BACKGROUND: Serogroup W meningococcal disease, caused by the bacterium Neisseria meningitidis, is a rare but severe infection. Following a serogroup W outbreak after the Hajj in 2000, serogroup W disease, predominantly caused by sequence type-11 clonal complex, has rapidly increased in South Africa, South America, and the United Kingdom. We describe the epidemiology of serogroup W meningococcal disease in the United States during 2010–2015.
METHODS: Data were collected from the National Notifiable Disease Surveillance System, Active Bacterial Core surveillance, and state health departments. Isolates were serogrouped via slide agglutination and real-time polymerase chain reaction. For cases lacking a serogroup result at CDC, the state result was used. Case-fatality ratios (CFR) were calculated using the proportion of cases with known outcomes as the denominator. Clonal complex (cc) and sequence type (ST) were determined using multilocus sequence typing (MLST).
RESULTS: From 2010–2015, 3,504 meningococcal disease cases were reported to CDC; 2,976 (85%) had a serogroup result, of which 290 (10%) were serogroup W. While the number of serogroup W cases reported annually remained fairly stable (range: 40–57), the total number of reported meningococcal disease cases decreased by 60%, and the proportion of cases due to serogroup W increased from 6% (42/830) in 2010 to 12% (40/332) in 2015. The majority of serogroup W cases were reported from five states: Florida (n=106), California (n=31), New York (n=25), Georgia (n=19), and Oregon (n=11). Half (50%) of people with serogroup W disease were male, 185 (64%) were white, and 84 (29%) were Hispanic. Median age was 51 years (interquartile range: 26–70). Overall, 20% (52/259) of serogroup W cases were fatal, as compared to CFRs for serogroups B (15%), Y (18%), or C (24%). Serogroup W CFR was highest among adults aged 50–59 years (38%). MLST results were available for 119 (41%) of serogroup W cases: 76 (64%) were cc11, 40 (34%) were cc22, and 1 each were cc23, cc32, and an unassigned cc. cc appeared to be geographically-associated: cc11 was concentrated in Florida and Georgia, while cc22 predominated on the West coast. Within cc11, the majority of isolates (86%) were ST-11, and within cc22 the majority (73%) were ST-22.
CONCLUSIONS: A rapid increase in serogroup W disease has not been observed in the United States. The majority of serogroup W cases were reported in a limited number of states, with geographic differences in clonal complex.