标题：Public Health Surveillance for Methicillin-Resistant Staphylococcus aureus: Comparison of Methods for Classifying Health Care– and Community-Associated Infections
摘要：Objectives. We compared 3 methods for classifying methicillin-resistant Staphylococcus aureus (MRSA) infections as health care associated or community associated for use in public health surveillance. Methods. We analyzed data on MRSA infections reported to the Michigan Department of Community Health from October 1, 2004, to December 31, 2005. Patient demographics, risk factors, infection information, and susceptibility were collected for 2151 cases. We classified each case by the health care risk factor, infection-type, and susceptibility pattern methods and compared the results of the 3 methods. Results. Demographic, clinical, and microbiological variables yielded similar health care–associated and community-associated distributions when classified by risk factor and infection type. When 2 methods yielded the same classifications, the overall distribution was similar to classification by 3 methods. No specific combination of 2 methods was superior. Conclusions. MRSA categorization by 2 methods is more accurate than it is by a single method. The health care risk factor and infection-type methods yield comparable classification results. Accuracy is increased by using more variables; however, further research is needed to identify the optimal combination. Methicillin-resistant Staphylococcus aureus (MRSA) emerged as a cause of hospital infections in the United States in the late 1960s, and reports of hospital MRSA outbreaks began increasing in the mid-1970s. 1 The incidence of MRSA grew steadily, and by the 1990s, MRSA was considered endemic in large, urban US medical centers. 2 – 4 The first reports of MRSA identified in community settings were published in the early 1980s, 5 – 7 and prevalence in that setting has also continued to increase. MRSA infections range from minor dermatological conditions, such as pustules, boils, and folliculitis, to serious systemic illnesses, such as osteomyelitis, pneumonia, and bacteremia. MRSA infections identified from health care and community settings often present differently at the epidemiological and molecular levels. These 2 types of MRSA infections usually occur among individuals with different risk factors, such as medical history, age, infection type, and resistance patterns. 8 – 14 Because of these differences, MRSA infections have been classified as either health care associated or community associated. 15 – 17 Public health professionals, health care providers, and researchers have used a variety of methods and definitions to classify MRSA infections as either health care associated or community associated. Molecular testing has been a useful method for some investigators, but it is time consuming and resource intensive, and the specific laboratory training and personnel needed often are not available. Collectively, factors of cost, time, and specialized training make it impractical for population-level MRSA surveillance of the type conducted by health departments. Three less resource-intensive methods are commonly used to classify MRSA infections as health care associated or community associated: classification according to health care risk factor, infection type, or susceptibility pattern. 18 – 24 All 3 methods have been used for both research and surveillance and have proven useful in categorizing infections as health care–associated MRSA (HA-MRSA) or community-associated MRSA (CA-MRSA). 15 , 25 – 32 Classification by health care risk factor helps to identify where and how a patient most likely acquired the organism but requires patient information that is difficult to collect accurately and consistently. Consequently, classification by health care risk factor is most often used in funded studies where patient chart review and interviews can be conducted, tasks that are impossible for most health departments to carry out in routine population-level MRSA surveillance. Classification by either infection type or susceptibility pattern relies on data that are more readily available, but these classifications lack risk and acquisition information. The choice of classification method has been left to investigators and clinicians, typically depending on availability of data and resources. Currently, only 9 states receive federal funding specifically for MRSA surveillance through the Centers for Disease Control and Prevention's Emerging Infections Program Active Bacterial Core Surveillance ( http://www.cdc.gov/ncidod/dbmd/abcs/team-start.htm ). Most state health departments, including Michigan's, must rely on internal resources for MRSA surveillance, the importance of which can be difficult for state legislators to accept in times of severe budgetary constraints. Consequently, states that seek to categorize health care–associated and community-associated infections for MRSA surveillance face serious resource limitations. We analyzed MRSA infection data reported to the Michigan Department of Community Health (MDCH). We separately applied 3 different classification methods—health care risk factor, infection type, and susceptibility pattern—to each case to identify them as health care associated or community associated. We then compared the 3 sets of results, seeking to assess the level of concordance among them and to determine whether these 3 methods were similar and interchangeable in the context of MRSA prevention and control efforts.
