Quantitative assessment of bacterial invasion of chronic ulcers. Statistical analysis

Seventy-four bacterial counts were performed on tissue specimens taken from seven chronic decubitus ulcers and two infected postoperative wounds to evaluate the reliability of a single determination as an indicator of the degree of bacterial contamination of the wound. Two methods of tissue sampling were compared. In Group I, a single tissue sample was divided into four specimens, which were then individually processed. In Group II, bacterial counts were made on tissue specimens taken from four widely separated areas of the wound. Data from 37 determinations were available in each group. The 95 percent confidence interval for a single determination was log10 +/- 0.9 for Group I and log10 +/- 1.3 for Group II. We conclude that the range of values at the 95 percent confidence interval is so large that a bacterial count made on a single tissue sample from a chronic ulcer has only limited value as a guide to the surgeon in determining the optimal time required to perform a surgical closure.