It is the second-leading cause of death in non-coronary intensive care unit (ICU) and the tenth-most-common cause of death overall (the first being heart disease). Children under 12 months of age and elderly people have the highest incidence of severe sepsis. Among people from the U.S. who had multiple sepsis hospital admissions in 2010, those who were discharged to a skilled nursing facility or long-term care following the initial hospitalization were more likely to be readmitted than those discharged to another form of care. A study of 18 U.S. states found that, amongst people with Medicare in 2011, sepsis was the second most common principal reason for readmission within 30 days.Several medical conditions increase a persons susceptibility to infection and developing sepsis. Common sepsis risk factors include age (especially the very young and old); conditions that weaken the immune system such as cancer, diabetes, or the absence of a spleen; and major trauma and burns.From 1979 to 2000, data from the United States National Hospital Discharge Survey showed that the incidence of sepsis increased fourfold, to 240 cases per 100,000 population, with a higher incidence in men when compared to women. However, the global prevalence of sepsis has been estimated to be higher in women. During the same time frame, the in-hospital case fatality rate was reduced from 28% to 18%.
Gram-positive bacteria were the primary cause of sepsis before the introduction of antibiotics in the 1950s. After the introduction of antibiotics, gram-negative bacteria became the predominant cause of sepsis from the 1960s to the 1980s. After the 1980s, gram-positive bacteria, most commonly staphylococci, are thought to cause more than 50% of cases of sepsis. Other commonly implicated bacteria include Streptococcus pyogenes, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella species. Fungal sepsis accounts for approximately 5% of severe sepsis and septic shock cases; the most common cause of fungal sepsis is an infection by Candida species of yeast, a frequent hospital-acquired infection. The most common causes for parasitic sepsis are Plasmodium (which leads to malaria), Schistosoma and Echinococcus. The most common sites of infection resulting in severe sepsis are the lungs, the abdomen, and the urinary tract. Typically, 50% of all sepsis cases start as an infection in the lungs. In one-third to one-half of cases, the source of infection is unclear. Pathophysiology
Sepsis is caused by a combination of factors related to the particular invading pathogen(s) and to the status of the immune system of the host. The early phase of sepsis characterized by excessive inflammation (sometimes resulting in a cytokine storm) may be followed by a prolonged period of decreased functioning of the immune system. Either of these phases may prove fatal. On the other hand, systemic inflammatory response syndrome (SIRS) occurs in people without the presence of infection, for example, in those with burns, polytrauma, or the initial state in pancreatitis and chemical pneumonitis.