Infectious disease/original researchIncreased US Emergency Department Visits for Skin and Soft Tissue Infections, and Changes in Antibiotic Choices, During the Emergence of Community-Associated Methicillin-Resistant Staphylococcus aureus
Introduction
Staphylococcus aureus is a major cause of both abscesses and nonpurulent skin and soft tissue infections.1, 2 Strains resistant to β-lactams, known as methicillin-resistant S aureus (MRSA), emerged in the 1960s. These were found predominantly in patients exposed to health care facilities. This changed when new “community-associated” strains emerged in the mid-1990s, and community-associated MRSA is now the leading identifiable cause of skin and soft tissue infections in US emergency department (ED) patients (though generally the cause is identifiable only when the infection is purulent).1, 2
Recent studies have shown that cultures of ED patients’ abscesses are likely to yield community-associated MRSA.1 However, we still do not know whether abscesses and other infections commonly caused by S aureus are more common since the emergence of community-associated MRSA. Have ED visits for skin and soft tissue infections increased since community-associated MRSA was discovered? Or has this organism merely replaced others, with the underlying disease incidence remaining the same? Given the heterogenous patterns of antibiotic resistance exhibited by this organism, it is also important to monitor physician prescribing practices. Have prescribing practices changed in parallel to changes in disease incidence and cause?
We seek to determine whether the annual rate of ED visits for skin and soft tissue infections often caused by S aureus has changed since community-associated MRSA was first described in the mid-1990s. We hypothesized that from 1993 to 2005, there was a nationwide increase in ED visits attributable to such infections. We also hypothesized that US ED clinicians increased their use of antibiotics typically active against community-associated MRSA when prescribing antibiotics for such infections. To test these hypotheses, we sought data on ED utilization for relevant infections and prescribing practices for not only today but also the period before community-associated MRSA was described. Because it is not possible to initiate prospective surveillance after the fact (ie, after the new organism was described), we required a preexisting surveillance data set. Only 1 such data set exists for the US ED setting: the National Hospital Ambulatory Medical Care Survey (NHAMCS).3
Section snippets
Study Design and Setting
We conducted a secondary analysis of NHAMCS data for 1993 to 2005. NHAMCS is a probability sample of ED visits in all 50 states and the District of Columbia, representing all US EDs, excluding federal, military, and Veterans Administration hospitals.3 Trained staff collect data using standardized forms during randomly assigned 4-week periods. All collected forms are sent to the Constella Group (Durham, NC) and coded by using the International Classification of Diseases, Ninth Revision, Clinical
Results
From 1993 through 2005, the NHAMCS sampled 374,891 ED visits. Each year, 352 to 418 EDs participated.10 An infection of interest was diagnosed at 6,628 of these visits. This allows us to estimate that there were 1.3 billion total ED visits in the United States during this period (95% CI 1.2 to 1.4 billion), with diagnosis of an infection of interest at 23 million (95% CI 21 to 25 million), or 1.7% of all ED visits (95% CI 1.6% to 1.8%). Patient age was younger than 18 years for 18% (95% CI 17%
Limitations
An important unanswered question is whether community-associated MRSA plays a role in nonpurulent skin and soft tissue infections (eg, cellulitis), as well as purulent ones (abscess, folliculitis, etc). A flaw in the ICD-9-CM diagnostic categorization system is that cellulitis and abscess are lumped together. Therefore, we could not distinguish purulent from nonpurulent infections. We also could not identify visits with incision and drainage (which would obviously indicate suspicion for
Discussion
We describe ED utilization and antibiotic choices during the period of emergence of community-associated MRSA, which is known to be important in purulent infections among ED patients.1 Analyzing 13 years of data from a representative sample of US EDs, we categorized visits according to whether they involved a skin and soft tissue infection and whether an antibiotic typically active against community-associated MRSA was chosen.
The data are consistent with our 2 hypotheses. From 1993 to 2005, we
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Supervising editor: David A. Talan, MD
Author contributions: All authors participated in conceptualization and planning of the analyses and manuscript preparation. AJP and JAE performed all analyses, and had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. DJP takes responsibility for the paper as a whole. None of the authors has any conflict of interest to declare.
Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article, that might create any potential conflict of interest. The authors have stated that no such relationships exist. See the Manuscript Submission Agreement in this issue for examples of specific conflicts covered by this statement.
Publication dates: Available online January 25, 2008.
Reprints not available from the authors.