INFECTION CONTROL Naoki Kagi – Tokyo Institute of Technology in Japan


Controlling airborne bacterial contamination


This article summarises findings on airborne microbial contamination obtained by field measurements from nine hospital waiting rooms and demonstrates the efficacy of a portable air cleaner in reducing airborne microbe concentrations.


Opportunistic infections are the subject of ongoing medical concern, especially with increasing numbers of immunocompromised patients. Total airborne microbial concentration has been shown to exhibit a pattern similar to that of nosocomial bacterial infection consistent with the human origin of such infections. A reduction of airborne microbe


concentrations in the hospital setting is expected to reduce the risk of nosocomial infection. From our study it is clear that the concentration of airborne bacteria in the hospitals measured fluctuate with occupant numbers and activity, with peak concentrations occurring in the mornings. The levels of indoor airborne microbes


were measured in the waiting rooms of nine different hospitals. Two types of air samplers were used to measure culturable airborne bacteria, and a bacterial detector was used to measure the total airborne microbes, including non-culturable bacteria, in real- time. The number of occupants in each waiting room was counted every 30 minutes. In order to obtain the relationship between the total microbes and culturable airborne bacteria, a slit-type air sampler, which can measure the airborne bacteria concentration versus elapsed time, was used in parallel. To control the dissemination of airborne


microbes, engineering controls are recommended, including local exhaust ventilation, general ventilation, air filtration, and ultraviolet germicidal irradiation (CDC MMWR, Vol. 43, No. RR-13, 1994). In our study, a commercial portable air cleaner equipped with an air filter was tested in situ for a reduction of the indoor airborne bacteria in a clinic waiting room. Airborne bacterial concentrations were measured continuously by a slit-type air sampler under the conditions of alternating the air cleaner


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between the ON and OFF modes. The results demonstrate that the air


purifier had remarkable efficacy in reducing the concentration of airborne bacteria.


Field measurements Nine hospitals (designated H to P) were included in this study. Each hospital had a total floor area of between 3,800 m2


and 58,000 m2, and contained 120 to 560 beds


each. Hospitals H, K, L, M, N, O, and P were equipped with air-handing units (AHUs); Hospital J used a fan coil unit; and Hospital I employed natural ventilation. Between the hours of 10:00 and 16:00,


culturable airborne bacterial were measured with MBS-1000 (Midori Anzen Co., Tokyo, Japan) air samplers, which employ a multi- orifice sieve impact method. Bacteria were grown on soybean casein digest agar (SCDA). Total airborne microbe levels were measured using Instantaneous Microbial Detection (IMD) (IMD; Bio Vigilant, Inc., USA). IMD measures the concentrations of suspended particles with different size distributions based on optical technology, and is able to simultaneously determine, in real-time, whether each particle is inert or biologic. Among the nine hospitals, measurements


of airborne microbes in six hospital waiting rooms, located in the Tokyo area, were conducted using both the IMD and an MG (Mattson-Garvin, Inc., USA) air sampler in parallel. The MG is a culture-based, slit-type air sampler consisting of a height-adjustable three-prong sample holder, a 60-minute


U. Yanagi


U. Yanagi is a professor at Kogakuin University in Japan. He is also a visiting researcher at the National Institute of Public Health and the Institute of Industrial Science of the University of Tokyo. Dr. Yanagi was the chief of the Building Hygiene Section of the National Institute of Public Health, Japan. His latest research has focused on microbial contamination in indoor environments, such as hospitals and office buildings.


‘A portable air cleaner reduced the indoor concentration of suspended microbes during high-occupancy periods in waiting rooms.’


timer, an SCFH (slow meter) air gauge, and a clear dome. The highest concentrations of suspended


bacteria occurred at the same time as the peak in the number of occupants in the waiting room areas (Fig. 1). These results were consistent with the notion of occupants being the major source of indoor suspended bacteria. With the exception of Hospital G, all sites demonstrated significant correlations between culturable airborne bacterial concentration and biological particle concentration (Fig. 2). These results also suggest that the


concentrations of biological particles, including culturable and non-culturable microbes, correlated with occupant numbers. Therefore, the risk of nosocomial infection in waiting room areas is relatively high, and a reduction in the level of airborne microbes in waiting room areas would be advantageous.


Naoki Kagi


Naoki Kagi is an associate professor at Tokyo Institute of Technology in Japan. He is also a visiting researcher at the National Institute of Public Health. His doctor of engineering was received from Tokyo Institute of Technology in 1999 and his latest research has focused on chemical pollutants and aerosols in indoor air.


U. Yanagi – Kogakuin University in Japan


IFHE DIGEST 2013


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