Objective To analyze the etiological and epidemiological characteristics of the first case of Neisseria meningitidis Y infection in Yulin, Guangxi Zhuang autonomous region.

Methods On January 5, 2024, a field investigation was condcuted in the school where the epidemic occurred by local center for disease control and prevention and face-to-face interview of the close contacts was conducted. The blood samples, cerebrospinal fluid samples and nasopharyngeal swabs of the cases were collected for the isoaltion, culture and identification of N. meningitidis. The drug susceptibility test, fluorescent polymerase chain reaction, whole genome sequencing, and single nucleotide polymorphism （SNP） analysis were performed.

Results The cases were two 15-year-old high school students, twin brothers. A total of 16 N. meningitidis strains were isolated from 2 cases and 53 close contacts, of which 15 N. meningitidis strains belonged to serogroup Y and 1 strain belonged to serogroup B. The sequence type of 14 N. meningitidis strains was ST-1655, which belonged to the ST-23 clonal group （cc23）, and 1 N. meningitidis Y strain and 1 N. meningitidis B strain were all ST-7962 and they were not been classified into any clonal group. The genome size of the N. meningitidis isolates was 2.07−2.08 Mbp, and the GC content was 51.88%−51.91%. Genome-wide SNP phylogenetic tree analysis showed that 16 N. meningitidis isolates were clustered in 2 branches. The results of in vitro drug susceptibility test showed that 14 N. meningitidis Y strains was all resistant to cotrimoxazole, and the sensitivity rate to levofloxacin was 78.57%. They were senstive to other 9 antibiotics: i.e. penicillin, ampicillin, meropenem, ceftriaxone, chloramphenicol, minocycline, azithromycin, rifampicin and ciprofloxacin.

Conclusion This was the first epidemic of N. meningitidis Y cc23 infection reported in Yulin, and the carriage of N. meningitidis Y cc23 was also detected in healthy population, indicating the potential of the epidemic in Yulin, and the N. meningitidis strains were all resistant to cotrimoxazole and 78.57% were sensitive to levofloxacin. It is necessary to further strengthen the etiological surveillance for the infection of N. meningitidis Y, and pay attention to the selections of preventive drugs, treatment drugs, and vaccination.