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Molecular analysis of 103 serogroup A Neisseria meningitidis strains isolated in Moscow from 1969 to 1997 showed that four independent clonal groupings were responsible for successive waves of meningococcal disease. An epidemic from 1969 to the mid-1970s was caused by genocloud 2 of subgroup III, possibly imported from China. Subsequent endemic disease through the early 1990s was caused by subgroup X and then by subgroup VI, which has also caused endemic disease elsewhere in eastern Europe. A 1996 epidemic was part of the pandemic spread from Asia of genocloud 8 of subgroup III. Recent genocloud 8 epidemic disease in Moscow may represent an early warning for spread of these bacteria to other countries in Europe.

The genetic variability at six polymorphic loci was examined within a global collection of 502 isolates of subgroup III, serogroup A Neisseria meningitidis. Nine "genoclouds" were identified, consisting of genotypes that were isolated repeatedly plus 48 descendent genotypes that were isolated rarely. These genoclouds have caused three pandemic waves of disease since the mid-1960s, the most recent of which was imported from East Asia to Europe and Africa in the mid-1990s. Many of the genotypes are escape variants, resulting from positive selection that we attribute to herd immunity. Despite positive selection, most escape variants are less fit than their parents and are lost because of competition and bottlenecks during spread from country to country. Competition between fit genotypes results in dramatic changes in population composition over short time periods.

Randomly amplified polymorphic DNA (RAPD) genotyping was applied to one representative strain of each of the 84 electrophoretic types (ETs) of Neisseria meningitidis serogroup A previously defined by multilocus enzyme electrophoresis (MEE) (J.-F. Wang et al., Infect. Immun. 60:5267-5282, 1992). Twenty-seven additional isolates comprising six ETs were also tested. MEE and RAPD genotyping yielded similar dendrograms at the subgroup level. Similar results were obtained by both methods for 18 serogroup A meningococci isolated in The Netherlands between 1989 and 1993. Ten of these isolates defined a new subgroup, designated subgroup IX. One isolate belonged to the ET-5 complex, normally associated with serogroup B strains (D. A. Caugant et al., Proc. Natl. Acad. Sci. USA 83:4927-4931, 1986). By RAPD genotyping, meningococci can be linked to previously characterized genotypes by using a computerized database, and dendrograms based on cluster analyses can easily be generated. RAPD analysis offers advantages over MEE since intermediate numbers of isolates of serogroup A meningococci can quickly be assigned to known subgroups and new subgroups can be defined.

In the study that is described the sensitivities and specificities of three commercial tests and the standard Reference Laboratory test, used since 1961, to identify Neisseria meningitidis serogroups were compared. The tests marketed by Difco, Murex/Wellcome, and Sanofi/Pasteur showed overall sensitivities of 92, 95, and 100%, respectively, and specificities of 67, 88, and 82%, respectively. When limited to the common serogroups A, B, and C, the three tests yielded sensitivities of 93, 97, and 100%, respectively, and specificities of 98, 100, and 98%, respectively. However, determination of the uncommon serogroups X, W-135, Y, Z, and 29E with these tests is either unreliable or not possible.

Acute- and convalescent-phase sera from 40 patients with meningococcal disease were evaluated for immunoreactivity with the meningococcal member of the hsp60 stress protein family. The IgG response was measured by ELISA, using bacterial cell lysate of the corresponding patients' strain, and purified hsp60 proteins from Neisseria meningitidis (MSP63), Escherichia coli (GroEL) and Mycobacterium bovis BCG (65K) as antigens. Analysis of the antibody responses revealed that 24/35 patients (69%) with elevated anti-meningococcal titres, generated anti-MSP63 antibodies during the time course of infection. Twelve of these patients generated antibodies specific for MSP63, in six patients anti-MSP63 levels exceeded anti-GroEL/65K antibodies. In the remaining six patients, equal levels of anti-MSP63 and anti-GroEL/65K were measured. We conclude that MSP63 is expressed and immunogenic during natural meningococcal infection, and that individual subjects have a restricted response to the antigen, resulting in the recognition of Neisseria-specific hsp60 epitopes and/or cross-reactive hsp60 determinants.