infection control and hospital epidemiology june 2007, vol. 28, no. 6 concise communication table 1. Frequency of Sequence Types Among Orthopedic Healthcare Workers With Cultures Positive for Staphylococcus aureus MLST sequence type (CC) spa type No. (%) of subjects Sample 1 (n p 29) Sample 2 (n p 28) Sample 3 (n p 24) 5 (CC5) t002 1 (3.4) 0 0 456 (CC5) t002 0 1 (3.6) 0 15 (CC15) t084 8 (27.6) 8 (28.6) 7 (29.2) t346 1 (3.4) 1 (3.6) 1 (4.2) t120 1 (3.4) 1 (3.6) 0 30 (CC30) t840 3 (10.3) 2 (7.1) 3 (12.5) t138 1 (3.4) 0 0 t012 1 (3.4) 2 (7.1) 1 (4.2) t021 1 (3.4) 0 1 (4.2) t166 0 1 (3.6) 0 34 (CC30) t839 1 (3.4) 1 (3.6) 1 (4.2) t138 1 (3.4) 0 0 t166 0 1 (3.6) 0 45 (CC45) t065 2 (6.9) 2 (7.1) 1 (4.2) t230 1 (3.4) 1 (3.6) 1 (4.2) t015 0 1 (3.6) 0 t026 2 (6.9) 2 (7.1) 3 (12.5) 47 (CC45) t065 1 (3.4) 0 1 (4.2) 455 (CC45) t012 1 (3.4) 1 (3.6) 0 452 (CC45) 0 0 1 (4.2) 101 (CC28) t056 1 (3.4) 0 1 (4.2) 182 (CC a ) t364 1 (3.4) 1 (3.6) 1 (4.2) 453 (CC a ) t084 0 1 (3.6) 1 (4.2) 454 (CC a ) t021 1 (3.4) 1 (3.6) 0 note. CC, clonal complex; MLST, multilocus sequence typing. a Singletons, which mean they do not fall into a CC with the sampled population seen in the S. aureus database. Nasal Carriage of Staphylococcus aureus: Which Sequence Types Do Orthopedic Surgical Healthcare Workers Carry? Inge Skra ˚mm, MD; Aina Elisabeth Fossum Moen, MSc; Kjetil Alm-Kristiansen, MSc; Geir Bukholm, MD, PhD Using sequence typing methods, we found that healthcare workers on our orthopedic surgery unit were persistent carriers of a limited number of sequence types of Staphylococcus aureus for a limited time. Multilocus sequence typing characterized 3 clonal complexes that accounted for more than 80% of the clonal complexes identified. Infect Control Hosp Epidemiol 2007; 28:737-739 Staphylococcus aureus is the microbial agent most often as- sociated with surgical site infections in orthopedic surgery. The bacterial source of such infections may be the normal flora of the individual patient, healthcare workers, or other external sources. 1,2 Individuals colonized with S. aureus are commonly referred to as persistent or intermittent carriers, depending on whether they carry S. aureus in all or only some of the samples taken. However, the definition of the term “carrier” is inconsistent. 3,4 Most studies indicate a carriage rate of 20%-30% in healthcare workers. 5 It is not known whether special clones of S. aureus are more common than carrier clones or whether clones associated with surgical site infection in orthopedic patients are related to the common carrier clones in an orthopedic surgical ward. The impact of S. aureus clones in both carriers and infected patients is difficult to estimate because of the lack of an internationally accepted algorithm for clonal definition. The agreement on a defined algorithm for multilocus sequence typing (MLST) and sequencing of the variable repeat region of the Staphylococcus protein A gene (spa typing) has made it possible to obtain such data. MLST and spa typing are stable methods that reflect clonal structure and allow the duration of carriage to be described. The aim of this study was to define S. aureus clonal types among healthcare workers from an orthopedic surgery ward and to use sequence typing techniques, including MLST and spa typing, to describe the occurrence of S. aureus in a potentially disease-transmitting environment that surrounds orthopedic surgical patients. methods Akershus University Hospital (Lorenskog, Norway) serves ap- proximately 340,000 people. The orthopedic surgical depart- ment consists of two 24-bed care units, including acute and elective surgery units. All 97 staff members in our orthopedic surgical department agreed to participate in our investigation of nasal carriage of S. aureus in November 2000. Five indi- viduals were available for follow-up 2 years later. Nasal swab specimens were collected at 2-week intervals by infection control personnel for a total of 3 samples from each individual. Samples were obtained using moist, sterile cotton-wool swabs, which were immediately placed in Stuart’s transport medium and reseeded within 24 hours. After in- cubation at 37°C on Chapman’s mannitol salt agar plates and blood agar plates for 48 hours, tested on coagulase and DNase, bacterial isolates were frozen at -80°C. All isolates were methicillin susceptible when tested with cefoxitin on Mueller-Hinton agar. Reculturing of isolates was followed by washing in phosphate-buffered saline (pH, 7.4), lysis with 5 mL of Lysostaphin (Sigma-Aldrich), and incubation at 37°C for 2 hours. Chromosomal DNA from S. aureus was then extracted using the Geno M-48 Robotic Workstation (Qiagen/ GenoVision) and the Mag Attract DNA tissue protocol. MLST was performed according to the protocol of Enright et al., 6 with a few modifications as described by Hanssen et al. 7 Sequences were sent to the MLST database (http://www.