Emergence of a Dominant Clone of Neisseria Meningitidis Serogroup W135 in Southeast Florida, 2008-2012

BACKGROUND: Beginning in 2008, a clone of Neisseria meningitidisserogroup W135, multilocus sequence type 11 clonal complex, was identified in Broward, Miami-Dade and Palm Beach counties. Since publication of the first 14 cases reported in 2008 and 2009, the clone has continued to spread and is now the predominant cause of invasive meningococcal disease in southeast Florida. The aim of this study is to describe the changing epidemiology of meningococcal disease in the region.

METHODS: All reported culture-confirmed cases of meningococcal disease in Florida from 2008 through 2012 were aggregated from the Florida reportable disease database. Southeast Florida was defined as Broward, Miami-Dade, and Palm Beach counties.  Isolates of N. meningitidiswere sent to the Florida Department of Health Bureau of Public Health Laboratories for serogrouping, and pulsed-field gel electrophoresis (PFGE) was performed on serogroup W135 isolates. Incidence rates were calculated using annual population estimates.  Geographic, demographic, clinical and microbiological characteristics of cases were compared.

RESULTS: From 2008 through 2012, 251 cases of meningococcal disease were reported in Florida; 79 (31%) were serogroup W135. Of the 120 cases of meningococcal disease from southeast Florida, 72 (60%) were identified as serogroup W135. Of 76 serogroup W135 isolates from across Florida that underwent PFGE, 72 (95%) were >95% similar. Of these, 70/72 (97%) were from southeast Florida. The incidence rate of meningococcal disease caused by serogroup W135 in southeast Florida increased from 0.4 to 3.4 cases per 1,000,000 from 2008 to 2012 (chi-square trend, p<0.01).  This has driven an overall increase in the incidence rate of meningococcal disease in the region, from 2.7 to 5.4 cases per 1,000,000 from 2008 to 2012 (chi-square trend, p=0.03). During the same time period the incidence rate of meningococcal disease in other Florida counties decreased from 2.5 to 1.0 cases per 1,000,000 (chi-square trend, p<0.01). Patients with the southeast Florida W135 clone were older (Median age of 50 vs. 34 years, U-test p<0.01), more likely to be Hispanic (54% vs. 20%, p<0.001), of Black race (29% vs. 19%, p=0.07), or have meningococcemia (86% vs. 62%, p<0.001) than cases with other genotypes. Mortality and hospitalization rates were similar.

CONCLUSIONS: The emergence of a dominant clone of N. meningitidis serogroup W135 in southeast Florida has resulted in changes in clinical presentation and epidemiology, including increased incidence of invasive meningococcal disease.  The dominance of serogroup W135 in southeast Florida should be considered when developing local meningococcal disease vaccine recommendations.