Factors influencing wound infection (a prospective study of 280 cases).
Wound infection is an important cause of morbidity in the surgical patient. This prospective study was undertaken to determine the factors influencing wound infection. With this knowledge, it may be possible to reduce wound infection rates to a considerable extent.
Two hundred and eighty cases undergoing various surgical procedures were analysed. There were 246 male patients and 34 female patients included in this study. The average age was 39 years. Cases showing evidence of extraneous infection (septic focus) such as ulcers, fever, a positive blood or urine culture or a clinically demonstrable respiratory problem, were noted. The type of surgery performed was classified according to definitions employed in the 1964 National Research Council study: (A) clean surgery where the gastro-intestinal, genitourinary or respiratory tracts were not entered into, no apparent inflammation was encountered in the operation and there was no break in aseptic technique and (B) clean contaminated surgery where the gastro-intestinal, respiratory or genito-urinary tracts were entered during clean surgery but there was no significant spillage.
Bacterial isolates were obtained from various exogenous sources like operation theatre and ward environments and gauze trolleys, endogenous sources like nasal and throat swabs, skin, blood and urine cultures, and from infected wounds postoperatively.
Wounds were examined daily and an infected wound defined as one showing a discharge of pus. Wound infections were classified as mild, moderate or severe, the moderately infected wounds showing superficial infection with a small amount of discharge, the severely infected ones showing deep infection, profuse pus discharge and widespread cellulitis and disintegration of the wound.
The overall rate of wound infection was 18.92% (53 of 280 cases). The rate increased with increasing age, being maximum in the 51-70 year age group. The infection rate in males and females was almost similar, being 19.1% in the former and 17.64% in the latter.
A definite association between the duration of pre-operative stay in days and duration of surgery on the one hand and wound sepsis on the other hand was found [Table - 1]. The position of the patient on the operation list also influenced the development of wound infection as seen by the 10.0%, 18.05% and 40.42% sepsis rates in cases operated on at the start, middle and towards the end of the surgical list order.
The presence of a drainage tube did not significantly influence development of subsequent wound infection, with 27 of 130 drained wounds getting infected (20.8%) and 26 of 150 undrained wounds getting infected (17.3%).
Cases with a septic focus had a 36.61% infection rate (26/71 cases) compared to a 12.91% infection rate in patients without such a focus (27/209 cases). Clean contaminated cases had an overall 38.2% wound infection rate (34/89 cases) compared to a 10.84% infection rate in clean cases (19/191 cases). The incidence of staphylococcal wound sepsis in nasal carriers and non-carriers was almost the same, being 5.6% (7/125 cases) and 4.51% (7/155) respectively.
Of the various possible exogenous sources of contamination, the operation theatre environment, the ward environment and dressing gauze cultures were studied [Table - 1]. The bacteria isolated from nasal swabs, throat swabs and skin swabs after preparation are as shown in [Table - 3]. The importance of endogenous sources of contamination is further emphasised by [Table - 4] where it is seen that the concordance between organisms recovered from infected wounds and endogenous sources was better than that for exogenous sources. The single most common organism isolated from post-operative infected wounds was Staphylococcus aureus. However, mixed infections accounted for the maximum number of infected cases. Infections caused by mixed bacteria were of a 'severe' type as were infections caused by pure cultures of Proteus and Pseudomonas. Wound infections caused by the rest of the bacteria were of a 'moderate' type.
Gentamicin was found to be the most effective antimicrobial drug tested, to which 87.57% of organisms were sensitive. Cloxacillin was very effective against staphylococci and streptococci, 93% being sensitive, however only 9.17% of Streptococcus fecalis were sensitive to it.
Post-operative wound infection still remains one of the most important causes of morbidity in surgically treated patients. Bacteria can infect the patient through two major sources, endogenous and exogenous. We found endogenous sources to be more important than exogenous sources in determining wound infection, as was similarly concluded by Davidson et, al and Shaw et al. In contrast to these findings, Shrivastava et al, Rao and Harsha, and Venkatraman et al found exogenous sources to be more important in the development of wound infection.
Our overall rate of wound infection was 18.92%, favourably comparing with the 20% rate reported by Agarwal, 25% by Rao and Harsha, 22.3% by Venkatraman et a1, 16.9% by Shaw et al, and 10.19% by Shrivastava et al. Cruse and Foord, however, in a prospective study of 23,649 surgical wounds reported an infection rate of only 4.8%.
Increasing age was found to directly influence wound infection in our series, as was reported also by Davidson et al and Cruse and Foord. An increasing interval between admission and surgery also increased our rate of wound infection. Similar were the findings by other authors.,,, Venkatraman et al observed that the infection rate was same in cases operated in the first 3 hours (20%), then increased significantly to 29%. The possible explanations for this finding were offered by Stewart and Douglas. Rao and Harsha found that post-operative wound infections were mostly confined to those operations which were lower down in the operating list order. We also confirmed this finding. The duration of surgery was also found to be an important factor in predicting wound sepsis.,,,
Magee et al, in an experimental study, found that surgical drains potentiated wound infection. Cruse and Foord reported a similar finding. Davidson et al, however, concluded that drainage did not significantly increase the risk of wound sepsis.
We found no significant difference in sepsis rate in staphylococcal carriers and non-carriers. Rao and Harsha, however, observed a 17% sepsis rate in carriers as compared to a 5% rate in non-carriers. Venkatraman et al proved that the high incidence of staphylococcal infection was due to the frequency with which pathogenic types were isolated in hospital patients and hospital staff as compared to the general population. Staphylococcus aureus was the single most common organism isolated in our series (22.44% isolation). Rao and Harsha and Venkatraman et al, however, reported higher isolation rates. Shaw et al reported that 72.3% post-operative wound infections were caused by Gram negative bacilli and 28% due to Staphylococcus aureus alone.