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INFECTION CONTROL


Shoichi Morimoto – Technical Supervision Division, Shinryo Corporation. Huaipeng Tang,* Shin-ichi Tanabe,†


Hitomi Tsutsumi,#


Infection risk reduction in multi-bedded ward


This study discusses a series of reduction methods of droplet nuclei concentration to reduce the airborne infection risk of four-bed hospital rooms.


Tuberculosis (TB), measles and chickenpox are well known airborne infectious diseases. When an outbreak of Severe Acute Respiratory Syndrome (SARS) or a new influenza occurs, it becomes a big social issue and medical workers use airborne precautions during those periods. However, there are many cases of TB in adults, which is also a known airborne infectious disease and there are many compromised patients in hospital in whom TB may recrudesce if they have had past infections. It is, however, difficult to immediately diagnose recrudescence which can put healthcare workers and other patients sharing a multi- bedded ward with the infected patient at risk. Japan is a TB intermediate danger country


and many patients host TB. For this reason prevention of the transmission of TB within the hospital environment is an important issue. Airborne transmitted pathogens are


particles called droplet nuclei. More than 90% of tubercle bacillus can be eliminated by a fine filter, EERV11 of ASHRAE or F6 of EN, which is generally adopted within ventilation systems in Japanese hospitals. It is, therefore, easy to reduce infection risk via a ventilation system.


HEAS-02-2013, established by the


Healthcare Engineering Association of Japan, provides the fresh air volume required to reduce bad smells and CO2


concentration.


It also provides the ventilation air volume for maintaining the indoor air quality and reducing the risk of infection. Droplet nuclei released from patients


spread through rooms from updrafts caused by the patient’s temperature. Preventing spread is expected to be achieved by isolating


*Technical Supervision Division, – Shinryo Corporation. †


# Department of Architecture, Waseda University, Tokyo.


Department of Human Environmental Science and Design, Showa Women’s University, Tokyo.


¥ Department of Infection Control Science, Juntendo University, Tokyo. 20 Table 1: Measurement conditions. Items Test room Measuring Size


Temperature Ventilation Instrument Volume Size


Particle


Interval Type


Instrument Source Volume


810 m3 Conditions


6.0 m x 6.0 m x 2.5 mH 25˚C


/hr (9 ACH)


Air Particle Sensor ZN-PD03-S (Omron Corp.) 3.5 l/min


0.3 µm, 0.5 µm, 1.0 µm 60 seconds


Baby powder (median 12.6 µm)


Dust feeder DF-3 (Sibata Scientific Technology Ltd) Patient 1 /hr


1.2 m3


the patient’s area. This isolation can be achieved using partition walls, curtains or air supply diffusers. The experiments were conducted in a full-


scale test room measuring 6.0 m x 6.0 m x 2.5 m. The test room was surrounded by buffer rooms which were air-conditioned to the same temperature. Figure 1 shows the outline of the test room. Table 1 shows the measurement conditions. We used baby powder with a median


particle size of 12.6 µm, as the substitute particle for droplet nuclei and this was supplied from patient 1. There are physical differences between baby powder and droplet nuclei. However, because we confirmed that baby powder spread in the whole test room we considered that we can ignore the difference. As a result of preliminary experiments, most of the particles were measured between 2 µm to 5 µm. There were a few less than 0.5 µm. The particles over 0.5 µm were measured by taking into account the size of the droplet nuclei (less than 5 µm) and the size of the tubercle bacillus (0.3 to 0.6 µm x 2 to 10 µm). Baby powder was released constantly on the bed of Patient 1 via a dust feeder. We did not simulate the cough because the high-speed cough is to 0.9 m and the velocity disappears at 1.8 m (Okajima et al 2012). As large particles were eliminated, baby powder


was supplied in a two-litre bottle on the bed of Patient 1 and diffused upward. The particle count was made three times for each condition at one-minute intervals, and one measurement lasted for 30 minutes. We used 60 W heaters on each bed to simulate a patients’ fever. Firstly, we examined the effectiveness of


partition walls. The 2.2 m x 1.0 m x 2.5 m partition walls were set between Patient 1 and Patient 2 and between Patient 3 and Patient 4. They extended from the floor to the ceiling. We also examined the combined effectiveness of a rolling screen and partition walls. The rolling screen was hung from the ceiling step side of Patient 1. The gap of the rolling screen was 0.6 m from the floor and 0.35 m from the wall and the partition wall. A square cone diffuser was set in the


Shoichi Morimoto


Shoichi Morimoto is a doctor of medical science employed as a Senior Researcher at Indoor Air Quality Group, R&D Center, Technical Supervision Division, Shinryo Corporation. He received the Japanese Society of Environmental infections prize in 2012. He has developed infection control systems such as a push-pull device for preventing air leakage, a new consultation room for fever clinic, and infection reduction methods for four-bed rooms.


IFHE DIGEST 2015 and Satoshi Hori.¥


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