Carriage of N. meningitidis in Freshmen able with a change in PorA type from P.1.18-21,25-39 to P1.18-21,25-40. DISCUSSION Asymptomatic pharyngeal colonization of N. meningitidis in young adults is relatively common and an age-dependent phenomenon, with point prevalence carriage rates usually ranging from 10% to 35%.7,8 Neal, et al.9 performed a longi- tudinal study and reported that carriage rates of meningococ- ci among university students increases rapidly throughout the first week of the term from 6.9% on day 1 to 23.1% on day 4. The average carriage rate during the first week of the term was 13.9%, with further increases throughout the term to 31.0% after one month. They also identified active smoking, intimate kissing and visiting nightclubs as risk factors for ac- quisition. To gain information concerning the pharyngeal carriage of N. meningitidis among freshmen aged 20-22 years in Korea, those admitted to Inha University dormitory were enrolled in our study. Each student was swabbed twice at an interval of four weeks between cultures. We maintained the same swabbing technique using the same trained opera- tors and culture conditions throughout the study to mini- mize the influence of confounding factors. In our results, the overall carriage rate was 11.8% (16/136) at the first culture, which is comparable with those reported in Western coun- tries. However, the overall carriage rate did not significantly increase from 11.8% to 14.1% after 4 weeks. A few expla- nations may explain this result. In fact, the prevalence of known risk factors for acquisition among the students was lower compared to Western studies. The prevalence was 4.41% (6/136) for active smoking, 10.29% (14/136) for inti- mate kissing and 1.47% (2/136) for visiting nightclubs at the first culture in our study. In comparison, in a study for social behavior and meningococcal carriage among British teenag- ers,10 the corresponding prevalence was 21.48% (2936/ 13668), 44.77% (6133/13697) and 62.06% (8447/13611), re- spectively. Lower prevalence of risk factors for acquisition in our study could explain the insignificant change of carriage rates over 4 weeks, to a certain extent. Furthermore, it might have been influenced by the difference in social behavior patterns of Korean students, which is more reserved, less communicative, resulting in decreased social mixing. There- fore, different results may be shown if we examined the stu- dents for longer periods of time. Table 4. Prevalence of the Neisseria meningitidis Genosub- types of 18 Meningococcal Isolates at the Second Culture Genosubtype Serogroup (number of isolates) P1.5,2-65 B (1) P1.5-1,2-2 W135 (1) P1.7,2-1 Non-groupable (1) P1.7,13 Non-groupable (1) P1.7-2,13-1 Non-groupable (1) P1.18,25-7 Non-groupable (1) P1.18,25-11 Non-groupable (1) P1.18,25-38 C (1) P1.18-21,25-40 Non-groupable (1) P1.19,15 B (2), 29E (1) P1.19-5,14-6 B (1) P1.22, 14-6 C (4) P1.22-4, 14-6 C (1) A number of risk factors have been shown to be associat- ed with meningococcal carriage. There are slightly fewer carriers in females than in males. Those with viral or bacte- rial respiratory tract infections could be at high risk to be- come carriers.11 Smoking, whether active or passive, is one of the strongest risk factors for becoming a meningococcal carrier12-14 and low socioeconomic position in some popula- tions appears to raise the risk of carriage.15 These risk factors are known to be independently correlated with carriage. Also, concerning the effect of bringing together groups of young adults, there was a study which identified a higher carriage rate in catered halls than in self-catered halls.9 On the other hand, it was reported that there was no evidence that increasing levels of crowding was associated with in- creasing levels of meningococcal carriage.10 The Inha Uni- versity dormitory where our study was performed is a ca- tered hall of residence with around 1000 students, and four students usually share a room which has an area of 21.49 m2. Interestingly, active smoking, visiting nightclubs, inti- mate kissing, travel abroad, and recent symptoms of upper respiratory tract infection were not significantly associated with being a carrier at our first culture. This might be be- cause the number of carriers in our study was too small to draw a meaningful interpretation. Indeed, students who smoked, kissed or visited nightclubs were small in number as shown in Table 2. It might also reflect cultural character- istics in Korea, which are less permissive. Nonetheless, vis- iting pubs was correlated with meningococcal carriage at both the first (p=0.047) and second cultures (p=0.026), which was similar to other studies. We also noted that there was no carriage at the first culture among 12 students who had a history of antibiotics use. This was probably because antibi- Yonsei Med J http://www.eymj.org Volume 53 Number 4 July 2012 745