Microbiological control in parenteral nutrition mixtures. Indices of contamination

Potential contamination of nutritional mixtures during preparation in the Pharmacy Services has led to the need for microbiological controls. In our study, we set out the techniques used in the Son Dureta Hospital between 1986 and 1991. During those six years 11,023 nutritional mixtures were prepared, and 1,714 bacteriological controls were carried out, representing 15.5% of the total. Between January 1986 and June 1989, the simple culture technique was used (culture of 10 ml of the prepared mixture). The contamination rate was 1.27%. Between July 1989 and December 1991, the double sample technique was applied, involving a culture of 10 ml of the mixture, keeping a further 10 ml for subsequent verification culture. With this technique, the contamination rate was fixed at 0.34%. The advantages and drawbacks of the techniques used are described, along with the problem of initial false positives, and a review is made of the 39 germs isolated during the period of study.