[Air microbiology monitoring in plenum-ventilated operating rooms. Proposed standards].

BACKGROUND: Microbiological standard for air in plenum ventilated operating theatres are not defined. The aim of this study was to analyze the microbiological contamination of air in HUSC theatres and to establish standards of reference.

METHODS: 408 air samples (80 l/sample) were taken from air intake and center of the theatres in three surgical areas, throughout five consecutive years (1991-1995). RCS air sampler was used. Media of microbiological counts were compared using the ANOVA and the Kruskall-Wallis tests. Microbiological standards were established based on upper limit of confidence interval of counts, when the degree of contamination was similar in two consecutive years.

RESULTS: A falling trend of microbiological counts was observed, with statistical significance between counts found in 1992 and those found in 1994 and 1995 (p < 0.01). There was no difference between results of the three surgical areas, but there was a significant difference between counts from air intake and center of theatres, regardless the year or the surgical area (p < 0.01). During this time a significant decrease in the percentage of samples with presence of fungi (p = 0.001) was produced. The results of years 1994 and 1995 were taken for establish the microbiological standards.

CONCLUSIONS: This control program allowed to evaluate and improve the hygienic conditions in the operating theatres and to establish a microbiological standards of reference for plenum ventilated theatres.