Sepsis trends: increasing incidence and decreasing mortality, or changing denominator?

Abstract

Numerous studies suggest that the incidence of sepsis has been steadily increasing over the past several decades while mortality rates are falling. However, reliably assessing trends in sepsis epidemiology is challenging due to changing diagnosis and coding practices over time. Ongoing efforts by clinicians, administrators, policy makers, and patient advocates to increase sepsis awareness, screening, and recognition are leading to more patients being labeled with sepsis. Subjective clinical definitions and heterogeneous presentations also allow for wide discretion in diagnosing sepsis rather than specific infections alone or non-specific syndromes. These factors create a potential ascertainment bias whereby the inclusion of less severely ill patients in sepsis case counts over time leads to a perceived increase in sepsis incidence and decrease in sepsis mortality rates. Analyses that rely on administrative data alone are further confounded by changing coding practices in response to new policies, financial incentives, and efforts to improve documentation. An alternate strategy for measuring sepsis incidence, outcomes, and trends is to use objective and consistent clinical criteria rather than administrative codes or registries to identify sepsis. This is feasible using data routinely found in electronic health record systems, such as blood culture draws and sustained courses of antibiotics to identify infection and laboratory values, vasopressors, and mechanical ventilation to measure acute organ dysfunction. Recent surveillance studies using this approach suggest that sepsis incidence and mortality rates have been essentially stable over the past decade. In this review, we summarize the major epidemiologic studies of sepsis trends, potential biases in these analyses, and the recent change in the surveillance paradigm toward using objective clinical data from electronic health records to more accurately characterize sepsis trends.

Keywords: Sepsis; incidence; surveillance; trends.

Figure 1

Summary of factors potentially biasing analyses of trends in sepsis incidence and mortality.

Figure 2

Trends in (A) sepsis incidence and (B) short-term mortality (in-hospital death or discharge to hospice) using clinical vs. administrative data in a nationally representative set of hospitals, 2009–2014. Figure adapted with permission from Rhee et al. (45). Percentages reflect relative changes per year, with 95% confidence intervals. “Explicit sepsis codes” refers to an administrative definition requiring ICD-9-CM codes for severe sepsis (995.92) or septic shock (785.52). “Implicit sepsis codes” refers to an administrative definition requiring concurrent ICD-9-CM codes for infection organ dysfunction (Angus method), or explicit severe sepsis or septic shock codes. The electronic health record (EHR)-based clinical surveillance definition requires clinical evidence of presumed serious infection (≥1 blood culture draw and concurrent administration of ≥4 consecutive days of antimicrobials, or fewer if patients die or are transferred to hospice or another acute care hospital) and concurrent organ dysfunction (vasopressors, mechanical ventilation, increase in baseline creatinine or bilirubin, or decrease in baseline platelet count) (see Table 2). The EHR-based definition was examined with and without a criterion for elevated lactate since lactate testing rates are increasing over time. Trends were adjusted for hospital characteristics to account for varying availability of data across years for certain hospitals in the dataset.