Evaluation of a rapid fluorescence immunoassay for detecting Campylobacter antigens in stool samples

The species most frequently causing campylobacteriosis are Campylobacter jejuni and Campylobacter coli, followed by Campylobacter fetus, Campylobacter upsaliensis, and Campylobacter lari. Although polymerase chain reaction (PCR) can be used to detect Campylobacter DNA in stool samples, PCR assays are often validated for C. jejuni and C. coli only, and coproculture results can take several days to receive. For laboratories that do not have access to PCR technology, rapid antigen tests can be of the utmost importance for early diagnosis of the disease. We evaluated the performance of the Sofia Campylobacter Fluorescence Immunoassay (SCFIA) for rapid detection of Campylobacter antigens in stool.

In total, 94 frozen and 205 fresh stool specimens were included in retrospective and prospective evaluations, respectively. The linearity of the assay and its limit of detection for different Campylobacter species was evaluated using serial dilutions. Cross reactivity to phylogenetically related species was also investigated. The PCR results from the BD MAX Enteric Panel were considered the gold standard.

The sensitivity of the SCFIA was 97.87% and 96.88% in retrospective and prospective evaluations, respectively. The specificity was 98.84%. The assay exhibited high linearity in serial dilutions for C. coli, C. jejuni, C. armoricus, C. ornithocola, C. lari, and C. upsaliensis, with correlation coefficients of 0.991-0.999, whereas C. fetus was not detected. No cross-reactivity was detected for Aliarcobacter butzleri, Helicobacter cinaedi, or Helicobacter pullorum. The minimum concentration for a positive result at the assay-specific cut-off was 4-17 million CFU/mL. The limit of detection ranged from 10⁶ to 10⁷ CFU/mL.

SCFIA results are highly correlated with PCR results, with no cross-reactivity with phylogenetically related species. The linear correlation between fluorescence and CFU/mL results was strong. The assay's ability to detect antigens of various Campylobacter species can aid early diagnosis. However, the inability to detect C. fetus must be considered.