Hospital Airborne Bacteria as Estimated by the Andersen Sampler versus the Gravity Settling Culture Plate

Abstract

Sayer, William J., MacKnight, Nancy M., and Wilson, Hal W.: Hospital air-borne bacteria as estimated by the Andersen sampler versus the gravity settling culture plate. Am. J. Clin. Pathol. 58: 558–566, 1972. The gravity settling culture (GSC) plate and Andersen’s sequential impaction cascade sieve volumetric air (SICSVA) sampler were compared, estimating airborne bacteria. Fifty-three samples were obtained in three Northern California hospitals. The SICSVA sampler collected 9,375 colonies; 865 colonies were collected in the GSC plates. Twenty-one GSC plate colonies and 247 of the Andersen sampler colonies were classified as potentially pathogenic. The GSC plate was falsely negative for coagulase-positive Staphylococcus aureus, Pseudomonas species, Pseudornonas achromobacter, Pseudomonas aeruginosa, and possible Erwinia, which were found repeatedly by the SICSVA sampler. Colonies isolated by the Andersen sampler may be logically grouped into a fraction that generally lodge in the upper respiratory tract and another fraction capable of entering the lung. Most of the potentially pathogenic bacterial colonies were collected in the so-called lung-penetrating fraction of the Andersen sampler. Falsely negative results were frequently indicated by the GSC plate. The GSC plate method cannot be endorsed for the quantitative evaluation of hospital airborne bacteria.