Importance of bacterial burden among methicillin-resistant Staphylococcus aureus carriers in a long-term care facility.

OBJECTIVE: To evaluate the prevalence and transmission of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization, as well as risk factors associated with MRSA carriage, among residents of a long-term care facility (LTCF). DESIGN: Prospective, longitudinal cohort study. SETTING: A 100-bed Veterans Administration LTCF. PARTICIPANTS: All current and newly admitted residents of the LTCF during an 8-week study period. METHODS: Nasal swab samples were obtained weekly and cultured on MRSA-selective media, and the cultures were graded for growth on a semiquantitative scale from 0 (no growth) to 6 (heavy growth). Epidemiologic data for the periods before and during the study were collected to assess risk factors for MRSA carriage. RESULTS: Of 83 LTCF residents, 49 (59%) had 1 or more nasal swab cultures that were positive for MRSA; 34 (41%) were consistently culture-negative (designated "noncarriers"). Of the 49 culture-positive residents, 30 (36% of the total of 83 residents) had all cultures positive for MRSA (designated "persistent carriers"), and 19 (23% of the 83 residents) had at least 1 culture, but not all cultures, positive for MRSA (designated "intermittent carriers"). Multivariate analysis showed that participants with at least 1 nasal swab culture positive for MRSA were likely to have had previous hospitalization (odds ratio, 3.9) or wounds (odds ratio, 8.2). Persistent carriers and intermittent carriers did not differ in epidemiologic characteristics but did differ in mean MRSA growth score (3.7 vs 0.7; P<.001). CONCLUSIONS: Epidemiologic characteristics differed between noncarriers and subjects with at least 1 nasal swab culture positive for MRSA. However, in this LTCF population, only the degree of bacterial colonization (as reflected by mean MRSA growth score) distinguished persistent carriers from intermittent carriers. Understanding the burden of colonization may be important when determining future surveillance and control strategies.

An epidemiologic investigation of occupational transmission of Mycobacterium tuberculosis infection to dental health care personnel: infection prevention and control implications.

BACKGROUND: The authors describe an investigation of a dental hygienist who developed active pulmonary tuberculosis (TB), worked for several months while infectious and likely transmitted Mycobacterium tuberculosis in a dental setting in Washington state. METHODS: Clark County Public Health (CCPH) conducted an epidemiologic investigation of 20 potentially exposed close contacts and 734 direct-care dental patients in 2010. RESULTS: Of 20 close contacts, one family member and two coworkers, all of whom were from countries in which TB is endemic, had latent TB infection (LTBI). One U.S.-born coworker experienced a tuberculin skin test (TST) conversion from 0 to 8 millimeters. Of the 305 of 731 (41.7 percent) potentially exposed patients who received a single TST, 23 (7.5 percent) had a positive TST result of at least 5 mm. Among the subset of 157 patients tested by CCPH staff, 16 (10.2 percent) had a positive TST result. The dental office did not have infection prevention and control policies related to TB identification, prevention or education. CONCLUSIONS: The coworker's TST conversion indicated a recent infection, likely owed to occupational transmission. The proportion of dental patients with positive TST results was greater than the 1999-2000 National Health and Nutrition Examination Survey prevalence estimate in the general population, and it may reflect transmission from the hygienist with active TB or a prevalence of LTBI in the community. Practical Implications All dental practices should implement administrative procedures for TB identification and control as described in this article, even if none of their patients are known to have TB.