Rapid Antibody Detection Test for Scrub Typhus

A recent study aimed to assess the diagnostic accuracy of a rapid antibody detection test using IgM immunochromatography for scrub typhus in children. 

In this cross-sectional, children aged 2 months to 18 years who were hospitalized with undifferentiated fever lasting five days or more were enrolled over 18 months. Blood samples were subjected to various serological tests, including – Weil-Felix, Scrub IgM ELISA, immunofluorescence assay (IFA), and the rapid diagnostic test (IgM Immunochromatography). The diagnostic accuracy of the rapid test was evaluated against IFA – considered the gold standard.

The study included 90 children, of whom 43 tested positive for scrub typhus with the gold standard IFA. The rapid diagnostic test demonstrated a sensitivity of 88.3%, a specificity of 89.3%, a positive predictive value (PPV) of 88.3%, and a negative predictive value (NPV) of 89.3%. In comparison, the Weil-Felix test exhibited a sensitivity of 39.5%, a specificity of 84.2%, a PPV of 58.6%, and an NPV of 71.1%. The IgM ELISA showed a sensitivity of 93%, a specificity of 89.3%, a PPV of 88.8%, and an NPV of 93.3%.

Therefore, IgM immunochromatography demonstrated good diagnostic accuracy for scrub typhus in children with acute undifferentiated fever. It can be considered a reliable option for diagnosing scrub typhus in resource-limited settings where IFA is not readily available or is cost-prohibitive.

Source: Narayanappa D, Geetha R, Rajani HS. Indian Pediatrics. 2023 Jul;60(7):546-8.