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Neisseria meningitidis serogroup Y (NmY) with resistance to penicillins and fluoroquinolones (dual-resistant) was first reported in 2020.1,2 Since then, an increase in cases of invasive meningococcal disease caused by dual-resistant NmY sequence type (ST) 3587, clonal complex (CC) 23, has been reported in the United States (U.S.).3

ingitidis serogroup Y (NmY) with resistance to penicillins and fluoroquinolones (dual-resistant) was first reported in 2020.1,2 Since then, an increase in cases of invasive meningococcal disease caused by dual-resistant NmY sequence type (ST) 3587, clonal complex (CC) 23, has been reported in the United States (U.S.).3 On April 24, 2024, the California Department of Public Health contacted the Centers for Disease Control and Prevention (CDC) regarding a dual-resistant isolate identified by a hospital laboratory. The state public health laboratory determined this isolate to be serogroup W (NmW) by both slide agglutination serogrouping (SASG) and polymerase chain reaction (PCR). Whole-genome sequencing (WGS) at CDC indicated the isolate was ST-3587 CC23 and possessed the previously reported genetic indicators of dual-resistance.2 Additionally, this isolate was very closely related4 to others in the ST-3587 dual-resistant clade at 15 single nucleotide polymorphisms (SNPs) away from the most closely related isolate in that clade. However, unlike previously reported ST-3587 CC23 strains which were NmY2, this isolate possessed serogroup W capsular genes suggesting serogroup switching to NmW. Phenotypic characterization at CDC supported the genomic results. Sequencing of additional recent isolates at CDC revealed two more ST-3587 CC23 dual-resistant isolates from Texas that were serogroup B (NmB). All three isolates fell within the U.S. dual-resistant clade (Figure 1), with 15–29 SNP differences between them and their nearest NmY dual-resistant neighbors. The two closely related Texas isolates had only four SNP differences. All three cases occurred in persons of Hispanic ethnicity with no known epidemiological links. None reported recent travel prior to illness; all survived.

ure 1), with 15–29 SNP differences between them and their nearest NmY dual-resistant neighbors. The two closely related Texas isolates had only four SNP differences. All three cases occurred in persons of Hispanic ethnicity with no known epidemiological links. None reported recent travel prior to illness; all survived. Rapid serogroup switching in N. meningitidis has been previously reported5; however, serogroup switching in ST-3587—a strain that has driven increased ciprofloxacin resistance—is concerning and requires a shift in testing strategy to ensure timely testing for ciprofloxacin resistance in serogroups other than NmY. CDC has requested jurisdictional health departments submit all N. meningitidis isolates to CDC at least every other month for timely antibiotic resistance surveillance to inform potential changes in prophylaxis guidance. Public health departments may reference Berry, et al3 for guidance regarding when to consider antibiotic alternatives to ciprofloxacin for post-exposure prophylaxis in close contacts of patients with invasive meningococcal disease. Clinicians and public health practitioners should be aware that the N. meningitidis ST-3587 dual-resistant strain that has caused most ciprofloxacin-resistant cases in the U.S. may not be limited to serogroup Y.