Introduction
Vertebral Osteomyelitis (VO, syn.: spondylodiscitis) is a severe infection of the spine, and in recent decades, it has become more frequent [
1‐
3]. However, despite wider availability of radiological imaging for the broader public and improvement of modern surgical techniques, VO remains life-threatening. Besides a mortality rate up to 17–23%, VO is associated with prolonged hospital stays, and has a high impact on a reduced quality of life in the long-term outcome [
4,
5].
Due to demographical change, the population of developed countries is turning older on average, and the increasing total number of elderly individuals that are more prone to immunosuppression, cardiovascular diseases, and surgical-site infection is expected to cause even higher incidence rates of VO [
6‐
9]. Moreover, increased use rates of reserve antibiotics due to emergence of multidrug-resistant bacteria, VO-associated infectious endocarditis, and other age-related complications will additionally challenge the treatment of those often multi-morbid patients [
10,
11]. These developments will seriously challenge established health care systems within the next decades by requiring more human and financial resources.
In order to provide a reliable estimation of future native VO incidence, we forecasted the sex and age-related changes according to numbers and incidence of VO based on a nationwide projective analysis.
Discussion
In this modeling study, we conducted a forecast analysis to approximate the future incidence of native VO as relevant burden of health care systems. We used cumulative data of 15 years in a cohort of more than 80 million women and men to project future age- and gender-related trends of this life-threatening infection.
Hereby, this modeling study provides some notable strengths. Most important, our projections are based on the most robust out of four established forecast models. Furthermore, the underlying database provides outright information on historical trends of native VO in a large, industrialized population. Thus, despite long-term forecasting, which can be extremely useful for research and resource planning, our projections show high accuracy in pure mathematical terms.
We found a continuous increase in incidence of VO with a steep increase in patients aged 75 years and older. By 2035, the age-adjusted incidence is projected to meet its climax. However, our modeling study predicts an ongoing increase of total incidence up to the year 2040, mainly driven by a demographic shift toward an aging population in Germany leading to a higher proportion of women and men aged 75 years and older.
This finding has important implications on healthcare systems and policymakers: higher age itself and age-associated diseases including diabetes, cardiovascular diseases, malignancy, immunocompromised status, and use of hemodialysis are strongly associated with higher need for surgical treatment of VO. These factors, however, are also associated with higher rates of adverse events, reduced quality of life, longer hospital stays and, finally, fewer return-to-home rates as well as increased mortality. In summary, this suggests a large increase of direct and indirect costs, leading to a serious socioeconomic challenge [
23‐
25].
The importance of this finding is highlighted by the high co-prevalence of infective endocarditis (IE) and emergence of antibiotic-resistant bacteria [
10,
26]. As the epidemiology of IE—characterized by high morbidity, mortality and costs—has changed in a similar proportion comparted to VO in recent decades, consequently, the predicted mounting numbers of VO in patients aged 75 and older also suggest rising incidence rates of IE that will additionally impact health care systems [
27‐
32]. Thus, managing human and financial resources effectively, focusing on prevention-research, developing interdisciplinary treatment strategies and networks will be of utmost importance to tackle this upcoming burden in future.
It is commonly accepted that VO most often results from hematogenic seeding. Our findings assume that this upcoming burden is not only due to native VO because iatrogenic or post-surgical VO need to be considered as an additional challenge for future healthcare systems [
33]. In 2004, Deyo et al. demanded a shift in research effort from “how to perform fusion to examining who should undergo fusion” [
34]. Ever since, the use of spinal surgery has been rising worldwide and a further increase of spinal surgical procedures is projected [
35]. The incidence of surgical-site infections (SSI) is 4.4% in patients undergoing instrumented surgery, and 1.4% in non-instrumented surgery [
36]. This ultimately could result in approximately 30% more VO when considering iatrogenic causes [
37]. However, it must not be forgotten that not all SSI cases can be considered as postsurgical VO. Superficial wound healing problem are also included in that cohort and do not necessarily lead to an infection of the vertebral body or the disk. However, given the rapidly increasing incidence of spinal surgery associated VO worldwide in the last decades, this emphasizes Deyos’ 20-year-old demand of need for reasonable decision-making when indicating spinal surgeries [
38]. Thus, considering an aging population innovative strategy of prolonged conservative care and modern minimal invasive surgical procedures patients may be considered as key factors for minimizing the burden of iatrogenic VO, with decreased costs as a result [
39‐
41].
Our model suggested that men will be more prone to VO than women, and the highest number of VO is projected to occur in men aged 75 and older. Because postmenopausal biological sex does not provide sufficient causality for differential incidence rates, gender and associated life-style should be evaluated as possible risk factors in future studies [
42].
Although our forecast model is highly accurate in pure mathematical terms, and projected numbers come along with small CI and high predictive accuracy, we used historical incidence rates to build the projections. As it is not predictable whether historical trends of native VO may change in future due to advances in biologics, genetics, antibiotic treatment, or preventive strategies, long-term projections are more prone to overestimation. However, a clinically relevant scientific breakthrough—which may result in relevant decrease in incidence of VO—is not very likely to occur in the imminent future, and, moreover, establishing new algorithms is laborious. Thus, we believe our projections to be highly accurate for the upcoming decade, and possibly thereafter. For this study, historical data of the past 15 years have been used only, as data documentation was insufficient before. Therefore, the projected incidence rates made in this study should be verified in future, evaluating whether a significant discrepancy to projected VO incidence is observed.
Although the data are provided by the Federal Statistical Office of Germany, an official national institution that demands high accuracy of data input and coding to provide complete, nationwide information, we could not separate VO in between different or multi-resistant pathogens. Furthermore, due to insufficient data accuracy, we could not additionally forecast iatrogenic VO. However, our projections provide a base for future studies to settle this issue and, thus, to quantify the upcoming burden.
It remains questionable, whether the projected tendency can be transferred into other health care systems in analogy. Although historical trends of VO in Germany face a similar direction as in other large European and Asian countries, population development differs into two principal directions within several large nations. The population in the United States and in some European countries, such as the United Kingdom, France, and Scandinavia, continues to grow driven by high fertility and immigrations rates, while others, such as Germany, Italy, Russia, and most Eastern European countries, face a decline in population resulting from low birth and immigration rates leading to a demographic shift—seek additional pressure human and financial recourses because of a shrinking working population [
43]. However, the proportion of people aged 75 and older will increase in many countries. This is both a European and global phenomenon, as within the next decades many populations worldwide are likely to follow this trend (
43,
44). Thus, the projected burden of VO linked to a higher amount women and men aged 75 and older is likely to apply to many other healthcare systems of developed countries.
In general perception, native VO is widely underestimated. Given current trends, we project the climax of age-dependent incidence of VO to occur in about ten years from now, however, the total numbers will further continue to increase substantially due to a shift toward patients aged 75 and older, with resultant serious socioeconomic challenges for health care systems in fast aging countries. This emphasizes the need for widespread establishment of interdisciplinary treatment strategies based on high-level evidence-based guidelines, as well as appropriate financial and human recourse management to challenge this serious burden in light of a worldwide aging population in the next decades.