Meningococcal Disease in Alaska: Recent Changes in Circulating Serogroups

BACKGROUND:  Neisseria meningitidis (Nm) is a gram-negative diplococcus that caused 800–1200 cases of invasive infection annually in the U.S. during 2005–2011. Invasive Nm disease is fatal in 5–15% of cases, and 11–19% of cases result in long-term disability. Serogroups B, C, and Y cause the majority of disease nationally. Invasive cases of Nm are reportable to the Alaska Section of Epidemiology (SOE). Until 2013, most meningococcal disease in Alaska was caused by serogroup B. This report characterizes the recent emergence of serogroup C Nm cases in Alaska.

METHODS:  We reviewed 2004–2015 Nm case reports in the SOE database to examine the changing epidemiology of Nm cases in Alaska. Serogroup testing and whole genome sequencing (WGS) were performed by the CDC’s Arctic Investigations Program and CDC-Atlanta, respectively.

RESULTS:  During 2004–2015, 42 cases of invasive Nm were reported to SOE, four of which occurred in non-Alaska residents who became ill while working in or visiting Alaska. Nineteen (45%) of the cases were White, and 16 (38%) were Alaska Native.  Five (12%) of the cases resulted in death. Clinical diagnoses included meningococcemia (35%), meningitis (60%), and pneumonia (5%). During 2004–2012, the predominant serogroup was B (79% of cases); since 2013, all eight cases were serogroup C. Six of the eight serogroup C isolates identified since 2013 were genetically related; clonal complex CC-11ET-37 by multi-locus sequence typing. No epidemiologic link was identified among the infected patients. Among the eight cases, one was aged <11 years, three were aged 11–25 years (all unvaccinated), and four were aged >25 years.

CONCLUSIONS:  Prior to 2013, most meningococcal disease in Alaska was caused by serogroup B Nm. Since 2013, all cases have been serogroup C, and six of the cases were caused by a single Nm clone. To our knowledge, a recent serogroup shift from B to C has not been seen elsewhere in the U.S. Some recent Nm cases occurred in unvaccinated person and were potentially vaccine-preventable.