Invasive non-typhoidal Salmonella infections: A regional UK-based retrospective narrative cohort analysis.

Background
Infections due to non-typhoidal Salmonella (NTS) are common, linked to food-borne exposure or overseas travel. While most cases are self-limiting, invasive non-typhoidal Salmonella (iNTS) infection can arise, presenting with bloodstream, CNS, bone and joint, or endovascular infection. Commonly affecting those at the extremes of age or the immunocompromised, these result in significant morbidity and mortality. We aimed to characterise cases of iNTS infection in a UK-based setting, exploring clinical syndromes, outcomes and antimicrobial susceptibilities.

Methods
Isolates of NTS from usually sterile sites (blood, CSF, tissues or fluids) were identified through an electronic laboratory database, incorporating three NHS trusts in South West England, from October 2016 to November 2022. Retrospective narrative analysis of identified cases was performed, reviewing data from clinical notes on demographics, risk factors, source, severity, sequelae, outcomes and management.

Results
Twenty-six episodes of iNTS infection were identified, in 25 patients, with a median age of 51 years (IQR 22.3y-67.8y), further illustrated in Figure 1. Four cases were in children, seven in patients >65 years and 50% in females. Twenty-one cases (81%) were bacteraemias, with no instances of meningitis. The most commonly identified serovar was S.enteritidis (38%). Pre-disposing risk factors were identified in 16 cases (62%), most frequently cardiovascular disease, type 2 diabetes mellitus, and malignancy. Twelve cases (46%) described recent foreign travel. Seventeen cases (65%) had preceding gastro-intestinal symptoms, however in nine (35%) a primary source was not established. The median duration of hospital stay was eight (range 2-241) days, with 13% one-year mortality. Twenty-five isolates (96%) had antimicrobial susceptibility testing performed, with 80% susceptible to all first-line antibiotics (amoxicillin, ceftriaxone, ciprofloxacin). Only two isolates (8%) displayed resistance to ciprofloxacin.

Conclusions
Our study describes current trends of iNTS infection in a UK-based cohort. Younger females and older males tended to be affected. Given that infections largely occurred in those with comorbidities, who are already at risk of prolonged hospital stays or death, further work investigating the interplay between multi-morbidity and iNTS disease is important, particularly in aging populations. Although a precise source may never be identifiable, travel history remains an important factor to elicit. Isolates were largely susceptible to first-line antibiotics.