**1. Introduction**

Surgical infections are infectious diseases that can be treated with surgical procedures or occur in the surgical site. Synthetically, these are a localized, closed infectious disease. In the first group, the autonomous infectious pathologies of single organs or closed sites, as abscesses, appendicitis, cholecystitis, colonic diverticulitis, etc., are included. However, in the other group, there are the surgical site infections, surgical wound infections, etc. It is important to remind that the post-surgical infections can develop as local disease or as general disease with startup of systemic inflammatory response syndrome (SIRS) and then sepsis, severe sepsis, and septic shock. The surgical site and wound infections can come from the external environment or from an endogenous contamination. The infections from external environment, hospital ward, operating room, and surgical equipment, are controlled and resolved by sterilization procedures. Very crucial is the role of perioperative nurses, which should control and save the sterile techniques, detect the occurred breaks, and communicate actively to all team members. Less easily the contaminations from endogenous infective agents, pathologic aerobes and anaerobes, that are present, as commensals, in the digestive, biliary and urinary tract, airways, etc., can be controlled. In the perspective of infective risk, surgical procedures have been subdivided into four types. This classification enables proper risk stratification of occurrence of infective complications [1]. Obviously, this risk is not only connected with the environmental or endogenous sources of contamination involved during surgical procedures, but is conditioned by the general conditions of patients, characteristics of occurred intraoperative contamination, etc. [2]. The surgical procedures are classified as following: class I clean intervention—during these procedures, there is no opening of the lumen of intestinal, urinary, respiratory, genital tract; also there is no treatment for inflamed tissues or septic outbreaks. Among these interventions, there are abdominal parietal hernias, thyroid and breast surgery, exploratory abdominal surgery, etc. Class II clean-contaminated intervention—in this class, interventions during which the opening of digestive, urinary, and respiratory tract is scheduled, with checked normal situation and without uncommon contamination are collected. We

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

can list in this the following: group biliary tract, urinary tract, gynecological surgery, appendectomy, etc. Class III contaminated intervention—this section encompasses the procedures with prolonged opening of digestive, biliary, and urinary tract, especially with major leak of intestinal or biliary content. Also there is the presence and treatment of inflamed sites. Usually large bowel surgery should be inserted in this class. Class IV dirty-infected intervention—this includes all surgical procedures for acute peritonitis, with septic collections, pus, and fecal contamination: ultimately all the pathologies with severe septic contamination to be treated by surgery [3].

abdominal surgery, as wound infections after large bowel and gynecological surgery, and intra-abdominal septic collections especially caused by anastomotic leakage. The characteristics of anaerobic infections are the presence of putrid exudate, feculent odor, and gas production [6]. In the immunosuppressed patients, the role of opportunistic bacteria Pseudomonas and Serratia is preeminent, which are external surface contaminants, but usually nonpathogenic. A particular problem is the possible peripheral dissemination of bacteria in case of contaminated wounds. *Streptococcus* bacteria release around the infected site speedily. On the contrary, *Escherichia coli* and *Staphylococcus* are more slower. In this septic scenario, the surgical action of the debridement in the infected wounds is in evidence. With debridement, all devitalized tissues from the site are removed. This action is important because the phagocytic activity of neutrophils in the site of inflammation is more efficacious in reducing the bacteria dissemination if the devitalized tissues have been removed [7]. Also fungi, yeasts, and parasites (*Echinococcus, Amoeba*) can cause infestations; sometime, these develop in the septic collections, abscesses, which require the surgical procedures. The tuberculous infections, usually treated with pharmacological therapy, may be treated by surgery in cases of drug-resistant forms, sequelae of pulmonary tuberculosis, pulmonary aspergilloma, nonfunctioning tubercu-

Introductory Chapter: Surgical Infections http://dx.doi.org/10.5772/intechopen.92259 3

The autonomous infectious diseases of single organs and the surgical site infections, surgical wound infections, in each class of risk, are affected in their clinical evolution by some predisposing conditions. Defective or missing control of external contaminations and imperfect check of intraoperative contaminations have been previously considered. In this scenario, the state and the condition of host's defense mechanisms are certainly crucial. The control of environmental source of contamination can be obtained by strict observance of sterilization procedures of ward, operating room, surgical equipment and devices, etc. To avoid or minimize the risk of intraoperative contaminations, it is decisive to follow the specified well-known procedures for each surgical intervention. More complex is the evaluation of host's defense mechanisms. The first obstacle to infections is the integrity of anatomical barriers: the skin and mucous membranes. Beside anatomical barriers, the immunity system is at the heart of defense mechanisms. Usually, the immunity in the scientific treaties is subdivided into nonspecific and specific immunity. The nonspecific immunity is based on the phagocytic activity of reticuloendothelial system which encompasses distributed phagocytes in the various organs: circulating monocytes and macrophages, polymorphonuclear granulocytes, neutrophils, connective tissue and mucosa mast cells, Kupffer cells in the liver, etc. The phagocytes incorporate pathogenic microorganisms, foreign materials, and cellular debris and destroy them. The macrophages also transport the antigen to the lymph nodes where this stimulates the lymphocytes. The antibodies, secreted by B lymphocytes and bound to particles, favor the recognition of the latter by phagocytes. These accessory cells play a predominant role in killing parasites and in controlling inflammatory processes. The mast cells and basophils contain various molecules which are mediators of inflammation. Consequently, they are very important in the correlations between immune responses and inflammatory reactions [8]. The specific immunity

lous kidney, etc.

**3. Host's defense mechanisms**

### **2. Pathogenesis**

In the clinical scenario of the surgical infections, some factors are in evidence: infectious agents, the patient's immune defenses, and finally, but most important, the physiopathological characteristics of the site of infections, for example, the type of site perfusion. The infections agents are bacteria, virus, fungi, etc. Their involvement can develop as contamination from outside the body or with the assumption of active pathogenetic function of endogenous infective agents and development of disease. The list of possible infectious agents is very long and varied. Aerobic bacteria are steadily on the skin. *Staphylococcus aureus* is always present in wounds infections. *Streptococcus* penetrates usually in the skin's lesions, fractures, and interests connective tissue [4], following which the bacteria invasion of the connective tissue develops a complex vascular, lymphatic, and local tissue reaction which is defined as inflammation. This is a basic reaction to injury is caused by a foreign and deleterious agent and is intended to locate and destroy it. When inflammation is caused by viable agent (bacteria, virus, etc.), it may be considered as the physical basis of infectious process. The morphological picture of inflammation can suggest that inflammation is a relatively static phenomenon. The viable agents in contact with the tissue will cause an inflammatory reaction of various degree of severity, from hyperemia to serious suppurative process. The first step of inflammation process is the alteration of local fluid exchange by an increase of capillary permeability. There is an immunological action of inflammation process, with the purpose to limit the bacteria, firstly by the initial increase of capillary permeability: with the increased passage of plasma protein, there is the accumulation of fibrinogen in the site of lesion, the formation of fibrous network, and occlusion of draining lymphatics by trombi. In this way, the site of inflammation is confined and limited. The celerity and effectiveness of the process of boundary are very important in the control of diffusion of the pathological microorganisms [5]. The staphylococcus is a very damaging agent but in turn causes rapid local fixation and poor dissemination. On the contrary the hemolytic *Streptococcus*, with a local bland action, is consequently more invasive. The role of inflammation in immunity is a control in bacterial invasiveness. Anaerobic microorganisms are more frequently identified in surgical infections. The important pathologic anaerobes with clinical role are *Clostridium*, *Bacteroides*, *Fusobacterium*, *Peptostreptococcus*. All these bacteria are commensals and therefore the origin of anaerobic infections is endogenous; especially in the colon, the anaerobic flora is largely prevalent. We have to add, for its great diffusion, also the *Escherichia coli*, which is anaerobic/aerobic. In fact, *Escherichia coli*, an enteric microorganism, and other enterococci are often detected together with anaerobes in the surgical infections. The most frequent anaerobic surgical infections are the complications of abdominal surgery, as wound infections after large bowel and gynecological surgery, and intra-abdominal septic collections especially caused by anastomotic leakage. The characteristics of anaerobic infections are the presence of putrid exudate, feculent odor, and gas production [6]. In the immunosuppressed patients, the role of opportunistic bacteria Pseudomonas and Serratia is preeminent, which are external surface contaminants, but usually nonpathogenic. A particular problem is the possible peripheral dissemination of bacteria in case of contaminated wounds. *Streptococcus* bacteria release around the infected site speedily. On the contrary, *Escherichia coli* and *Staphylococcus* are more slower. In this septic scenario, the surgical action of the debridement in the infected wounds is in evidence. With debridement, all devitalized tissues from the site are removed. This action is important because the phagocytic activity of neutrophils in the site of inflammation is more efficacious in reducing the bacteria dissemination if the devitalized tissues have been removed [7]. Also fungi, yeasts, and parasites (*Echinococcus, Amoeba*) can cause infestations; sometime, these develop in the septic collections, abscesses, which require the surgical procedures. The tuberculous infections, usually treated with pharmacological therapy, may be treated by surgery in cases of drug-resistant forms, sequelae of pulmonary tuberculosis, pulmonary aspergilloma, nonfunctioning tuberculous kidney, etc.
