Febrile agglutinins

Immunoenzymatic dot-blot test for the diagnosis of enteric fever caused by Salmonella typhi in an endemic area

OBJECTIVE: To develop a quick, solid-phase immunoenzymatic test, dot blot, to diagnose typhoid fever by the detection of IgG and IgM antibodies against three Salmonella typhi antigens (lipopolysaccharide, crude and flagellar) and to compare the dot-blot test with an enzyme-linked immunosorbent assay (ELISA) using the same antigens and with the Widal agglutination test. METHODS: Blood culture was used as the definitive test. All tests were used for the study of the sera from three groups of individuals: 33 patients suffering typhoid fever, diagnosed by isolation of S. typhi in blood culture; 35 patients with other enterobacterial infections documented by culture; and 156 asymptomatic volunteers, all residents of the same endemic region (Urabá, Colombia). RESULTS: The best diagnostic efficiency was obtained by detecting IgG against a flagellar antigen dot blot, giving a sensitivity and specificity of 88%. Widal and ELISA tests showed lower diagnostic efficiencies. CONCLUSIONS: The dot-blot test may be useful to diagnose typhoid fever in rural areas lacking technological resources with which to carry out blood cultures or ELISA tests. The visual reading makes this test practical and cheap for these regions.

Serological diagnosis of salmonella infections by enzyme immunoassay

An enzyme immunoassay (EIA) for the detection and measurement of serum IgM, IgG, and IgA antibodies to salmonella was developed with commercially available lipopolysaccharides (LPSs) of Salmonella typhimurium and S enteritidis combined as antigen. Of 130 sera from patients with culture-confirmed salmonella infections, 115 (88.5%) were positive in this assay. The classic Widal agglutination test was positive in only 50 (38.5%) cases. This EIA method offers a substantial advance in the serological diagnosis of acute salmonella infections; it detects antibodies to the salmonellae of groups B and D, which constitute about 70% of culture-positive cases of human salmonellosis. Antibodies to other salmonellae are also detected. This EIA is particularly valuable for the detection of salmonella antibodies during post-infectious complications when isolation of the organism is often no longer possible.