JOURNAL OF CLINICAL MICROBIOLOGY, Mar. 2010, p. 683–689
Copyright © 2010, American Society for Microbiology. All Rights Reserved.
Vol. 48, No. 3
To Screen or Not To Screen for Methicillin-Resistant
There are few more compelling questions in clinical microbiology today than the issue of whether or not to
screen for the presence of methicillin-resistant Staphylococcus aureus (MRSA), with the results being used to
institute infection control interventions aimed at preventing transmission of MRSA in health care environ-
ments. Numerous different matters must be addressed when considering a screening program. Who is to be
screened, what method is to be employed to detect MRSA, and what sites should be sampled? When and how
often should the screening be performed? Who is going to pay for the screening, and, finally and perhaps most
importantly, how are screening results to be communicated to health care providers and what kind of inter-
ventions are best undertaken based on the results? Numerous governmental agencies have mandated MRSA
screening programs, and yet several authorities in infection control organizations have questioned the appro-
priateness of mandated screening.
In this Point-Counterpoint feature, Dr. Lance Peterson of Evanston Hospital (Evanston, IL) offers his
perspective on why screening for MRSA is to be encouraged. Dr. Daniel Diekema of the University of Iowa
Carver College of Medicine (Iowa City, IA) offers an opposing view.
The issue as to whether or not U.S. health care orga-
nizations should aggressively deploy programs to control
MRSA hinges on three critical questions. First, is the
burden of MRSA disease sufficiently high so that human
effort and financial resources should be directed toward
this problem? If the answer is yes, then the second ques-
tion is this: how do the policymakers in a health care
organization decide whether MRSA is a problem for its
patients? The last question, then, involves implementa-
tion: what type of MRSA control program is likely to
reduce disease cost effectively?
There is considerable literature assessing MRSA dis-
ease burden across the United States. Delorme and col-
leagues measured the change in the incidence of S. au-
reus disease between 2006 and 2007 in northeast Ohio
(2). They found an overall 77% increase in infections
(59% MRSA); a 58% disease increase for outpatients, a
43% increase for hospital inpatients, and a 183% in-
crease in residents of long-term care facilities (2). The
overall burden of disease was 589/100,000 inhabitants,
and for 66% of the affected persons, there were no risk
factors for staphylococcal infection (2). A similar burden
of disease was reported in a prevalence survey done
during 2004 and 2005 in San Francisco, CA; there were
347 MRSA disease cases/100,000 population (13). To
place these numbers in context, in 2007 the United
States had a reported total of 13,293 tuberculosis (TB)
cases, which translates to a rate of 4.4 cases/100,000
population (1); thus, the MRSA burden of disease is
approximately 100-fold that of TB. Another pivotal
study on MRSA was the 2005 prospective surveillance
investigation of invasive disease reported by Klevens and
colleagues, who found that 77% of MRSA health care-
associated infections consisted of cases of bacteremia—a
doubling in 6 years (12). They discovered a disease rate
of 31.8/100,000 population, with an annual mortality of
20% (18,650 deaths), representing more deaths than
those due to HIV-AIDS (12). If one assumes that a
disease burden 100-fold higher than that of TB and with
an annual mortality rate exceeding that of HIV-AIDS is
a significant illness for the United States, then the an-
swer to the first question is yes.
The response to the second question is also straight-
forward. The Joint Commission requires infection con-
trol personnel at each health care organization to per-
form an annual risk assessment to determine the key
health problems (22). For MRSA, as well as for any
multidrug-resistant organism, the Centers for Disease
Control and Prevention (CDC) recommend that all
health care organizations assess their rate of multidrug-
resistant organism infections and demonstrate that the
rate is actually diminishing over time or, if not, to im-
plement additional (Tier 2) disease control measures
(20). One of the most important Tier 2 measures is
active surveillance (20). For a laboratory to assist in this
assessment, one appropriate approach is to determine
the number of organisms (e.g., MRSA) recovered from
clinical specimens and to track the change in the rate
?Published ahead of print on 13 January 2010.
(per 1,000 admissions or 1,000 patient days) over time.
While this method may detect some colonization as well
as disease, such an approach has been shown to accu-
rately identify 77.1% of actual S. aureus infections (5)
and to provide significant changes in disease rates much
faster than when only bacteremia rates are measured
(24). Another useful tool to assess MRSA risk for pa-
tients is to perform a point prevalence survey for MRSA
(nasal) colonization. We found this undertaking enlight-
ening for both infection control and senior management
when 8.5% of our inpatients showed nasal MRSA colo-
nization (18), a rate which was some threefold higher
than the 2.7% reported by Jernigan and colleagues from
an admission MRSA prevalence survey done 6 years
earlier (10). These data led to institution-wide recogni-
tion that there was a high level of MRSA colonization in
our patient population and facilitated deployment of an
aggressive MRSA control program. Once a local prob-
lem has been shown to exist, the next step is to design an
intervention that is likely to succeed in lowering MRSA
infection—remembering that the most expensive pro-
gram, no matter how much or how little is done, is one
that does not reduce MRSA disease.
A key to reducing MRSA dissemination and subse-
quent disease is the need to enhance practices that re-
duce spread; those practices are currently considered to
be barrier precautions or contact isolation. Figure 1 il-
lustrates how this can be effective. In each pictured sce-
nario, there is a constant influx of new MRSA carriers
(due to person-to-person spread); in the first scenario
(Fig. 1A), the rates of both colonization and eventual
disease rise until a higher plateau is reached. Only when
90% of disease spread has been blocked (as illustrated in
the third scenario [Fig. 1C]) are there actual reductions
in both colonization and infection. The required level
of detection (via surveillance through screening for
MRSA) to reduce MRSA spread varies with the preva-
lence of colonization and disease. For any given MRSA
prevalence rate, the factor that seems most crucial in
reducing spread is the percentage of potential isolation
days captured for patients admitted who are infected or
colonized with this pathogen. The influential operational
processes are (i) the sensitivity of the screening test, (ii)
the speed with which newly detected positive patients
are reported to the nursing unit (assuming that pre-
emptive isolation is not employed), and (iii) the selec-
tion of patient population(s) who are to undergo surveil-
The utility of various testing approaches for MRSA
surveillance has recently been investigated by meta-anal-
ysis (21), and the conclusion of the authors was that
surveillance for MRSA colonization was beneficial in
reducing disease. However, they also concluded that
rapid testing had not been proven to be superior to
culture-based methods. A lapse in their analysis was that
the authors did not investigate the effect of the levels of
sensitivity and speed of reporting on the success or fail-
ure of MRSA control programs in the reviewed articles
(21). Several recent publications give insights into this
critical aspect of laboratory practice when dealing with a
population with modest (5 to 7%) MRSA colonization
prevalence (6, 7, 8, 11, 19). In a report by Robicsek and
colleagues, the authors suggest that the capture of po-
tential MRSA isolation days has the greatest effect on
whether or not a MRSA control program exerts a sig-
nificant impact on disease reduction (19). They reported
that admissions policies that omitted active MRSA sur-
veillance (capturing only those persons who had given
MRSA-positive results in the past) placed admitted pa-
FIG. 1. Representationoftheimpactofbarriers(contactisolation)on
MRSA. Each “boxed” segment represents 1 year of time, with panels A,
B, and C representing three levels of effective barrier precautions (no
prevention of spread, 50% prevention, and 90% prevention).
684 TO SCREEN OR NOT TO SCREEN FOR MRSAJ. CLIN. MICROBIOL.
tients into appropriate isolation for approximately 18%
of their inpatient days and that adding active surveil-
lance for intensive care unit (ICU)-admitted patients
increased that to 33% of inpatient days, with neither
approach having any impact on MRSA disease control
over sequential 12-month periods of time (19). Only
when all admission active surveillance was implemented
using a test that was 98% sensitive and had a reporting
time of ?15 h was there capture of 85% of potential
inpatient MRSA isolation days; this led to a significant
(?70%) reduction in MRSA infection (19).
The relevant articles and important characteristics lead-
ing to the estimation of captured MRSA isolation days
are presented in Table 1. For each of these reports, one
can calculate the approximate percentage of captured
potential MRSA isolation days based on test sensitivity,
time to reporting, and length of hospital stay. As can be
seen in these reports, no success was recognized in re-
duction of either MRSA transmission or infection dur-
ing the relatively brief intervention periods until the
estimated captured MRSA isolation days exceeded 80%.
Thus, it appears that if a relatively short period of time
(?1 year) is used to evaluate a MRSA control program,
then a very aggressive, broadly directed surveillance pro-
gram is required. Importantly for the laboratory, the
shorter reporting time and lower sensitivity of culture for
MRSA detection can influence the percentage MRSA
isolation days captured (15), which implies that the ac-
tual assay selection is critical to the outcome of any
intervention and that only a rapid test with high sensi-
tivity may provide a satisfactory programmatic result.
While there has been success in lowering the incidence
of MRSA disease without the use of active surveillance,
these interventions have been in the setting of very high
infection prevalence. For example, Grayson and col-
leagues reported on the reduction of the rate of recovery
of monthly MRSA clinical isolates by their laboratory
from 1.39 to 0.73 per 100 discharges, a change which was
considered to have been associated with an improve-
ment of hand hygiene compliance from 21% to 48%
over 2 years (4). Monthly bacteremia rates also fell from
0.05 to 0.02 per 100 discharges (4). Similarly, Edmond
and colleagues reported a significant reduction in device-
related MRSA infection from 2.9 to 0.76 infections per
1,000 patient-days over 4 years of multiple interventions
(3). However, the ending infection rates for both studies at
the conclusion of their interventions were higher than the
initial disease rate found by Robicsek et al. (19), suggesting
that in a very high prevalence setting nearly any interven-
tion can be beneficial but that at some point active surveil-
lance must be undertaken. In support of this concept,
Huang and colleagues reported on sequential ICU inter-
ventions aimed at lowering MRSA blood stream infection
rates (9). They serially introduced maximally sterile central
venous catheter placement, an alcohol hand rub, a hand
hygiene campaign, and ICU MRSA surveillance; the only
intervention that had a sustained impact on lowering the
incidence of MRSA bacteremia was active surveillance (9).
Finally, there is the question of cost-effectiveness for any
program designed to reduce the spread of MRSA coloni-
zation and disease. As noted earlier, the program that is
most costly in human and financial resources is one that
has no measurable beneficial impact over the time allotted
for assessment. We have previously reported using a very
conservative model that each patient developing a health
of nearly $24,000 (18). On 31 July 2009, we completed the
first 4 years of our MRSA program at NorthShore Univer-
sity HealthSystem; by that time, there had been (compared
to baseline) 406 MRSA infections avoided, with an $8.8
million excess that had not needed to be spent for this
preventable illness (17). Importantly, using the mortality
deaths from invasive MRSA disease (17).
In conclusion, the available data indicate that MRSA
infection is a serious health risk for the U.S. population.
It is also likely that MRSA infection is a problem for
most health care organizations and that assessing that
TABLE 1. Summary of published reports that illustrate the impact of different levels of test sensitivity and time to reporting of
results on the reduction of MRSA in the involved population
Mean length of
Time to result
Success of program in reducing
Harbarth et al. (7)
Harbarth et al. (6)
Robicsek et al. (18)
3.7 to 4
?22 to 23
5 to 17
No reduction in disease
No reduction in disease
Reduction in disease with
No reduction in transmission
Reduction in transmissiona
No reduction in transmission
Jeyaratnam et al. (11)6.73.887.8
Hardy et al. (8)
Hardy et al. (8)
aResults represented statistically significant reductions.
bSensitivity data were calculated based on the methods presented in reference 14.
VOL. 48, 2010POINT-COUNTERPOINT685
risk can be done with minimal time and financial resources.
Finally, active surveillance for this pathogen can reduce
disease, both locally and nationally (19, 23). Arguments
statistical methods and adverse effects of isolation and fo-
cus on a single problem, but these concerns stand on very
little evidence (16). The appropriate prevention and con-
saves lives, and is cost-beneficial.
NorthShore University HealthSystem supported this work. I thank
LoAnn C. Peterson and Donna M. Hacek for critical review and
comments on this work.
L. R. Peterson has received research support from Cepheid,
ENH, Excelsior, GeneOhm, MicroPhage, Nanaosphere, NAIAD,
Roche, 3M, Washington Square Health Foundation, Wyeth, and
Merck and has served as a consultant for Cephied, GeneOhm,
MicroPhage, Nanosphere, Roche, and 3M.
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Lance R. Peterson
NorthShore University HealthSystem
Department of Laboratory Medicine and Pathology
2650 Ridge Avenue, Walgreen Bldg., SB525
Evanston, IL 60201
Phone: (847) 570-1637
Fax: (847) 733-5093
I begin by emphasizing two points upon which Dr.
Peterson and I agree. First, methicillin-resistant Staphy-
lococcus aureus (MRSA) is an important cause of mor-
bidity and mortality and should be a focus of infection
prevention efforts. Second, there is a role for “active
detection and isolation” (ADI) in the control of multi-
drug-resistant organisms (MDROs), including MRSA.
As outlined by the Centers for Disease Control and
Prevention guidelines, ADI is one of several “second
tier” interventions that should be considered when “first
tier” infection prevention measures fail to prevent
MDRO transmission (e.g. during outbreaks) (16).
686TO SCREEN OR NOT TO SCREEN FOR MRSAJ. CLIN. MICROBIOL.
The question I will address is whether universal ADI
should be implemented as a routine MRSA infection
prevention measure. In other words, should all hospitals
screen newly admitted patients for MRSA? My answer
to this question is no, for the reasons I outline below.
The effectiveness of ADI remains in question. The
effectiveness of ADI for MRSA infection prevention has
been argued ad nauseam in the infection control litera-
ture, so in the interest of conserving space I refer the
reader to two recent systematic reviews (2, 13), to the
CDC MDRO guidelines (16), and to a joint statement
issued by the two major U.S. infection prevention pro-
fessional societies (the Society for Healthcare Epidemi-
ology of America and the Association for Professionals
in Infection Control) (19). These publications summa-
rize the state of the literature on ADI for MRSA control
and present conclusions indicating that the existing evi-
dence is not strong enough to support adoption of MRSA
ADI as a routine infection prevention measure. Why? Be-
in most cases due to an observational, before-and-after
determine the contribution of ADI to the observed MRSA
reductions (2, 13). For example, the most widely cited re-
cent study of universal ADI lacked a control group and
included interventions other than ADI (e.g., widespread
decolonization) (15). By contrast, the largest-ever con-
trolled trial of universal ADI to reduce MRSA infections
demonstrated no difference in MRSA infection rates asso-
ciated with ADI use (8).
ADI interventions are complex and resource inten-
sive. The reader is referred to our more comprehensive
guidance for details (3), but in brief, the implementation
of ADI is a resource-intensive, multidisciplinary effort.
In addition to the cost of the screening test itself (up to
$25 to $45 per test for the commercial PCR tests), there
are costs associated with sample acquisition and trans-
port, laboratory validation and reporting, process and
outcome monitoring, personal protective equipment,
bed management, and patient/family education (3). The
argument that these costs are offset by savings from
MRSA infection prevention assumes that MRSA infec-
tions cannot be prevented using measures other than
ADI—a flawed assumption.
Importantly, the resources invested in MRSA ADI
are designed to prevent only MRSA infections. Indeed,
MRSA ADI papers frequently cite the failure of MRSA
ADI to impact non-MRSA infection rates as evidence in
support of the specificity of the intervention (15). Infec-
tion prevention programs obviously must focus on sev-
eral problems at once. However, resources are not infi-
nite, and every dollar spent on an MRSA-specific ADI
intervention is a dollar not available for population-
based interventions designed to prevent both MRSA
and all other health care-associated infections (20).
ADI may have unintended adverse consequences. A
premise of ADI is that there are many asymptomatic
carriers of MRSA, each of whom serves as a reservoir
for nosocomial transmission unless detected and placed
in isolation. Therefore, any comprehensive ADI pro-
gram will significantly increase the number of patients
being cared for under conditions of contact precautions
(3). Unfortunately, several studies have demonstrated
adverse consequences for patients under those condi-
tions, including fewer health care worker visits, more
noninfectious adverse events (missed medication doses,
falls, decubitus ulcers, electrolyte disorders), more de-
pression and anxiety, and lower satisfaction with hospital
care (14, 17).
While it may be possible for some hospitals to imple-
ment ADI and protect patients from unintended adverse
consequences of contact precautions, there is an urgent
need for more research in this area. A limitation of the
ADI literature is that it focuses narrowly on infection out-
comes and ignores noninfectious adverse outcomes and
overall patient satisfaction with respect to care (3, 5).
Given its uncertain effectiveness, the potential for
harm, and the existence of alternative interventions for
MRSA prevention, it is appropriate to examine the eth-
ical implications of implementing universal MRSA ADI.
Due to space limitations, the reader is referred to a
previously published detailed ethical assessment of ADI
for MDRO prevention (5).
ADI is not necessary for MRSA prevention. The stron-
gest argument against routine, universal ADI is that it is
not necessary for MRSA prevention. Several hospitals
have reported significant reductions in MRSA infection
or transmission by the use of approaches that do not
include ADI (4, 9, 12). While these studies share the
flaws of studies supporting MRSA ADI (e.g., before-
after design and absence of control groups), the MRSA
outcome reductions have been of similar or greater mag-
nitude (see Table 1). For example, the most recent such
report presents findings showing a 73% reduction in
device-associated MRSA infection rates in all adult in-
tensive care units over a 4-year period and indicates that
the reduction was associated with broad-based infection
control strategies (e.g. hand hygiene and implementa-
tion of bundled interventions to reduce device-associ-
ated infections) (4). This hospital, after adding chlo-
rhexidine body washes for all ICU patients, has more
recently reported even greater reductions in MRSA in-
fection rates (6). In the medical ICU of my own hospital,
we are entering our fifth consecutive month with no
device-associated infections of any kind, MRSA or
other. We attribute this success to sustained hand hy-
giene adherence of 70 to 90% and bundled interventions
VOL. 48, 2010 POINT-COUNTERPOINT 687
to prevent device-associated infections. We do not prac-
tice MRSA ADI.
In addition to individual hospital reports of reduc-
tions of rates of MRSA infection without ADI, there
are several lines of evidence indicating that health
care-associated MRSA infection rates are declining as
increased attention is paid to basic hospital infection
prevention. Catheter-associated bloodstream infec-
tions due to MRSA have declined by over 50% in U.S.
ICUs since 2001 without widespread use of ADI (1). The
United Kingdom successfully reduced MRSA blood-
stream infections by 57% from 2007 to 2009 without
adoption of universal ADI (a mandatory ADI program
for elective admissions was not introduced in the United
Kingdom until April 2009) (10). Finally, the European
Antimicrobial Resistance Surveillance System now has
more countries with decreasing trends in MRSA rates as
opposed to increasing trends, and most participating
countries do not perform universal MRSA ADI (7).
ADI is a flawed infection prevention approach. Infec-
tion prevention practices are designed to prevent pa-
tients from becoming infected with their own flora or
with flora from other persons or the hospital environ-
ment. This applies to all potential microbial pathogens
and not just MRSA. Universal ADI interventions as-
sume that we cannot prevent MRSA infections without
knowing exactly who carries the organism. If this is to be
our new paradigm—that MDRO infections can be pre-
vented only if we know who carries each MDRO—then
the path ahead will be extremely difficult. For as much
attention as MRSA receives, it accounts for only 8% of
all health care-associated bacterial infections in the United
What organisms make up the remaining 90%? Among
them are a stunning array of multiply resistant Gram-neg-
ative rods. Compared with the emerging multiply resis-
tant Gram-negative rods, MRSA is a relatively simple
pathogen—one major resistance mechanism and one
gene (mecA) to detect, with abundant data on human
carriage patterns available. Applying ADI to multiply
monas organisms, and to the multiplicity of extended-
spectrum-beta-lactamase and carbapenemase produc-
ers, will be a much greater challenge.
Alternatively, we could devote our full attention, and
our resources, to strengthening broad-based infection
prevention programs designed to eliminate all health
care-associated bacterial infections, those due to MRSA
In the past 12 months, D. Diekema has received research funding
from Astellas, bioMe ´rieux, Merck, Pfizer, and Schering.
1. Burton, D. C., J. R. Edwards, T. C. Horan, J. A. Jernigan, and S. K. Fridkin.
2009. Methicillin-resistant Staphylococcus aureus central-line associated
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TABLE 1. Examples of declining MRSA infection rates without the use of universal ADIa
Study design or
Setting and datesMajor interventions Outcome measure(s)
% Decrease(s) in MRSA
Before-and-afterAdult ICUs, 820-bed hospital
in Virginia, 2003–2009
Hand hygiene, unit-level
Hand hygiene, environmental
cleaning, “culture change”
Hand hygiene, unit-level S&F
By 2006, 73 (pooled); By
2009, 91 (CLABSI)
(94% VAP, 71% UTI)
Before-and-after840-bed hospital, Australia,
350-bed hospital, Australia,
Before-and-afterNew MRSA isolation,
United Kingdom National
Health Service (HPA)c
NNIS and NHSN
United Kingdom hospitals,
U.S. ICUs, 1997–2007
Public reporting; variousd
Proportion of MRSA
among invasive S.
In 9 countries, significant
decrease over previous
4 years (versus 2
countries with an
aS&F, surveillance and feedback of infection rates to each unit; CLABSI, central line-associated bloodstream infection; VAP, ventilator-associated pneumonia; UTI,
urinary tract infection; HPA, Health Protection Agency; NNIS, National Nosocomial Infection Surveillance System; NHSN, National Healthcare Safety Network;
EARSS, European Antimicrobial Resistance Surveillance System.
bValues refer to percent decrease in new MRSA isolation and MRSA bacteremia, respectively.
cThe Health Protection Agency in the United Kingdom has mandated reporting of MRSA bloodstream infection since 2001.
dUniversal ADI was not practiced across these surveillance programs. Because each program represents hundreds of hospitals, it is not possible to list all
interventions that were performed.
688TO SCREEN OR NOT TO SCREEN FOR MRSAJ. CLIN. MICROBIOL.
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Daniel J. Diekema
University of Iowa Carver College of Medicine
200 Hawkins Drive
Iowa City, IA
Phone: (319) 356–7740
Fax: (319) 356–4916
In this Point-Counterpoint feature, Dr. Peterson presents a compelling case in favor of active, broad-based,
patient-directed surveillance of both colonization and infection with MRSA linked to aggressive infection control
intervention as a means of reducing the burden of MRSA disease in acute care hospitals. He cites the results of three
published studies (Robicsek et al., Harrington et al., and Huang et al.) as supporting a comprehensive screening
program and argues that such screening can result in lower MRSA infection rates and institutional cost savings. Dr.
Peterson emphasizes the need for using molecular methods characterized by high detection sensitivity and same-day
provision of test results when screening for MRSA and asserts that only when ?90% of transmission is blocked can
there be a meaningful reduction is infection rates. He also elucidates the concept of “captured MRSA isolation days”
and points out that only when this value exceeds 80% can an MRSA screening program be expected to have a
measurable positive impact.
Dr. Diekema presents an equally compelling case for not performing routine comprehensive MRSA surveillance.
First, Dr. Diekema elucidates many of the design shortcomings in the studies used to justify MRSA screening linked
to infection control interventions. He also points out that in the largest published study to date assessing the value of
MRSA screening, no impact on infection rates was observed. He states that two major concerns with any compre-
hensive MRSA screening program are the associated costs, some of which are hidden and therefore often not taken
into account when performing economic analyses, and the increase in numbers of patients being cared for under
conditions of contact precautions, with the resulting potentially negative impact of these precautions on patient care
and patient well-being. And finally and importantly, Dr. Diekema makes the point, based on three published studies,
that decreases in MRSA infection rates can be achieved using methods other than comprehensive MRSA surveillance
(Edmond et al., Harrington et al., Johnson et al.).
I would like to thank both Lance Peterson and Daniel Diekema for their most insightful discussions of this very
complex matter. The fact that two experienced authorities in this area can have such different views underscores the
complex nature of the many issues surrounding MRSA screening. Their commentaries provide an important platform
for further discussion, debate, and study of those factors that can lead to a reasoned and coherent approach for
decreasing the burden of MRSA infections.
Gary V. Doern
Editor in chief, Journal of Clinical Microbiology
The views expressed in this feature do not necessarily represent the views of the journal or of ASM.
VOL. 48, 2010POINT-COUNTERPOINT689