Iqbal Hassan Khan, Md. Abu Sayeed, Nishat Sultana, Kamrul Islam, Jakia Amin, Md. Omar Faruk, Umama Khan, Farhana Khanam, Edward T. Ryan, and Firdausi Qadri
Enteric fever is a systemic infection caused by typhoidal strains of Salmonella enterica, and is a significant cause of mortality and morbidity in many parts of the world, especially in resource-limited areas. Unfortunately, currently available diagnostic tests for enteric fever lack sensitivity and/or specificity. No true clinically practical gold standard for diagnosing patients with enteric fever exists. Unfortunately, microbiologic culturing of blood is only 30-70% sensitive, although 100% specific. Here we report development of a lateral-flow immunochoramatographic dipstick assay based on the detection of Salmonella enterica serovar Typhi (S. Typhi) LPS-specific IgG in lymphocyte culture secretion. We tested the assay using samples from 142 clinically suspected enteric fever patients, 28 healthy individuals residing in an enteric fever endemic zone, and 35 patients with other febrile illnesses. In our analysis, the dipstick detected all blood culture confirmed S. Typhi cases (48/48), and 5 of 6 S. Paratyphi A blood cultured confirmed cases. The test was negative in all 35 individuals febrile with other illnesses and all 28 endemic zone healthy controls. The test was positive in 19 of 88 individuals with suspected enteric fever but negative blood cultures. Thus, the dipstick had a sensitivity of 98% compared to blood culture, and specificity that ranged from 78-100% (70-100, 95% CI), depending on the definition of a true negative. These results suggest that this dipstick assay can be very useful for the detection of enteric fever patients especially in endemic regions.
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