Which diagnoses are associated with hospital admissions in Germany?

According to the Federal Statistical Office, there were 1,942 hospitals in Germany in 2017 with a total of 497,182 beds. Approximately 19 million hospital admissions were reported [1]. Krämer & Schreyögg found a sharp increase in inpatient admissions over the course of ten years, from 16.5 million in 2005 to 19.2 million in 2015 [2]. In Germany, hospital admissions due to chronic diseases are considered potentially preventable through effective outpatient care. Published studies have shown that a certain proportion of hospital admissions could be avoided through the use of primary care providers [3, 4]. In recent years, several studies have been published addressing hospital admissions due to various diseases or acute events; For example, studies have been published linking hospital admissions with traumatic brain injury [5], heart failure [6], diabetes [7-9], stroke [10], cerebral hemorrhage [11], acute pancreatitis [12], and dementia [13]. Although a significant body of literature has addressed hospital admissions, there is a lack of research examining the influence of different primary and secondary medical specialties (i.e., gynecologists, neurologists, psychiatrists, etc.) and different diagnoses on the likelihood of hospital admission. The aim of this retrospective study, which included more than two million adults from Germany, was therefore to analyze possible associations between hospital admission and various diagnoses.

methods
>> This retrospective cross-sectional study was based on data from the Disease Analyzer (IQVIA) database, which compiles drug prescriptions, diagnoses, and basic medical and demographic data obtained directly and in anonymized format from computer systems used in the practices of general practitioners and specialists [14].
The study included patients aged 18 years and older who were between
January 2019 and December 2019 had at least one visit to one of 900 general practices (GPs) in Germany.
The outcome of the study was the association between predefined diagnoses, demographic variables (age and gender), and hospital admissions.
The index date for patients with hospital admissions was the day of the first hospital admission in 2019. For patients without hospital admissions, the last visit was defined as the index date. Diagnoses documented on the index date or within three months prior to the index date were analyzed if they were documented in at least one percent of patients with hospital admissions.
The prevalence of hospital admission was calculated as the number of patients with at least one hospital admission divided by the number of patients with at least one physician visit in 2019.
Admission prevalence was calculated separately by sex and age group (18-40, 41-50, 51-60, 61-70, 71-80, >80). A multivariate logistic regression model was performed to examine the association between age, sex, the predefined diagnoses, and hospital admission. This model was adjusted for age, sex, and diagnoses. Because the regression model included 38 variables, a Bonferroni correction was performed for the p-value, and a p-value of <0.001 (calculated as <0.05/38) was considered statistically significant. Analyses were performed using SAS version 9.4.
Results
The present study included 2,050,453 patients. The baseline characteristics of the study patients are presented in Table 1. The mean age [standard deviation] was 52.3 [19.8] years, and 531% of the patients were women.
Of the patients treated by general practitioners, 6.6% were admitted to hospital in 2019. The proportion of patients admitted to hospital increased with age, from 3.5% in the 18-40 age group to 12.5% in the over-80 age group. The proportion of hospital admissions was slightly higher among men than among women (6.8% and 6.5%, respectively) (Fig. 1).
In multivariate regression analyses, 24 diseases were significantly associated with hospital admission (Table 2). The strongest association was observed for acute appendicitis (odds ratio (OR: 15.64 (CI: 14.70-16.64)), followed by hernias (OR: 4.36 (CI: 4.21-4.51)) and cholelithiasis (OR: 3.08 (CI: 2.95-3.22)). The risk of hospital admission was also at least twice as high in patients with respiratory disorders (OR: 2.58 (CI: 2.49-2.69)), cancer (OR: 2.32 (CI: 2.26-2.37)), and abdominal and pelvic pain (OR: 2.28 (CI: 2.23-2.34)). Other diseases that showed a significant association with hospital admission were ischemic heart disease, cardiac arrhythmias, heart failure, cerebrovascular disease, gastritis and duodenitis, liver disease, COPD, osteoarthritis, shoulder lesions, sleep disorders, dizziness and lightheadedness, pain, depression, anxiety disorders, somatoform disorders, reaction to severe stress and adjustment disorders, and unknown and unspecified morbidity (Table 2).
discussion
Using a sample of more than two million adults from 900 general practices, this cross-sectional study showed that 24 physical and psychiatric disorders were positively associated with hospital admission, and that the odds ratios were particularly high for acute appendicitis, inguinal hernia, abdominal and pelvic pain, cholelithiasis, respiratory disorders, and cancer. To the best of our knowledge, this study is the first to examine the associations between a broad spectrum of conditions and hospital admission.
Acute appendicitis is considered one of the most common acute surgical conditions worldwide, occurring most frequently in adolescents and young adults. Although mild appendicitis is treated with antibiotics as first-line therapy, hospitalization for appendectomy is required in most cases [15, 16].
Surgical treatment of an inguinal hernia is also one of the most common operations performed by general surgeons in hospitals. However, many patients first consult their primary care physician about the hernia, who then refers them for surgery [17, 18].
The ICD-10 code for abdominal and pelvic pain includes "acute abdomen," which can be caused by infection, vascular occlusion, inflammation, or obstruction. All of these conditions require urgent treatment, which explains the strong association of abdominal and pelvic pain with hospital admission [19].
Acute cholecystitis can cause pain and fever, and there is a risk of complications; therefore, primary care physicians refer patients to hospitals where intravenous fluids and antibiotics can be administered. In the United States, the number of hospital discharges related to acute cholecystitis has increased significantly in recent years [20].
Respiratory disorders include dyspnea, stridor, wheezing, periodic breathing, and hyperventilation. Dyspnea is the most common respiratory abnormality and can be a symptom of a serious condition, especially if it occurs suddenly. There is a long list of conditions that can cause dyspnea, including asthma, allergies, pneumonia, or heart problems. Patients with dyspnea are often hospitalized for a prompt diagnosis and to reduce mortality and complications [21].
In the present study, ischemic heart disease, cardiac arrhythmias, and heart failure were associated with hospital admissions. A total of 19.5% of patients with heart failure were admitted to hospitals. Störk et al. reported that 55% of patients with heart failure were hospitalized during their two-year follow-up period. These hospitalizations included both emergency treatments without hospital admission and hospital admissions based on referrals from general practitioners and other specialists. Interestingly, more than 70% of hospital admissions were not related to cardiovascular events [22].
In this study, 14.7% of COPD patients were admitted to hospitals, and COPD was significantly associated with hospital admission. Wacker et al. showed that hospitalization was the main cost driver for severe COPD patients in Germany; however, most hospital admissions of COPD patients were for non-respiratory conditions [23]. In Canada, COPD patients had 63% higher rates of hospitalization than patients without COPD [24]. In Sweden, hospitalization for non-respiratory conditions was also the main cost driver in COPD treatment [25].
Psychiatric disorders such as depression and anxiety disorders, and to a lesser extent, somatoform disorders and reactions to severe stress, were associated with hospital admission in this study. Wagner et al. analyzed 18,139 patients with depression and reported that most of them were treated by a general practitioner or psychiatrist, and only 4.6% were treated in a hospital setting [26]. In the systematic review by Prina et al., depressive symptoms were associated with a higher likelihood of hospital admission; however, the authors found that depressive symptoms did not increase the likelihood of hospital admission in the absence of medical comorbidity [27]. In the present study, all four psychiatric disorders we analyzed can lead to depressive symptoms, and their effects were adjusted for several comorbidities. Although psychiatric disorders are not necessarily a reason for hospital admission, the risk of hospital admission is increased in patients diagnosed with these disorders in general practice.
Osteoarthritis was another diagnosis associated with hospital admission, with 13.2% of patients being admitted to hospital. Willer & Swart analyzed claims data from a German statutory health insurance fund for the period from 2005 to 2008. Of 1,551 osteoarthritis patients, two-thirds had at least one documented hospital admission. The patients were admitted, for example, for hip or knee replacement surgery [28].
General practitioners are the primary care contact for most patients. They are responsible for the diagnosis and treatment of all common illnesses. However, they also refer patients to hospitals and other medical services for urgent care and specialist consultations. Our study confirms that the proportion of patients admitted to hospital is relatively high and that hospital care plays an important role in the treatment of acute appendicitis, hernias, abdominal and pelvic pain, cholelithiasis, respiratory disorders, cancer, cardiovascular and cerebrovascular diseases, COPD, and other conditions.
The results of this study should be interpreted against the background of several limitations. First, the diagnoses were based only on ICD-10 codes, whereas more information on the severity and duration of these disorders might have enabled more detailed statistical analyses. Second, factors such as smoking habits and alcohol consumption were missing. Third, this study included patients treated in general practices; therefore, the results may not be generalizable to patients treated in specialist practices. Finally, the data were analyzed in Germany, and these results may not be consistent with those of populations in other countries.