# Chronic Periodontitis and Acute Respiratory Infections: A Nationwide Cohort Study
## 4 Discussion  
Poor oral hygiene associated with local oral infections, especially CP, is known to be a risk factor for acute and chronic respiratory infections. In this study, a significant positive association was found between CP and acute respiratory infections, excluding influenza and acute pneumonia, even after adjusting for sociodemographic variables and comorbidities. Various possible underlying physiological mechanisms for the role of oral bacteria in the pathogenesis of acute and chronic respiratory infections have been suggested [17; 18]. First, dental plaque and calculus can serve as a reservoir for pulmonary pathogens that cause respiratory infection in high-risk elderly people in medical or surgical units. Second, salivary enzymes associated with CP can promote the adhesion of respiratory pathogens to the mucosal tissues of the oral cavity and respiratory tract. In particular, _Porphyromonas gingivalis_-induced hydrolytic enzymes may destroy the salivary pellicles that resist pathogenic bacteria. Finally, a large variety of cytokines and other biologically active inflammatory mediators induce alteration of respiratory epithelial tissues, which is another potential biological mechanism in the pathogenesis of respiratory infections. The incidence and severity of chronic respiratory infections are likely to be affected by the severity of CP [19; 20; 21; 22]. A cross-sectional study of the National Health and Nutrition Examination Survey (NHANES) III database reported an increased risk of respiratory infection in patients with clinical attachment loss \(\geq\)3 mm compared to those with clinical  
Figure 2: Associations of acute respiratory infections with chronic periodontitis in the univariate and multivariate logistic regression analysis. Model 1: unadjusted, Model 2: adjusted for age and sex, Model 3: model 2 plus adjustment for smoking and household income status, and Model 4: model 3 plus adjustment for diabetes mellitus. attachment loss <3 mm (OR, 1.45; 95% CI, 1.02-2.05). Another long-term study found that increased alveolar bone loss is associated with an increased risk of respiratory infection (OR, 1.8; 95% CI, 1.3-2.5). [19,20] [PERSON] et al. suggested that the comparative risk of developing postoperative respiratory infection in patients with severe CP was 3.5-fold higher than that in patients with incipient CP (\(p<0.0001\)) [21]. Moreover, a longitudinal retrospective investigation demonstrated that elderly patients (aged > 80 years) with CP may have a higher and increased risk of mortality associated with respiratory infection (Hazard ratio, 3.9; 95% CI, 1.1-3.9; \(p<0.05\)) [22]. However, there are very few studies on the association between CP and acute respiratory infections. This cohort study found that both acute upper and lower respiratory tract infections (including acute nasopharyngealitis, acute pharyngitis, acute tonsillitis, acute laryngitis and tracheitis, acute bronchitis, and acute bronchiditis) were significantly associated with CP; these findings are similar to the corresponding findings with regard to chronic respiratory infections. The results of this study did not show a statistically significant association between CP and influenza and acute pneumonia (\(p>0.05\)). In particular, there was a negative correlation between CP and acute pneumonia, although this was not statistically significant (OR, 0.96; 95% CI, 0.93-1.00; \(p=0.068\)). The relationship between CP and respiratory infections remains unclear because influenza and acute pneumonia are fast-developing respiratory illnesses. Underestimation of the prevalence of influenza and acute pneumonia may weaken the causal relationship and association of CP with influenza and acute pneumonia. Various clinical and epidemiological studies have demonstrated that self- or professional-driven good oral hygiene practices, such as tooth brushing and professional periodontal treatment, can significantly reduce the incidence or severity of respiratory infections [23,24].