Patients suspected with infection is one of the major groups, who are admitted to the Danish Emergency Departments (ED). Currently, there is no overall description of the distribution of these infections. The aim of this study is to characterize ED patients with a suspected infection whereby the focus of the infection is of an unknown origin.

Bacteria resistant to antibiotics are associated with high antibiotic consumption and are identified by the World Health Organisation as a major public health threat. Despite efforts to optimize antibiotic consumption in Denmark, the total consumption in the hospital sector increased from 2009-2018 and the incidence of multi-resistance bacteria (MRB) is increasing. A Danish multicenter study has shown that every 20th patient in the emergency department has MRB. Patients with an infection of unknown origin tend to be prescribed a broad-spectrum antibiotic, as physicians endeavour to target probable origins in the body. The uncertainty associated with the diagnosis may lead to an overconsumption of antibiotics, which contributes to increased development of resistant bacteria and threatens future treatment options.

The aim of this study is to characterize patients admitted to the ED suspected with infection. The study will have three objectives:

• To describe the distribution of ED infections according to the registered diagnosis in the medical record compared to a clinical expert panel assessment
• To identify clinically relevant information available at admission associated with a patients infection of unknown origin.
• To investigate the association between an adverse event and clinically relevant information for patients with infection of unknown origin

The investigators' hypothesis is that with an improvement of knowledge about patients with an infection of unknown origin, a more accurate diagnosis can be made leading to a more appropriate antibiotic therapy and contributing to the fight against resistance to antibiotics.

Inclusion Criteria:

• Adults admitted to the ED will be invited to participate in the study, if the physician, receiving the patient, suspect the patient has an infection (e.g. indication for blood culture).

Exclusion Criteria:

• If the attending physician considers that participation will delay a life-saving treatment or patient needs direct transfer to the intensive care unit.
• Admission within the last 14 days
• Verified COVID-19 disease within 14 days before admission
• Pregnant women
• Severe immunodeficiencies: Primary immunodeficiencies and secondary immunodeficiencies (HIV positive CD4 <200, Patients receiving immunosuppressive treatment (ATC L04A), Corticosteroid treatment (>20 mg/day prednisone or equivalent for >14 days within the last 30 days), Chemotherapy within 30 days)

Acutely admitted patients suspected with infection at three hospitals in the region of Southern Denmark - Hosptial Sonderjylland, Hospital Lillebaelt and Odense University Hospital.