The figure is higher than would be expected for surgery in an area of the body not known for having high bacterial levels.
Most at risk are overweight or obese women, although younger women are also said to be more prone.
Now the Health Protection Agency, which carried out the study, is calling on hospitals to make reducing the rates of post C-Section infection a “priority” through closer monitoring after surgery and by improving surgical techniques.
Dr Elizabeth Sheridan, head of Healthcare Associated Infections at the HPA, said: “Reducing rates of surgical site infections following a caesarean should be made a priority.
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“Given that one in four women deliver their baby by caesarean section, these infections represent a substantial burden. They will impact not only directly on the mother and her family but also are a significant cost in terms of antibiotic use, GP time and midwife care and every effort should be made to avoid them.”
She said women opting for elective Caesareans should be made aware of the risk of infection, particularly if they are overweight.
And she added: “As has been seen in both this study and several others, there is an established link between BMI and an increase in the risk of developing a surgical site infection. Monitoring infections in women having a Caesarean section is important as a means to drive down infection rates.
“As levels of obesity are rising, optimising surgical techniques and identifying the most appropriate dosing of antibiotics could provide a means for reducing wound infections in obese women.”
Post-Caesarean surveillance for surgical site infection is compulsory in Scotland, Wales and Northern Ireland, but not in England.
Yet the Advisory Committee in Antimicrobial Resistance and Healthcare Associated Infection advised in 2010 that it should be made mandatory. The HPA is seeking funding to establish such a programme for England.
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The research – published today in the British Journal of Obstetrics and Gynaecology - identified 394 so-called “surgical site” infections among 4,107 women surveyed following C-Sections (9.6 per cent).
In comparison, infection levels following hysterectomy are much lower at 6.6 per cent.
Although the majority – 88 per cent – were minor infections, they still required antibiotic treatment.
Around five per cent were deep incisional surgical infections affecting deeper tissues beneath the skin, requiring antibiotics along with possible hospitalisation and even additional surgery in the most serious cases.
Nearly seven per cent were organ/space infections – most of which involved the lining of the womb and required intravenous antibiotics and often hospitalisation.
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The risk was also found to be greater among those with a higher body mass index (BMI). Those who were overweight and had a BMI of 25 to 30 were 1.6 times more likely to develop an infection, while obese women (with a BMI of between 30 and 35) were 2.4 times more likely. Those with a BMI over 35 were 3.7 times more likely.
Those under the age of 20 were nearly twice as likely to develop an infection than those aged from 25 to 30. The reason for this is not known and the HPA has called for more research in this area.
The study also found that the average time to infection was ten days after surgery – meaning that, as the average length of hospital stay was three days, they occurred after discharge.