THE BACTERIAL FLORA OF CLEAN SURGICAL WOUNDS

Risk factors for postoperative infection

During a 4-year period, we collected prospective epidemiologic data and intraoperative wound cultures from 1,852 surgery patients at a university-affiliated community hospital in order to identify the critical risk factors for postoperative wound infections and study the impact of perioperative antibiotics on the bacteriology of infected wounds. Stepwise logistic regression analysis revealed four risk factors that were independent of each other and highly predictive for subsequent wound infection. These were the surgical wound class, American Society of Anesthesiologists physical status grouping, duration of surgery, and results of intraoperative cultures. Addition of other variables to our model did not increase the predicted probability of infection. Even though patients with positive intraoperative cultures had an increased rate of infection, this information had limited clinical utility. The predictive value of a positive culture was low (32%), false-positive rate was high (82%), and concordance with isolates from infected wounds was low (41% when both cultures were positive). Patients who had received perioperative antibiotics and who developed infections were frequently infected with organisms that were resistant to the perioperative drug regimen, compared with patients who had not received antibiotics. A better understanding of the variables that affect the epidemiology and pathogenesis of postoperative wound infection will enable us to make more valid comparisons of rates among hospitals, help us to develop more effective infection control strategies and provide us with more effective treatments.

Comparison of nonwoven and woven gown and drape fabric to prevent intraoperative wound contamination and postoperative infection

In a prospective, controlled clinical trial, nonwoven, disposable gown and drape fabrics were no better barriers to intraoperative wound contamination or postoperative wound infection than reusable cotton poplin. We observed no difference between the two study groups in either the frequency or level of intraoperative wound contamination as judged by cultures of specimens collected at the time of wound closure. Of procedures in which reusable fabrics were used, 13.1 percent had positive cultures compared with 15.5 percent of those in which disposable fabrics were used (difference not statistically significant). We recovered coagulase-negative Staphylococci from more than 95 percent of contaminated wounds. Rates of postoperative wound infection were virtually identical in the two groups. Our data suggest that either both fabrics were similar in their ability to block bacteria that were shed from skin surfaces from entering the wound, or that bacteria which contaminate the wound in clean surgical procedures are derived from sources other than skin.

Primary postoperative wound infection due to Staphylococcus pyogenes

Using S. pyogenes as a tracer organism, an examination of the importance of air-borne infection of clean wounds in the modern, plenum-ventilated operating room has been made. It appears that, for most surgical procedures, additional ultra-clean air installations are not necessary. It has been shown that even if the air is sterile, the skin remains a possible source of infection. This is especially so as far as the patient's skin is concerned. It will remain so, since the skin cannot be sterilized. Indeed, until the ecology of the skin is better understood, rigorous efforts directed toward its disinfection may compromise its inherent defense mechanisms and its protective bacterial flora. It will be argued by some that operating rooms with ultraclean air should be afforded for certain specialized procedures in sugery; for example, those in which prosthetic materials are being implanted or in which the patient's immune mechanisms are depressed. Although not disagreeing with this, I wish to note that the only controlled trial on this aspect of surgery that exists to date shows no advantage for patients randomly apportioned to have hip arthroplasty, either in an isolator or in the same modern operating room but without the isolator. From this experience, I believe that any further trial of this nature, if it is to be controlled to a similar high level, will require very large numbers of patients to show even a marginal advantage for ultraclean air or isolator installations over the modern, plenum-ventilated and meticulously managed operating suite. The verdict on the need to install ultraclean air plant for operating rooms must, therefore, be couched in the third alternative that exists under Scots Law-- "not proved." I suggest the money could be better spent on devising methods to keep skin pathogens out of surgical wounds. Perhaps more urgently, there is a need to discover how to increase the defense mechanisms of the wound milieu to implanted harmful bacteria. There is also a pressing need to improve the ward environment with the aim of diminishing secondary infections of surgical wounds.

A bacteriological study of the immediate environment of a surgical wound

In an attempt to assess the importance of different aspects of the immediate wound environment during an operation, detailed bacteriological data were obtained in the operating theatre from 1000 patients operated upon in two different theatres.

Nasal and skin carriage of Staphylococcus pyogenes were found to be associated with a small number of autogenous infections, but no significant increase in the staphylococcal wound infection incidence could be shown in these groups. Skin carriage of other pathogens seemed to be of no importance with the disinfection methods used in the present study.

Settle-plate studies showed no apparent difference in the bacteriological hazard of the two operating theatre environments, neither appearing to constitute any real danger. Samples at the end of operation confirmed the importance of endogenous contamination with intestinal organisms during potentially dirty operations. Apart from the few autogenous infections, there was little evidence of staphylococcal wound sepsis arising as a result of contamination in the operating theatre. Hands and masks of members of the operating team could not be demonstrated as sources of contamination during operation.

There was no apparent difference in the bacteriological findings as they related to the different operating theatre environments.

Staphylococcal Infections in the Hospital and Community

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Early Wounds in and about the Orbit

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