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Additional file 1: Table S1. Odds ratio of Streptococcus pneumoniae nasopharygeal carriage by hypothesised risk factors. A study among children in kindergartens in Arkhangelsk Russia 2006, N = 438*.

The bacterium Neisseria meningitidis of serogroups A and W-135 has in the recent decade caused most of the cases of meningococcal meningitis in the African meningitis belt, and there is currently no efficient and affordable vaccine available demonstrated to protect against both these serogroups. Previously, deoxycholate-extracted outer membrane vesicle (OMV) vaccines against serogroup B meningococci have been shown to be safe and induce protection in humans in clonal outbreaks. The serogroup A and W-135 strains isolated from meningitis belt epidemics demonstrate strikingly limited variation in major surface-exposed protein structures. We have here investigated whether the OMV vaccine strategy also can be applied to prevent both serogroups A and W-135 meningococcal disease. A novel vaccine combining OMV extracted from recent African serogroup A and W-135 strains and adsorbed to aluminium hydroxide was developed and its antigenic characteristics and immunogenicity were studied in mice. The specificity of the antibody responses was analysed by immunoblotting and serum bactericidal activity (SBA) assays. Moreover, the bivalent A+W-135 vaccine was compared with monovalent A and W-135 OMV vaccines. The bivalent OMV vaccine was able to induce similar SBA titres as the monovalent A or W-135 OMV towards both serogroups. High SBA titres were also observed against a meningococcal serogroup C strain. These results show that subcapsular antigens may be of importance when developing broadly protective and affordable vaccines for the meningitis belt.

Group A streptococcus (GAS) harbours several virulence factors, including M protein (coded by the emm gene) and superantigens (SAgs). SAgs are extracellular toxins that directly activate the immune system by cross-binding to the HLA class II molecule and T cell receptor (TCR), thereby causing activation of up to 30% of the T cells and subsequent massive secretion of cytokines. Forty-eight GAS strains isolated from patients at Norwegian hospitals between 1988 and 2004 were included in this study. Of these, 24 were invasive streptococcal toxic shock syndrome (STSS) or necrotizing fasciitis (NF) isolates and 24 were non-invasive pharyngitis isolates, matched for having the same T-type and year of isolation as the invasive isolates. The isolates were characterized by emm sequence typing, multilocus sequence typing (MLST) and SAg gene profiles. A correlation between T-type, emm type, sequence type and SAg gene profile was revealed. No difference between invasive and non-invasive isolates regarding serotype or genotype was demonstrated. Selected invasive and non-invasive isolates with identical SAg gene profiles were analysed for SAg activity in bacterial growth culture media with and without human cell culture media added. A human T cell proliferation assay was used as measurement for SAg activity and simultaneously we also measured the cytokine content in normal human peripheral blood leucocyte cell culture media. The results revealed that invasive and non-invasive isolates did not differ significantly in SAg activity as it is present in semipurified bacterial culture medium.

The unambiguous identification of epidemic Neisseria meningitidis strains and their clear distinction from other less pathogenic meningococci is required for the global epidemiology of meningococcal disease. Until the recent development of multi-locus sequence typing (1), multi-locus enzyme electrophoresis (abbreviated MEE or MLEE) was the only method to permit large-scale analysis of N. meningitidis strains causing disease in various parts of the world and to document the intercontinental spread of particularly pathogenic organisms (2-8).

In the absence of an affordable conjugate meningococcal vaccine, mass vaccination campaigns with polysaccharide vaccines are the means to control meningitis epidemics in sub-Saharan Africa. Facing global vaccine shortage, the use of reduced doses, which have been shown to be protective by serum bactericidal activity, can save many lives. In this study, we investigated the antibody responses and avidity of IgG antibodies evoked against the serogroup A capsule of Neisseria meningitidis by different doses of an A/C/Y/W135 polysaccharide vaccine. Volunteers in Uganda were vaccinated with 1/10, 1/5 or a full dose (50 μg) and revaccinated with a full dose after 1 year. Specific IgG geometric mean concentrations and geometric mean avidity indices (GMAI) were determined by a modified enzyme-linked immunosorbent assay (ELISA) using thiocyanate as a chaotropic agent. After vaccination with 1/10 or 1/5 doses, the GMAI increased from 1 month to 1 year. One year following the initial dose, the GMAI levels were higher in the arm receiving reduced doses than for the arm receiving a full dose. Following the second full dose, avidity indices equalized at approximately the same level in the three arms. Although there are practical challenges to the use of reduced doses in the field, our findings suggest that reduced doses of polysaccharide vaccine are able to elicit antibodies of as good avidity against serogroup A polysaccharide as a full dose.

By using the techniques of molecular biology, such as multilocus enzyme electrophoresis and multilocus sequence typing, it has been possible to identify the clones of meningococci that have been responsible for major epidemics in the world and to elucidate the routes of spread of these bacteria. Although meningococci can rearrange very rapidly their genome through the process of transformation, some clones or some groups of closely related clones have been stable and have been associated with increases of incidence of disease during decades. A clone with an epidemic potential can be disseminated globally within a few years, but the reasons for the development of an epidemic in a particular population are still not fully understood.

Three hundred and one (301) strains of Neisseria meningitidis serogroup B, isolated from patients with meningococcal disease during the years 1994-1996, were subjected to multilocus enzyme electrophoresis, serotyping, and serosubtyping. Based on the analyses of 14 enzyme loci, 177 electrophoretic types (ETs) were identified. Of these, 136 were represented by single isolates and 41 were represented by multiple isolates (range 2-31). The mean genetic diversity for isolates was 0.444 and for ETs was 0.440. The index of association (I(A)) between loci was 0.530 +/- 0.08 for isolates and 0.256 +/- 0.10 for ETs. Cluster analysis revealed the presence of 39 lineages each represented by a single ET or clusters of ETs. The most common serotypes were 4, 15, and 14 and accounted for 84 (28.0%), 53 (17.6%), and 32 (10.6%) of the isolates, respectively, and were dispersed amongst 46 ETs (1-122), 35 ETs (3-165), and 26 ETs (18-76), respectively. The 109 (36.6%) nontypable (NT) isolates were amongst 74 ETs (6-177). The mean genetic diversity for serotypes 4, 15, and 14 and NT isolates was 0.368, 0.371, 0.343, and 0.442, respectively, and for ETs was 0.363, 0.354, 0.397, and 0.440, respectively. Combinations of serotypes and serosubtypes (number of isolates) that occurred most frequently were 4:P1.14 (17), 14:P1.16 (16), NT:P1.16 (16), 15:P1.16 (13), and NT:P1.13 (13). The majority of group B disease in Canada during 1994-1996 was caused by meningococci of considerable genetic diversity, and reflects a situation of endemic disease. However, the results also indicate that organisms belonging to the ET-5 complex, which has been responsible for outbreaks of group B disease globally for several decades, have been introduced into the country.

Under non-epidemic conditions, Neisseria meningitidis causes disease primarily in children under the age of 5 and the cases are sporadic without any evident relationship between them. Occasionally, localized outbreaks of meningococcal disease occur, and sometimes epidemic waves of disease may spread to several countries or even continents and constitute a pandemic. In the past 10 years or so, population genetic analyses have provided insights into the biology of the bacterium and the epidemiology of meningococcal disease, improving our understanding of the cause of epidemics. Through the application of molecular methods, and especially multilocus enzyme electrophoresis, to N. meningitidis strains of worldwide origin, it has been possible to identify virulent clones and provide a surveillance system to warn of meningococcal epidemics. The characteristics of the predominant clones which are nowadays causing meningococcal disease in the world are summarized here and the importance of population genetics in interpreting the epidemiological data is illustrated.

Beginning in 1988, the incidence of meningococcal disease in the area of greater São Paulo began to surpass the upper confidence limit of an 8-year average incidence (from 1979 to 1986), thus characterizing a new epidemic in the region of greater São Paulo. This epidemic, which extended to 1990, was different from previous epidemics in that it was caused by serogroup B. The increased incidence of meningococcal disease was paralleled by an increased prevalence of a single group B clone, B:4:P1.15, of the ET-5 complex. ET-5 strains have been present in the greater São Paulo area since 1979; however, they have been associated with a high percentage of the group B disease only from 1987 to the present. On the basis of the increased incidence of group B disease in São Paulo, a mass vaccination program with a serotype 4:P1.15 meningococcal protein vaccine was undertaken. The impact of this vaccination program is under analysis.

Serogroup C isolates of Neisseria meningitidis recovered from 121 patients with meningitis or septicemia in Greater São Paulo, Brazil, between 1976 and 1990 were analyzed with respect to serotype and multilocus enzyme genotype. The distribution of serotypes has changed since 1989 when serotype 2b started to replace serotype 2a. There were 48 distinct multilocus genotypes (electrophoretic types [ETs]) and 13 distinct complexes. Among the 41 serotype C:2b:- strains analyzed, 38 (93%) were found in complex 11. The percentage of complex 11 increased from 8% in 1988 to 50 and 66% in 1989 and 1990, respectively. Although we have been in an epidemic situation due to serogroup B:4:P1.15 ET-5 complex since 1988, the appearance and increase of a new unrelated strain, C:2b:- of ET-11 complex, in 1989 and 1990 provide enough data to conclude that the presence of two different complexes, ET-5 and -11, of N. meningitidis were responsible for the high levels of meningococcal disease in Greater São Paulo during this period.