapidly rising prevalence of CA-MRSA in the United States (U.S.) and with only one
study of MRSA in a day care center in the U.S. published 10 years ago, studies of the
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epidemiology of MRSA in day care centers in the U.S. are needed to determine the
prevalence of MRSA in these facilities and to define the best methods of detection and
prevention.
The objectives of this study were to: determine the prevalence of MRSA in a day
care center in a university medical center, determine the proportions of isolates that were
CA-MRSA and HA-MRSA, compare the recovery of MRSA from different body sites by
swab samples, compare isolates of MRSA by molecular typing, and to identify risk
factors for MRSA colonization in day care.
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Chapter 2: Methods
The day care center at the University of Texas Medical Branch (UTMB) is
located on campus.
The center cares for approximately 135 children and has 35
employees. Only children of UTMB employees are eligible for enrollment at the child
care center. There are 11 classrooms, 4 indoor common play areas, and 2 outdoor
playgrounds at the child care center. Children range from 6 weeks to 5 years of age. All
children in child care and employees of the child care center were eligible to participate.
There were no known MRSA infections in children or employees of the child care center
when the study was initiated. A cross-sectional study design was used. Data were
collected for the children and employees by cultures of predetermined body sites and by
self-administered questionnaires completed by children’s parents and by employees.
This study was approved by the University of Texas Medical Branch Institutional Review
Board. Signed informed consent was obtained from the parent/guardian of each child and
from each employee who participated in the study.
Subjects were recruited by a letter sent to parents or by contact with parents
during peak drop-off and pick-up hours at the day care center over a 1 week period. Day
care center employees were recruited by letter as well as by communication with the
Principal Investigator (ALH). Questionnaires were distributed to parents and employees
with the recruitment letter.
CULTURES
Cultures were taken using cotton swabs moistened in sterile water without
preservatives. Cultures of children were obtained from the nares, oropharynx, axillae,
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inguinal area, and perirectal area. Cultures of adults were taken from the nares and
oropharynx. Cultures were also taken from 195 sites in the inanimate environment,
including toys, nap mats, and other surfaces. Parents of children and employees of the
child care center found to have one or more positive cultures for MRSA were notified by
phone and asked to answer further epidemiologic questions via telephone interview.
Parents of children found to be colonized with MRSA were then asked to submit nasal
and oropharyngeal cultures from themselves and to help obtain cultures from other
household members. The employee found to be colonized with MRSA was also asked to
assist with obtaining cultures from her household members. These samples were cultured
using the same techniques utilized for the initial screening.
MICROBIOLOGY
Culture samples were inoculated directly into phenyl mannitol broth (PHMB+)
containing aztreonam, incubated at 37oC for 72 hours, and observed daily for color
change. Phenyl mannitol broth (PHMB+) was prepared by a modification of the method
of Wertheim et al [17]. Twenty mg of dehydrated PHMB+ (Becton Dickinson) was
added to 1 liter of sterile water. The broth was autoclaved at 121oC for 15 minutes and
then allowed to cool to room temperature. The aztreonam solution was created by
mixing 480 mg of aztreonam with 12 ml of sterile water. Next, 2 ml of the aztreonam
solution was placed into 1 liter of PHMB+ (40µg/ml). Sterile tubes were filled with 5 ml
of PHMB+ and stored at 4oC.
The PHMB+ was evaluated for sterility by incubation of a sample of broth at 37oC
for 72 hours. No color change was observed. To determine the sensitivity of the
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modified method to detect MRSA, ten known isolates MRSA were streaked onto blood
agar and incubated at 37oC for 18 hours. The plates were examined and colonies were
selected and inoculated into 0.9% NaCl to achieve a 0.5 McFarland turbidity standard
(108 CFU/ml). A dilution series (108-100 CFU/ml) was made, and 500 µl of each dilution
was placed into 5 ml of PHMB+. The PHMB+ dilutions were incubated at 37oC for 72
hours and inspected daily for color change. No color change was observed in the 100
dilution. Color change was observed in all other dilutions at 24 hours. The PHMB+ was
also tested against 4 American Type Culture Collection (ATCC) gram-negative
organisms, (Escherichia coli, Enterobacter cloacae, Proteus mirabilis, and Klebsiella
pneumoniae) and none of the strains induced a color change.
A portion of every sample that underwent color change was plated on Columbia
CNA agar (Becton Dickinson) and incubated at 37oC for 48 hours. Colonies appearing to
be S. aureus morphologically were selected, and the Staphaurex (Remel) rapid latex test
was utilized to confirm the presence of S. aureus. The organisms identified as S. aureus
were then transferred to Trypticase Soy Broth (TSB) until a 0.5 McFarland turbidity
standard was achieved.
The broth was spot inoculated onto Oxacillin Screen Agar
(Becton Dickinson) and incubated at 37oC for 24 hours. The plates were examined for
growth or no growth and identified as either MRSA or MSSA, respectively.
MOLECULAR TYPING
The interrelatedness of the MRSA isolates was evaluated using the DiversiLab
Microbial Genotyping System (Biomérieux). This system was also used to determine the
USA type of each isolate. The fingerprint patterns of each sample were used to evaluate
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the number of band differences between each isolate. The T5000 Universal Biosensor
(Ibis) was used to evaluate the isolates for the presence of the Panton-Valentine
leukociden (PVL) genetic elements, as well as the mupA, ermA and ermC genes. The
staphylococcal cassette chromosome (SCC) type was identified for each isolate using
multiplex PCR [18, 19].
STATISTICAL ANALYSIS
Data from the standardized questionnaire forms and microbiologic data were
entered twice in software for data management.
After double entry, data was
downloaded to SAS statistical software, version 9.1.3 (SAS Institute) for statistical
analysis using the T-test, two-sided Fisher’s Exact test and Exact Logistic Regression.
Children found to be colonized with MRSA were compared to children without MRSA
colonization using univariate and multivariable logistic regression.
Multivariable
analysis was performed using all variables from univariate analysis with a p value ≤ 0.20.
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Chapter 3: Results
CULTURES FROM CHILDREN
A total of 104 of the 135 children (77%) enrolled at the child care center
participated in the study. Seven of the participating children (6.73%) who attended the
child care center were found to be colonized with MRSA. One hundred three of the 104
participating children who attended the child care center (99.04%) had all 5 body sites
(nose, oropharynx, axillae, groin, perirectal) sampled. One child had 4 of the 5 sites
sampled, for a total of 519 body sites sampled. MRSA was recovered from a total of 9
sites on these children (table 1). Cultures of the nose and oropharynx, which individually
identified 4 of the 7 MRSA colonized children (57%), were equally sensitive. When used
together, cultures of the nose and oropharynx identified all (100%) of the colonized
children.
Table 1: Results by culture site of children enrolled at the childcare center.
Sites
sampled on
each child
Number of
sites with
MRSA (%)
Nose
4 (44.4)
Oropharynx
4 (44.4)
Axilla
0
Groin
0
Peri-rectal
1 (11.1)
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CULTURES FROM EMPLOYEES AND THE ENVIRONMENT
Nasal and oropharyngeal samples were obtained from 32 of the 35 employees
(91.4%) of the child care center. Only 1 (3.13%) employee was positive for MRSA.
Cultures were obtained from a total of 195 environmental sites at the child care center.
MRSA was recovered from 4 of these environmental sites (2.05%). The positive sites
included 2 cribs, a cloth toy, and a nap mat.
CULTURES FROM HOUSEHOLD CONTACTS
A total of 21 household contacts of the children and employee found to be
colonized with MRSA were identified. Seventeen of these household contacts (81%)
were cultured. Six of these individuals (35.29%) were found to be colonized with MRSA
at 1 or more sites (table 2).
Table 2: Results of cultures from 17 household contacts.
Subjects sampled
Adults
Children
Total
No. positive (%)
3 (27.3)
3 (50)
6 (35)
No. negative (%)
8 (72.7)
3 (50)
11 (65)
Total no. (%)
11 (100)
6 (100)
17 (100)
QUESTIONNAIRE DATA AND STATISTICAL ANALYSIS
Questionnaires were obtained from parents of all 104 participating children and
all 32 participating employees. Epidemiologic data obtained from the children’s
questionnaires and the corresponding univariate analyses are shown in table 3.
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Table 3: Univariate comparison of children with MRSA colonization and children
without MRSA colonization.
Univariate analysis
Variable
Age, mean months ± SD
Male Sex
Race
White
Hispanic
Black/African American
Asian
Hawaiian/Pacific Islander
Length of time in child care, mean
months ± SD
Length of time at UTMB day care
center, mean months ± SD
Currently wears diapers or training
pants
Traveled within Texas in the past 6
months
Traveled outside of Texas, within U.S.
in the past 6 months
Traveled outside U.S. in the past 6
months
Visited nursing home in the past 6
months
Household member provides direct
patient care
Household member works with
Staphylococcus in laboratory setting
History of skin infection in household
member
History of MRSA infection in household
member
History of Hospitalization
Emergency room visit in the past 6
months
Previous Surgery
History of Ear tubes
History of other type of surgery (cleft
palate repair, hernia repair, lung biopsy,
epispadius repair)
Asthma
Diabetes
Cancer
Skin Disease (eczema, atopic
dermatitis)
Other (acid reflux, cleft palate, heart
murmur, hypothyroidism)
Children with
MRSA (n=7)
Children
without
MRSA
(n=97)
32.7 ± 18.2
3 (42.9)
31.3 ± 18.1
44 (45.4)
5 (71.4)
1 (14.3)
0
1 (14.3)
0
52 (54.2)
15 (15.6)
5 (5.2)
23 (24.0)
1 (1.0)
22.0 ± 17.4
22.3 ± 16.3
0.971
13.1 ± 7.5
18.4 ± 15.1
0.134
6 (85.7)
64 (66.0)
3.09 (0.36-26.78)
0.422
4 (57.1)
73 (75.3)
0.44 (0.09-2.10)
0.372
2 (28.6)
62 (63.9)
0.23 (0.04-1.23)
0.104
2 (28.6)
20 (20.6)
1.54 (0.28-8.53)
0.637
0
13 (13.4)
∞
0.592
2 (28.6)
41 (42.3)
0.55 (0.10-2.96)
0.697
0
2 (2.1)
∞
1.000
0
11 (11.3)
∞
1.000
0
1 (14.3)
8 (8.3)
19 (19.6)
∞
0.68 (0.08-6.03)
1.000
1.000
2 (28.6)
2 (28.6)
1 (14.3)
8 (8.3)
13 (13.4)
11 (11.3)
4.45 (0.74-26.71)
2.58 (0.45-14.74)
1.30 (0.14-11.86)
0.135
0.265
0.588
2 (28.6)
2 (28.6)
0
0
2 (2.1)
7 (7.2)
0
0
19.00 (2.20-164-16)
5.14 (0.84-31.46)
0.022
0.112
1 (14.3)
10 (10.3)
1.45 (0.16-13.30)
0.554
2 (28.6)
5 (5.2)
7.36 (1.13-47.78)
0.070
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Odds Ratio
(95% CI)
0.90 (0.19-4.25)
P
0.849
1.000
0.901
History of skin infection (boil/abscess,
cellulitis, infected bite) in the past year
History of Staphylococcal infection
History of MRSA infection
Medications
Steroid inhaler
Allergy medication
Asthma medication
Oral steroid
Other (antibiotic ointment,
levothyroxine, antibiotics)
Received antibiotics in the past 6
months
Courses of antibiotics in the past 6
months
0
1
2
3
4
5
>5
Type of Antibiotics received
Beta-lactam
Macrolide
Trimethoprim-sulfamethoxazole
unknown
History of Infections treated with
antibiotics in the past 6 months
Ear infection
Upper respiratory infection
Sinus infection
Pneumonia
Other illness
1 (14.3)
10 (10.3)
1.45 (0.16-13.30)
0.554
0
0
4 (4.1)
2 (2.1)
∞
∞
1.000
1.000
1 (14.3)
1 (14.3)
2 (28.6)
0
4 (4.1)
4 (4.1)
3 (3.1)
1 (1.0)
3.88 (0.37-40.29)
3.88 (0.37-40.29)
12.53 (1.69-92.85)
∞
0.299
0.299
0.036
1.000
2 (28.6)
3 (3.1)
12.53 (1.69-92.85)
0.036
4 (57.1)
50 (51.6)
1.25 (0.27-5.90)
1.000
3 (42.9)
1 (14.3)
2 (28.6)
0
1 (14.3)
0
0
47 (48.5)
24 (24.7)
18 (18.6)
4 (4.1)
2 (2.1)
1 (1.0)
1 (1.0)
2 (28.6)
3 (42.9)
0
1 (14.3)
32 (33.0)
3 (3.1)
1 (1.0)
20 (20.6)
0.81 (0.15-4.42)
23.50 (3.56-155.15)
∞
0.64 (0.07-5.64)
1.000
0.004
1.000
1.000
3 (42.9)
2 (28.6)
0
1 (14.3)
0
34 (35.1)
14 (14.4)
9 (9.3)
1 (1.0)
3 (3.1)
1.39 (0.29-6.57)
2.37 (0.42-13.44)
∞
16.00 (0.89-288.45)
∞
0.697
0.293
1.000
0.131
1.000
0.525
Data are number (%) of children, unless otherwise indicated.
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Univariate analysis identified receipt of macrolide antibiotics (p=0.004), asthma
medications (p=0.036), other medications (p=0.036), and previous surgery (p=0.022) as
risk factors for MRSA colonization. In multivariable analysis only receipt of macrolide
antibiotics (p=0.002; OR 39.6; 95% CI 3.4-651.4), and receipt of asthma medications
(p=0.024; OR 26.9; 95% CI 1.5-500.7) remained related to MRSA colonization.
Epidemiologic data obtained from the employee questionnaire are shown in table
4. Statistical analysis was not performed on the employee data since only one employee
was colonized with MRSA.
Table 4: Employee epidemiologic data.
No. of
employees (%)
Variable
Age, mean years ± SD
Female Sex
Race
White
Hispanic
Black/African American
Asian
Hawaiian/Pacific Islander
Length of time in child care, mean months ± SD
Length of time at this day care center, mean months ±
SD
Traveled within Texas in the past 6 months
Traveled outside of Texas, within U.S. in the past 6
months
Traveled outside U.S. in the past 6 months
Visited nursing home in the past 6 months
Household member provides direct patient care
Household member works with Staphylococcus in
laboratory setting
History of skin infection in household member
History of MRSA infection in household member
History of hospitalization
History of mechanical ventilation
Emergency room visit in the past 6 months
Previous surgery
History of skin infection (boil/abscess, cellulitis, infected
bite) in the past year
History of Staphylococcal infection
11
40.3 ± 14.0
32 (100)
15 (47)
5 (16)
11 (34)
1 (3)
0 (0)
97.3 ± 87.0
52.7 ± 63.2
21 (66)
5 (16)
2 (6)
3 (9)
2 (6)
1 (3)
7 (22)
1 (3)
19 (59)
2 (6)
8 (25)
18 (31)
5 (16)
1 (3)
History of MRSA infection
Medical Conditions
Asthma
Diabetes
Cancer
Skin Disease (eczema, atopic dermatitis)
Other (acid reflux, hypertension, hyperlipidemia,
hypothyroidism, osteoporosis)
Medications
Steroid inhaler
Allergy medication
Asthma medication
Oral steroid
Diabetes medication
Other (antihypertensive, proton pump inhibitor, statin,
pain medications, levothyroxine)
Received antibiotics in the past 6 months
Courses of antibiotics in the past 6 months
0
1
2
3
4
5
1 (3)
2 (6)
3 (9)
0 (0)
0 (0)
11 (34)
1 (3)
0 (0)
1 (3)
0 (0)
2 (6)
11 (34)
8 (25)
24 (75)
5 (16)
2 (6)
0 (0)
0 (0)
1 (3)
Type of Antibiotics received
Beta-lactam
Macrolide
Trimethoprim-sulfamethoxazole
unknown
0 (0)
3 (9)
2 (6)
5 (16)
History of Infections treated with antibiotics in the past 6
months
Ear infection
Upper respiratory infection
Sinus infection
Pneumonia
Other illness
0 (0)
2 (6)
3 (9)
1 (3)
2 (6)
.
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MOLECULAR ANALYSIS
A total of 21 MRSA samples obtained from children, employees, household
contacts and the environment were analyzed (table 5).
Table 5: Molecular characteristics of MRSA isolates.
Isolate
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Sites cultured
Employee A's child 1 (OP)
Child A (nose)
Cloth toy in room with Child A
Employee A's child 1 (peri-rectal)
Crib in room adjacent to Child A
Child B (nose)
Crib in room with Child A
Employee A (nose)
Nap mat in room with Child A
Employee A's child 1 (groin)
Child C (OP)
Child D (nose)
Child D (peri-rectal)
Employee A's child 2 (nose)
Child E (OP)
Child E (nose)
Parent 1 of Child F and Child G
(nose)
Child F (OP)
Parent 1 of Child F and Child G
(OP)
Child G (OP)
Parent 2 of Child F and Child G
(nose)
PFGE type
USA 300
USA 300
USA 300
USA 300
USA 300
USA 300
USA 300
USA 300
USA 300
USA 300
USA 300
USA 300
USA 300
USA 100
USA 100
USA 100
SCCmec
IVa
IVa
IVa
IVa
n/t
IVa
IVa
IVa
IVa
IVa
IVa
IVa
IVa
II
II
II
PVL
PVL+
PVL+
PVL+
PVL+
n/t
PVL+
PVL+
PVL+
PVL+
PVL+
PVL+
PVL+
PVL+
neg
neg
neg
mupA
neg
neg
neg
neg
n/t
neg
neg
neg
neg
neg
neg
neg
neg
neg
neg
neg
ermA
neg
neg
neg
neg
n/t
neg
neg
neg
neg
neg
neg
neg
neg
ermA+
ermA+
ermA+
ermC
neg
neg
neg
neg
n/t
neg
neg
neg
neg
neg
neg
neg
neg
neg
neg
neg
USA 600
USA 600
IVa
IVa
neg
neg
neg
neg
ermA+
ermA+
neg
neg
USA 600
USA 600
IVa
IVa
neg
neg
neg
neg
ermA+
ermA+
neg
neg
USA 600
IVa
neg
neg
ermA+
neg
PFGE- Pulsed-field gel electrophoresis
PVL- Panton-Valentine leukocidin
SCCmec- Staphylococcal cassette chromosome mec
OP- Oropharynx
n/t- Not tested. Sample unable to be recovered following Hurricane Ike.
13
The similarity matrix generated by the DiversiLab Microbial Genotyping System
(Biomérieux) is shown in figure 1.
Figure 1: Similarity matrix
Figure 1 legend. Interpreting the similarity matrix.
The number in the box where the two samples intersect is the percent similarity. The
colors of the boxes indicate the percent similarity of the sample according to the scale.
OP- Oropharynx
Isolates 1-10 were obtained from an employee and her child, 2 children enrolled
at the child care center, and several environmental sites in close proximity to the
colonized children.
These isolates were all found to be indistinguishable (0 band
14
differences) or similar (1-2 band differences). Isolates 11-13 were found to be similar to
each other but different from all other isolates, and were obtained from 2 children
enrolled in the same classroom at the child care center. Isolate 14 was obtained from
another child of employee A, and was not related to any of the other isolates. Isolates 1516 were indistinguishable, but different from all other isolates and were obtained from 2
sites on a child enrolled at the center. Indistinguishable isolates 17-21 were obtained
from a family where both parents and 2 children enrolled at the center were found to be
colonized. These isolates were unrelated to other MRSA isolates obtained from the child
care center.
Most of the isolates were CA-MRSA (USA300, USA600); however, isolates 1416 were HA-MRSA (USA100). None of the isolates were found to carry the mupirocin
resistance gene (mupA). The HA-MRSA isolates (14-16) and the USA600 CA-MRSA
isolates (17-21) all carried the erythromycin resistance gene (ermA). Only the USA300
isolates were found to contain the PVL genes.
15
Chapter 4: Discussion
To the knowledge of our study group, this is the first investigation into the
epidemiology of MRSA in day care since 1999. In the three previously published studies
of day care populations, the prevalence of MRSA colonization ranged between 1.2% and
24% [13, 15, 16]. Except for the MRSA prevalence of 24% in one of two child care
centers in the first published study, MRSA prevalence ranged from 1.2% to 3% [13, 15,
16]. The observed prevalence of MRSA in children in our day care center of 6.7% may
represent an increasing prevalence over the past 10 years. A more recently published
study in children cultured during health maintenance visits found that 9.2% were
colonized with MRSA [9]. Alternatively, we may have detected a higher prevalence by
sampling more body sites and utilizing broth amplification prior to culture on solid
media. We sampled five body sites and swabs were inoculated to broth that could detect
as few as 10 cfu per ml.
Of the 5 body sites cultured, the oropharyngeal and nasal sites yielded 8 of the 9
positive cultures, and identified 100% of the colonized children (table 1). All cultures
from the axillae and inguinal areas were negative with a single positive culture from the
perirectal area. Cultures taken in the earlier studies were from anterior nares only, 1 nare
and the axilla, or 1 to 3 cultures from throat, nares and perirectal area [13, 15, 16]. Thus,
the most sensitive technique for detecting MRSA colonization may be cultures from
nares, oropharynx and perirectal area with broth amplification prior to plating for
isolation and identification.
One of the 32 child care providers (3.1%) in our study was positive for MRSA.
None of the care providers in the 3 previously published studies were colonized with
16
MRSA [13, 15, 16]. Four of 195 (2.05%) of environmental samples were positive for
MRSA. Environmental cultures were not taken during one of the previous studies and no
data on environmental site cultures were reported in the other studies [13, 15, 16]. The
culture positive sites in our study were those frequently contacted by both children and
care providers but not routinely cleaned.
We observed the highest percentage of cultures positive for MRSA in household
and employee contacts of children colonized with MRSA. Six of 17 (35.3%) contacts
were culture positive (table 2). One of the previous studies did not sample household
contacts, and another reported insufficient data to determine the percent of household
contacts colonized with MRSA [13, 15]. Another study found that 16.7% of family
contacts were colonized with MRSA [16]. Our higher rate of colonization in household
contacts may have been related to culture of more sites or use of a more sensitive method
for detecting small numbers of colonizing microorganisms.
We observed no differences in age, gender or race between patients colonized and
those not colonized with MRSA (table 3). In two earlier studies, younger age was
significantly associated with colonization in one, and in the other older age was
significantly related to acquisition of MRSA [15, 16]. We were unable to show a
relationship between total duration of day care or duration of child care in our center and
colonization of children. This observation is consistent with the absence of a relationship
in previously published studies [13, 15, 16].
The absence of a relationship between skin diseases such as eczema and atopic
dermatitis and colonization with MRSA is notable given the tendency for such skin
lesions to become colonized with S. aureus. Seventy-five to 80% of patients with atopic
17
dermatitis are colonized with S. aureus, and 16%-18.3% of these S. aureus isolates are
MRSA [20, 21]. We may have failed to show such a relationship due to small numbers
of children with atopic dermatitis. As in a previously published report, we found that a
history of hospitalization or a history of an emergency department visit in the six months
prior to study entry was not a risk factor for colonization with MRSA [16].
We noted no relationship between whether a parent provided direct patient care
and colonization of attendees at the child care center. Two previously published studies
performed on children during well-child visits have shown a significant association
between parents who work in healthcare and acquisition of MRSA by their children or
other household members [7, 9]. We observed no association between skin infection in a
household member or an MRSA infection in a household member and colonization with
MRSA. We also failed to show a relationship between a member of the household
working with S. aureus in a laboratory and acquisition by household members.
The relationship between administration of asthma medications and acquisition of
MRSA may be due to the predominance of steroids in these drugs. Failure to show an
association of receipt of antibiotics in the past 6 months, the number of courses of
antibiotics administered, or the types of infections treated with antibiotics may be due to
absence of an association or to the small numbers of observations.
However,
administration of macrolide antibiotics was significantly related to MRSA colonization in
both univariate (p=0.004) and multivariable analysis (p=0.002).
Molecular analysis revealed that many MRSA isolates obtained from the child
care center were indistinguishable. The same strain of MRSA was recovered from an
employee and her child (who had not attended this day care) and children and the
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environment at the day care center (isolates 1-10). These isolates also had the same
genetic profile as evaluated by our molecular typing. All of these strains were USA300,
SCCmec type IVa, and contained PVL but not the mupA, ermA, or ermC genes (table 5).
USA300 isolates 11-13, found in 2 children in the same classroom, were also similar to
each other, but different from the other USA300 isolates. This suggests that transmission
of MRSA in these groups occurred in the day care center.
Two different strains of HA-MRSA (USA100) were recovered from a child of the
employee colonized with CA-MRSA, and a child who attended the day care center
(isolates 14-16). On further questioning, the child with HA-MRSA who attended the day
care center had had close contact with someone with a history of multiple
hospitalizations.
Although most of our CA-MRSA isolates were USA300 strains, several USA600
CA-MRSA isolates were also recovered. Interestingly, these isolates were obtained from
a family where both parents were healthcare workers who provided direct patient care.
This CA-MRSA strain, which was different from the other MRSA isolates, appeared to
be limited to this family unit.
As a result of this study a tailored cleaning protocol was created for the UTMB
child care center.
This protocol emphasized routinely cleaned surfaces as well as
detailing the specialized cleaning of sites found to be contaminated with Staphylococcus
aureus in our study. The protocol was implemented at the child care center in July, 2008.
Unfortunately no follow-up studies on the success of this new cleaning protocol were
conducted due to the closure of the child care center following Hurricane Ike.
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The major limitations of this study were the small sample size and evaluation of a
single center. Despite these limitations, we believe that this study demonstrated the
potential complexity of the clinical and molecular epidemiology of MRSA in a child care
center. Further studies are needed to expand this knowledge to enhance prevention and
control of MRSA in the day care setting
20
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Vita
Angela L. Hewlett M.D. was born in Houston, Texas on October 9, 1974 to Gene and
Helen Green. She graduated from the University of Texas at Austin in 1998, and earned
her M.D. from the University of Texas Medical Branch (UTMB) in Galveston, Texas in
2002. After graduation she remained at UTMB and completed an Internal Medicine
residency. She then served as Chief Medical Resident from 2005-2006. She began her
fellowship training in the Division of Infectious Diseases at UTMB in 2006, and is now
completing an additional year of research training while concurrently pursuing a Masters
of Science in Clinical Investigation. After the completion of her fellowship in June 2009
she will continue her career in academic Infectious Diseases at the University of
Nebraska Medical Center in Omaha, Nebraska.
Permanent address:
1406 Chaparral Crossing League City, Texas 77573
This dissertation was typed by Angela L. Hewlett.
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