Food-borne salmonellosis is an important public health concern worldwide. This study aimed to characterize the epidemiological patterns and resistance profile of clinical Salmonella enterica strains sent to the National Reference Laboratory for Gastrointestinal Infections of the National Institute of Health Doutor Ricardo Jorge (INSA), between January 2014 and November 2017. During the four-year period of study, 1082 clinical isolates were sent to INSA from several Portuguese hospitals and laboratories. Serotyping was performed according to Kauffman-White-Le Minor scheme and antimicrobial susceptibility was tested according to EUCAST recommendations. Multiple-Locus Variable number tandem repeat Analysis (MLVA) and Whole Genome Sequencing (WGS) was performed for outbreaks identification.
Among the 1082 isolates received, 83.0% were isolate in faeces, 10.8% in blood, 2.1% in faeces and blood, and 4.1% in other biological products. Fifty-five serotypes were identified. The top five most frequent serotypes, Salmonella 4,5:i:- (33.6%), Salmonella Enteritidis (29.3%), Salmonella Typhimurium (18.4%), Salmonella Rissen (2.3%) and Salmonella Typhi (2.3%), accounted for 85.9% of fully serotyped isolates. All cases of S. Typhi were acquired in endemic zones. Antibiotic susceptibility was tested in 943 isolates (2015-2017). Rates of resistance to at least one antibiotic and to ≥ 4 antibiotics were observed in 56.7% and 1.7% isolates, respectively, in either the more frequent serotypes, S. 4,5:i:- and S. Typhimurium, and the more uncommon, S. Brandenburg and S. Infantis. MLVA and WGS allowed the identification of national and multinational outbreaks of S. Enteritidis.
Although overall incidence rates of Salmonella did not change over time, trends and epidemiological factors differed remarkably by serotype. Indeed, there was a significantly increase of S. Enteritidis isolates during this period (2014 – 15.9%; 2015 - 25.0%; 2016 - 31.6%; 2017 - 37.1%). Continued surveillance of susceptibility is important due to the risk of resistance, particularly to fluoroquinolones and 3th and 4th generation cephalosporin’s. A better understanding of Salmonella epidemiology will assist in responding to this disease and in planning and implementing prevention activities.N/
