This is a cross-sectional diagnostic cohort study in older adults presenting to primary care, including a follow-up period of 30 days. This study will be used to construct an algorithm consisting of clinical features and blood test results to identify serious infections.~The study will run in general practices in Flanders. Recruitment is expected to last 20 months, with each patient entering the study only once. Older adults will be approached for possible participation in the study by practice staff. There is only one study visit.~Those who agree to participate via written informed consent will have demographics and clinical features recorded. A blood sample will be taken in all participants on study entry. Follow-up information for all participants will be collected using general practice notes (EMD) and patient diaries.~Treatment and other management decisions will be left to the treating physicians' discretion.~If we are unable to reach our predefined sample size in primary care, we will also start recruitment at emergency departments. In that case, we will send an amendment to this protocol to the involved ethics committees.
The aim of this diagnostic accuracy study is to develop a clinical prediction rule based on signs, symptoms, patient characteristics and blood tests, to be used in ambulatory care to help physicians safely rule out a serious infection in an older patient.~It will be performed in general practices across Flanders (Belgium).