The expanded application of most probable number to the quantitative evaluation of extremely low microbial count.

This paper is about the evaluation of the extremely low microbial counts from the field by expanding the most probable number (MPN) methodology when the data follow Poisson distribution in order to achieve more accurate estimation with limited number of data. Several data sets with extremely low microbial counts from pharmaceutical clean room and laboratory clean bench monitoring were found with good Poisson distribution fitness by chi2 test (P < 0.05), and the MPN calculations were conducted for these data by using the Halvorson and Ziegler equation. The MPN values are generally larger than the arithmetic average, indicating a higher sensitivity of the data assay. This approach is justified because Poisson distribution is the mathematical background of the MPN procedure, with the Halvorson and Ziegler equation as its foundation. It is considered that the MPN methodology has a potential application for quality control in the extremely low level microbial counting environment in the clean rooms levels ISO class 7 or above. Further studies on the precision of this method and development of a sampling plan based on careful mathematical analysis will help to refine the approach.

Relationship between the contamination of the nurse's caps and their period of use in terms of microorganism numbers.

Nosocomial infections are a great problem in the health care facilities. The white uniforms of nurses are often washed to keep them clean, but the nurse's caps are not washed as frequently in comparison. It could be that the importance of these caps is being overlooked. If these caps are providing a residence for microorganisms causing nosocomial infection in the health care facility, then they should be washed as frequently as the uniforms. So far, the relationship between the contamination of the nurse's caps and nosocomial infection has not yet been studied. Therefore, this study was conducted to confirm if relationships exist among factors regarding the number of microorganisms on the nurse's caps, the period in which caps were used without being washed, and the individual characteristics of nurse wearing the caps. Results showed that the degree of contamination of the nurse's caps depended on individual characteristics and the period of use. Finally, results led to the conclusion that the nurse's caps should not be worn if their only purpose is to symbolize female workers in the health care facilities because, in actually, they provide a resistance for microorganisms causing nosocomial infections.