Summary auto-generated
Researchers developed a simple adherence test to detect IgM antibodies against Salmonella typhi, the causative agent of typhoid fever. The test uses an IgM-capture approach where serum samples are applied to microtitration plates coated with anti-human IgM, followed by stained S. typhi antigen suspensions. Among 61 confirmed typhoid cases, 95% tested positive for IgM antibodies to H or O antigens. In 76 patients diagnosed with typhoid based solely on Widal test results, 41% were IgM-positive. Importantly, no cross-reactivity occurred with sera from patients with leptospirosis, typhus, or dengue fever, and normal sera showed minimal reactivity. The method proved simple, economical, and sensitive compared to existing serological tests. Some cross-reactivity with S. paratyphi antigens was observed, particularly with O antigens. The test's main advantage is requiring only a single serum specimen, making it valuable for diagnosis in endemic areas where paired sera collection is impractical. The authors suggest this test could serve as either a primary diagnostic method or confirmatory test following Widal screening.
Key findings
- The IgM adherence test detected IgM antibodies in 95% of confirmed typhoid cases (58 of 61 patients), with high sensitivity to S. typhi H and O antigens
- The test showed excellent specificity, producing no false positives in sera from patients with leptospirosis, typhus, or dengue fever
- The method is simple, economical, and requires only a single serum specimen, unlike traditional Widal tests which require paired sera for meaningful interpretation
- Some cross-reactivity with S. paratyphi A and B antigens was detected, particularly for O antigens (33% of reactive sera)
- Among patients with elevated Widal titers but no culture-confirmed typhoid, only 41% were IgM-positive, suggesting many had false-positive Widal results from anamnestic responses
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Abstract
A simple adherence test to detect IgM antibodies in patients with typhoid is described. The test utilises the IgM-"capture" approach, in which the test serum is applied to microtitration plate wells previously coated with anti-human IgM, followed by application of a stained Salmonella typhi antigen suspension which shows adherence in positive cases. By this test, 58 (95%) of 61 sera from confirmed cases of typhoid possessed IgM antibodies to the H or O or both antigens of S. typhi. In patients for whom a diagnosis of typhoid was based only on a significant Widal-test titre, 31 (41%) of 76 sera had IgM antibodies to the H or O or both antigens of S. typhi. Some cross-reactivity of the IgM antibodies was detected, especially with the O antigens of S. paratyphi A and B. A total of 82 sera from non-typhoidal fevers (leptospirosis, typhus, dengue fever) showed no reactivity in this test. In normal sera there was no detectable IgM to the O antigen of S. typhi and only a small number (3.9%) had low levels of IgM to the H antigen. The significance and potential importance of this simple, sensitive, specific and economical test is discussed.