title: Longitudinal analysis of methicillin-resistant and methicillin-susceptible Staphylococcus aureus carriage in healthy adolescents.
abstract: To determine the long-term carriage patterns, strain relatedness, and incidence of subsequent infections among methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) carriers, we screened 154 high school students for nasal carriage of S. aureus on 8 occasions over 11 months. Persistent carriage was defined as a positive culture on ≥7 occasions. Two consecutive isolates from the same subject comprised a pair, and strain relatedness was determined for each pair by molecular typing. Of 1,232 nasal swab cultures obtained on 8 occasions, 323 (26.2%) were positive for S. aureus. Forty-five isolates (3.7%) were MRSA and 278 isolates (22.6%) were MSSA from 12 and 63 subjects, respectively. Thirty-five (77.8%) MRSA isolates harbored a type IV or VT staphylococcal chromosomal cassette mec element. Among the 154 subjects, 52 (33.8%) were intermittent (1 to 6 positive swabs) carriers. Persistent carriage was identified in 23 (14.9%) subjects, and the incidence was not significantly different for MRSA and MSSA carriers (3/12 [25%] versus 20/63 [31.7%]; P=0.7449). The MRSA and MSSA isolates were composed of 33 and 215 strain pairs, respectively. Of them, an indistinguishable genotype was identified in 33 (100%) MRSA pairs and 173 (80.5%) MSSA pairs (P=0.0053). Five subjects developed cellulitis, and the incidence of this was higher for MRSA carriers (2/12 [16.7%]) than for MSSA carriers (1/63 [1.58%]; P=0.0632) and noncarriers (2/79 [2.56%]; P=0.0828). In conclusion, the long-term carriage patterns for MRSA and MSSA in healthy individuals were similar. MRSA carriers were more likely to carry a single strain, with a trend toward a higher chance of developing cellulitis than for MSSA carriers.
authors.affiliation: Division of Pediatric Infectious Diseases, Department of Pediatrics, Chang Gung Children's Hospital, Taoyuan, Taiwan. chinjung@adm.cgmh.org.tw
authors.forename: Chih-Jung
authors.initials: CJ
authors.lastname: Chen
authors.forename: Shao-Chung
authors.initials: SC
authors.lastname: Wang
authors.forename: Hsin-Yu
authors.initials: HY
authors.lastname: Chang
authors.forename: Yhu-Chering
authors.initials: YC
authors.lastname: Huang
mesh_terms: D000293:Adolescent; D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology; D005260:Female; D005838:Genotype; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D008297:Male; D016106:Methicillin Resistance; D058889:Molecular Typing; D009297:Nasal Mucosa / Q000382:microbiology; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification*