Carriage of N. meningitidis in Freshmen disease outbreaks among military recruits. A study in Maryland conducted by Harrison, et al.2 indicat- ed that the overall incidence of meningococcal disease among university students was comparable to that among the U.S. population of people of the same age (1.7/100000 and 1.4/100000, respectively); meanwhile, rates of disease among students living in dormitories were higher than those among students living off campus (3.2/100000 and 1.0/100000, re- spectively; p=0.05). In 2000, the Advisory Committee on Immunization Practices and the Committee on Infectious Diseases of the American Academy of Pediatrics concluded that college students, especially those living in dormitories, are at moderately increased risk for meningococcal disease, compared with other persons of the same age, and recom- mended meningococcal vaccination for college freshmen.3 Between 2001 and 2006, 7 to 38 probable cases of me- ningococcal disease were reported to the Korea Centers for Disease Control and Prevention annually. During the period from 2007 to 2008, the number of reported cases of menin- gococcal disease in Korea decreased (4 cases in 2007 and 1 cases in 2008). The disease has been regarded as a rare in- fection in Korea. Although carriage studies are important to improve our understanding of the epidemiology and patho- genesis of meningococcal disease, there have been no stud- ies published on the epidemiology of meningococcal car- riage or acquisition among university students in Korea, probably because of the low incidence of the disease. There- fore, we performed a longitudinal study of first year univer- sity students who resided in a student dormitory at the start of the academic year to determine the rates of carriage of N. meningitidis and thes changes thereof after one month, to- gether with risk factors and serogroups. MATERIALS AND METHODS Recruitment of students We recruited Inha University freshmen who were, at that time, admitted to a university dormitory in the first week of March 2009. Each student was given an information sheet and a consent form. Those agreeing to take part in the study completed a questionnaire covering: personal characteris- tics, place of residence, recent symptoms of upper respira- tory tract infection, recent history of antibiotics use, travel abroad, active smoking, intimate kissing in the past month and visits to nightclubs or pubs in the past two weeks. After each student had completed the questionnaire, a trained op- erator took a posterior pharyngeal swab behind the uvula. Follow-up A second round of swabbing was undertaken 4 weeks later. At the time of reswabbing, the questionnaire was repeated. Culture and characterization of isolates Cotton swabs were used and they were directly plated onto Thayer-Martin media. Strains were confirmed to be N. meningitidis by conventional methods including colony morphology, Gram staining, oxidase tests, catalase tests, carbohydrate fermentation tests, and the API NH kit. PCR-based serogrouping of isolates Serogroups could not be determined by the slide agglutina- tion method with polyclonal antisera (Difco, Detroit, MI, USA) because frequent non-specific reactions or cross reac- tions were observed. Therefore, serogrouping by poly- merase chain reaction (PCR) was performed. For the detec- tion and identification of serogroups A, B, C, Y, W135, a multiplex PCR was performed simultaneously with oligo- nucleotides in the siaD gene (serogroups B, C, Y, and W135) and in a gene cassette of orf-2 required for the bio- synthesis of the capsule of serogroup A.4 For the detection and identification of serogroups 29E, X, and Z, the ctrA gene, exclusive to meningococci and forming part of the capsule biosynthesis locus, was chosen as the PCR target according to the methods described by Bennett, et al.5 PorA genosubtyping Amplification of the porA gene by PCR and sequencing of the porA variable regions (VR1 and VR2) were performed as described by Sacchi, et al.6 All nucleotide sequences for each VR were aligned with reference to both the nucleotide and the corresponding amino acid sequences through a Web-accessible PorA database (http://neisseria.org/nm/typ- ing/pora) and defined subtype families. Statistical analysis Data collected at the time of the pharyngeal swabs were used for the correlation analysis on carriage of N. meningit- idis. Statistical analysis was conducted for crosstabs in Pearson Chi-Square statistics using the Statistical Package of Social Science software (SPSS, SPSS Inc., Chicago, IL, USA). Two-sided probability values of <0.05 were consid- ered statistically significant. We did not perform multiple comparisons. Yonsei Med J http://www.eymj.org Volume 53 Number 4 July 2012 743