New rapid test for paratyphoid a fever: usefulness, cross-detection, and solution

Diagn Microbiol Infect Dis. 2008 Oct;62(2):142-50. doi: 10.1016/j.diagmicrobio.2008.07.002. Epub 2008 Aug 20.


We described a 5-min colorimetric test for paratyphoid A fever, which detects anti-Salmonella O2 antibodies by inhibiting the binding between 2 types of reagent particles. This test (TUBEX-PA) is based on that (TUBEX-TF) used for typhoid fever, which detects anti-O9 antibodies. TUBEX-PA showed a sensitivity of 81.0% (47/58 culture-confirmed patients) to 93.3% (14/15) and was 98.1% (52/53) specific for healthy subjects. However, TUBEX-PA also detected 50% (7/14) to 81.8% (9/11) of typhoid patients, and conversely, TUBEX-TF detected 46.7% (7/15) to 73.3% (11/15) of paratyphoid A cases. This cross-detection could be abrogated in both tests by adding a blocker (heterologous antigen) to remove the antibodies responsible, which presumably bind to a common antigen (O12) located close to O2 and O9. The presence of anti-O12 antibodies in typhoid (9/12 or 75.0% sensitive) and paratyphoid A (22/33 or 66.7%) patients was demonstrated directly using a prototypic TUBEX test designed specifically to detect these antibodies. Thus, using TUBEX-PA and TUBEX-TF together can increase the diagnostic accuracy of detecting both typhoid and paratyphoid A fever, while the further use of differential tests allows possible immediate discrimination between these diseases.

Publication types

  • Evaluation Study

MeSH terms

  • Adolescent
  • Adult
  • Antibodies, Bacterial / blood*
  • Child
  • Child, Preschool
  • Colorimetry / methods*
  • Humans
  • Immunoassay
  • Middle Aged
  • O Antigens / immunology*
  • Paratyphoid Fever / diagnosis*
  • Paratyphoid Fever / microbiology
  • Reagent Kits, Diagnostic*
  • Salmonella paratyphi A / classification
  • Salmonella paratyphi A / immunology*
  • Serotyping
  • Time Factors


  • Antibodies, Bacterial
  • O Antigens
  • Reagent Kits, Diagnostic