In most OECD countries, emergency departments (EDs) are struggling with high – and in many cases increasing – patient numbers [1]. On average three out of ten patients used ED services per year between 2011 and 2013. Nevertheless, the percentage of patients visiting an ED varies widely among 31 investigated European countries – ranging from 18% in Bulgaria, Denmark, the Netherlands to around 40% in Greece, Portugal and Spain – on average three out of ten patients used ED services per year [2]. Effects of ED crowding include adverse outcomes such as increased mortality, reduced treatment quality, delayed medication, prolonged pain for patients, long waiting times, patient and staff dissatisfaction and also aggressive behavior [3], [4], [5]. A systematic review showed that the length of stay in an ED, boarding time and total occupancy were associated with patient safety and effectiveness of care [6].

In addition, an increasing utilization of emergency departments (EDs) has placed considerable pressure on their respective organization and staff. It affects not only the quality of emergency care but also clinical decisions on the admission itself. Studies found an association between the likelihood of hospital admission and increased ED overcrowding [6,7]. It could be shown that admission rates increased with higher levels of overcrowding, surprisingly especially in lower triage categories [8].

Many studies investigated reasons of increasing ED utilization. Those reasons are multifaceted and, on the demand-side, related to patient characteristics and demographic as well as societal changes [9,10]. Examples include risk aversion (i.e., patients´ perceived urgency) and convenience in terms of an easy access to specialized care [11,12]: patients perceive that EDs are more convenient as comprehensive care is provided including appropriate diagnostics delivered by a specialist team [12], [13], [14], [15]. However, the use of emergency departments may also reflect progression or exacerbations of poorly controlled chronic diseases. Additionally, it may indicate potential barriers in the access to primary and specialist care outside of the hospital [16].

Due to reasons described above and effects of ED crowding, hospitals and health care systems are struggling with the provision of effective and efficient health care. Therefore, many countries are currently in the process of reforming their emergency care systems [17]. Parkinson et al. distinguish types of undesirable utilization that vary by underlying causes and potential solutions from the health systems’ perspective into clinically divertible attendances, clinically avoidable attendances, and clinically unnecessary attendances. While patients are often treated in the initial clinic upon admission, it would likely be better to refer them elsewhere due to their current health care needs. The group of clinically avoidable attendances includes patients who need the type of specialized ED care, but whose attendance could potentially have been prevented by earlier interventions or better management of their condition. The third clinically avoidable group includes patients who did not require any clinical care at all (clinically unnecessary) [18]. These different groups clearly demonstrate the diversity and, although reducing ED attendances is an important goal in many health systems, policy initiatives to reduce visits might also be risky and therefore should proceed with caution [19].

Our study therefore sheds light on the most frequent treatment occasions in the ED and the utilization of different health care providers by patients before and after an ED visit. We aimed at (1) performing a descriptive analysis of ED patients in Germany according to coded diagnoses, gender, and age, distinguishing between outpatient and inpatient care in EDs, and (2) describing as well as visualizing patient paths and cross-sectoral patterns of care before and after an ED visit for the most frequent outpatient and inpatient diagnoses of ED visits in Germany.