OBJECTIVES: Collectively, the Hajj and Umrah pilgrimages draw >30 million pilgrims to the Kingdom of Saudi Arabia (KSA) each year. Before Hajj 2024 (14 to 19 June), the meningococcal serogroup W ST-11 complex (W:cc11) Hajj-strain sublineage caused multiple international cases of invasive meningococcal disease (IMD) associated with travel to the Middle East and Asia. Here we identify the strains responsible. METHODS: All Hajj strain sublineage genomes on PubMLST.org underwent core genome MLST comparisons (PubMLST.org). RESULTS: Isolates from 30 cases, across seven countries, formed five phylogenetic clusters within two distinct strains. Travel histories included KSA, other Middle Eastern countries, India, Mauritius, via Turkey, and no known associated travel. The prevalent strain, representing four clusters, had no African, and limited Middle Eastern, representation. The geo-temporal distribution of available genomes suggested Eastern Europe as a possible source. CONCLUSIONS: The rapid expansion of Umrah/travel-related W:cc11 IMD cases in early 2024 was due to multiple strains/sublineages. Despite the involvement of non-KSA travel-destinations, the coincidence of cases with the busy month of Ramadan, and the abrupt cessation during Hajj (when vaccine compliance is maximal), suggest that Umrah was a key driver and highlight the need to reinforce mandatory vaccination whilst maintaining global vigilance.

BACKGROUND: High quality surveillance data are important to monitor U.S. epidemiology of meningococcal disease. Enhanced Meningococcal Disease Surveillance (EMDS) was established in 2015 to collect additional data and isolates from reported cases. METHODS: Epidemiologic information and isolates obtained through EMDS for meningococcal disease cases reported through the National Notifiable Diseases Surveillance System (NNDSS) during 2015-2019 were included in the analysis. Isolates were characterized by serogrouping and molecular typing using either Sanger sequencing or whole genome sequencing. Case fatality ratios (CFRs) were calculated using cases with known outcome as the denominator. Odds ratios (ORs) were calculated using logistic regression. RESULTS: A total of 1,806 meningococcal disease cases were reported during 2015-2019. The average annual incidence was 0.11 cases per 100,000 population. For key variables already collected through NNDSS, EMDS improved completeness over NNDSS by 21%-39% each year during 2015-2019. Completeness of key variables in EMDS improved over time by an average of 18%. Testing of isolates submitted through EMDS showed that serogroups B and C were predominant in all five years. For serogroup B, the most common clonal complex (CC) was CC32 in 2015-2017 and CC41/44 in 2018-2019; for serogroup C, CC11 was most common in 2015-2017 and CC103 in 2018-2019. The CFR was significantly lower for CC103 (6.7%) compared to other CCs (13.6%) (OR 0.44, 95% CI: 0.22-0.89). CONCLUSIONS: U.S. incidence of meningococcal disease remained low during 2015-2019. Data and isolates obtained from EMDS supplement NNDSS and are critical to monitor U.S. meningococcal disease epidemiology.

Invasive meningococcal disease (IMD), caused by infection with the bacterium Neisseria meningitidis, usually manifests as meningitis or septicemia and can be severe and life-threatening (1). Six serogroups (A, B, C, W, X, and Y) account for most cases (2). N. meningitidis is transmitted person-to-person via respiratory droplets and oropharyngeal secretions. Asymptomatic persons can carry N. meningitidis and transmit the bacteria to others, potentially causing illness among susceptible persons. Outbreaks can occur in conjunction with large gatherings (3,4). Vaccines are available to prevent meningococcal disease. Antibiotic prophylaxis for close contacts of infected persons is critical to preventing secondary cases (2).