Susan X. Lin

A U.S. Population-Based Survey of Staphylococcus aureus Colonization

Context Epidemiology and risk factors for colonization with methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in the U.S. population are poorly understood. Contribution Extrapolation of 20012002 National Health and Nutrition Examination Survey (NHANES) data indicates that 84 million noninstitutionalized persons in the U.S. population are colonized with MSSA and 2 million are colonized with MRSA. Long-term care facility residence, diabetes, and age 65 years or older are associated with MRSA colonization. Men are at greater risk for MSSA colonization, and women are at greater risk for MRSA colonization. Black persons and those of Mexican birth are at decreased risk for colonization. Implications Risk for MRSA colonization differs according to previously unrecognized population characteristics. The Editors Although Staphylococcus aureus is one of the most common causes of community- and health careassociated infections, little is known about its effects on the U.S. population as a whole. We analyzed newly available data from the 20012002 National Health and Nutrition Examination Survey (NHANES) to expand our understanding of the national epidemiology of S. aureus colonization. This most recent version of the survey is the first to contain information about S. aureus nasal colonization. We aimed to describe the U.S. population epidemiology of S. aureus colonization, compare risk factors for colonization with methicillin-sensitive S. aureus (MSSA) versus methicillin-resistant S. aureus (MRSA), and compare genetic factors and toxin production genes in colonizing strains of both MSSA and MRSA and antibiotic resistance patterns for staphylococcal chromosomal cassette mec (SCCmec) type II (a methicillin resistance gene locus commonly seen in health careassociated MRSA) versus SCCmec type IV (a methicillin resistance gene locus commonly seen in community-associated MRSA). Methods Data Sources We undertook a secondary analysis of NHANES, 20012002 (1). Since the early 1960s, the National Center for Health Statistics has conducted NHANES to obtain representative information on the health and nutritional status of the U.S. population. The survey used a stratified, multistage probability design to sample the civilian, noninstitutionalized U.S. population. The sampling design allows calculation of estimates of the U.S. population (2). Beginning in 1999, NHANES became a continuous annual survey rather than a periodic survey. The data are released on public use data files every 2 years. The 20012002 NHANES is the most recent release of this cross-sectional national survey, which included in-home interview data, examination data from a mobile examination center, and laboratory data. Furthermore, NHANES included data on S. aureus colonization for the first time in this version. Study Sample Of 11039 persons interviewed, 10477 (94.9%) had physical examination data. Among them, 9622 (91.8%) had a nasal swab for S. aureus obtained, and we included these participants in our analysis. We compared the demographic characteristics (age, sex, and race or ethnicity) of those who were interviewed with those who had nasal swabs obtained. We found that they were essentially the same, and therefore, we considered patients who had swabs obtained to be representative of the national sample. Study Variables Microbiological Analysis Nasal swabs were first examined for proper labeling and integrity. They were then plated on mannitol salt agar (MSA), a selective medium for the isolation of S. aureus. The MSA plates were incubated at 37C for 48 hours. Mannitol-fermenting colonies were selected from the MSA plates and subcultured to trypticase soy agar and 5% sheep blood agar plates (BAPs) and incubated at 37C overnight. The MSA plates with little or no growth were reincubated at 37C overnight, and plates with nonmannitol-fermenting growth were held at room temperature. These plates were reexamined the next day, and any yellow or gold colonies were subcultured to BAPs. Overnight cultures on BAPs were first screened by using Staphaurex (Remel, Lenexa, Kansas), a rapid latex kit for identifying S. aureus. A tube coagulase test using rabbit plasma with EDTA was then performed on Staphaurex-negative isolates from BAPs with structure consistent with that of S. aureus and on Staphaurex-positive isolates with structure inconsistent with that of S. aureus (nonhemolytic). Staphaurex-positive isolates and Staphaurex-negative, tube coagulasepositive isolates were identified as S. aureus and were saved for further testing. Staphaurex-positive, tube coagulasenegative isolates were discarded. Staphylococcus aureus isolates were screened for methicillin resistance following the National Committee for Clinical Laboratory Standards (NCCLS) disk-diffusion method. Overnight cultures from BAP were plated on MuellerHinton agar, and a 1-g oxacillin disk was placed on the inoculated plate. Zone diameters were measured and recorded after 24-hour incubation at 37C as sensitive (13 mm), intermediate (11 mm to 12 mm), or resistant (10 mm). Isolates that were resistant to oxacillin (MRSA), those that were intermediate to oxacillin (MSSA), and every tenth isolate that was sensitive to oxacillin (MSSA) by disk diffusion were saved for additional testing of organism characteristics. These tests included antibiotic susceptibility testing (minimal inhibitory concentration [MIC]) using broth microdilution according to NCCLS reference methods; strain typing by pulsed-field gel electrophoresis using SmaI enzyme; singleplex polymerase chain reaction (PCR) for detection of genes encoding enterotoxins, toxic shock syndrome toxin-1, and PantonValentine leukocidin toxin; and SCCmec typing by PCR (3). The NHANES quality control and quality assurance protocols meet the 1988 Clinical Laboratory Improvement Act mandates. Detailed quality control and quality assurance instructions are discussed in the NHANES Laboratory Procedures Manual (4). Risk Factors We examined potential risk factors associated with MSSA and MRSA available in the NHANES data set. These were demographic variables (age, sex, race or ethnicity, education, and birthplace), insurance coverage, health or disease status, and hospitalization or long-term care. We expected that older people would have more chronic conditions and more exposure to antibiotic therapy and hospitalization and, therefore, could be at higher risk for acquiring MRSA. We arbitrarily defined older age groups as age 65 years or older and all other age groups as age less than 65 years. Statistical Analysis We estimated the prevalence of MRSA and MSSA colonization in the U.S. population by using appropriate weighting variables provided with the data set (2). We estimated the prevalence of S. aureus and MRSA, categorized by risk factor, by using weighted samples. We first performed bivariate analyses to examine the association of each individual risk factor with S. aureus and with MRSA. Then, we performed logistic regression analyses to examine risk factors for S. aureus and MRSA, respectively. The multivariate models allowed us to examine the effect of each potential risk factor while controlling for other variables. We ran a series of stepwise regressions, and the final models only included the statistically significant independent variables. We used Wald statistics to test the statistical significance of each independent variable. We calculated odds ratios and 95% CIs. We used weighted samples in chi-square tests and logistic regressions. We compared antimicrobial resistance profiles and genes for toxin production in a subset of MSSA versus MRSA and in a subset of SCCmec type II versus SCCmec type IV by using chi-square tests. We used unweighted samples because of the small size of these subsamples. We performed data analyses by using SUDAAN-callable SAS, version 9 (Research Triangle Institute, Research Triangle Park, North Carolina), which is often used to analyze data collected from surveys with complex sampling designs. Role of the Funding Sources Dr. Graham received salary support from a National Institutes of Health Mentored Clinical Research Scholar Grant, and Drs. Larson and Lin received salary support from the Center for Interdisciplinary Research on Antimicrobial Resistance, National Center for Research Resources, and National Institutes of Health. The funding sources were not involved in the design, analysis, and interpretation of data or in the decision to submit the manuscript for publication. Results Population Epidemiology A total of 9622 participants had cultures for S. aureus obtained. Of these participants, 2889 (31.6% [95% CI, 29.8% to 33.4%]) and 75 (0.84% [CI, 0.4% to 1.2%]) were colonized with MSSA and with MRSA, respectively. On the basis of these data, approximately 84 million and 2 million noninstitutionalized persons in the U.S. population are colonized with MSSA and MRSA, respectively. Prevalence of S. aureus was as low as 26.8% among black persons and was as high as 38% among men (Table 1). The highest prevalence of MRSA was among people who had been in a long-term care facility in the past 12 months (30.9%), people with diabetes (8.5%), and people 65 years of age or older (8.3%) (Table 2). Of persons with MRSA, half are estimated to be colonized with SCCmec type II and half with SCCmec type IV. Table 1. Colonization withStaphylococcus aureus(Methicillin-Sensitive and Methicillin-Resistant) by Risk Factor among the U.S. Population Table 2. Methicillin Resistance among Persons Colonized withStaphylococcus aureusby Risk Factor Staphylococcal Colonization Risks In a multivariate logistic regression model, persons younger than 65 years of age, men, those with less than a high school education, and those with asthma were more likely to have acquired staphylococcal colonization. Black persons and those of Mexican birth were at lower risk than white persons and than those born in the United Stat

Primary care outcomes in patients treated by nurse practitioners or physicians: Two-year follow-up

This study reports results of the 2-year follow-up phase of a randomized study comparing outcomes of patients assigned to a nurse practitioner or a physician primary care practice. In the sample of 406 adults, no differences were found between the groups in health status, disease-specific physiologic measures, satisfaction or use of specialist, emergency room or inpatient services. Physician patients averaged more primary care visits than nurse practitioner patients. The results are consistent with the 6-month findings and with a growing body of evidence that the quality of primary care delivered by nurse practitioners is equivalent to that by physicians.

Diabetes care processes and outcomes in patients treated by nurse practitioners or physicians.

PURPOSE the purpose of this study was to compare selected diabetes care processes and outcomes of nurse practitioners (NPs) and physicians (MDs) in the primary care of adults with type 2 diabetes. METHODS Adults with type 2 diabetes and no regular source of primary care were enrolled from the emergency room and randomized to an NP or MD practice. Chart reviews were conducted to assess processes of care; patient interviews and hemoglobin Al C (Al C) testing were performed to measure patient outcomes. RESULTS NPs were more likely than MDs to document provision of general diabetes education and education about nutrition, weight, exercise, and medications. They were more likely to document patient height, urinalyses results, and Al C values. No differences were found in documenting current medications; alcohol, illicit drug, or tobacco use; depression; weight and blood pressure; foot and cardiovascular exams; blood glucose and creatinine testing; or referral to ophthalmologists. No differences were found in patient outcomes. CONCLUSIONS This study provides preliminary evidence of interdisciplinary differences in the processes of care employed by primary care NPs and MDs in caring for patients with type 2 diabetes. NPs documented the provision of diabetes education and selected monitoring tests more frequently than MDs; however, these differences were not reflected in 6-month patient outcomes.

Antibiotic Use in Hispanic Households, New York City

Trained interviewers visited 631 inner city households to determine community prevalence and predictors of antibiotic use. Infectious disease symptoms were reported in 911 (33.2%) of 2,743 household members in the previous 30 days: medical attention was sought by 441 (48.4%) of 911 persons, and 354 (38.9%) of 911 took antibiotics for symptoms. Reported symptoms were respiratory (68.9%), gastrointestinal (15.3%), fever (12.8%), and skin infection (2.8%). Medical attention was sought significantly more often among those with chronic illness, those born in the United States, and those with fever, runny nose, or skin infections (all p<0.05). Antibiotics were taken significantly more often among those with poor health, those who spent more time at home, and those with fever and respiratory symptoms. Interventions to promote judicious use of antibiotics must include clinicians and the public, and for the Hispanic population such interventions must also be culturally relevant and provided in Spanish.

Predictors of infectious disease symptoms in inner city households.

BackgroundDespite the fact that hygienic practices have been associated with reduced risk of infection for decades, the potential role of specific home hygiene and cleaning practices in reducing risk have not been explicated. ObjectiveThis study aimed to determine the incidence and predictors of infectious disease symptoms over a 48-week period in inner city households. MethodsCleaning and hygiene practices and the incidence of infectious disease symptoms were closely monitored prospectively for 48 months in 238 households. Each household was contacted by trained interviewers weekly via telephone, was visited monthly, and underwent an extensive home interview quarterly. ResultsThe incidence of new symptoms in the month before quarterly home visits ranged from 8.9% to 12.4% for individuals and from 32% to 39.7% for households. Four factors were significantly associated with infection. Drinking only bottled water increased risk (relative risk [RR], 2.1; 95% confidence interval [CI], 1.2–3.7). Using hot water (RR, 0.7; 95% CI, .5–.9) and bleach (RR, 0.29; 95% CI, .23–.66) for laundry and reporting that germs were most likely to be picked up in the kitchen (RR, 0.5; 95% CI, .3–.8) were protective. No other hygiene practices, including hand washing, were associated with infection risk. ConclusionsFurther studies of a potential role for bottled water in infections are warranted, as is a renewed appreciation for the potential protective role of laundry practices such as using bleach and hot water.