Areum Durey, et al. Table 1. Carriage Rates of Neisseria meningitidis Number of students swDaabtebionfg Swabbed N.Pmoseintiivnegiftoidris Carriage rate (%) 3-4 March 136 16 11.8 30-31 March 128 18 14.1 Table 2. Correlation Analysis on Carriage of Neisseria men- ingitidis at the First Culture of the 106 Students Who Were Followed Up (Pearson Chi-Square) Positive number of students Exposure Carriers Non-carriers p value (n=16) (n=90) URI symptoms 3 24 0.503 Antibiotics use 0 9 0.073 Travel abroad 2 3 0.111 Active smoking 0 4 0.390 Intimate kissing 3 8 0.233 Visiting nightclubs 1 1 0.164 Visiting pubs 15 63 0.047 URI, upper respiratory tract infection. Table 3. Serogroup Distribution among the Meningococcal Isolates in the 106 Students Who Were Followed Up 1st culture 2nd culture (number of students) (number of students) Serogroup C (5) SNeergoagtrioveupcoCnv(4e)rsion (1) Serogroup B (3) SNeergoagtrioveupcoBnv(2e)rsion (1) Non-groupable (8) NNeogna-gtirvoeucpoanbvleer(s6i)on (2) Serogroup B (2) Initial negative (90) SSeerrooggrroouupp W291E3(51)(1) Negative (86) RESULTS Carriage rates A total of 136 first year students were enrolled at the first culture. After four weeks, 128 students were enrolled at the second culture, including 106 re-participants. The overall carriage rates were 11.8% (16/136) at the first culture and 14.1% (18/128) at the second culture (Table 1). Among the follow-up results for the 106 re-participants who were re- swabbed one month later, carriage rates did not change from the first culture to the second culture at 15.1% (16/106). Of the carriers initially identified, 75% (12/16) were still posi- tive at the second culture. Of the 90 noncarriers who were followed up, 4.4% (4/90) acquired carriage and 95.6% (86/90) remained as noncarriers one month later. Correlation analysis Table 2 shows the correlation analysis on carriage of N. meningitidis at the first culture of the 106 students who were followed up. Active smoking, visiting nightclubs, intimate kissing, travel abroad, and recent symptoms of upper respi- ratory tract infection were not significantly associated with being a carrier. Only “visiting pubs” two weeks before ex- aminations was associated with carriage of N. meningitidis at both the first (p=0.047) and second cultures (p=0.026) in an analysis of the 106 students who were followed up. We also noted that there was no carriage at the first culture among 12 students who had a history of antibiotics use. Serogroups of carrier strains Table 3 summarizes the serogroup distribution among the me- ningococcal isolates in the 106 students who were followed up. Of the 16 total meningococcal isolates of the first culture, serogroup C was found to be the most frequent (5 isolates) and 3 isolates were found from serogroup B. We could not de- termine a serogroup by PCR for 8 isolates (non-groupable, 50%). Four students who were carriers at the first culture were discovered to be negative at the second culture. Two of them were non-groupable, one was from serogroup C and the other was from serogroup B. Of 90 noncarriers followed up, 4 stu- dents acquired carriage one month later at the second culture. Two isolates were from serogroup B, one was from serogroup 29E, and the other was from serogroup W135. PorA genotyping We obtained 18 meningococcal isolates out of 128 students who were enrolled at the second culture and 13 different PorA VR sequences were identified among them (Table 4). The most prevalent PorA types were P1.22,14-6 (4 isolates) and P1.19,15 (3 isolates). PorA types among the serogroup C isolates were relatively uniform, and serogroup C isolates expressing P1.22,14-6 was predominant, accounting for 66.6% (4/6) of all serogroup C isolates. We also analyzed and compared the PorA VR sequences of the 12 students who maintained their carrier state over the 4-week interval between cultures to assess the stability of the porA gene on prolonged carriage. PorA VR2 sequences were changed in 2 students, although their serogroups remained unchanged. One was serogroup B with a change in PorA type from P1.19-5,15-48 to P1.19-5,14-6 and the other was non-group- 744 Yonsei Med J http://www.eymj.org Volume 53 Number 4 July 2012