Introduction
Inflammatory bowel disease (IBD), consisting of ulcerative colitis (UC) and Crohn’s disease (CD), is a gastrointestinal disease characterized by relapsing chronic inflammation. The past few decades have witnessed dramatic increase in the incidence of IBD and the number of IBD-related hospitalizations in newly developing countries [
1,
2]. The prognosis of IBD patients has improved with the advancement of medication, ranging from glucocorticoids and immunosuppressants to biological drugs. However, the increasing use of immunosuppressive and biological drugs has raised concerns about the occurrence of opportunistic infections, [
3,
4] which pose a safety risk for IBD patients due to their dysregulated immune responses and malnutrition.
An opportunistic infection may be defined as a usually progressive infection by a microorganism that has limited (or no) pathogenic capacity under ordinary circumstances, but which is able to cause serious disease as a result of the predisposing effect of another disease or of its treatment [
5]. Opportunistic infections can lead to frequent disease relapse and worse clinical outcomes, including higher surgery rates and mortality [
6,
7]. Additionally, they are associated with longer hospitalizations, increased hospital costs, and higher overall mortality [
8,
9]. Both iatrogenic factors (such as biologics or corticosteroid treatments) and personal factors, including malnutrition, high body mass index, comorbidities, active disease, living in less economically developed regions, and older age, can increase the risk of opportunistic infections [
5,
10]. Therefore, studying the characteristics and risk factors associated with opportunistic infections in IBD patients may provide valuable insights into understanding the current burden of IBD in China.
Various studies have indicated a significant influence of environmental and economic factors on infection rates [
11], making this relationship of great interest to scientists. The aforementioned studies demonstrated a greater risk of gastrointestinal infections among individuals with lower economic income, resulting in illness consequences such as heightened symptom severity and increased absenteeism from work or school [
12]. Furthermore, the influence of climate and sunlight on infection rates was noted [
13,
14]. Considering that individuals with IBD undergoing immunosuppression are immunocompromised and prone to various opportunistic infections, the precise relationship between social-environmental factors and opportunistic infections associated with IBD remains yet to be elucidated.
For this study, we gathered data on hospitalizations of Chinese IBD patients with opportunistic infections from the Health Statistics and Information Reporting System (HSRS), which serves as the largest inpatient database in mainland China. Moreover, we accessed environmental data from the China Statistical Yearbook (
http://www.stats.gov.cn). The primary aim of our research was to describe the characteristics of opportunistic infections associated with IBD among Chinese hospitalized patients and examine their potential correlation with social-environmental factors.
Discussion
This study represents the first comprehensive investigation on the characteristics of opportunistic infections in IBD hospitalized patients across mainland China, covering a significant temporal and spatial range. The key findings can be summarized as follows. Firstly, OIs are a common occurrence during the course of IBD, with a total of 17,503 individuals suffered from at least one opportunistic infection, constituting 4.46% between 2014 and 2019 in China. Secondly, the presence of opportunistic infections significantly exacerbates the burden on both individuals and the national healthcare system. There are four main aspects to consider: Firstly, the incidence rate of IBD with opportunistic infections is increasing year by year, particularly among UC patients. The ratio change in IBD is 5.3%, while in UC it is 25.8% and in CD it is 1.2%. Additionally, opportunistic infections not only lead to prolonged hospital stays and increased healthcare expenditures for patients, but also raise the risk of gastrointestinal complications and the need for surgery. Thirdly, the most common pathogens associated with opportunistic infections in both UC and CD patients were C. diff, followed by EBV and CMV. Moreover, there was a higher proportion of males among IBD patients with opportunistic infections, and younger hospitalized patients exhibited a higher prevalence of C. diff, CMV, and EBV infections. Lastly, lower GDP regions (indicating less economic development) and shorter exposure to sunlight were associated with an increased likelihood of opportunistic infections in IBD patients.
Firstly, it was observed that opportunistic infections were prevalent among IBD inpatients in China, and their incidence has been consistently increasing over time. This finding supports the current understanding that the ratio of opportunistic infections among IBD patients is on the rise. A nationwide survey on intestinal infections in IBD patients conducted in the United States showed a significant increase in incidence rates from 18.0 to 47.4/1000 CD hospitalizations and 39.5-110.1/1000 UC hospitalizations (
Ptrend < 0.01) during the period spanning from 1998 to 2014 [
8]. A comprehensive nationwide study conducted in the United States between 1999 and 2018 reported a prevalence of opportunistic infections in CD patients at 17.8% and in UC patients at 19.2% [
19]. Despite the current lower prevalence of IBD-associated opportunistic infections in China compared to countries with a higher incidence of IBD, it is imperative to prioritize the management of opportunistic infections. This becomes even more significant given the growing number of IBD patients and the aging population in China.
More specifically, UC patients exhibited a statistically higher ratio of
C.diff, CMV, and EBV infections compared to other pathogens. Notably,
C.diff infections accounted for the largest proportion among all the opportunistic infections included in the study. Moreover, previous research has consistently shown a higher prevalence of
C.diff infections among UC patients when compared to CD patients. In a retrospective case-control study conducted in China among hospitalized patients with IBD and
C.diff infections, the estimated prevalence of C.diff infections was reported to be 6.06% for CD patients and 7.41% for UC patients [
20]. In Canada, the prevalence of
C.diff infection was observed to be 3.73% among UC patients and 1.09% among CD patients [
12]. From 1998 to 2014, there was a notable rise in the incidence of
C.diff infections leading to hospitalization among UC patients in the United States, almost doubling over that period. Notably,
C.diff infection was associated with a significantly higher mortality rate among patients with UC (OR = 3.79, 95% CI 2.84–5.06), whereas this association was not observed in CD patients (OR 1.66, 95% CI 0.75–3.66). Moreover,
C.diff infections were also associated with longer hospital stays and higher average hospital charges. In relation to CMV infection, a prior study conducted in China demonstrated that the prevalence of anti-CMV IgG positivity among IBD patients was 76.11%, surpassing the rate observed in healthy controls (50.69%). Furthermore, the study indicated that pancolitis could enhance CMV proliferation [
22]. Regarding CMV colitis, a recent multicenter study carried out in China revealed a prevalence of 3.1% in UC patients and 0.8% in CD patients, [
23], which is consistent with several previous reports from Asia [
24]. In terms of EBV infection, earlier single-center studies conducted in China have revealed a broad range of prevalence rates for EBV in the intestinal mucosa of patients, ranging from 33–79.4% [
25‐
28]. These studies have additionally established a connection between EBV presence and clinical disease activities. Notably, the observed prevalence rates were considerably higher than those observed in our current study. In our study, we noted that the proportions of
C.diff, EBV, and CMV infections were comparatively lower when compared to previous studies conducted in China. This disparity can be attributed to several factors. Firstly, other studies may have predominantly included more severe cases, while our study encompassed a diverse representation of patients across varying severity levels. Additionally, the underestimation of pathogen detection could be due to the limited availability of laboratory equipment in certain regions of China.
Our study revealed that IBD-associated opportunistic infections had a substantial influence on both the duration and expenses related to hospital stays. Furthermore, these infections were identified as a significant risk factor for poor outcomes, especially in relation to surgery rates among UC patients. Notably, the ratio of emergent operations could potentially rise as high as 50% in UC patients with opportunistic infections [
29]. In the era of biologics, although several meta-analyses have shown the efficacy of anti-TNF biologics in significantly reducing hospitalization rates by approximately 50% and surgery rates by 33–77% in IBD patients, [
30] it is essential to recognize the potential adverse effects of these medications in terms of triggering opportunistic infections. Infected patients typically face more intricate gastrointestinal inflammation and are prone to being less responsive to corticosteroid treatment, necessitating an increased likelihood of therapy escalation [
31‐
33]. Given that the existing data in China mainly stem from retrospective studies conducted in single centers, there is a clear need for future prospective multicenter studies to comprehensively evaluate the influence of opportunistic infections on IBD outcomes. In the meantime, it is vital to emphasize regular screening, early detection, and appropriate treatment of opportunistic infections. By doing so, we can not only enhance patient outcomes but also minimize avoidable costs associated with their management.
Regions with lower GDP tend to have a higher proportion of patients with IBD-associated opportunistic infections. Numerous studies have underscored the crucial role of socioeconomic factors, including poverty, overcrowding, and poor nutrition, in the genesis of opportunistic infections. This relationship extends throughout different diseases, from historical cholera outbreaks to the current landscape of tuberculosis [
34‐
36]. Gastrointestinal infections are commonly caused by factors such as contaminated food or water, environmental conditions, and contact with animals. It has been observed that in high-income countries like the UK, where a significant portion of the population enjoys access to healthcare, sanitation facilities, and clean water, the mortality rate due to gastrointestinal infections remains relatively low [
37]. Given the negative impact of underdeveloped economies on the occurrence of infections and the potential increase in the number of IBD patients in less developed regions, [
38] it is essential to recognize the heightened burden of IBD-associated opportunistic infections in these areas. Additionally, it is important to note that patients in these regions face challenges in accessing timely diagnosis and treatment, often due to limited healthcare resources and the absence of adequate medical insurance coverage, which can contribute to worse outcomes.
Additionally, we performed an examination of the relationship between meteorological factors and the risk of opportunistic infections. In both CD and UC patient groups, we discovered that decreased sunlight exposure was associated with an increased likelihood of opportunistic infections. Specifically, among CD patients, we noted a higher proportion of hospitalized individuals with opportunistic infections in Northern China, indicating regions located at higher latitudes. Conversely, among UC patients, opportunistic infections were more prevalent in Southern China, despite exhibiting a negative correlation with sunlight exposure. Throughout history, people have long acknowledged the vital role of sunlight as an important defense against infections [
39‐
41]. Insufficient sunlight exposure has demonstrated a robust association with the activation or dissemination of various pathogens, such as respiratory syncytial virus and, notably, COVID-19 [
13,
42]. Sunlight and ultraviolet radiation are known to exert dual effects in combating infections. On one hand, they can effectively eradicate pathogens, including
C.diff. On the other hand, they play a role in bolstering an individual’s resistance to infections by regulating the biological rhythms of specific anti-inflammatory molecules, such as the Vitamin D receptor [
43,
44]. Findings from a rigorously conducted randomized controlled trial revealed that the administration of oral vitamin D supplementation effectively decreased the likelihood of upper respiratory infections in individuals diagnosed with IBD [
45]. Drawing upon the case of tuberculosis (TB) treatment, [
46] it is important to highlight that interventions involving vitamin D, phototherapy, and sunlight exposure have consistently exhibited their capacity to effectively eliminate TB infections, culminating in their recognition through the prestigious Nobel Prize. Translating this knowledge into clinical practice, it becomes imperative to integrate routine monitoring of serum vitamin D levels and administer appropriate supplementation to IBD patients, especially those residing in geographical regions characterized by higher latitudes or who face limitations in accessing regular sunlight exposure (e.g., the elderly, disabled individuals). By implementing these interventions, there exists a promising opportunity to achieve both cost-effective and safe methods of reducing the incidence of opportunistic infections.
This comprehensive and nationwide database greatly strengthens the statistical power to identify statistically significant associations between IBD-associated opportunistic infections and vital clinical outcomes, including colectomy rates and mortality. The broad coverage encompassing diverse geographic regions and hospitals contributes to the robust generalizability of these findings. Furthermore, the incorporation of demographic and social-environmental data enables a stratified analysis that effectively controls for various potential confounding variables. Since the travel history and immigration harder the differentiation of infectious colitis and IBD as well as increasing the possibility for pathogens prevail, [
46] we suggest that doctors should always take infectious diseases into consideration when they meet patients from areas with low GDP and shorter sun shine hours.
This study is subject to several limitations. Firstly, the reliance on ICD-10 codes for case retrieval from the HSRS database limits the availability of detailed clinical or laboratory data on opportunistic infections and the diagnosis of IBD. Consequently, some opportunistic pathogens were excluded from our analysis due to the absence of confirmatory testing results. To ensure the accuracy of the IBD and OI diagnoses, we employed cross-checking of information, examining not only the ICD codes but also variables related to the descriptions and wordings used in the diagnoses. Additionally, we reviewed other supporting evidence such as pathology results from biopsies and surgical operations. Secondly, we lacked data on the specific immunosuppressive agents prescribed to hospitalized IBD patients, impeding a comprehensive assessment of the association between IBD and opportunistic infections. Nevertheless, it is indeed important to assess the correlation between advanced medical modalities and opportunistic infections and a more comprehensive database is needed for the aforementioned relationship analysis. Thirdly, the HSRS database does not provide information on the specific disease behavior and location within the spectrum of CD or UC, despite these factors being known to influence the incidence of opportunistic infections. At last, specific bacterial infections or viral infections (pneumonia, meningitis) were excluded in this study due to the difficulty to withdraw the diagnosis only from the patients’ home page. To address these limitations and gather more nuanced insights into the disease, future multi-center studies are warranted, allowing for the inclusion of detailed disease profiles and assessment of associated risk factors.
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