Health care-associated infections acquired by patients during the course of treatment for other medical conditions are among the top 10 leading causes of death in the United States. Finding effective diagnostic methods and treatments for the increasing number of multiple antibiotic-resistant infections has become an urgent challenge for the medical community.
In particular, infections caused by methicillin-resistant Staphylococcus aureus (MRSA) pose the greatest threats as infections due to these multidrug-resistant organisms (MDROs) increase in incidence.
Drug-Resistant Organisms: The Scope of the Problem
According to the Centers for Disease Control and Prevention (CDC), MRSA was first isolated in the United States in 1968. By the early 1990s, MRSA accounted for 20% to 25% of S. aureus isolates from hospitalized patients. In 1999, MRSA accounted for more than 50% of S. aureus isolates from patients in ICUs in the National Nosocomial Infection Surveillance (NNIS) system; in 2003, 59% of S. aureus isolates in NNIS ICUs were MRSA.
S. aureus is notorious for asymptomatic colonization. A report late last year in the American Journal of Infection Control estimated that 46 out of every 1,000 inpatients were either colonized or infected by MRSA.
Successful control of these and other MDROs has been documented in the United States and abroad using a variety of combined interventions. These include improvements in hand hygiene, use of contact precautions until patients are culture-negative for a target MDRO, active surveillance cultures, education, enhanced environmental cleaning, and improvements in communication about patients with MDROs within and among health care facilities.
Surveillance is a critically important component in any control program, allowing detection of newly emerging pathogens, monitoring epidemiologic trends, and measuring the effectiveness of interventions. The simplest form of surveillance is monitoring of clinical microbiology isolates resulting from tests ordered as part of routine clinical care.
However, active surveillance strategies (such as universal screening) are controversial. The local epidemiology of MRSA, for example, varies widely among hospitals. There currently is no one-size-fits-all solution to the problem of MRSA prevention.
Consider that two recent reports—one published in Journal of the American Medical Association, the other in Annals of Internal Medicine—presented conflicting conclusions about universal screening. In the JAMA paper, Swiss authors concluded that universal rapid screening with a multiplex polymerase chain reaction (PCR) test did not reduce nosocomial MRSA infection in a teaching hospital’s surgical department that had endemic MRSA prevalence. In contrast, investigators from Evanston Northwestern Healthcare (reporting in AIM) reported a 70% reduction in disease related to MRSA when universal screening was used.
Perhaps more insightful was a finding in the Swiss study about the role of communication in surveillance strategies. Despite the use by the lab of rapid molecular tests, in a significant percentage of cases information on positive results wasn’t available until after surgery—too late for antibiotic prophylaxis.
MRSA is diagnosed only through laboratory examination of a sample, such as a tissue swab, urine, or wound culture. The agar-based screening test for oxacillin-resistant S. aureus is recommended by the National Committee for Clinical Laboratory Standards to test for MRSA. Also useful is a nasal swab for rapid PCR testing to document MRSA status. However, it’s estimated that only about 10% of all hospital laboratories and only 35% of all independent laboratories in the United States are licensed for high-complexity testing and can use PCR to perform molecular diagnostic testing.
Providing physicians with the critical laboratory data needed to make a decision within a few hours instead of a few days is vital not only to save lives but to help control the spread of infections in health care settings.
In recent months, two consortiums—one in the United States, the other in Great Britain—have announced their formation. Each will work to establish connections between hospital laboratories and leading academic laboratories in order to track evolving drug-resistance patterns and the emergence of new multiple antibiotic-resistant strains. The resulting information will be used in the design of rapid and definitive new tests.
Hospital-acquired infections and, in particular, MRSA have received extensive media coverage in recent years, and it seems as if everyone has an interest and opinion on antibiotic-resistant infections. The “Medical Dispatch” column of the August 11, 2008, issue of The New Yorker featured a 4,800-word article on the topic of so-called “super bugs” authored by columnist and Harvard Medical School Professor Jerome Groopman, MD. And for several weeks the story line of the newspaper comic strip Rex Morgan, MD focused on the problem of MRSA infection.
Public discussion and debate on the problem have quickly moved onto the agenda of elected officials determined to enact legislation that will “fix” the problem. Many of the bills currently making their way through statehouses characterize the solution as “simple” and call for universal screening of patients.
In addition to the economic impact of adopting universal screening, there’s another issue worthy of note: a conflict between the interests of the individual patient and the patient population not already colonized with the organism. Ethicists point out that universal screening can bring with it unintended effects related to decreased contact with health care workers, increased depression and anxiety, and increased rates of noninfectious adverse events among patients isolated through increased screening.
On the Front—What Hospital Physicians Are Seeing and Ordering
What are physicians and others in the field seeing, and how does it affect how they are ordering tests? Leslie J. Caskey, MT (ASCP) SM,SM (AAM), manager, microbiology and molecular biology laboratories, Scripps Clinic Medical Laboratories, San Diego, says this is a very controversial subject and there are differing opinions throughout the nation. She emphasized that her opinions on the subject are hers only, and do not reflect Scripps’ position on this subject. (Scripps has no official stance at this time, although the subject is being discussed. Each Scripps hospital is doing what its infectious disease physicians and infection control practitioners believe is best for their patient population and environment.)
Caskey says that PCR (amplified nucleic acid testing) is the fastest and most sensitive assay. “It is also more costly than conventional culture screening. Most physicians order ‘MRSA screen,’ and the laboratory uses what is available at that institution. More institutions are converting from culture to PCR testing in order to achieve faster turnaround time,” Caskey says.
But should screening be done at all? Caskey says it’s a complex question, one that should be determined based on the hospital’s current rate of MRSA infection and type of patients being admitted under the guidance of the infectious disease physicians and infection control practitioners, in her opinion. That being said, however, Medicare has decreased reimbursement for nosocomial infections, and unless patients are prescreened, it will be difficult to prove that an MRSA infection was not acquired in the hospital and reimbursement may be denied, she says.
Also, she notes, there has been a lot of media coverage relating to the negative consequences of MRSA infections, and this has caused widespread concern; thus, some states’ legislatures have mandated screening as a result. More and more hospitals are starting to prescreen patients (including all the VA hospitals in the country), and this may become standard of practice. More guidelines are needed from sources such as the CDC and will probably be forthcoming as data is collected and published, Caskey says.
According to Kirk Doing, PhD, director of the microbiology laboratory at Affiliated Laboratory Inc, Portland, Me, screening patients for MRSA has become standard care in many institutions and is largely directed by the hospital’s infection control or prevention department.
The goal of this screening is to identify the patients who are carrying MRSA, to initiate infection control measures to try and prevent the organism from being carried to other patients—in other words to stop transmission. S. aureus is a “people bug,” Doing says, and up to 40% of the population is carrying the organism in the nares at any time with no ill effects. Of these 40%,up to 15% may be carrying a strain of MRSA, again with no ill effects. So it is not so striking that this organism is so prevalent in infections, Doing notes.
If surveillance testing is initiated, each hospital must define the patient populations they wish to screen—all new admissions, admissions to high-risk units like the ICU, transfers from other facilities, etc. “It is also possible that those colonized with MRSA may also be colonized with other resistant bacteria, so in identifying these patients we may actually be detecting patients colonized with these other organisms (two birds with one stone),” Doing continues. “This is only one arm of MRSA prevention. A second and likely more important point is that simple hand washing is the single most important factor in preventing spread of this or any bacteria from health care worker to patient, and alcohol-based hand gels work great here.”
A second screening protocol being requested in some institutions is to identify patients who are carrying S. aureus and awaiting surgery, specifically, cardiac and some orthopedic procedures. Knowing their S. aureus carrier status can help in preventing infection—so on one hand there are hospitals attempting to limit transmission, and on the other they are identifying colonized patients to prevent infection.
However, Doing says, despite all this there have not been any good scientific studies that prove routine screening for S. aureus, or surveillance testing, is the best clinical practice. Therefore, when state legislatures begin mandating that this testing be performed, they are reacting more to emotion than they are to data—and Doing thinks this is a problem. In addition, this testing is an added cost to health care, costing anywhere from $5 to $45 for testing materials, and in many instances these charges are not reimbursed by insurance companies to the hospital, he adds.
“So while we all want to lower health care-associated infections, surveillance is likely not the silver bullet, and this is no guarantee that an infection does not occur as a number of other variables are in play,” Doing says.
Lynne Friedmann is a freelance science and medical journalist based in San Diego. She is founder and president of the San Diego Science Writer’s Association. Gary Tufel is a contributing writer for CLP.
