More on MRSA: Long-Term Risk of Infection Following Acquisition
Abstract & Commentary
Synopsis: Twenty-nine percent of patients newly identified as carrying MRSA will have subsequent MRSA infection over the following 18 months.
Source: Huang SS, Platt R. Risk of methicillin-resistant Staphylococcus aureus infection after previous infection or colonization. Clin Infect Dis. 2003;36:281-285.
Huang and colleagues reviewed the course of patients newly identified as having MRSA colonization or infection in a large university teaching hospital. They identified 209 patients who were newly recognized as being infected or colonized; fifty-four percent were infected according to CDC definitions, and 46% were colonized. The median time from admission to the first MRSA-positive culture was 9 days. Huang et al followed the patients for 18 months for evidence of subsequent MRSA infection. Of these 209 patients, 60 (29%) developed 90 subsequent MRSA infections (average 1.5 per patient). Of the 60, 48 patients had 67 infections at sites different from the site of initial MRSA isolation. Twenty-two patients had infections at the site from which MRSA was initially isolated. The most common infections were bacteremia (28%), pneumonia (20%), soft tissue (16%), and bone and joint (16%).
The risk of subsequent MRSA did not differ significantly based on whether the initial isolation represented infection or colonization. Subsequent MRSA infection first became manifest after discharge from the index hospitalization in 52%.
Comment by Robert Muder, MD
It is well known that MRSA infection is often preceded by MRSA colonization. The rate of subsequent MRSA infection among inpatients colonized with MRSA has varied between 10% and 40%, with the highest rates found, not surprisingly, in ICU patients.1-3 The study of Huang et al adds a new dimension to assessment of the subsequent risk of MRSA infection by following patients newly recognized as infected or colonized with MRSA over an 18-month period. They found that 29% of patients had an average of 1.5 subsequent MRSA infections. Nearly half of these infections were either bacteremia or pneumonia, which are clearly life threatening. Half of the patients had their first MRSA infection following discharge from the index hospitalization. These infections would have been missed had follow-up ceased at discharge.
There are several potential biases inherent in this study. The first is that all admitted patients did not undergo surveillance for MRSA colonization during hospitalization. This may have biased the study toward identifying higher-risk patients. On the other hand, a number of patients died or were lost to follow-up after the index hospitalization, and follow-up was limited to 18 months. Thus, it is quite likely that additional, unidentified MRSA infections occurred in the study cohort.
This study emphasizes that acquisition of MRSA can have adverse consequences that extend over a prolonged period of time. The long-term risk of MRSA infection after acquisition can be addressed in several ways. The first is to prevent MRSA transmission within health care settings; obviously, patients who never acquire MRSA in the first place will not become infected. The measures by which MRSA transmission can be interrupted are well known; the implementation of these measures is often lacking. The second is to identify patients colonized with MRSA and eradicate colonization. A number of topical, systemic, and combination antimicrobial regimens have been studied for the eradication of MRSA carriage.4 All of these regimens have distinct drawbacks, the most problematic of which are poor efficacy in patients with colonization at multiple body sites and emergence of MRSA strains resistant to the agent or agents used. An effective regimen for MRSA de-colonization could potentially prevent a considerable amount of morbidity and mortality. Development of effective agents is clearly worth pursuing.
References
1. Pujol M, et al. Nosocomial Staphylococcus aureus bacteremia among nasal carriers of methicillin-resistant and methicillin-susceptible strains. Am J Med. 1996;100:509-516.
2. Coello R, et al. Risk factors for developing clinical infection with methicillin-resistant Staphylococcus aureus (MRSA) amongst hospital patients initially only colonized with MRSA. J Hosp Infect. 1997;37: 39-46.
3. Squier C, et al. Staphylococcus aureus rectal carriage and its association with infections in patients in a surgical intensive care unit and a liver transplant unit. Infect Control Hosp Epidemiol. 2002;23:491-494.
4. Boyce JM. MRSA patients: Proven methods to treat colonization and infection. J Hosp Infect. 2001;48(Suppl A):S9-S14.
Twenty-nine percent of patients newly identified as carrying MRSA will have subsequent MRSA infection over the following 18 months.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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