Clinical research study
The Risk of Infection after Nasal Colonization with Staphylococcus Aureus

https://doi.org/10.1016/j.amjmed.2007.07.034Get rights and content

Abstract

Purpose

Nasal, axillary, or inguinal colonization with Staphylococcus aureus generally precedes invasive infection. Some studies have found that colonization with methicillin-resistant S. aureus (MRSA) poses a greater risk of clinical infection than colonization with methicillin-susceptible S. aureus (MSSA). However, the magnitude of risk is unclear.

Methods

We undertook a systematic review to provide an overall estimate of the risk of infection following colonization with MRSA compared with colonization by MSSA. Ten observational studies, with a total of 1170 patients, were identified that provided data on both MSSA and MRSA colonization and infection. A random-effects model was used to obtain pooled estimates of the odds ratio and 95% confidence interval.

Results

Overall, colonization by MRSA was associated with a 4-fold increase in the risk of infection (odds ratio 4.08, 95% confidence interval, 2.10-7.44). Studies differed in the choice of patient population, severity of illness, and frequency of sampling to detect colonization.

Conclusion

Further research is needed to identify effective methods for sustained eradication of MRSA carriage to reduce the high risk of subsequent infection.

Introduction

The late 20th century witnessed a rapidly growing crisis in antimicrobial resistance, especially among microorganisms that cause nosocomial infections.1, 2, 3, 4 In particular, methicillin-resistant Staphylococcus aureus (MRSA) continues to be a major threat in hospitalized patients,5, 6, 7, 8 and also now is the main cause of community-acquired skin and soft tissue infections in the United States.9 When compared with methicillin-susceptible Staphylococcus aureus (MSSA), several studies have shown that infection caused by MRSA is associated with greater morbidity and mortality.10, 11, 12, 13, 14

Nasal, inguinal, axillary, or rectal colonization with S. aureus, whether methicillin susceptible or resistant, generally precedes infection.15 Several studies have found that MRSA-colonized patients are at higher risk for invasive infection as compared with noncolonized patients15, 16 and those colonized by MSSA.17, 18, 19, 20 However, an overall estimate of the increased risk of infection posed by MRSA colonization compared with MSSA colonization is lacking. We undertook a systematic review of studies that assessed MRSA and MSSA carriage and reported subsequent invasive infection with these pathogens.

Section snippets

Methods

We searched PubMed, MEDLINE, EMBASE, and the Cochrane Library databases from inception until December 12, 2006 for relevant publications. No language restrictions were applied. The following keywords were used alone or in combination: “Staphylococcus aureus, methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), colonization, infection.” We also reviewed the reference lists of the retrieved articles and of recent review articles.

Results

Our search yielded 528 published reports (Figure 1); of these, 113 studies were potentially relevant and were reviewed in detail. Of these, 103 were excluded because data on MRSA colonization and infection or MSSA colonization or infection were lacking.

Ten studies fulfilled inclusion criteria.17, 18, 19, 20, 24, 25, 26, 27, 28, 29 All were observational studies. No randomized trials were identified. The characteristics of the included studies are shown in Table 1. These studies encompassed 1170

Discussion

Our results show that compared with MSSA, patients colonized with MRSA are at substantially higher risk for clinical infection. Individual studies have found an increased risk of infection with MRSA colonization but the magnitude of increase was unclear; our study summarizes the results of these studies and shows that MRSA colonization poses a 4- fold increased risk for infection compared with MSSA colonization.

Why colonization by MRSA should pose a greater risk of infection than MSSA

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    Supported by a Society of Critical Care Medicine Vision Grant (NS). Dr. Safdar was also supported by an institutional K-12 training grant from the Institute of Aging, National Institutes of Health, Bethesda, Md.

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