Postoperative SSI are an important marker of surgical quality and are associated with longer hospital stays, higher rates of reoperation and readmission, and increased mortality. Poor survival was observed in patients with various types of cancer who exhibited SSI after surgery. It has also been suggested that SSI are associated with shorter disease-free and overall survival in several types of cancer, such as head and neck cancer, breast cancer, colon cancer, and gastric cancer2. Furthermore, Nespoli et al. showed that postoperative infections were associated with a poor 5-year survival rate among colon cancer patients . SSI are one of the most common postoperative morbidities, occurring in 5–40% of patients who undergo colorectal surgery2. In addition, it was reported that SSI occur in 7.6% of patients after major abdominal surgery. In the present study, SSI arose in 9.9% of patients, which was compatible with the findings of previous studies. As SSI occur quite frequently, measures aimed at preventing them are required.
Many investigators have studied the factors that influence the prevalence of SSI after abdominal surgery. Togo et al. revealed that SSI were significantly associated with a long operation time, marked intraoperative blood loss, a high blood transfusion requirement, and bile fistulas among liver cancer patients . Mingmei et al. demonstrated that SSI were significantly associated with the type of surgery; the surgical procedure (laparoscopic or open); and hospital size; i.e., the number of beds, in patients with colorectal cancer . Fukuda et al. showed that SSI were significantly associated with blood transfusions, the use of antidiabetic drugs, the use of steroids, the operation time, the ASA classification, the surgical procedure, emergency surgery, and age . In the current study, we retrospectively reviewed the cases of patients who underwent abdominal surgery and tried to identify factors that influence the prevalence of SSI. As a result, we found that hepatic, biliary, or pancreatic surgery; a poorer ASA physical status; and a longer operation time were significantly associated with a higher prevalence of SSI. Most of these risk factors are difficult to control before surgery.
On the other hand, this study revealed that POM interventions had independent, significant, and beneficial impacts on the risk of SSI after abdominal surgery. Recently, Nobuhara et al. reported that POM reduced the risk of SSI after surgery for colorectal cancer4. Our findings were compatible with those of the latter study. Other studies have found that preoperative oral care reduced the risk of postoperative pneumonia after surgery for esophageal, lung, or major cancer [14–16]. As the aspiration of oral/oropharyngeal fluid containing pathogenic microorganisms is considered to be the main cause of postoperative pneumonia, it is logical that controlling oral bacteria reduces the risk of postoperative pneumonia. Similarly, our results suggested that the use of POM might significantly reduce the risk of SSI after abdominal surgery.
Gingivitis and periodontal disease provide opportunities for bacterial overgrowth, and the richly vascularized and often ulcerated tissues associated with these diseases are susceptible to bacterial invasion . The bulk of dental plaque, such as biofilm, is composed of microcolonies of oral bacteria . Nobuhara et al. mentioned that the oral cavity is recognized as a significant reservoir of pathogenic microorganisms, which can infect multiple organs . Oral bacteria are known to influence various general diseases, such as pneumonia, cardiovascular disease, cerebrovascular disease, rheumatoid arthritis, preterm or low-weight births, sepsis, carcinogenesis, and non-alcoholic steatohepatitis, and SSI [18, 19]. Therefore, achieving quantitative and qualitative control of oral bacteria via oral healthcare is considered to be important for preventing infectious diseases.
The direct transfer of oral bacteria might cause SSI after head and neck or upper digestive tract surgery, as well as postoperative aspiration pneumonia5. In addition, the intravascular invasion of odontogenic bacteria, inflammatory cytokines, and/or endotoxins, and their transport to remote organs through blood vessels or lymph ducts might cause SSI at various surgical sites . It is well known that transient bacteremia often occurs after tooth extraction and tooth brushing. The CDC guidelines suggest that preoperative infectious lesions at remote sites are a risk factor for SSI . In 2012, POM started to be covered by the Japanese national health insurance system, and it has since been widely performed in patients that are scheduled to undergo cancer treatment, organ transplantation, cardiovascular surgery, or orthopedic implant surgery. We assessed the changes in the prevalence of oral bacteria detected in blood cultures before and after the introduction of insurance coverage for POM and found that the introduction of insurance coverage for POM had a beneficial effect on the frequency of systemic infections caused by oral bacteria .
In addition, we recently found that POM had significant positive effects on perioperative serum albumin levels in patients that were treated surgically under general anesthesia (submitted for publication). It has been reported that a decreased serum albumin level is an independent risk factor for severe postoperative complications and a poor prognosis . Some researchers have reported that dental infections and poor oral health are closely related to lower serum albumin levels. POM, including oral care, the removal of chronic dental infections, and prosthodontic treatments, has positive effects on serum albumin levels, which might consequently reduce the risk of SSI after abdominal surgery .
One of the major advantages of the present study is that it was the first to clarify the beneficial effects of POM on the risk of SSI in patients that undergo abdominal surgery, based on a multicenter retrospective study involving a large number of cases. As for the limitations of the present study, the POM criteria and treatment protocols differed from institute to institute because of the study’s retrospective nature. In addition, the POM intervention rate was quite low (28.0%). However, there are ethical difficulties associated with conducting a prospective randomized control study to evaluate the efficacy of POM because POM has only been covered by the Japanese national health insurance system since 2012, and most Japanese patients now receive POM before undergoing cancer, cardiovascular, or transplant treatment. Furthermore, the protocols for and aims of dental interventions are still subject to debate. The establishment of guidelines for POM in patients that are scheduled to undergo surgery is needed in order to standardize such dental interventions.