Objectives:

1. To compare the immune response of patients with or without sepsis presenting to the ED with a(n) (suspected) infection.
2. To determine immune response aberrations that are associated with an increased risk of developing sepsis in patients presenting to the ED with a(n) (suspected) infection without sepsis.
3. To determine the long term cognitive and physical sequelae of sepsis after admission.

Sepsis will be defined in accordance with the current Sepsis 3.0 criteria as a(n) (suspected) infection with evidence of organ failure, as reflected by a SOFA (Sequential Organ Failure Assessment) score of ≥2. Notably, a molecular definition of sepsis does not exist and there is no pathological gold standard; therefore, in accordance with the current international consensus, the investigators consider the commonly used clinical organ failure (SOFA) criteria as the best option. The SOFA score is composed of six organ dysfunctions (cardiovascular, pulmonary, renal, hepatic, coagulation and neurological). The SOFA score was developed for ICU patients, but its components can be easily scored in an ED (and hospital ward) setting with the exception of the pulmonary component; this pulmonary dysfunction score is based on the PaO2/FiO2 (PF) ratio, wherein PaO2 is the partial pressure of oxygen in arterial blood and FiO2 the fraction of inspired oxygen. Measurement of the PaO2 requires an arterial blood puncture, which is not routinely done on the ER or hospital ward. Therefore, the investigators will use an alternative method to determine the respiratory SOFA by determining the SpO2/FiO2 (SF) ratio, wherein SpO2 is peripheral oxygen saturation. SpO2 is routinely measured by finger pulse oximeter in patients with suspected infection; FiO2 is 21% when breathing room temperature and increases by 4% with each liter of oxygen provided per minute to a patient via a nasal cannula. Cut-off values for SF ratios correlating with SOFA pulmonary scores based on PF ratios have been validated in large data sets.

Inclusion Criteria:

• Age 18 years or higher
• Presentation at the Emergency Department (ED)
• Clinical suspicion of infection or earlier confirmed infection
• Modified Early Warning Score (MEWS) of 2 or higher

Exclusion Criteria:

• No informed consent given

The research population will include adult patients that present to the ED of participating hospitals. In order to be eligible to participate in the BIOSEP study there must also be a clinical suspicion of an infection or a confirmed infection and MEWS of 2 or higher.