False sero-positivity of Salmonella typhi Specific Antibody in Dengue and Corona Virus Infected Patients: An Observational Study

Abstract

Typhoid fever is a major concern in developing nations. People living in endemic area may frequently get exposed to the typhoid bacilli and can carry some amount of antibody in their circulations which can easily lead to misdiagnosis during other febrile illness. To assess the frequency of false sero-positivity of Salmonella specific antibody in Dengue and COVID-19 patients. An observational case control study was conducted in a multispecialty teaching hospital in north India. A total of 110 serum samples which included dengue IgM positive patients (N= 40), COVID-19 RT-PCR positive patients (N=40) and control subjects (N=30) without any febrile illness were studied. All the samples were tested for Salmonella specific antibody by Widal test and by immune chromatography strip test (ICT). Patient’s detail were documented in a structured Performa. Out of 110 samples 63(57%) were male and 47(43%) were female with age mean age ±45 years. Among the dengue IgM positive patients 8(20%) patients sample showed significant O and H titre of Salmonella typhi (O:80; H:160) in Widal test. Similarly in SARS-CoV-2 RT-PCR positive patients sample 8(20%) patients serum sample showed significant titre of O and H antigen. In control group population significant O antigen along with H antigen of Salmonella typhi were observed in 2(6.6%) sample. False positivity in the serological test should be reported with caution and repeated test should be performed until the etiological agents were not confirmed, in this way we can minimize the misdiagnosis and can prevent the morbidity and mortality as well.