Blood invasiveness of <e1>Salmonella enterica</e1> as a function of age and serotype

We explored the dual influence of the patient's age and the infecting serotype on the blood invasiveness patterns of non-Typhi <e1>Salmonella enterica</e1> (NTS). Blood invasiveness ratio (BIR) was calculated as the ratio between the number of blood and blood+stool isolates. Analysis of 14951 NTS isolates showed that the BIR increased drastically above the age of 60 years, reaching levels 3·5–7 times higher compared to age group &lt;2 years. Different patterns of age-related invasiveness were observed for the five most common NTS serotypes (Enteritidis, Typhimurium, Virchow, Hadar, Infantis). Among children &lt;2 years, the BIR was highest for serotype Virchow and lowest for serotype Hadar, while in persons 60 years it was highest for serotypes Enteritidis and lowest for serotype Infantis. The tendency of NTS serotypes to invade the bloodstream was significantly influenced by the patient's age, however the impact of age differed for various NTS serotypes.