A surgical site infection (SSI) is an infection that occurs at or near a surgical incision site within 30 days following a surgical procedure. SSIs are primarily caused by bacteria entering the body through the incision, leading to localised signs of infection such as redness, swelling, warmth, and pain. Globally, the incidence of SSIs ranges from 3% to 15%, with approximately 11 out of every 100 surgical patients developing an infection within 30 days (Gillespie et al, 2021). SSIs are becoming increasingly prevalent among women giving birth, particularly due to the growing number of caesarean deliveries. This trend is closely associated with rising rates of overweight and obesity among women of childbearing age (Weiss et al, 2004; Callaway et al, 2006).
The NHS in the UK reported a significant increase in births by caesarean section, rising from 9% in 1980 to 25% by 2009/2010 (Bragg et al, 2010). In 2010, for a hospital performing 800 caesarean sections annually with a 9.6% infection risk, the associated costs were estimated at £18914, with 28% (£5370) attributed to community care. Adjusted for inflation to 2019 prices, the total annual cost of all caesarean sections performed in England during 2018–2019 was estimated at £5.0 million, with each infection contributing an average of 10 extra hospital days per patient (Wloch et al, 2020). The cost per infection was approximately £1866 for hospital care and £93 for community care. Further studies have shown that SSIs significantly increase the risk of maternal sepsis, wound dehiscence, and maternal mortality (Ali and Lamont, 2019). SSIs also negatively impact both maternal and fetal wellbeing, extend hospital stays, and complicate breastfeeding, which can hinder the bonding process between mother and child (Smorti et al, 2019).
Wound infection
SSIs typically present with symptoms such as erythema, pain, discharge, and induration around the surgical incision, accompanied by localised signs of infection, including elevated body temperature, fever, chills, raised white blood cell count, and purulent discharge. These complications occur in 2–7% of patients and generally develop between 4 and 7 days post surgery. SSIs are classified into three categories depending on how deep the infection is (Table 1).
| Superficial SSI |
| An infection that develops within 30 days of surgery and affects only the skin and subcutaneous tissue at the incision site is classified as a superficial surgical site infection if any of the following criteria are met:
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| Deep incisional SSI |
| An infection that develops within 30 days of surgery (if no implant is used) or within 1 year (if an implant is involved) is considered a deep incisional surgical site infection if it affects the deep soft tissues, such as the fascia and muscle, at the incision site and meets at least one of the following criteria:
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| Organ/space SSI |
| An infection is classified as an organ/space surgical site infection if it occurs within 30 days after the operation when no implant is involved, or within 1 year if an implant is present, and the infection is related to the surgical procedure, involving any part of the anatomy, such as organs. The infection must meet at least one of the following criteria:
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Source: Wounds UK, 2020
In caesarean section surgeries, groups A and B haemolytic Streptococcus are the most common pathogens causing SSIs. Other frequently identified pathogens include Ureaplasma urealyticum, Staphylococcus epidermidis, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, and Proteus mirabilis (Roberts et al, 1993; Martens et al, 1995).
Risk factors
Risk factors for caesarean SSI can be categorised into three main groups: host-related risk factors (Box 1), pregnancy and intrapartum-related risk factors (Box 2), and procedure-related factors (Box 3).
Host-related risk factors for caesarean section surgical site infection
Pregnancy and intrapartum-related risk factors for caesarean section surgical site infection
Procedure-related risk factors for caesarean section surgical site infection
Host-related
Mothers aged under 35 years are less likely to have an SSI after caesarean section than those over the age of 35 (Zejnullahu et al, 2019). Having had a previous caesarian section is often assumed to mean the mother is at increased risk of SSI due to poor healing of previous scarred tissue in which an incision is repeated, relative avascularity, more blood loss during surgery and longer duration. However, research by Jido and Garba (2012), among others, found this was not the case: women with previous caesarean section had lower odds than primary caesarean section.
As discussed above, the increase in the number of caesarean deliveries has been linked to a rise in overweight and obesity in childbearing women, and some studies have shown that obesity should be considered as an independent risk factor for post-caesarean infectious morbidity (Tran et al, 2000; Weiss et al, 2004). Factors associated with poor wound healing in obese women following caesarean section include not only comorbidities such as diabetes and prolonged use of steroids (De Vivo et al, 2010) but also length of surgery, use of prophylactic antibiotics (Hopkins and Smaill, 2012), type of skin preparation (Olsen et al, 2010) and skin closure technique (Vermillion et al, 2000; Johnson et al, 2006). Obesity reduces the availability of oxygen to the wound. Skin folds can harbour bacteria and damage can be caused by skin-to-skin friction and increase the risk of pressure ulcer development (Mitchell, 2018).
Poorly controlled diabetes impairs the host immune response and delays re-epithelialisation of wounds. Elevated blood sugars decrease red blood cells, which carry nutrients to the tissue, and lowers the efficacy of white blood cells (neutrophils and monocytes) to fight infection (Mitchell, 2020). The risk of SSI is also affected by other previous medical conditions that impact on metabolism, circulation/oxygenation of tissues, inflammation or immune response, such as hyperthyroidism, anaemia, heart disease, respiratory tract infections with fever, immune-mediated disorders, renal and liver impairment, or immunosuppression (whether due to medications (eg, corticosteroids, chemotherapy), HIV, or other conditions) (Mitchell, 2020).
For example, hyperthyroidism accelerates the body's metabolism and affects the body's response to stress and injury, potentially leading to impaired immune function and delayed wound healing, while increased metabolic demands can result in nutritional deficiencies, compromising wound healing. Many medications interfere with clot formation or platelet function, inflammatory responses and cell proliferation. Common among these are steroids and non-steroidal antiinflammatory drug. On the other hand, ineffective wound pain management can delay wound healing and contribute to a lack of concordance with treatment (Frescos, 2011).
The pathophysiological mechanisms for increased SSIs in smokers are thought to involve carbon monoxide, nitric oxide, and nicotine. These agents may have a direct action on endothelial dysfunction or other vasoactive effects that may lead to postoperative tissue necrosis, impairment of the inflammatory healing response or bactericidal mechanisms and delay proliferative healing responses. Smoking causes vasoconstriction, which leads to hypoxia. Neutrophil and monocyte (cells that help prevent infection) activity are reduced, and fibroblast proliferation and migration are reduced. Collagen is reduced in smokers, which means less tensile wound strength (Mitchell, 2020).
Another factor is whether the person's nutritional intake can meet the increased energy demands during the healing process. Inadequate protein leads to skin fragility, decreased immune function and poor wound healing. The body requires 30–35 Kcal daily to heal a wound (Mitchell, 2020). Dehydration increases the risk as fluids are required for oxygen profusion, hydration of the wound bed, transportation of nutrients, as a solvent for vitamins, minerals, glucose, amino acids and to transport waste away from cells (Mitchell, 2020).
Pre-existing psychiatric morbidity (ie anxiety, depression and post-traumatic stress disorder) and acute stress and anxiety also have an impact. Depression in pregnancy is associated with poorer obstetric outcomes, ie pre-term delivery due to elevated cortisol (O’Keane and Marsh, 2007). Stress delays wound healing by altering the multiple physiological pathways required in the repair processes (Gouin and Kiecolt-Glaser, 2012). Stressors can lead to negative emotional states, for example, anxiety and depression, which have an impact on physiological processes and behavioural patterns that influence health outcomes (Guo and DiPietro, 2010).
Pregnancy and intrapartum-related
Multifetal gestations are more likely to result in a caesarean section, but twin (or multiple) gestations are considered to increase the risk of SSI for several reasons. One of these is an increased number of vaginal examinations – multiple vaginal examinations increase the risk that the endogenous vaginal microbiota that causes SSI might spread to the upper genital tract. Prolonged surgery, as would be the case when delivering more than one infant, increases wound exposure time to potential pathogen.
Furthermore, the physiological changes in pregnancy that alter the pharmacokinetic handling of many medications are more pronounced in multifetal gestations (Norwitz et al, 2005). During pregnancy with twins or more, the increased total body water and higher glomerular filtration rate affect how the kidneys distribute and clear the antibiotic, cephalosporin. These changes may result in lower tissue antibiotic concentration during caesarean delivery, potentially impacting its effectiveness. Similar alterations in cephalosporin clearance and volume of distribution occur in obese patients. However, it is worth noting that some groups have observed a decreased risk of post-partum infection in twin caesarean compared with singleton caesarean delivery (Alexander et al, 1997).
Premature rupture of membranes increases exposure time to potential pathogen and a restrospective study carried out in Ethiopia (Molla et al, 2019) found that in women with premature rupture of membranes, the occurrence of SSI was more than twice as high than for those without. It is thought that the amniotic fluid, amniotic membrane and cervical mucus plug act as natural barriers to infection throughout pregnancy. However, when these barriers are compromised due to amniotic fluid losing its sterility, the protective role is compromised. It is also thought that contaminated amniotic fluid can act as a point of entry for bacteria into the skin incision and uterus, contributing to the development of chorioamnionitis and related inflammation (Molla et al, 2019).
Chorioamnionitis is a serious intrauterine infection that occurs during pregnancy, which involves the membranes surrounding the fetus in the uterus, specifically the chorion (outer membrane) and the amnion (inner membrane). Chorioamnionitis leads to tissue inflammation and damage, impairing tissue integrity and increasing the risk of infection (Gomaa et al, 2021).
Prolonged second stage of labour or prolonged rupture of membranes can compromise tissue integrity and blood circulation to tissues resulting in tissue ischaemia (Kawakita and Landy, 2017). Nulliparity (having never given birth) is considered a risk factor because of the likelihood of a longer labour, but also because of hormonal changes affecting the immune response, increased anxiety and stress, and a prolonged hospital stay increasing exposure to hospital-acquired infections (Tran et al, 2000). Limited prenatal care (fewer than 7 visits) is linked to an increased risk of SSI because it can mean uncontrolled or undiagnosed pre-existing conditions, limited health monitoring and advice, and a lack of maternal education (Killian et al, 2001).
Research shows a five-fold increase in the risk of developing an SSI for mothers who develop pregnancy-induced hypertension (Gomaa et al, 2021). The possible explanation for this is that the peripheral vasoconstriction effect of pregnancy-induced hypertension causes hypoperfusion of the wound. Bacteria thrive on poorly perfused hypoxic wounds, the inflammatory phase is prolonged, which delays wound closure and increases the risk of infection. In addition, these mothers may have oedematous wound edges, which impairs the migration of immune cells such as neutrophils to the wound site during the inflammatory phase (Wu et al, 2023). Oedema competes for oxygen from the tissue and infection can alter the balance of inflammation. Myofibroblast activity, collagen disposition and cross-linking disruption caused by periwound oedema inhibits the proliferation phase resulting in delayed wound closure.
Post-partum anaemia requiring blood transfusion presents an increased risk of SSI because it depletes the mother of erythrocytes and white blood cells, which play an important role in hosting an immune response (Caljé et al, 2024).
Endometritis is infection of the inner lining of the uterus, causing inflammation, which impairs wound healing and increases susceptibility to SSIs. It is the most common postpartum infection (Taylor et al, 2024). Bacteria from the infected endometrium can spread to the surgical incision site (Kawakita and Landy, 2017).
Procedure-related
Skin is a main source of pathogens causing SSI. Preoperative skin preparation with antiseptic agents has been proven to reduce the risk of SSI (Mangram et al, 1999). However, there is no consensus regarding what type of skin preparation may be most efficient for prevention of post-caesarean SSI. There is no adequate literature to rely on regarding hair removal techniques before caesarean section, and the recommendations are extrapolated from other types of surgery. Although a Cochrane review (Tanner et al, 2021) concluded that hair removal appeared to reduce SSIs at the time of surgery, it advised that more studies were needed to determine whether time of hair removal had an effect on wound complications, length of hospital stay or costs. Shaving the surgical site has been shown to be associated with significantly higher rates of SSI compared with clipping, as a result of microscopic breaks in the skin caused by the razor (Zuarez-Easton et al, 2017). Hair shaving, particularly on the day before the procedure, has been linked to a higher percentage of SSIs in elective gynaecological surgery (Kamat et al, 2000).
Emergency surgery has a four times higher chance of SSI than elective surgery. Emergency caesarean section may involve larger incisions or suboptimal wound closure (Kawakita and Landy, 2017). Excessive blood loss during emergency caesarean can lead to tissue hypoxia, reduced white blood cells such as neutrophils and macrophages, and haematoma formation, which provides a favourable environment for bacterial growth; also, prolonged surgery duration increases the risk of contamination (Berríos–Torres et al, 2017).
As well as the risks associated with obesity already discussed, the relative avascularity of adipose tissue presents a risk during the procedure. Handling of adipose tissue can also result in more trauma to the anterior abdominal wall or difficulty in obliterating dead space in the fatty tissue of the abdominal wall (Dagshinjav et al, 2017).
In caesarean deliveries the placenta is usually removed by hand or by a technique known as ‘cord traction’. A systematic review by Anorlu et al (2008) showed that cord traction poses less risk of introducing bacteria than manual removal.
Skin closure with staples has been shown to increase the risk of wound infection or wound separation. Suture closure of subcutaneous tissue if wound thickness is greater than 2 cm has been shown to decrease the rate of wound complications, and lower risk of seroma and haematoma, or wound infections (Chelmow et al, 2004). Subcutaneous haematomas and seromas (collection of serum) can cause the incision to separate. When the wound edges separate bacteria can gain access and grow inhibited in the stagnant fluid (Kawakita and Landy, 2017).
Finally, it is worth noting that variations in local hospital practices can also have an impact on the risk of SSIs – different protocols for wound care, antibiotic administration and surgical techniques.
Interventions
Interventions for preventing and managing SSIs encompass a range of strategies throughout the perioperative period. These interventions can be categorised into preoperative, intraoperative, and postoperative measures:
Preoperative interventions
Smoking cessation
Education
Preoperative screening
Intraoperative interventions
Patients are encouraged to bathe or shower with an antiseptic agent, such as chlorhexidine, before surgery to lower the skin's microbial count. Using chlorhexidine-alcohol solutions for skin preparation prior to incision has been shown to decrease the risk of SSI (Fitzwater and Tita, 2014). Additionally, pre-operative vaginal cleansing with iodine, or off-label chlorhexidine, is recommended (Haas et al, 2020). The use of clippers or depilatory cream instead of a razor is advised to avoid the risk of wound infection due to small skin abrasions caused by shaving (Tanner et al, 2021).
Administering antibiotics within 60 minutes before making the incision is recommended, typically using those that are effective against common skin pathogens. Research indicates that administering prophylactic antibiotics before incision (Owens et al, 2009) significantly reduces SSI risk, particularly for high-risk groups such as smokers, individuals with obesity, those with multifetal pregnancies, and diabetic patients. Increased doses of preoperative antibiotics may be needed in these cases (Bratzler et al, 2013; Anderson et al, 2014). The use of firstgeneration cephalosporins after caesarean sections has been associated with a lower risk of SSI compared with no antibiotics (Smaill and Grivell, 2014; Kawakita and Landy, 2017).
Optimising blood sugar levels (glycaemic control), especially in diabetic patients, is crucial for reducing infection risks (Guo and DiPietro, 2010). The surgical team would seek to keep the patient's body temperature within a normal range during the surgery, as hypothermia can impair immune function and increase infection risk (National Institute for Health and Care Excellence (NICE), 2013).
Other interventions would include ensuring strict adherence to sterile techniques and maintaining a sterile environment during surgery (aseptic technique), applying an appropriate antiseptic agent (eg, alcohol-based solutions containing chlorhexidine or povidone-iodine) to the surgical site (NICE, 2020), and intraoperative wound irrigation with saline or antiseptic solutions to reduce bacterial contamination (Mueller et al, 2023). Keeping operative time shorter also minimises the risk of infection, compared with longer duration (Kawakita and Landy, 2017).
Extracting the placenta through controlled umbilical cord traction, as opposed to manual removal, is recommended (Norwitz et al, 2005). When it comes to closing the wound, suggested measures to prevent SSI are suturing the subcutaneous tissue if the wound depth exceeds 2 cm (Chelmow et al, 2004), and using 4-0 poliglecaprone 25 sutures for skin closure instead of staples.
Postoperative interventions
Hygiene is one preventive measure that can reduce SSIs in the postoperative period, encouraging women to take daily showers with 2% chlorhexidine gluconate for 7 days 24 hours after the dressing is removed (Kawakita and Landy, 2017). Early mobilisation after surgery is encouraged to promote circulation and healing. Blood glucose levels should be monitored and controlled to reduce infection risk. If an infection does develop, appropriate antibiotic therapy should be provided based on culture and sensitivity testing results.
Wound care: NPWT and hydrocolloid dressings
Negative pressure wound therapy (NPWT) is a term describing a broad system that aids wound healing through the application of sub-atmospheric pressure to reduce inflammatory exudate and promote granulation. NPWT optimises the physiology involved in wound healing through the principal mechanisms of macro deformation (reduces wound space by applying 125 mmHg of sub-atmospheric pressure to the wound bed by the foam dressing), micro deformation, excess fluid removal and equilibration of the wound microenvironment (Yamashiro et al, 2023).
The benefits of NPWT is likely related to improved dressing integrity, especially in the setting of a sub-panniculus incision, as well as increased absorption of wound exudate. A sub-panniculus incision helps surgeons to manage the challenges posed by the tissue. It involves making the incision below the panniculus, typically just above the pubic area, to ensure better visibility and access to the uterus while minimising the risk of wound complications.
In a study involving 50 high-risk patients with a BMI of 35 kg/m2 or more, the use of single-use NPWT for 7 days post-surgery successfully prevented infections and hospital readmissions (Bullough et al, 2014). There have been individual efforts to apply NPWT in the management of necrotising fasciitis in women following caesarean sections. Through a comprehensive treatment approach, which included surgical removal of necrotic tissue, use of broad-spectrum antibiotics, and the simultaneous use of NPWT, the wounds of two patients diagnosed with this potentially fatal postoperative infection were successfully healed (Nissman et al, 2011; Durai et al, 2012).
Hydrocolloid dressings have similar properties to NWPT in terms of dressing integrity and absorption of exudate to a lesser extent. The cost of hydrocolloid dressings is significantly cheaper than negative pressure dressings, and typically similar to basic contact dressings (hydrocolloid dressings may be cheaper than frequently used advanced basic contact dressings) (Gillespie et al, 2021). Table 2 considers the difference between the two dressing options.
| NPWT | Hydrocolloid dressings |
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Contraindications of NWPT
Although less common in caesarean section SSIs, NPWT must be used with caution to minimise associated risks. NPWT can pose significant dangers when applied to certain types of wounds or conditions. For example, in malignant lesions, NPWT may inadvertently stimulate tumour growth and metastasis by improving blood flow and promoting cellular activity that could benefit malignant cells, with a potential risk of spreading these cells through the lymphatic or circulatory systems. In cases of extensive necrosis, NPWT might exacerbate tissue damage and worsen ischemia (Beral et al, 2009). When osteomyelitis, an infection of the bone, is present, NPWT can spread the infection, complicate treatment, and potentially worsen the condition, as it does not address the need for targeted antibiotic therapy or surgical intervention. Applying NPWT to fistulas, abnormal connections between body parts, can further damage tissues, disrupt the healing process, and potentially enlarge the wound or create new infection pathways.
Additionally, NPWT should be avoided when there are exposed blood vessels, nerves, bones, or organs, as it may cause direct trauma to these sensitive structures, resulting in severe pain, nerve damage, bone erosion, or organ injury, while also increasing the risk of infection and hindering the natural healing process (Rasko et al, 2018).
Recommendations for practice
Conclusion
The rising prevalence of surgical site infections following caesarean sections indicates a need for revised practices to address risk factors before, during, and after surgery. Changes in interoperative interventions and postoperative interventions can help to mitigate risk factors alongside clinicians’ understanding of the intrinsic and extrinsic factors that influence wound healing. To enhance dressing integrity and minimise complications, the use of NPWT and hydrocolloid dressings has shown promise. However, NPWT should be applied with caution and strictly in line with local trust guidelines to ensure its safe and effective use.