The usefulness of Diffusion-In-Gel-ELISA in clinical practice as illustrated by a Campylobacter jejuni outbreak

In this study, the DIG-ELISA (Diffusion-In-Gel Enzyme Linked Immunosorbent Assay) is presented as a tool for the determination of antibodies with improved quantitation over other solid phase assays. The method combines the diffusion of antibodies in agar with the EIA concept in Petri dishes. Diffusion of native, undiluted sera results in (1) a concentration gradient in the effort to reach equilibrium, i.e., an end point titration; (2) a separation of serum components of different sizes; (3) unlimited possibilities for migrating antibodies to bind antigenic epitopes because of the constant antigen excess. Low affinity antibodies can bind divalently and are more readily detected; and (4) elimination of dilution errors. The combination of undiluted sera and Petri dishes as solid phase also permits a large number of samples to be tested with less effort and simplifies the practical handling of EIAs, including easy coating and washing procedures, reuse of antigen and quantitation by zone areas without instrumentation. Plates can be stored for months and are available for re-examination, demonstration and transport. The whole procedure can be conducted in a closed system, i.e., when testing highly contaminated samples. The usefulness of the procedure is demonstrated by a food-borne outbreak of Campylobacter jejuni. The outbreak involved 86 persons of whom 20% were culture positive in contrast to a seropositivity of 74% with DIG-ELISA. A diffusion time of 24 h was used for diagnostic purposes. Extended diffusion times of 48 h and 72 h were utilized when consecutive series of sera showed identical values after 24 h, indicating high antibody content that resulted in a peak serum (end point). For infectious diseases with a rapid course, this assay could be used as an acute test. With the diffusion step prepared in advance, DIG-ELISA is a ready-to-use test. When frequent sampling of sera is performed in the very early phase of the disease, DIG-ELISA reveals that all Ig-classes can be present at high titer and the diagnostic potential of the immune response is better utilized. The DIG-ELISA has the methodological flexibility and the physical qualities to be an effective, inexpensive technique for quantitation of antibodies at any laboratory.