Critical illness leading to intensive care means suffering and high risk of death for the individual, and costs to society. There are several reasons why patients end up in intensive care units (ICU), but common to them is that they develop failure in vital organs. Sepsis, COVID-19 infection, and surgical trauma are common causes of failure of vital organs. During the past year, these conditions have accounted for a very large proportion of all admissions to IVA in Sweden. Apart from causing significant hospitalization, these three causes of illness are also responsible for great suffering and significant mortality. One in three patients admitted to ICUs in Sweden with sepsis dies 30 days after admission. Similarly, one-in-four patients admitted to a Swedish ICU in the first wave of COVID-19 (Corona virus disease-19) died. 15% of patients die who are admitted unplanned to ICU after surgery according to the Swedish Intensive Care Registry's output portal (30-04-2021). These mortality figures are comparable to figures seen for 5-year mortality from cancer, with the difference that they are measured one month after the illness. Furthermore, these admissions to IVA are associated with substantial burden on costs and human resources. Sepsis alone caused 10,000 care admissions (11% of all ICU care admissions) and 49,000 days (20% of all ICU days) in Swedish intensive care units during 2018-2019 with an estimated cost of SEK 2.5 billion for intensive care alone. The cost of COVID-19 is significantly higher. Unplanned admission to IVA after surgery means 12,000 ICU days each year and entails an additional cost of half a billion kronor. Given the high mortality for these hospitalization causes, a small reduction in mortality can be of great importance to the individual, healthcare and society. We have previously shown that genetic factors are important in disease severity and outcome in COVID-19. With an increased understanding of disease mechanisms, key factors that affect disease severity and outcome after illness can be identified, as well as risk groups of individuals where healthcare can make preventive measures or long-term targeted treatment measures. Research aim/hypothesis: We have hypothesized that specific genetic factors are of great importance for the severity of disease in in critical illness such as sepsis, infection with Sars-CoV-2 and infectious or thromboembolic complications after surgery. The project will identify whether specific genetic factors contribute to increased severity of disease, increased need for care and increased mortality. We will merge pseudo-anonymised data from Epihealth, Simpler, the Swedish Twin Registry, the Swedish ICU registry, the Swedish perioperative registry, Patientregistret on comorbidities, Läkemedelsregistret for comorbidities, socioeconomic factors from SCB, microbiologic data from Smtnet and regional microbiological labs. SCB will handle personal ID data.