Enteric fever caused by Salmonella enterica serovar paratyphi A: An emerging health concern in Nepal

Enteric fever is an invasive life-threatening systemic disease caused by the Salmonella enterica human-adapted serovars typhi and paratyphi. Increased incidence of infection with S. enterica serovar paratyphi A poses a significant health concern in some areas of the world. In this study, the incidence of enteric fever confirmed by isolation of Salmonella paratypi A or S. typhi from blood cultures of patients presenting with clinical symptoms was 5.1%. Of the total isolates, 64.13% were S. paratyphi A, and 35.87% were Salmonella typhi. All isolates were susceptible to amoxicillin, ceftriaxone and cefixime. Conventional antibiotics (ampicillin, cloramphenicol and co-trimoxazole) showed 100% sensitivity rate towards S. paratyphi A and 96.9% towards S. typhi. Overall nalidixic acid-resistance (NAR) rate was extremely high (92.39%). Nalidixic acid resistant (MIC ≥ 32 µg/ml) S. paratyphi A showed increased MICs of the fluoroquinolone than nalidixic acid resistant S. typhi ranges from 0.125-8 µg/ml with ciprofloxacin and 0.25-4 µg/ml with levofloxacin and was statistically significant (p≤0.001). Immunization with currently available vaccines against typhoid fever does not provide cross protection against paratyphoid fever. This may contribute to the emergence of paratyphoid fever as the major cause of enteric fever in Nepal and possibly other geographical locations.