Shigella flexneri O-antigen-specific enzyme immunoassay: class-specific antibody titres against lipopolysaccharide antigens in healthy Vietnamese and Swedish populations

Abstract

Sera collected from 397 healthy Vietnamese individuals, living in two districts in the surroundings of Hanoi, and 62 healthy Swedish individuals, living in the greater Stockholm area were analysed in enzyme-immunoassays (EIA) for their class-specific immunoglobulin titres against a panel of 10 O-antigen containing lipopolysaccharides (LPS) from Shigella flexneri, Shigella dysenteriae serotype I, Shigella sonnei and Salmonella serogroups A and B. The Vietnamese population was divided into age groups: 0·1–5 year, 1–2, 3–4, 5–9, 10–14 years, etc. Young Vietnamese children had low anti- S. flexneri LPS IgA, IgG and IgM titres which reached adult levels for IgA in the 10- to 14-year-old group, and for IgG and IgM in the 3- to-4-year-old group. The IgA, IgG and IgM titres were significantly higher ( P < 0·001) in sera from Vietnamese individuals than in sera from Swedish individuals. The EIA titres against S dysenteriae serotype 1 and S. sonnei LPSs were higher in the Vietnamese than in Swedish population, but to a lesser extent than seen for S. flexneri. The titres against Salmonella serogroups A and B LPS antigens did not differ significantly in the study populations. These results suggest that the incidence of S. flexneri infections is high in Vietnam, followed in frequency by S. dysenteriae serotype I and S. sonnei infections. On the contrary the incidence of salmonellosis appears to be low.