Community-Associated Methicillin-Resistant Staphylococcus aureus Skin and Soft Tissue Infections at a Public Hospital
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ORIGINAL INVESTIGATION
Community-Associated Methicillin-Resistant
Staphylococcus aureus Skin and Soft Tissue
Infections at a Public Hospital
Do Public Housing and Incarceration Amplify Transmission?
Bala Hota, MD, MPH; Charlotte Ellenbogen, MD; Mary K. Hayden, MD; Alla Aroutcheva, MD, PhD;
Thomas W. Rice, PhD; Robert A. Weinstein, MD
Background: Community-associated methicillin- terval [CI], 1.00-3.67), African American race/ethnicity
resistant Staphylococcus aureus (CA-MRSA) infections (OR, 1.91; 95% CI, 1.28-2.87), and residence at a group
have emerged among patients without health care– of geographically proximate public housing complexes
associated risk factors. Understanding the epidemiology (OR, 2.50; 95% CI, 1.25-4.98); older age was inversely
of CA-MRSA is critical for developing control measures. related (OR, 0.89; 95% CI, 0.82-0.96 [for each decade
increase]). Of 73 strains tested, 79% were pulsed-field
Methods: At a 464-bed public hospital in Chicago and gel electrophoresis type USA300.
its more than 100 associated clinics, surveillance of soft
tissue, abscess fluid, joint fluid, and bone cultures for Conclusions: Clonal CA-MRSA infection has emerged
S aureus was performed. We estimated rates of infection among Chicago’s urban poor. It has occurred in addi-
and geographic and other risks for CA-MRSA through tion to, not in place of, methicillin-susceptible S aureus
laboratory-based surveillance and a case-control study. infection. Epidemiological analysis suggests that con-
trol measures could focus initially on core groups that
Results: The incidence of CA-MRSA skin and soft tis- have contributed disproportionately to risk, although
sue infections increased from 24.0 cases per 100 000 CA-MRSA becomes endemic as it disseminates within
people in 2000 to 164.2 cases per 100 000 people in 2005 communities.
(relative risk, 6.84 [2005 vs 2000]). Risk factors were in-
carceration (odds ratio [OR], 1.92; 95% confidence in- Arch Intern Med. 2007;167:1026-1033
S
INCE 1998, COMMUNITY - help identify specific high-risk commu-
associated methicillin- nity settings and groups.
resistant Staphylococcus au- We conducted surveillance at a public
reus (CA-MRSA) infections health care system for patients with CA-
have emerged among patient MRSA isolated from soft tissue, abscess,
groups with risk factors unassociated with joint, or bone specimens. We examined
health care, including sports exposure,1-5 in- strain clonality, effect of community over-
carceration,6-10 intravenous drug use,11 over- crowding and group housing, and changes
crowded housing,12-16 tattooing,17,18 and in rates and geographic distribution of in-
fection with CA-MRSA during 6 years, and
CME course available at we evaluated risk factors for infection in
a nested case-control study.
www.archinternmed.com
Author Affiliations: Division of METHODS
Infectious Diseases, Department poor hygiene.11-13,19 An understanding of
of Medicine, Rush University factors promoting acquisition and emer-
Medical Center (Drs Hota, gence of CA-MRSA may aid in the devel- SETTING
Ellenbogen, Hayden, opment of prevention strategies. For some
Aroutcheva, and Weinstein) and infectious diseases, such as sexually trans- The study was performed at John H. Stroger,
Division of Infectious Diseases, Jr Hospital of Cook County (CCH), a 464-
Department of Medicine,
mitted infections, transmission can occur bed public hospital in Chicago, Ill, and its more
John H. Stroger, Jr Hospital of via infected core groups that contribute dis- than 100 associated clinics; CCH primarily
Cook County (Drs Hota, proportionately to new cases.20 Surveil- serves the urban poor (ie, uninsured or indi-
Aroutcheva, Rice, and lance of the geographic distribution and gent individuals) in Cook County. The mean
Weinstein), Chicago, Ill. secular trends of CA-MRSA infection may annual patient care volumes from 2001 through
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ment visits, and 23 041 hospital admissions. lates from patients with cultures performed on or after January
The study was reviewed by our institutional review board. 1, 2004, were available for further analysis. Isolates from pa-
The need for informed consent was waived. tients with recent incarceration, with cultures performed in July
2004, or with residence within the borders of 2 specific geo-
CASE DEFINITION graphic clusters were studied for pulsed-field gel electrophore-
sis type, staphylococcal chromosome cassette mec type, and pres-
Using a previously validated electronic case definition ( statis- ence of the Panton-Valentine leukocidin genes28-31 to assess
tic, 0.97 [100% sensitive and 97% specific for community- clonality among isolates clustered geographically, temporally, and
associated infection compared with medical record review]),21 with a common exposure (eg, incarceration). Antibiogram data
we identified individuals without health care exposures with com- were used to examine isolates before January 1, 2004.
munity-onset S aureus infections. Individuals older than 1 year
with MRSA or methicillin-susceptible S aureus (MSSA) grow- STATISTICAL ANALYSIS
ing from microbiological cultures of soft tissue, abscess fluid, joint
fluid, or bone with (1) culture obtained while an outpatient or Prevalence (the number of positive culture results divided by
within the first 3 days of a hospitalization, (2) no clinical isolate the number of cultured patients) and incidence (the number
of MRSA in the last 6 months, (3) no hospitalization or surgery of positive culture results among Cook County patients seen
within 1 year, and (4) no hemodialysis were designated as hav- at CCH divided by the CCH catchment population residing in
ing community-associated infection; all other infections were de- Cook County) of infection with CA-MRSA or CA-MSSA were
fined as health care–associated infection.22,23 Only the first iso- calculated. The CCH catchment population was calculated from
late from a patient within 6 months was counted as CA-MRSA an estimation of the proportion of all Cook County residents
or CA-MSSA. who seek care at CCH. This proportion was determined by di-
viding the number of Cook County residents hospitalized at
STUDY DESIGN CCH in 2004 for infections of skin or subcutaneous tissue or
erysipelas (International Classification of Diseases, Ninth Revi-
Using the electronic case definition, we conducted surveil- sion code 035 or 680-686) by the number with these diag-
lance from January 1, 2000, through August 31, 2005, among noses hospitalized at all Cook County hospitals in that year,
a cohort of individuals infected with community-associated stratified by ZIP code of residence. Data for all Cook County
S aureus in clinical cultures of soft tissue, abscess fluid, joint hospitalizations were obtained from the Illinois Hospital As-
fluid, or bone specimens. Isolates were obtained from patients sociation; 2004 was chosen because it was the first year avail-
seen at the CCH emergency department, at affiliated clinics, able with complete data. The proportion for each ZIP code was
or on CCH inpatient wards. These clinical infection sites were then multiplied by the total number of residents in each ZIP
selected because they account for more than 90% of infections code as reported in the most recent US census ZIP code tabu-
and have a low likelihood of attribution to nosocomial acqui- lation areas from 2000; these values were summed for all ZIP
sition (ie, from intravenous catheters). codes in Cook County to produce an unadjusted estimate of
A nested case-control study was conducted using CA- the catchment population for CCH.32 Two hundred nineteen
MRSA cases compared with CA-MSSA controls. Cases and con- patients with addresses outside of Cook County or without ad-
trols were identified from September 1, 2001, through August dresses (ie, homeless) were excluded for these calculations.
31, 2004, to ensure complete data for all covariates. Addresses were geocoded using commercially available soft-
ware (Arcview 9.0; ESRI, Redlands, Calif ), and these data were
entered using SaTScan software version 5.1.33,34 Clusters of cases
DATA COLLECTION of CA-MRSA were detected by the Bernoulli method of the spa-
tial scan statistic35; this analysis was stratified into 4 periods be-
Data were collected from our clinical data repository.24 Elec- cause of a temporal trend among cases. The periods, chosen a priori
tronic records were queried for presence of diabetes melli- to create approximately equal time frames, were period 1 ( Janu-
tus,25 human immunodeficiency virus, chronic renal insuffi- ary1,2000,throughJune30,2001),period2(July1,2001,through
ciency, and infection relapses within 1 year. Prior antimicrobial December 31, 2002), period 3 (January 1, 2003, through June 30,
use was determined from antimicrobial prescriptions from in- 2004), and period 4 ( July 1, 2004, through August 31, 2005).
patient or outpatient pharmacies and were categorized as hav- To assess the effect of overcrowding on risk of infection with
ing been given within 1 week or within 1 year to 1 week be- CA-MRSA, we used the Cook County US Census Bureau 2000
fore the culture date. Exposures to the Cook County Jail within occupancy data (percentage of the population living with ⬎1
1 year before positive culture results were obtained from ar- person per room36) for the block group of a patient’s resi-
rest records of the Cook County Department of Corrections. dence. Strata were created based on quartiles of level of over-
Home addresses were obtained from electronic data; if mul- crowding after examination of the frequency distribution of per-
tiple addresses were available for a patient, the address histori- sons per room in the cohort. Counts of MRSA cases were
cally closest to the culture results was used. compared with counts of MSSA cases and with counts of all
patients who had had cultures performed for each strata of over-
MICROBIOLOGICAL ANALYSIS crowding. The association of public housing and overcrowd-
ing with CA-MRSA infection was assessed using the 2 statis-
Clinical isolates were identified as S aureus using routine meth- tic for univariate analysis.
ods.26 Antimicrobial resistance was determined by automated Logistic regression was used to perform multivariate analy-
broth microdilution (MicroScan; Dade Behring, West Sacra- sis, with presence or absence of CA-MRSA as the outcome vari-
mento, Calif ). Isolates were considered resistant to methicil- able. Variables were those with P⬍.15 on univariate analysis
lin if the oxacillin minimum inhibitory concentration was at and year of culture. Antimicrobial use was excluded from mul-
least 4 µg/mL. Clindamycin resistance was determined in all tivariate analysis because differences were only noted within 1
periods by automated broth microdilution. Inducible clinda- week of culture, which may have reflected therapy for active
mycin resistance was determined by D test27 when requested infections. Interaction was assessed for comorbidities and re-
by clinicians. cent incarceration, as was collinearity.37 Residence in public
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2000 2001 2002 2003 2004 2005
180 180
CA-MRSA Cases CA-MRSA Incidence
CA-MSSA Cases CA-MSSA Incidence
160 160
140 140
No. of Cases per 100 000 People per Year
120 120
No. of Cases
100 100
80 80
60 60
40 40
20 20
0 0
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3
Quarter
Figure 1. Counts and incidence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) and community-associated methicillin-
susceptible S aureus (CA-MSSA) skin and soft tissue infections among patients at John H. Stroger, Jr Hospital of Cook County (Illinois) from January 1, 2000,
through August 31, 2005.
housing regardless of period was used in multivariate analy- CCH catchment population of 212 815, CA-MRSA skin
sis, and interaction between period and residence was as- and soft tissue infections increased from 24.0 cases per
sessed. Public housing units were categorized based on whether 100 000 people in 2000 to 164.2 cases per 100 000
they were contained within clusters detected by SaTScan. Vari- people in 2005, while the incidence of CA-MSSA skin
ables were eliminated using backward elimination for P⬎.15.
and soft tissue infections was 90.7 cases per 100 000
Statistical analyses were performed using SAS software ver-
sion 8 (SAS institute, Cary, NC). people in 2000 and 121.9 cases per 100 000 people in
2005. During this period, 56% of CA-MRSA infections
and 55% of CA-MSSA infections occurred in outpatients
RESULTS or in nonhospitalized emergency department patients,
while 44% of CA-MRSA infections and 45% of CA-MSSA
LABORATORY-BASED SURVEILLANCE infections required hospitalization. There were 5 deaths
among CA-MSSA patients and 2 deaths among CA-
During 6 years (January 1, 2000, through August 31, 2005), MRSA patients (mortality rates of 5 per 1000 and 1 per
soft tissue, abscess fluid, joint fluid, or bone specimens from 1000, respectively).
2346 (34.0%) of 6894 patients without health care–
associated risk factors grew S aureus; 971 (41.4%) and 1375
GEOGRAPHIC ANALYSIS
(58.6%) isolates met our previously defined criteria for
CA-MRSA and CA-MSSA, respectively. Community-
associated methicillin-resistant S aureus isolates were Geographic analysis revealed 4 clusters of CA-MRSA in-
mostly susceptible to aminoglycosides (95%), fluoroqui- fections (Figure 2). Cluster 1 (July 1, 2001, through
nolones (76%), and trimethoprim-sulfamethoxazole December 31, 2002) had 15 patients with CA-MRSA
(99%). Erythromycin resistance steadily increased from (10.7% of that period’s cases). Cluster 2 (January 1, 2003,
51% in 2000 to 87% in 2004; erythromycin-resistant and through June 30, 2004) had 17 patients with CA-MRSA
clindamycin-susceptible strains accounted for most of (6.4% of cases). Cluster 3 (January 1, 2003, through June
this increase (25%, 28%, 54%, 69%, 80%, and 81% of 30, 2004) had 44 patients with CA-MRSA (15.0% of
CA-MRSA isolates during 2000, 2001, 2002, 2003, 2004, cases). Within the borders of cluster 3 were 5 high-rise
and 2005, respectively). D test results were available for public housing complexes; 8 (18.2%) of 44 patients within
47 isolates (performed between 2004 and 2005) and were cluster 3 were residents of this housing. Cluster 4 (July
positive in only 2. 1, 2004, through August 31, 2005) included a region with
Over time, CA-MRSA skin and soft tissue infections its center near CCH and a perimeter that included the
increased 6.84-fold (Figure 1). Based on the estimated geographic area with the highest CCH use in Cook
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Cluster 1
ZCTA Population at Risk
Cluster 4
0%
0.1%-1.0%
1.1%-1.5%
1.6%-2.6%
Cluster 2
2.7%-3.5%
3.6%-5.8%
5.9%-9.4%
>9.4%
Figure 2. John H. Stroger, Jr Hospital of Cook County (CCH) catchment by ZIP code tabulation area (ZCTA). Clusters of methicillin-resistant Staphylococcus
aureus skin and soft tissue infections in Cook County (Illinois) from January 1, 2000, through August 31, 2005, identified by SaTScan. Cluster 1, P = .004; cluster
2, P = .03; cluster 3, P =.06; and cluster 4, P=.004. See the “Geographic Analysis” subsection of the “Methods” section for explanation of cluster groups.
County; 185 patients with CA-MRSA (47.1% of cases) through 2005, which was statistically significant in 2005
were within this cluster. (P⬍.001) (Figure 3).
We found no association between case status and over-
RISKS OF PUBLIC HOUSING, crowding; patients with S aureus infections from census
INCARCERATION, AND OVERCROWDING block groups that were more overcrowded were not more
likely to be infected with CA-MRSA. Similarly, we found
The proportion of community-associated S aureus skin no association between high-occupancy block groups and
and soft tissue isolates that was methicillin resistant was CA-MRSA infection regardless of whether the compari-
higher among residents who lived in public housing com- son group was patients with CA-MSSA infections or all
plexes in cluster 3 (55.4%) than among non–public hous- patients from whom cultures were obtained, nor did we
ing residents (41.6%). Public housing residents in clus- find an association when occupancy was stratified by race/
ter 3 had a higher prevalence of CA-MRSA from 2000 ethnicity or by year of culture.
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Downloaded From: https://jamanetwork.com/ on 03/11/2022Table 1. Univariate Analysis of Demographic and Clinical
Non–Public Housing
Cluster 3 Public Housing
Characteristics of Patients With Community-Associated
100 Non–Cluster 3 Public Housing Staphylococcus aureus Skin and Soft Tissue Infections
From September 1, 2001, Through August 31, 2004*
75 CA-MRSA CA-MSSA
Characteristic (n = 518) (n = 704) P Value
CA-MRSA, %
Age, mean ± SD, y 35.4 ± 7.0 39.5 ± 18.2 ⬍.001
50 Male-female ratio 1:6 1:82 .30
Race/ethnicity
African American 389 (75.1) 372 (52.8)
White 45 (8.7) 88 (12.5)
25 ⬍.001
Hispanic 62 (12.0) 177 (25.1)
Other 22 (4.2) 67 (9.5)
Incarceration within 1 y† 32 (6.2) 22 (3.1) .007
0 Residence in public housing 21 (4.1) 14 (2.0) .04
2000 2001 2002 2003 2004 2005 within cluster 3‡
Year Degree of overcrowding in
census block group of
Figure 3. Community-associated methicillin-resistant Staphylococcus patients, % of units with more
aureus (CA-MRSA) as a proportion of all community-associated S aureus than 1 person per room§
skin and soft tissue infections in relation to public housing from January 1, 0-5.1 119 (24.7) 158 (25.2)
2000, through August 31, 2005. CI indicates confidence interval. See the ⬎5.1-11.1 132 (27.4) 148 (23.6)
.08
“Geographic Analysis” subsection of the “Methods” section for explanation ⬎11.1-18.5 134 (27.9) 147 (23.5)
of cluster groups. ⬎18.5 96 (20.0) 163 (26.0)
Diabetes mellitus㛳 118 (22.8) 235 (33.4) ⬍.001
Human immunodeficiency virus 49 (9.5) 44 (6.3) .04
NESTED CASE-CONTROL STUDY infection¶
Chronic renal insufficiency 4 (0.8) 9 (1.3) .39
On univariate analysis, the following variables were as- Associated bacteremia 11 (2.1) 12 (1.7) .75
sociated with CA-MRSA skin and soft tissue infections: Relapse
younger age, incarceration within 1 year, African Ameri- ⬍1 mo 9 (1.7) 18 (2.6) .43
can race/ethnicity, and human immunodeficiency virus 1 mo to ⬍6 mo 25 (4.8) 39 (5.5) .61
6 mo to 1 y 12 (2.3) 14 (2.0) .69
infection (Table 1). More patients with CA-MRSA re-
ceived an antibiotic within 1 week before cultures were Abbreviations: CA-MRSA, community-associated methicillin-resistant
performed (9% vs 6%, P =.03), and 44% of patients with Staphylococcus aureus; CA-MSSA, community-associated
CA-MRSA infections received inadequate therapy with methicillin-susceptible S aureus.
a -lactam antibiotic following culture (no differences *Data are given as number (percentage) unless otherwise indicated.
†Odds ratio, 2.04; 95% confidence interval, 1.13-3.69.
in deaths or readmissions were noted as a result of in- ‡Odds ratio, 2.06; 95% confidence interval, 1.03-4.09.
adequate therapy). Residence in the 5 public housing com- §The numbers of subjects differ for this variable because of missing data
plexes within cluster 3 during any period was associ- (MRSA, 481 subjects; MSSA, 626 subjects).
㛳Odds ratio, 0.59; 95% confidence interval, 0.45-0.77.
ated with CA-MRSA skin and soft tissue infections on ¶Odds ratio, 1.57; 95% confidence interval, 1.00-2.45.
univariate analysis, while residence in public housing de-
velopments outside of cluster 3 was not.
cently incarcerated subjects, 8 of 11 isolates from cluster
MULTIVARIATE ANALYSIS
2, 16 of 23 isolates from cluster 3, and 24 of 28 isolates
obtained in July 2004). USA300 isolates were erythro-
On multivariate analysis (Table 2), year of culture
mycin resistant, did not carry inducible clindamycin re-
showed a strong secular trend. Residence in the public
sistance, and were positive for staphylococcal chromo-
housing complexes within cluster 3 was also a risk fac-
some cassette mec type IV and Panton-Valentine
tor for MRSA skin and soft tissue infections (odds ratio,
leukocidin genes. USA400 strains were found in 6 infec-
2.50; 95% confidence interval, 1.25-4.98) regardless of
tions. Regardless of pulsed-field gel electrophoresis type,
year of culture, as was recent incarceration (odds ratio,
most isolates from all groups were positive for staphy-
1.92; 95% confidence interval, 1.00-3.67). African Ameri-
lococcal chromosome cassette mec type IV (67 of 73) and
can race/ethnicity increased the risk of CA-MRSA infec-
Panton-Valentine leukocidin genes (65 of 73).
tion, and older age and Hispanic race/ethnicity were pro-
tective. Human immunodeficiency virus status and recent
incarceration exhibited interaction and resulted in de- COMMENT
creased risk when both were present.
In the major public safety net health care system of Cook
MICROBIOLOGICAL ANALYSIS County, we noted a 6.84-fold increase in the risk of skin
and soft tissue infections with CA-MRSA from 2000 through
Community-associated methicillin-resistant S aureus iso- 2005. This increase occurred in addition to a stable rate of
lates tested were predominantly pulsed-field gel electro- CA-MSSA infections. Although at the start of the surveil-
phoresis type USA300 (ie, 10 of 11 isolates from re- lance period our incidence of CA-MRSA infections was simi-
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study,23 by 2005 it was higher, which may reflect our high- Table 2. Multivariate Analysis of Risk Factors
risk patient population (62% African American, 5% re- for Community-Associated Methicillin-Resistant
Staphylococcus aureus Skin and Soft Tissue Infections
cent incarceration, and 6% public housing residents).
African American race/ethnicity and recent incarcera- Odds Ratio
tion were risk factors for CA-MRSA skin and soft tissue (95% Confidence
infections; Hispanic race/ethnicity was protective, a find- Risk Factor Interval) P Value
ing consistent with the results of prior studies.6-10,23,38 Resi- Age, each decade increase, y 0.89 (0.82-0.96) .004
dence in specific public housing complexes was also a Diabetes mellitus 0.75 (0.55-1.02) .07
risk factor and increased the odds of CA-MRSA infec- HIV infection 1.45 (0.91-2.31) .12
tion almost 3-fold (Table 2), even after adjustment for Incarceration within 1 y 1.92 (1.00-3.67) .05
the countywide secular increase. HIV-positive and incarceration 0.16 (0.04-0.71) .03
within 1 y
Why CA-MRSA has emerged at such a rapid pace re-
Race/ethnicity
mains unclear. Cross-sectional studies38,39 examining other Other 0.62 (0.33-1.17) .14
community populations have found MRSA colonization Hispanic 0.61 (0.37-0.99) .048
rates far below those of MSSA, generally not exceeding African American 1.91 (1.28-2.87) .002
4% for CA-MRSA compared with 30% for CA-MSSA. De- White 1 [Reference] ...
spite the apparently lower prevalence of MRSA coloni- Culture obtained
August 2003 to July 2004 2.77 (2.04-3.75) ⬍.001
zation, infection rates are approaching or exceeding those
August 2002 to July 2003 1.94 (1.39-2.69) ⬍.001
of CA-MSSA. Potential host or pathogen explanations for August 2001 to July 2002 1 [Reference] ...
this discordance include CA-MRSA colonization at sites Residence
not tested (eg, skin, gastrointestinal tract, or deeper than Public housing in cluster 3 2.50 (1.25-4.98) .009
the anterior nares), greater risk of person-to-person spread Public housing not in cluster 3 1.24 (0.58-2.67) .57
from infected patients or of spread from contaminated Not in public housing 1 [Reference] ...
fomites (eg, towels in locker rooms),3,40 virulence fac-
tors (eg, Panton-Valentine leukocidin genes) that trump Abbreviation: HIV, human immunodeficiency virus.
the traditional colonization before infection sequence (ie,
“hit-and-run” infections),41 or yet-to-be-measured in-
creasing rates of CA-MRSA colonization.42 housing complexes,45 potentially contributing to over-
An additional explanation for rapid emergence of CA- crowding not measured by census data. In addition, pub-
MRSA is that some community settings may promote lic housing residents are part of a network associated with
cross-transmission. Hospitals and long-term care facili- inmates; in a 2002 study,46 29% of respondents reported
ties have long been considered “epicenters” for antimi- that they had been incarcerated or were expecting a
crobial resistance, housing colonized and noncolonized resident to arrive from jail or prison. Public housing may
individuals in close proximity, and offering the oppor- also house individuals with severe drug problems, and
tunity for cross-transmission. Hartley et al43 suggested squatters (or nonlease tenants) may transiently reside in
that prisons, with their large at-risk populations and long nondemolished public housing between episodes of home-
lengths of stay, can be sources of MRSA-colonized indi- lessness.45 Triangulation of risks for CA-MRSA transmis-
viduals at rates comparable to those of hospitals. Other sion47 may occur in the public housing complexes iden-
community settings such as public housing and halfway tified in cluster 3, with personal contacts or contaminated
houses may amplify CA-MRSA spread; for example, the fomites promoting cross-transmission among suscep-
geographic clusters of CA-MRSA detected in our study tible host populations. However, whether and what in-
that were not related to public housing may represent teractions among these populations have contributed to
foci of increased cross-transmission. CA-MRSA dissemination require further study.
The concept of a “core group” of colonized or in- Strain typing by pulsed-field gel electrophoresis did
fected individuals that is responsible for many new in- not discriminate between the various populations as-
fections is basic to the epidemiology of sexually trans- sessed in our study; however, it confirmed that most iso-
mitted and some viral infections (eg, severe acute lates tested were strain type USA300, whether or not re-
respiratory syndrome)20,44; geographically disparate clus- lated to incarceration or public housing exposure. These
ters of infection may represent networks of individuals findings are consistent with those of a 31⁄2-month labo-
who transmit infection through person-to-person con- ratory-based survey from Atlanta, Ga,48 and a cross-
tact, with further spread by individuals who bridge these sectional study49 among emergency department pa-
networks.44 In the case of CA-MRSA, geographically closed tients in which most CA-MRSA skin and soft tissue
community foci (eg, prisons) may be promoting spread, infections were caused by USA300.
while other settings or factors (eg, athletics or intrave- Because of a lack of historical isolates available for typ-
nous drug use) act as bridges for transmission. ing, we were unable to ascertain if USA300 replaced other
Public housing also may represent a bridge between CA-MRSA strains in the community. Prior work exam-
high-risk individuals in Chicago. Since the late 1990s, ining CA-MRSA among Chicago children found clonal-
demolition of high-rise public housing complexes and ity in one instance: 69 (78.4%) of 88 clindamycin-
widespread relocation of public housing residents have susceptible CA-MRSA isolates obtained from 1987 to 2000
occurred as part of the HOPE VI plan.45 In 2003, 62% of were USA400, 70% were erythromycin-susceptible, and
relocated families were moved to other Chicago public D test results were positive in 31 of 33 isolates with dis-
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Downloaded From: https://jamanetwork.com/ on 03/11/2022cordant erythromycin and clindamycin susceptibili- Hota, Rice, and Weinstein. Drafting of the manuscript: Hota
ties.50 Prior work examining CA-MRSA among Chicago and Aroutcheva. Critical revision of the manuscript for im-
children in one instance found clonality: 69 (78%) of 88 portant intellectual content: Hota, Ellenbogen, Hayden,
clindamycin-susceptible CA-MRSA isolates obtained from Rice, and Weinstein. Statistical analysis: Hota. Obtained
1987 to 2000 were USA-400, 70% were erythromycin- funding: Weinstein. Administrative, technical, and mate-
susceptible, and D-test results were positive for 31 of 33 rial support: Ellenbogen, Aroutcheva, Rice, and Wein-
isolates with discordant erythromycin and clindamycin stein. Study supervision: Weinstein.
susceptiblities.50 In another instance, however, poly- Financial Disclosure: None reported.
clonal infection was described.51 Given the rapid in- Previous Presentation: This study was presented in part
creases among our patients in prevalence of clindamycin- at the 45th Interscience Conference on Antimicrobial
susceptible, erythromycin-resistant isolates and the low Agents and Chemotherapy; December 14, 2005; Wash-
rate of inducible clindamycin-resistance, replacement of ington, DC (abstract L-142).
another CA-MRSA strain (possibly USA400) by USA300 Acknowledgment: Control strains for staphylococcal
as the major cause of CA-MRSA infection seems to have chromosome cassette mec types and subtypes, Panton-
occurred between 2000 and 2006 in our patients. Valentine leukocidin genes, and pulsed-field gel electro-
Our data should be interpreted in light of several epi- phoresis were received from the Network for Antimicro-
demiological limitations. First, geographic clustering bial Resistance in S aureus repository and from colleagues.
among cases may have been because of the differences Cook County admission diagnosis information was ob-
between cases and controls in the use of CCH unrelated tained through the assistance of the Illinois Hospital As-
to infection status. The stability of MSSA rates over time sociation. We appreciate the assistance of Ellen Holfels
argues against systematic changes in health care use, and in the preparation of the manuscript.
Figure 3 shows that public housing complexes in clus-
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Correction
Error in Figure Key. In the article titled “Community-
Associated Methicillin-Resistant Staphylococcus aureus
Skin and Soft Tissue Infections at a Public Hospital: Do
Public Housing and Incarceration Amplify Transmis-
sion?” by Hota et al, published in the May 28 issue of
the Archives (2007;167[10]:1026-1033), the symbols for
the right side of the key in Figure 1 (page 1028) should
have been switched. Therefore, the circles indicate CA-
MRSA incidence; squares, the CA-MSSA incidence. The
online version of this article was corrected for typo-
graphical errors on May 28, 2007.
(REPRINTED) ARCH INTERN MED/ VOL 167 (NO. 14), JULY 23, 2007 WWW.ARCHINTERNMED.COM
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©2007 American Medical Association. All rights reserved.
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