Neisseria meningitidis serogroup W135 isolates associated with the ET-37 complex.

To the Editor: As of April 20, 2000, >300 laboratory confirmed cases of meningococcal disease caused by N. meningitidis serogroup W135 (NMW135) have been reported in Saudi Arabia and nine other countries among Hajj pilgrims or their close contacts (1). This is the first reported multinational outbreak of W135 meningococcal disease. NMW135 accounts for <5% of meningococcal disease in the United States and worldwide. The main cause of meningococcal disease outbreaks, especially in the African " meningitis belt, " which extends from Ethiopia in the east to Senegal in the west, has long been N. meningitidis serogroup A. An epidemic, caused by a particular clonal group of serogroup A, identified by multilocus enzyme electrophoresis (MEE) as subgroup (2) and may have caused earlier epidemics in China. In 1987, an outbreak of group A meningococcal disease caused by the same clonal group occurred in association with the annual Moslem pilgrimage to Mecca (Hajj) (3). At that time, Saudi Arabia implemented vaccination requirements for all entering pilgrims. The vaccine formulations vary; bivalent A/C vaccine or quadrivalent A/C/ Y/W135 vaccine (as licensed in the United States) is used. We present molecular characterization results of NMW135 isolates from four U.S. patients with meningococcal disease. These cases were epidemiologically linked to this year's Hajj in Saudi Arabia, which concluded on March 17, 2000 (4). We examine the origin and potential relatedness of the NMW135 isolates to some of the major N. meningitidis virulent clones. Two patients (both vaccinated with quadrivalent A/C/Y/W135 vaccine) were returning pilgrims; one was a close household contact of another pilgrim, the other had other possible contacts with the U.S. pilgrims. Three isolates were identified as NMW135 at the New York City Health Department and the fourth at the California Department of Health. Serogroup identification was confirmed at the Centers for Disease Control and Prevention (CDC) by standard microbiologic methods (5). MEE has long been the standard method for molecular subtyping of N. meningitidis and has allowed identification of several major epidemic prone clones. When the MEE system established by Caugant et al. (6) and that used at CDC were recently compared, they demonstrated excellent correlation segregating individual electrophoretic types (ETs) into similar clusters. A virulent clone, designated ET-37 complex, which contains >50 different ETs, is mainly composed of N. meningitidis serogroup C. In the United States, strains of ET-24 (within the ET-37 complex) are the main cause of meningococcal disease outbreaks …