Most Common Nosocomial Infections Biology Essay


Surgical wound infections are one of the most common nosocomial infections and not usually localized to the surgical site, in some cases can also extend into deeper tissues; thus, the term surgical wound infection has now been replaced by Disease Control (CDC) with the more appropriate name, Surgical Site Infection (SSI). It is difficult to define SSI accurately with specific definition because it has a wide range of possible clinical symptoms, for this reason, there are criteria to identify SSI including; Infection must occur not more 30 days of the surgical operation date, purulent discharge from the surgical site, organisms isolated from aseptically obtained wound culture and at least one of the signs and symptoms of infection pain or tenderness, localized swelling or redness/heat. For more clarification, it is also classified according to the site of infection into two types; incisional SSIs, which can be superficial when organisms are isolated from fluid/tissue of the superficial incision or deep involves deep soft tissues of the incision and organ or deep layers SSIs, which affect the rest of the body other than the body wall layers and involves anatomical structures not opened during the operation.

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All surgical wounds are contaminated by microbes, but the infection in most cases does not develop because innate host defenses are quite efficient in the elimination of contaminants. Risk of infection is a function of both patient susceptibility and exposure. Although patient-related factors had a statistically significant association with risk of infections, a complex interaction between host, microbial, and surgical factors ultimately determines the prevention or establishment of a wound infection. Factors that affect surgical site infections will be discussed in the next pages.

Among surgical patients, SSIs are the most important infection, accounting for about a third of all such infections. It is difficult to independently identifying the influence the risk of infection due to the complex nature of SSIs and to the great difficulty in designing and conducting studies that accurately isolates the effect of a single factor.

The risk factors and their affecting on each other are shown in Figure 1.

The most widely accepted patient and operative characteristics risk factors that may increase a client’s risk of surgical site infection can be grouped into three categories; patients-related, microbial-related and surgical-related factors:

Patients-relate factors:

Diabetes Mellitus:

Although diabetes and high blood pressure are not independent risk factors, they should be under control before elective surgery. Maintaining a normal blood glucose level is important during the surgery and during the post surgery period. High levels of blood sugar are linked to a higher risk of post-surgical infections.

Immunocompromised patients

Those with HIV/AIDS, cancer, chronic corticosteroid use such as occur with asthma and heavy smokers or users of other tobacco products are at significantly greater risk of SSIs.


Surgical-related factors

Prolonged preoperative stay

Surgical technique

Hair removal

Long operation time

Tissue ischaemia


Microbial-related factors

Colonization with microorganisms

Pre-existing infection

Antibiotic resistance


Patient-related factors

Age, sex, and chronic diseases

Diabetes Mellitus




Increased immunosuppresion

Affected by A and B


Recurrent of bacterial infection

Affected by A and C

Wound contamination

Decrease Collagen synthesis

Affected by B and C

Increase amount of resistant bacteria

Decrease neutrophil bactericidal activity

Recurrent of bacterial infection

Decrease Collagen deposition

Increase wound infection

Wound breakdown

Delay of wound healing

Poor wound healing

Increase the risk of SSI

Figure 1 - Factors that affect surgical site infection and wound healing.


Increases risk substantially when the subcutaneous abdominal fat layer exceeds 3 cm. The risk is increased by the need for a larger and deep incision decreased the blood circulation to the fat tissue or the technical difficulty of operating through a large fat layer.


Malnutrition may or may not be a contributing factor. Unfortunately, most studies have been conducted in developed countries where severe malnutrition is less common than developing countries, so the obtained data are not reflect the exact risk factor degree.

Age, race, socioeconomic status and chronic diseases,

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Such as diabetes and malignancy, are difficult to assess because they are frequently associated with other factors that independently contribute to risk. For example, age over 70 may be accompanied by decreased defense mechanisms, poor nutrition and anemia.

Microbial-related factors:

Colonization with microorganisms

Microbial factors that influence the establishment of SSI are the bacterial inoculum, virulence, and the effect of the microenvironment. When these microbial factors are in combination with impaired host defenses set the stage for start the sequential of events that lead to wound infection. Most SSIs are contaminated by the patient's own endogenous flora, which are present normally on the skin, mucous membranes. The pathogens isolated from infections differ, primarily depending on the type and site of surgical procedure. In clean surgical procedures, the usual pathogens on skin and mucosal surfaces are gram-positive cocci (e.g staphylococci) whereas gram-negative aerobes and anaerobic bacteria contaminate skin in the deep areas. The contaminating pathogens in gastrointestinal surgery are usually from bowel flora, which include gram-negative bacilli (eg, E. coli) and gram-positive microbes, including enterococci and anaerobic organisms. Gram-positive organisms, particularly staphylococci and streptococci, account for most exogenous flora involved in SSIs. The possible sources for the contamination with these pathogens are including surgical personnel and intraoperative circumstances including poor surgical instruments.

The most common group of bacteria responsible for SSIs is Staphylococcus aureus and with emergence of resistant strains which considerably increased the burden of morbidity and mortality associated with wound infections. Like other strains of S aureus, MRSA can colonize the skin and body without causing any symptoms, and, in this way, it can be passed to deep tissues when the integrity of skin is compromised by surgery procedure. MRSA infections appear to be increasing in frequency and displaying resistance to a wider range of antibiotics which increase the challenges in the treatment of the infections with MRSA because treatment options with antibiotics are very limited.

Pre-existing remote body site infection:

The major concerns about the presence of a pre-existing infection are that it may be the source for infection spread, causing late infections to the surgical site, or be a contiguous site for bacterial transfer. These infections at a site remote from the wound have been linked to increasing SSI rates three- to five-fold.

Patients with infections remote to the surgical site should be treated if possible or their surgery postponed as in certain surgical cases, especially those requiring implanted devices, may demand that the operation be postponed until the infection is resolved

Surgical-related factors:

Prolonged preoperative stay

Prolonged preoperative hospitalization exposes patients to hospital flora, including multidrug-resistant organisms. Completing pre surgical evaluations and correcting underlying conditions before admission to a hospital decreases this risk. Also, performing elective surgery, where feasible, in ambulatory surgery centers rather than acute care hospitals decreases the risk of exposure to hospital flora.

Surgical technique and practice:

Intra operative contamination, including infected operation staff, instruments and inadequate ventilation are the most important factors to SSI. Good surgical practice minimizes tissue trauma, controls bleeding, eliminates dead space, removes dead tissue and foreign bodies, uses minimal suture and maintains adequate blood supply and oxygenation are important to prevent or at least decrease SSI.

Hair removal:

Shaving is a proven risk factor for SSIs and it is now recognized that shaving damages the skin and that the risk of infection increases with the length of time between shaving and surgery, so preoperative hair removal should be avoided if it is unnecessary. If hair must be removed, it should be performed as close to the time of surgery as possible.

Long operation time (>2 hours)

Increased length of surgical procedures is associated with increased risk of SSIs. It is estimated that the infection rate nearly doubles with each hour of surgery.