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Posted On Jul 07, 2025

Updated On Jul 07, 2025

The Correlation Between Intraoperative Contamination And Postop Surgical Infections

Surgery

Surgical site classifications are used to estimate the risk of postoperative infection based on the condition of the surgical field. These classifications are well-established in both human and veterinary medicine and include clean, clean-contaminated, contaminated, and dirty surgeries. Here's a breakdown of each:

  • Clean Surgery: Non-traumatic, non-inflamed operative wounds with no entry into the respiratory, gastrointestinal, or genitourinary tracts. The skin is intact and has no evidence of infection. Examples include elective orthopedic procedures (e.g., TPLO), routine spay or neuter, and mass removals from healthy skin. The risk of infection (in veterinary medicine) is 3.6-5.8% and for TPLO, the surgical site infection rate is 4.7-13%.

  • Clean-Contaminated Surgery: A procedure where a normally sterile body cavity is entered under controlled conditions without unusual contamination. Examples include: cystotomy (bladder surgery), enterotomy (intestinal surgery with no gross contamination), and biliary or respiratory tract surgery with no infection. The reported risk of infection is typically 3–7%.

  • Contaminated Surgery: Include open, fresh traumatic wounds, operations with major breaks in sterile technique, or gross spillage from the gastrointestinal tract. Examples include: open fractures (>4 hrs duration), wounds with necrotic tissue or visible dirt, intestinal surgery with leakage of contents, and any surgery lasting over 4 hours. The reported incidence of surgical site infections in these cases range from 4.6% to 12%.

  • Dirty (or Infected) Surgery: Traumatic wounds with retained devitalized tissue and/or existing infection, perforated viscera, fecal contamination, presence of foreign bodies, or associated abscesses. Examples include: abscess drainage, peritonitis due to intestinal rupture, and removal of infected implants. The reported rate of surgical site infections are range from 6.7% to as high as 18.1%.


Complications can develop in association with any type of surgical procedure and despite a surgeon’s level of expertise. When speaking with a client about their pet’s planned surgical procedure, it’s always important to also discuss any known potential complications including wound dehiscence, surgical failure (e.g. fracture repair failure or failed anastomoses), strictures of organs like the esophagus or colon and, importantly, postoperative infections.

Infections can develop despite adherence to aseptic technique, good surgical technique, and keeping the surgical field and instrumentation sterile. Surgical site infections can develop due to intraoperative or postoperative contamination. Intraoperative contamination may originate from several sources. In human medicine, 57% of infections are attributed to environmental causes and 7% to the surgeon. Contamination sources can include the patient's skin or wraps placed around the leg (as in orthopedic procedures). Other sources include the surgeon’s hand(s) due to surgical glove perforation (reported incidence of 10.2%-26.2%) and bacterial migration from the surgeon's skin. Potential environmental sources of contamination include the anesthesia induction tables, gurneys, ancillary equipment and, in the OR, the operating room lights.

A prospective study[1] out the University of Georgia (published in 2016) examined the correlation between bacterial contamination and surgical site infections in dogs undergoing clean orthopedic surgery. It assessed contamination frequency, sources (surgeon vs. patient vs. environment), glove perforation, and the relationship between contamination and surgical site infections.

Dogs with previous stifle surgery, concurrent skin infections, or taking preoperative antibiotics were excluded. The operating room environment was cultured every six months—this included the lights, computers, scrub sinks, gurneys, anesthetic equipment, and radiology tables. All patients received prophylactic antibiotics (cefazolin 22 mg/kg IV) 30 minutes before surgery and every 90 minutes intraoperatively.

Standard surgical site preparation included clipping the hair from the hip to the metatarsals, wrapping the foot with non-sterile latex gloves and Vetwrap, scrubbing with 4% chlorhexidine and 70% isopropyl alcohol, and repeating the scrub once the animal was in the operating room. The surgical team performed either a 5-minute scrub with chlorhexidine, a chlorhexidine-alcohol hand rub, or a chlorhexidine scrub plus a chlorhexidine-alcohol hand rub. Instruments were opened on sterile wraps and drapes. Legs were draped in sterile towels and, at the surgeon’s discretion, with iodine-impregnated adherent drapes (in 62 cases).

Intraoperative cultures were taken from the sterile foot wrap, patient skin (around the incision), medial tibia, surgical gloves (at the end of the surgery), and surgical team’s hands (at the end of the surgery). Glove perforation was tested postoperatively by performing a water test. Incisions were covered for two days with adhesive dressing, a Robert Jones bandage was placed for 24 hours, and dogs wore E-collars until suture removal (at two weeks). Rechecks were performed at two and eight weeks and activity was restricted for eight weeks.

Monitoring for signs of infection included observing for surgical site redness, swelling, discharge, and dehiscense. Stifle radiographs were performed at 8 weeks. If signs of infection were evident, a culture and sensitivity was performed.

There were a total of 100 dogs in this study with a median age of five years (range 1 to 11 years). Ninety dogs received TPLO and ten received TTA to stabilize a cranial cruciate ligament rupture. Common breeds included Labrador Retrievers, American Staffordshire Terriers, Boxers, mixed breeds, and German Shepherds. Premedication protocols varied and included drugs like morphine, acepromazine, hydromorphone, midazolam, and dexmedetomidine. Induction agents included ketamine/valium or propofol. Median anesthesia time was 4.58 hours (range, 197-410 mins), and surgery time was 2.25 hours (range, 70-217 mins). Since this was a teaching hospital, longer surgical times were expected and did occur. Shorter surgical procedure times are more common for these types of procedures performed in the private practice setting.

Postoperative antibiotics were given in 33% of dogs—24 dogs received cephalexin, others received drugs like Simplicef, Clavamox, metronidazole, or clindamycin. Of 710 gloves tested, 18% had perforations and there was a median of 1.5 perforations per glove (range, 0-5). These were most commonly found on the non-dominant hand and on the primary (not assistant) surgeon. Most perforations occurred in surgeries that took longer than 60 minutes. The index finger of the glove was most commonly affected (40%). Perforations were also discovered on the palm (19%) and thumb (10%).

Eighty-one percent of these clean orthopedic procedures had bacterial contamination from one or more sources, with almost 10% showing high contamination. Fifty-eight percent had intraoperative hand contamination; 46% had intraoperative glove contamination. Contamination sources included patient skin (23%), foot wrap (12%), and environmental air (8%). Environmental sampling revealed contamination primarily at the scrub sink, radiology table and gurney.

Isolated organisms included Staphylococcus species (from surgical team hands and patient skin), Micrococcus luteus (from computers and foot wrap), Staphylococcus pseudintermedius (from gurneys and radiology table), and Mycobacterium species (from scrub sink).

The surgical site infection rate was 9%. Two dogs cultured Staph intermedius, one cultured beta-hemolytic Streptococcus. Five dogs had wound exudates and four had incisional dehiscence. All dogs with infections had positive intraoperative cultures however, no significant association was found between intraoperative contamination and post-op infections. This was consistent with human data showing many surgical site bacteria are aerosol-transmitted rather than via direct contact.

Contamination in room air increases with personnel entering and exiting the OR, emphasizing the importance of limiting movement in and out of the operating room. Intraoperative and postoperative bacterial isolates differed, suggesting colonization occurred after surgery. Use of prophylactic antibiotics is controversial — the CDC does not recommend routine post-op antibiotics. Despite this, many surgeons still use them.

From a practical standpoint, it’s critical to keep the environment clean—including prep tables, gurneys, anesthesia equipment, surgical surfaces, and hands. Gloves should be worn when handling surgical sites and during bandage changes. Proper hygiene, floor and kennel cleanliness, and bandage changes on clean surfaces are essential. Owner education is vital—they must keep E-collars on and restrict activity as directed. Veterinary professionals need to emphasize to clients that complications can lead to re-anesthesia and further treatments. Monitoring the incision for drainage, redness, swelling, or dehiscence is essential and cultures must be taken if any issues arise.

One major takeaway from this study is that contamination seen in intraoperative cultures differs from organisms causing post-op infections. Infections most likely develop after discharge from the hospital as a result of licking, self-trauma, or environmental exposure. Hospitals, themselves, could be a source for post-op infections if cages are not cleaned properly between patients.

Regarding hygiene, everyone on the team must understand sterile technique, proper instrument care, and sterilization protocols. Caps, masks, and booties should always be worn in the OR and, even when not in use, people shouldn’t enter casually without proper attire. Clipper cleanliness is also very important. Hospitals should separate clippers used for prepping surgery patients (e.g ortho surgery) from general use (e.g. clipping wounds, etc). Suture selection should also be appropriate and the size should match the strength required for the tissue being sutured —larger sutures have the potential of harboring bacteria. It should be noted that the hand rub technique has become more commonly used (compared to the traditional 5-minute scrub) in some institutions.

Empirical use of antibiotics should be avoided if possible. Culture and sensitivity testing is necessary for draining wounds or suspected infections. Notably, in this study, none of the surgical site infections were sensitive to cephalexin, raising the question of resistance due to overuse. Ultimately, surgical infection prevention must be approached from multiple angles—aseptic technique, environmental cleanliness, post-op care, owner compliance, and prudent use of antibiotics (if indicated).



[1] Survey of Intraoperative Bacterial Contamination in Dogs Undergoing Elective Orthopedic Surgery. Vet Surg. 2016 Feb;45(2):214-22. doi: 10.1111/vsu.12438