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Background Development of sepsis is a process with significant variation among individuals. The precise elements of this variation need to be defined. This study was designed to define the way in which comorbidities contribute to sepsis development. Methods Three thousand five hundred nine patients with acute pyelonephritis (AP), community-acquired pneumonia (CAP), intraabdominal infections (IAI) or primary bacteremia (BSI) and at least two signs of the systemic inflammatory response syndrome were analyzed. The study primary endpoint was to define how comorbidities as expressed in the Charlson’s comorbidity index (CCI) and the underlying type of infection contribute to development of organ dysfunction. The precise comorbidities that mediate sepsis development and risk for death among 18 comorbidities recorded were the secondary study endpoints. Results CCI more than 2 had an odds ratio of 5.67 for sepsis progression in patients with IAI between significantly higher than AP and BSI. Forward logistic regression analysis indicated seven comorbidities that determine transition into sepsis in patients with AP, four comorbidities in CAP, six comorbidities in IAI and one in BSI. The odds ratio both for progression to sepsis and death with one comorbidity or with two and more comorbidities was greater than in the absence of comorbidities. Conclusions The study described how different kinds of infection vary in the degree to which they lead to sepsis. The number of comorbidities that enhances the risk of sepsis and death varies depending on the underlying infections. Electronic supplementary material The online version of this article (10.1186/s12879-018-3156-z) contains supplementary material, which is available to authorized users.

Former studies of our group have shown that the innate and adaptive immune status may differ in relation with the causative infection. To this same end, it was investigated if kinetics of circulating lipopolysaccharide (LPS) leading to inflammatory response may differ. Blood was sampled from 189 patients with sepsis and 206 with severe sepsis/shock starting 24h from advent of sepsis and repeating on day 3. Serum LPS was measured by Limulus Amebocyte Lysate (LAL) assay. From 59 patients, circulating monocytes were isolated and incubated in the absence/presence of LPS. Concentrations of tumor necrosis factor-alpha (TNFα) were measured in supernatants by an enzyme immunoassay. In either category of severity, circulating LPS was greater among sufferers from primary Gram-negative bacteremia (BSI) and from community-acquired pneumonia (CAP) than sufferers from other underlying infections. LPS were greater among patients with BSI compared to patients with secondary Gram-negative bacteremia and patients without bacteremia. Greater decrease of circulating LPS over 48h was recorded for survivors compared to non-survivors only within sufferers from BSI and CAP. Significant endotoxemia was considered for patients with serum LPS within the upper quartile of distribution; their monocytes were less potent for release of TNFα. It is concluded that endotoxemia in sepsis varies greatly with the underlying infection; this is related with immunoparalysis of monocytes with implications on final outcome.