Mix-infection of S. typhi and Paratyphi A in Typhoid Fever and Chronic Typhoid Carriers: A Nested PCR Based Study in North India


Chandra Bhan Pratap, Gopal Kumar, Saurabh Kumar Patel, Vijay K Shukla, Kailash Kumar, Tej Bali Singh, Gopal Nath.


Introduction: Enteric fever is a systemic disease caused by Salmonella organism such as serotypes Typhi and Paratyphi A, B, C. Salmonella Paratyphi A contributes more than 50% of all the enteric fever cases and it has recently been projected as an emerging pathogen.

Materials and Methods: The present study was aimed to detect Salmonella Typhi and Paratyphi A in urine, blood and stool specimens collected from cases of enteric fever (110), chronic typhoid carriers (46) and healthy controls (75) to explore the possibility of mixed infection by nested PCR. A new nested PCR primer was designed targeting putative fimbrial protein ( stkG ) gene which is one of the fimbrial gene families to Salmonella Paratyphi A and for S. Typhi already reported primers targeting flagellin ( fliC ) gene.

Results: Large volume of urine specimens (15 ml) was found to be the best for detection of Salmonella serotypes. The urine sample was found to have mixed-infection by both the serotypes in 40.9% of the cases but lower in blood (27.3%) and stool (13.6%).

Conclusion: The present study concludes that occurrence of mixed infection may be quite frequent in typhoid and chronic typhoid carriers’ individuals, although the reported recent rise in Paratyphi A incidence may not be real.


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