In our previous national study, SS was proven to be a risk factor for CRS [17]. According to our findings, SS-CRS is predominantly sinusitis without polyposis, and the secretions of patients with SS-CRS have been clinically observed to be yellow and sticky. Precise oral antibiotic administration or nasal irrigation combined with antibiotic treatment could help improve therapeutic efficiency [31,32,33].

Poly-microbial infections were the majority in either SS-CRS or non-SS-CRS in our study. This results were consistent with the findings of previous studies analyzing the bacterial compositions of CRS [34, 35]. A previous study reported the number of bacteria identified from pus cultures in patients with CRS ranged from two to five [35] and another study discovered an average of 3.4 kinds of bacteria isolated from each CRS patients [34]. Our study demonstrated that the average number of isolated bacteria grown from one individual patient was 2.4 in SS-CRS and non-SS-CRS. Besides, the compositions of bacterial infections of each patient in the speculum of facultative anaerobes or aerobes and anaerobes with SS-CRS and non-SS-CRS were not significantly different.

Comparing the results of previous studies with our findings, our study analyzed the bacterial species of a large number of patients with sinusitis, and the results were consistent with the previous studies, all of which were dominated by poly-microbial infections, and the data was similar. It means that the results of our database-research are reliable, and the results of bacterial cultures in our study were obtained from specimens during sinusitis surgery, which can improve the accuracy of studying the bacterial species of CRS. In addition, the bacterial compositions of SS-CRS and non-SS-CRS, whether compared with all bacteria, or when facultative anaerobes or aerobic bacteria and anaerobes were compared separately, the results were similar between the two groups (Fig. 2), indicating that the SS patients’ sinusitis is not different from the non-SS patients’ sinusitis in terms of bacterial composition. Therefore, on this basis, our study analyzing the differences in bacterial species between the two groups would not be confounded by a different bacterial composition.

Observing the compositions of facultative anaerobic or aerobic bacteria in SS-CRS and non-SS-CRS, it can be found that two-infections accounted for the highest proportion (50% for SS-CRS; 45% for non-SS-CRS). Because facultative anaerobic or aerobic bacteria is generally the main target for our clinicians to think about the use of antibiotics. According to the findings of the bacterial spectrum of CRS in our study, when the therapeutic effect on CRS is not optimal and no clear information of bacterial infection can be obtained, it is necessary for clinicians to know which possible bacteria should be considered as an alternative target for treatment of CRS. In addition, further observation of the composition of anaerobic bacteria in SS-CRS and non-SS-CRS can find the mono-infection was the main type of anaerobic bacterial infection in patients with CRS (57.1% for SS-CRS; 54.3% for non-SS-CRS). This finding highlights the importance of our study, because anaerobic bacteria are generally not the main target of empiric antibiotics, but without effective treatment, sinusitis may persist or recur. Therefore, the findings of this study can provide clinicians an important information on thinking about an adequate combination of antibiotics for treating CRS.

In this study, the most common bacterial genus responsible for CRS in patients without SS was Staphylococcus followed by Streptococcus. Our study’s control group results were consistent with those of several previous studies [20, 23, 36, 37], and this indirectly reflected that the bacterial spectra identified in our study to be responsible for SS-CRS were highly reliable.

The primary finding of our study was that the causative bacteria in SS-CRS differed from those in non-SS-CRS. Based on the results of this study, the null-hypothesis of the present study that CRS patients with SS do not have different bacterial compositions as compared to non-SS-CRS patients was declined. With respect to the main identified bacteria, non-SS-CRS was S. epidermidis (29.3%) and then CoNS (25.6%), and SS-CRS was CoNS (34.3%) and then P. aeruginosa (28.6%). CoNS is generally considered to be the bacteria that constitutes the commonly encountered flora in the nasal cavity, and the choice of empirical antibiotics is generally similar to that used in the treatment of S. epidermidis. However, in patients with SS-CRS, P. aeruginosa plays a prominent role. Therefore, for patients with SS-CRS, the choice of antibiotics is important in the treatment of P. aeruginosa infection. P. aeruginosa was uncommonly found in the nasal culture of normal individuals, and, in general, the isolation of P. aeruginosa from symptomatic patients indicates that it is pathogenic and a potential cause of CRS [38]. P. aeruginosa has been shown to be a common pathogen in patients with CRS among special populations, including patients in intensive care units and those with immunodeficiency, DM, and mucociliary dysfunction such as cystic fibrosis [39]. P. aeruginosa was also found to be more common in patients receiving systemic steroids [40]. Thus, it may explain this study’s finding that P. aeruginosa was the commonly isolated bacterial species in SS-CRS. However, P. aeruginosa-related CRS is considered difficult to treat, as it can secrete various virulence factors and organize a tough biofilm to escape the immune system and destroy host cells, developing antibiotic resistance [41]. Therefore, P. aeruginosa-CRS must be treated with appropriate antibiotics.

S. aureus colonizes 20–30% of the nasal mucosa of normal individuals and is more common in patients with CRS [42]. It is known that S. aureus toxin-producing strains are effective disease modifiers that can destroy barrier function, invade epithelial cells, regulate immune cells, and promote polyp formation [43]. Although S. aureus is the main pathogen in CRS, most species are still MSSA [44], as our study showed. However, the proportion of MRSA identified from bacterial cultures was higher in the SS-CRS group than in the non-SS-CRS group (MRSA: SS-CRS vs. non-SS-CRS: 5.7% vs. 1.7%) (Additional file 1: Table S1). Research on MRSA nasal colonization has recently increased [45], and MRSA is now known to cause slow mucosal healing and infection at the surgical site and biofilm formation [46]. Biofilm formation, associated with increased disease severity, is a response to selective pressure in the mucosal niche, including the use of antibiotics and loss of integrity of the host epithelial immune barrier, which may lead to a greater overall morbidity [47].

A. baumannii, an aerobic Gram-negative coccobacilli, is a significant bacteria that can cause severe and recurrent infections with consequent morbidities [48]. This pathogen is usually identified in immunocompromised individuals or patients with comorbidities or chronic illnesses such as prolonged hospital stays, poorly controlled DM, or malignancies, et al. [49]. A. baumannii, which can effectively evade the effects of antibacterial drugs, rapidly develops resistance to antimicrobials, and a high incidence of multidrug-resistant strains (MDRAB) has been identified [48]. In this study, the SS-CRS group had a higher proportion of patients with MDRAB-induced sinonasal infection than the non-SS-CRS group (Fig. 5). This finding could provide clinicians with important information, and when encountering sinusitis that is resistant to medical treatment, the possibility of infection caused by drug-resistant bacteria should be considered.

The common genera of anaerobes in CRS were Cutibacterium and Peptostreptococcus [36] as shown in this study. Fusobacterium was another major pathogen in SS-CRS, which differed from those identified in non-SS-CRS. Anaerobic bacteria typically influence antibiotic selection to include anaerobic bacterial coverage; therefore, this finding is essential for promoting effective SS-CRS management. Fusobacterium are known to have mobile genetic components that increase their antibiotic resistance and virulence with other opportunistic bacteria in the community, creating a pathogenic niche [50]. Moreover, Fusobacterium may cause serious CRS complications, such as intracranial abscesses [21]. Therefore, in patients with SS-CRS, Fusobacterium infection may be latent, necessitating prompt and appropriate antibiotic treatment.

Our study has several strengths. We identified up to 14,678 CRS cases from the CGRD database, which comprised more than 14% of inpatient coverage of Taiwan [30], and the characteristics of the study population were similar to those of the population in our previous population-based nationwide study in Taiwan [17]; therefore, the results of this study could present real-world evidence. In addition, the Registry of Catastrophic Illness Patients Database affiliated with the National Health Insurance Research Database was used to confirm the SS diagnoses of the patients and to confirm their CRS diagnoses depending not only on CRS-related ICD-9 codes but also on surgery codes specifically by otolaryngologists. It provided accurate and reliable patient data.

In addition, the strong point of this research was that the bacterial cultures of the sinusitis cases were based on the pus obtained during surgical operations. They differed from the bacterial cultures of the nasal secretions collected in the outpatient clinic. These bacterial culture results could be more accurate and better represent the actual pathogenic bacteria of sinusitis. Although we only collected data on the results of sinusitis strains of patients who underwent surgery, it could not represent the status of all sinusitis cases; however, patients who need surgery are generally considered to have more serious or refractory disease manifestation and are clinically difficult to treat. In our study, the analysis of the bacterial species responsible for sinusitis in patients who agreed to undergo surgery was beneficial to clinicians for subsequent reference for the selection of antibiotics.

Our study also has some limitations. For patients with sinusitis, most of the bacterial culture results varied. Nevertheless, we added up the proportion of each bacterial species and compared the difference between SS-CRS and non-SS-CRS, but in fact, the bacterial compositions in patients with CRS were complicated. In addition, age and other comorbidities may be a source of potential bias that could affect the results. Although, the demographic characteristics and comparison of bacterial growth of SS-CRS and non-SS-CRS (Additional file 2: Table S2 and Additional file 3: Table S3) as well as the percentages of top three bacterial genera and species of facultative anaerobes or aerobes and anaerobe in the age of SS-CRS and non-SS-CRS (Additional files 4 and 5: Figs. S1 and S2) were investigated, but the numbers of SS-CRS used for bacterial composition analysis were insufficient to provide matching data on these confounding factors. In the follow-up study, more data for predictive analysis of age and other system diseases and the relationship between the disease severity and pathogenic bacteria as well as the linkage between the bacteria and SS disease activity, and the changes in trends of bacteria, and their antibiotic resistance over time are all areas worthy of research and discussion.

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