Several control variables were included in multivariable regression models based on the existing literature [1 , 2 , 6 , 8 (link)]: sex (male/female), age (age groups 0–4, 5–9, 10–14, 15–24, 25–44, 45–65 and 65+), rurality/urbanicity, travel abroad status (yes/no), organism identified (Salmonella Typhi, Paratyphi A and Paratyphi B) and antibiotic administration (yes/no). Antibiotic administration was included as a control variable as it can reduce the severity of symptoms [1 ]. Urbanicity–rurality data were obtained through LSOA codes classification from Office for National Statistics (ONS) Geography [14 ].