The 19 isolates belonging to ST-11 showed moderate diversity in restriction patterns (Figure 1).
Although most of the ST-2881 isolates belonged to group W135, their PFGE patterns were unrelated to ST-11 isolates in group W135; they were closely related to ST-2881 invasive strains of serogroup W135 found in 2003 in Niger (16).
Molecular epidemiology of Neisseria meningitidis isolated in the African meningitis belt between 1988 and 2003 shows dominance of sequence type 5 (ST-5) and ST-11 complexes.
Molecular epidemiology of meningococci isolated in Niger in 2003 shows serogroup A sequence type (ST)-7 and serogroup W135 ST-11 or ST-2881 strains.
ST-11 is most commonly associated with the hypervirulent ET-37 complex (6,7).
The absence of the hyper-virulent W-135 ET ST-11 in returning Singaporean pilgrims from the Hajj 2002 is reflected by an absence of Hajj-associated clinical cases of W-135 disease in Singapore in 2002.
The significant decrease of W-135 meningococcal carriage and the absence of ST-11 in returning pilgrims from the Hajj 2002 are important findings with regard to public health policy.