This study will look for new biomarkers of infection and evaluate current biomarkers of infection in stroke patients. Patients with acute stroke will be monitored with daily blood samples for seven days and by clinical examination to detect infections for 10 days.

Rationale: Stroke is one of the leading causes of death globally, and infections after stroke contribute to a large part of the stroke-related mortality. The current study, which has a prospective, observational design, constitutes the second phase out of four in the Inflammatory Biomarkers In Stroke (IBIS) project, of which the overall goal is to enable early treatment of post-stroke infections.

Aim: To develop a combined clinical and molecular biological signature for early detection of pneumonia in patients with stroke.

Design: Prospective nested case control study

Methods:Patients (n=200) with acute stroke will be monitored with clinical examinations for ten days and by daily blood samples for seven days. When cases of pneumonia have been established, samples and examination results from days preceding overt pneumonia will be compared to samples from similar patients that did not develop pneumonia.

Outcome: Using proteomic and metabolomic methods, novel markers of upcoming pneumonia after stroke will be sought. Such laboratory markers will be combined with current biomarkers (such as C-reactive protein and procalcitonin) and data from clinical examinations, with the aim of constructing a biological signature that enables early detection of pneumonia.

Inclusion Criteria:

• Symptoms and radiology consistent with acute cerebral infarction or atraumatic intracerebral hemorrhage.
• National Institutes of Health Stroke Scale (NIHSS) ≤5; mild stroke (n=25), NIHSS ≤10 and ≥ 6; moderate stroke (n=25) or NIHSS ≥ 11; severe stroke (n=150)
• Onset of symptoms less than 48 hours before first study blood sampling.

Exclusion Criteria:

• Symptoms and radiology consistent with acute cerebral infarction but full reversal of symptoms within 24 hours of onset. (i.e. transient ischemic attack, TIA)
• Hemoglobin less than 90 g/l.
• Ongoing inflammatory disease, such as rheumatoid arthritis or active inflammatory bowel disease.
• Inability to undergo MRI scan (only patients with NIHSS ≤10 will be excluded by this criteria)

Eligible patients admitted to Örebro University hospital will be consecutively offered enrollement. The sample is weighted to include more patients with severe stroke (defined as NIHSS ≥ 11) than with moderate (NIHSS ≤10 and ≥ 6) or mild (NIHSS ≤5) stroke. The purpose of this is to ensure that a high proportion of participants will contract pneumonia since patients with a more severe stroke have a higher risk of pneumonia.