The aim of the study was to explore risk factors associated with surgical intervention in OMSI patients. Although we found that several variables showed a correlation tendency with the outcome in the single-factor screening, binary logistic regression ultimately identified 4 key variables: male sex showed negative associations, increased NLR showed positive associations, and abnormal MONO count and RBC count showed positive associations. Among all the factors, NLR, as a composite index, was found to have a significant association with surgical intervention. When used as an independent predictor, the NLR showed good discrimination between outcomes. Additionally, when included as a component in the multivariable regression model, it improved the prediction performance, making the model's ability to predict superior to that of a single factor.
The proportion of male and female patients in the study was relatively balanced, and males comprised 58.7% of the study population. The average age was 53.6 years, which was also close to the population characteristics in other studies on OMSI.18,19
Gender differences are a controversial risk factor related to OMSI. Samuel et al. analysed 1002 hospitalized patients diagnosed with OMSI and found that the probability of males needing immediate airway management was significantly higher than that of females (male 7% vs. female 2%, p=0.001), the WBC count in males was significantly higher than that in females (male 12.4*109/L vs. female 11.1*109/L, p=0.000), and C-reactive protein was also significantly higher than that in females (male 78 mg/L vs. female 59 mg/L, p=0.001).20 Multiple studies have indicated that male patients face a higher risk of hospitalization following surgeries and a greater likelihood of requiring intensive care unit (ICU) treatment.14,21 However, there were also studies showing little correlation between gender and OMSI severity in terms of length and cost of hospitalization, severe complications and reoperation risk.3,10,17 The final regression model of our study retained gender as a risk factor associated with the outcome. The OR value of sex was 0.21<1, indicating that female sex was a protective factor, which was consistent with previous studies. The final regression model of our study found that gender was not statistically significant in relation to the outcome (p=0.092). However, importantly, insignificance does not necessarily mean that the variable should be removed from the model, as a small sample size could also contribute to this result. The use of backwards stepwise selection based on AIC made the result acceptable.
Serum laboratory tests are relatively simple and inexpensive. They are easy to perform and widely accepted by most individuals. We selected routine blood tests and CRP levels as the parameters to be examined, which can provide results quickly. Since these parameters are routinely tested in almost every infection patient who visits the hospital, the prediction can be made at no additional cost. In summary, the prediction can be done quickly and does not impose any extra financial or time burden on the patients.
The NLR has been widely used in prognostic prediction in inflammation-associated diseases such as malignant tumours. In the context of OMSI, it is commonly used as a predictive factor for severe complications and the length of hospitalization. 9,10,22 However, we have not come across any research related to NLR in relation to mild OMSI. Our study demonstrated that the NLR significantly influenced surgical intervention and acted as a risk factor (p=0.045, OR=1.26 [95% CI 1.01-1.57]). The ROC curve analysis revealed that NLR had higher accuracy than other risk factors (AUC=0.725, p=0.01), indicating its ability to correctly identify patients in need of surgical intervention. The determined cut-off value was 5.50, which may provide a reference for clinical work. Furthermore, the final regression model showed even better discrimination (AUC=0.837, p<0.001), suggesting that multiple variables have a stronger impact on the outcome and yield higher discrimination in the results. This provides a reliable basis for determining further surgery and can be considered a criterion for judgement in subsequent clinical decisions. The forest plot and nomogram were used to visualize the results of the regression model. The nomogram, in particular, makes it easy and quick to use the model. These tools provide reliable references for clinical doctors and enable a higher level of nurse care for patients. Additionally, they can help decrease unnecessary consumption of medical resources.
During infection, MONOs further differentiate into tissue macrophages and dendritic cells, thereby mediating the immune response. They also possess the ability to be recruited to the site of infection and directly engage in antibacterial activity. Additionally, they participate in the initial inflammatory response by releasing factors such as tumour necrosis factor (TNF) and chemokines.23,24 All 32 abnormal MONO counts in our study were higher than the normal range. In our statistical analysis, MONO count was found to be significantly associated with the outcome (p=0.023), suggesting that a higher MONO count could be regarded as a risk factor (OR=9.53 [95% CI 1.37-66.17]). However, the confidence interval for this association was wide, possibly due to the use of categorical variables in the statistical analysis or the small sample size and unstable distribution. In further studies, it is recommended to increase the sample size and report MONO count as a continuous variable to better observe its impact on the outcome.
RBCs undergo activation during inflammation triggered by bacterial infection, leading to a sequence of pathological alterations such as erythrocyte deformation and programmed cell death.25 E. Pretorius et al. reported that the erythrocyte membrane interacts with inflammatory molecules, resulting in erythrocyte deformation and programmed cell death. These processes have an impact on haemorheology and can serve as a parameter for identifying the presence and extent of inflammation.26 In our study, all 17 abnormal MONO counts were found to be lower than the normal range, which is consistent with previous studies. The final model in our study included RBCs as a factor (OR=4.37 [95% CI 1.37-66.17], p=0.103]). Similar to the MONO count, the confidence interval was also wide, indicating that further confirmation is needed to determine its specific impact on the outcome.
In addition, we observed a lack of correlation between surgical drainage and CRP levels. This finding is in contrast to previous studies that have demonstrated a relationship between CRP levels and factors such as the length of hospitalization, the number of spaces involved, and the rate of reoperation in OMSI patients.15,17,27 In our study cohort, 82.6% of patients had abnormal CRP levels. This high prevalence can be attributed to the fact that CRP is a highly sensitive and responsive indicator of acute infection. 28,29 Furthermore, we treated CRP level as a categorical variable in our analysis, so the results we obtained showed no significant difference between the group that underwent a surgical intervention and the group that did not.
The study is an exploratory retrospective case‒control study, which inherently has limitations. The small sample size resulted in some statistical results being unstable. Only population characteristics and simple serum laboratory test results were analysed, while other potential risk factors, such as spaces involved, potential systemic diseases, clinical symptoms at admission (fever, pain, mouth opening, etc.), and basic vital signs (blood pressure, pulse, temperature, etc.), were not included in the analysis.