Spread of Neisseria meningitidis Serogroup W Clone, China

During February 2011–June 2012, invasive infection with Neisseria meningitidis serogroup W was identified in 11 persons in southeastern China. All isolates tested had matching or near-matching pulsed-field gel electrophoresis patterns and belonged to multilocus sequence type 11. The epidemiologic investigation suggested recent transmission of this clonal complex in southeastern China.

N eisseria meningitidis is a major public health threat in many parts of the world, including China. Since 2003, most meningococcal diseases in China have been caused by N. meningitidis serogroups A and C; only 3 cases of serogroup W meningococcal disease were reported before 2011 (1,2). However, during February 2011-June 2012, an increase in invasive disease caused by serogroup W N. meningitidis (11 cases total) was seen in southeastern China. To determine if this serogroup is emerging in China, we analyzed strains from 6 of the 11 infected patients reported during 2011-2012, from 16 of their close contacts, and from 3 serogroup W patients reported during 2006-2008.

The Study
Meningococcal disease is reportable in China. N. meningitidis isolates, cerebrospinal fluid (CSF), and blood samples from persons with invasive disease are forwarded to the Chinese Centers for Disease Control and Prevention (CDC) for serogroup determination by slide agglutination and/or PCR. Strains are further characterized by use of pulsed-field gel electrophoresis (PFGE) after NheI restriction enzyme digestion (3).
During February 2011-June 2012, we observed an increase in invasive meningococcal disease caused by N. meningitidis serogroup W in southeastern China. Of 11 cases total, 9 were diagnosed by strain isolation and 2 by PCR and real-time PCR of CSF samples (Table). Strains isolated from patients 1, 4, and 5 became nonviable during storage in the hospital laboratory. The 6 remaining strains (from patients 2, 3, 7, and 9-11) were submitted to the Chinese CDC along with 16 serotype W strains from close contacts of patients 4, 6, and 8-10. Thus, during 2011-2012, a total of 22 strains were submitted to the Chinese CDC, where they were confirmed as N. meningitidis serogroup W by slide agglutination with specific antiserum (Remel, Lenexa, KS, USA). In addition, CSF samples from patients 1, 4-6, and 8 were submitted and confirmed positive for N. meningitidis serogroup W by PCR and real-time PCR.
The 22 serogroup W strains from 2011-2012 were analyzed by PFGE; for comparison, 3 strains isolated from patients during 2006-2008 were also analyzed. PFGE patterns were distinguishable for 16 of the 22 strains from 2011-2012. Five strains associated with patient 9 and 1 strain isolated from a close contact of patient 4 had PFGE patterns that differed by 1 and 2 bands, respectively, indicating >94% similarity with the dominant pattern ( Of the 11 patients with cases reported during 2011-2012, 4 resided in Guangxi Province, 2 in Guangdong Province, and 1 each in Jiangsu, Zhejiang, Anhui, Henan, and Hunan Provinces (online Technical Appendix, wwwnc.cdc.gov/EID/article/19/9/13-0160-Techapp1.pdf). The median age of patients was 20 years (range 3-46), 9 (81.8%) were male, and all denied recent foreign travel. Three of the 11 patients died of bacteremia. The epidemiologic investigation did not identify any common exposures, social settings, or other connections among the patients.  Since 2003, the annual incidence of meningococcal disease in China has stayed below 0.2 cases/100,000 population. Surveillance data in China suggest a historical trend for seasonal peaks of meningococcal disease during February-April. This peak season corresponds with the spring dry season in China, a time when tourists are most likely to visit the country, especially southern China. Among the 45 cases of meningococcal disease confirmed during 2011-2012 by meningococcal etiology and PCR methods, 11 (24.4%) were caused by serogroup W N. meningitidis ( Figure 2); 8 of these 11 cases occurred during February-April. The 3 cases reported during 2006-2008 occurred during May, June, and October, respectively.

Conclusions
The incidence of serogroup W infections reported during In some African countries, repeated vaccination against N. meningitidis serogroups A and C is thought to have led to a selective increase in the incidence of meningococci of other serogroups, thereby resulting in a changed profile of meningococcal disease (10)(11)(12). Therefore, meningococcal disease caused by N. meningitidis strains that belong to serogroups other than A and C, especially those that belong to hyperinvasive lineages, appears to be an emerging problem in China.
The 11 cases of meningococcal disease caused by ST11 serogroup W N. meningitidis strains described here had successively emerged in southeastern China; furthermore, ST11 serogroup W meningococci were isolated from close contacts of the patients and from healthy carriers. These observations suggest the possible establishment and spread of a clonal complex of serogroup W meningococci in southeastern China. Carriage and transmission of this strain have led to the emergence of ST11 serogroup W organisms as a cause of endemic meningococcal disease. Further epidemiologic and microbiological surveillance is needed for monitoring of meningococcal diseases caused by serogroup W in southeastern China and preventing the spread of this clone to other regions.