False-positive typhidot IgM assay in COVID-19 patients: A potential public health problem in tropical countries during COVID-19 endemic phase

Abstract

BACKGROUND: Since the beginning of the coronavirus disease 2019 (COVID-19) pandemic, reports of false-positive serological test results were reported in COVID-19 patients. Typhidot IgM test is reported in a few studies to give false-positive results in various viral illnesses in the past. The aim of this study was to estimate the typhidot IgM positivity rate in reverse transcription-polymerase chain reaction (RT-PCR)-confirmed COVID-19 patients. MATERIALS AND METHODS: The present study was a cross-sectional study conducted at a tertiary care hospital. All symptomatic patients having fever that were admitted between April 1, 2021, and July 15, 2021, with a confirmed RT-PCR-positive result for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) were included in the study. Serological testing was done by typhoid IgM/IgG rapid diagnostic test for all SARS-CoV-2 RT-PCR-positive patients. The primary outcome studied was to estimate the typhidot IgM positivity rate among RT-PCR-confirmed COVID-19 patients. The secondary outcome studied was to determine the correlation between SARS-CoV-2 RT PCR cycle threshold (CT) value and typhidot-positive result. RESULTS: Three hundred and five (17.99%) out of 1695 samples of confirmed COVID-19 patients were positive for typhoid serology by typhidot IgM test. However, upon performing Point-Biserial correlation analysis (P = 0.832, r = 0.021), no correlation was seen between RT-PCR CT value and typhidot result. CONCLUSIONS: Typhidot test is a nonspecific diagnostic test for typhoid fever which can be false positive in COVID-19 patients. Hence, physicians should take this into consideration to avoid misdiagnosis and delay in accurate treatment of acute febrile illness cases, especially in the present scenario of COVID-19 endemicity.

Keywords

• coronavirus disease 2019
• enteric fever
• false positive
• serology
• typhidot