Negative pressure of the environmental air in the cleaning area of the materials and sterilization center: a systematic review

ABSTRACT Objective: to analyze the scientific evidence on aerosols generated during cleaning activities of health products in the Central Service Department (CSD) and the impact of the negative pressure of the ambient air in the cleaning area to control the dispersion of aerosols to adjacent areas. Method: for this literature systematic review the following searches were done: search guidelines, manuals or national and international technical standards given by experts; search in the portal and databases PubMed, Scopus, CINAHL and Web of Science; and a manual search of scientific articles. Results: the five technical documents reviewed recommend that the CSD cleaning area should have a negative differential ambient air pressure, but scientific articles on the impact of this intervention were not found. The four articles included talked about aerosols formed after the use of a ultrasonic cleaner (an increased in the contamination especially during use) and pressurized water jet (formation of smaller aerosols 5μm). In a study, the aerosols formed from contaminated the hot tap water with Legionella pneumophila were evaluated. Conclusions: there is evidence of aerosol formation during cleanup activities in CSD. Studies on occupational diseases of respiratory origin of workers who work in CSD should be performed.


Introduction
Aerosols are generated and released by humans in various activities, such as breathing, talking, coughing and sneezing; Bathing with contaminated water; aerosolization of sewage waste in toilets or drainage system for outdoor environments; cleaning and rinsing surfaces indoors; spraying in agriculture (1) . Aerosols are defined as smaller particles or equal to 5μm, that may or may not contain an infectious agent and, due to their size, can remain suspended in the atmosphere for hours, slowly being transported over long distances and achieve adjacent areas (2) .
Aerosols containing an infectious agent that remain in the environment can be inhaled by susceptible individuals, even if there is no close contact with the disposing source, or contaminated surfaces (3) . The main diseases transmitted by aerosols are tuberculosis, measles and chicken pox. However, there are reports of aerosolization of other microorganisms such as fungi, Clostridium difficile and Staphilococcus aureus (4)(5) .
The droplets that are larger than 5μm, remain suspended for a few seconds and quickly lay on the floor or other surfaces due to gravity. Its liquid portion can evaporate, depending on the environmental conditions, resulting in aerosols. There are slight variations of the nomenclature and definition of sizes, however the Brazilian National Health Surveillance Agency (ANVISA) uses the definition that aerosols are smaller than 5μm, which was adopted for this study (2)(3) .
Ventilation systems and air conditioning in various establishments promote comfort, and are useful in the prevention and treatment of diseases transmitted via aerosols. The use of these systems in health services (HS) requires special attention. The basic differences stem from the need to restrict the dispersion of air within an environment to adjacent areas; the specific requirements for ventilation and filtration aiming to dilute and eliminate contamination; the different requirements of temperature and humidity for each area; and sophistication that is demanded for the project (6) .
Among hospital sectors that require air pressure control, temperature and humidity we highlight the Central Service Department (CSD). The CSD is responsible for medical device (MD) from one use to another, it must contain a reception and cleaning room; a preparation and sterilization room; a chemical disinfection room (where applicable); a monitoring area of the sterilization process and a storage and distribution of sterile materials room (7) .
The RDC Resolution 15, of March 15, 2012 from ANVISA, disposes on the good practice requirements for the processing of MD and other measures. According to this resolution, the CSD class II (which processes complex materials) and processing companies must maintain a negative differential air pressure between the cleaning area and adjacent areas (7) . The areas adjacent to the reception and cleaning room consist mainly of the preparation and sterilization room of MD and circulation areas of other professionals.
Differential ambient air pressure means that there is a difference in measuring the relative air pressure between two areas. This parameter works to provide a positive or negative pressure within a particular area in order to prevent air from migrating from one to the other. If a room has a negative air pressure it means that the air supply is less than the exhaustion (6) .
With the growing concern for the safety of patients and health professionals, there is a need for implementation of best practices that should be based on proven scientific evidence. Thus, the objective of this systematic literature review was to analyze the scientific evidence for the formation of aerosols during the MD cleaning activities in CSD and the impact of negative air pressure, or to the safety of the material to be sterilized, and for health professionals in the adjacent areas too.

Method
The steps of this systematic review followed the guidelines published in the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) Statement, which aims to help the authors to carry out complete and clear records of a systematic review and meta-analysis (8) .  numerical assignments, level zero being considered low risk and level three the ambient with high-risk health problems related to air quality. The CSD was classified as level one "an area where it was not found the risk of health problems related to air quality, but some authorities, organizations and researchers suggest that the risk should be considered." All the technical documents analyzed (6,(9)(10)(11)(12)  In Brazil, the NBR 7256/2005 (9) is followed, referring to CSD in the cleaning area, which resembles the international recommendations, as shown in Figure 2.
Documents ASHRAE* (2011) (  The four scientific articles included (13)(14)(15)(16) are studies in English: three (13)(14)(15) published between the decades of 1960-1980 and only one in the 2000s (16) ; three (13)(14)16) are laboratory experimental studies and one is transversal (15) (held in hospital bathrooms); three (13-15) studies conducted in the United States and one in Australia (16) . No studies that evaluated the negative air pressure in MD cleaning areas were found on the searches. Therefore, studies that evaluated the formation of aerosols during cleaning products or surfaces were included, even if not specifically made in a CSD environment.
In three studies (13)(14)16) , experiments were performed to analyze the aerosol recovery generated from equipment commonly used in the CSD: ultrasonic cleaner and scrubbers with pressurized water.
In the study conducted with the ultrasonic cleaner (14) , air samples above the water surface in the washer tank were collected (the air gatherer had a flexible termination that was placed inside the washing machine), aiming to recover aerosols with Pseudomonas aeruginosa. Air specimens were obtained in four moments: before the washer was turned on (during Comparative analyzes using statistical tests were not performed. In another study (16) , in order to evaluate the formation of aerosols during household activities, a car cleaning experiment was conducted in a controlled environment, sealed with plastic. Two ways of using the hose with pressurized water were tested: spraying (used for rinsing) and a water jet with controlled flow (used to remove dirt), conventional (low pressurization -manual trigger) and efficient (high pressurization). The authors used three gauges of particle sizes not aiming to identify microorganisms in aerosols. It was observed that when used in higher pressurization (efficient method), more and smaller particles were identified (up to 2μm). However, there were no statistically significant differences between the methods: efficient and conventional or between the spray modes and jet.
The authors reported that they observed the formation of visible fog in the tent where the experiments were carried out, especially after the high pressurization method, and cogitated they were hydrated aerosols, possibly lower than 500ηm.
A study (15) was included considering the possibility that the CSD could be equipped with hot tap water. In The summary of the results is shown in Figure 3. High-pressure hose with manual trigger device (conventional method) and high pressurization (efficient method); two types of water flows (spray and jet). Three particle gauges (500ηm to 5μm).
The average of aerosols produced by the high pressurization device were higher in all experiments (high standard deviations) when compared to the conventional, and a greater number of particles smaller than 2μm (more than 96% went until 6μm).
High-pressure devices: greater concern with air transmission of microorganisms. Partially Air samples were positive for Legionella pneumophila in six of the 14 areas. There was variation in the water samples (0-> 200 CFU) and air (0,10-0,33UFC / ft3). There was correspondence between subtypes of water and air strains.
Shower heads and taps may produce aerosols with a reduced number of L. pneumophila during routine use, that may penetrate the lower respiratory system. Inconclusive.  Increase of 255 times of aerosols compared to the initial contamination, with the lid of the washer on, and 28 times without the lid (respectively, p = 0.006 and p = 0.0006). Higher contamination during operation.
Air contamination from the washer may be minimized by daily cleaning of the cleaning solution storage using germicide in it. Use lid washer. Partially conclusive.
Braymen, 1969 (13) / Experimental laboratorial Intentional contamination of the wall; automatic washer with pressurized jet, with water and disinfectant solutions. Air samples to determine the particle size (during and after the procedure).
After spraying, about 50% of the particles were up to 5μm (aerosols). After brushing, approximately 72.4% were greater than 5μm (droplets). All disinfecting solutions reduced the number of viable microorganisms in aerosols.
Microorganisms are aerosolized in a number enough to contaminate susceptible individuals or products. Healthcare professionals that clean must use respiratory personal protection equipment. Partially conclusive. cleaning area, the construction of an anteroom should be considered (6,11) .
The influence of the movement of doors and people traffic in the negative pressure air efficiency in isolation rooms was demonstrated in the study by Adams, Johnson and Lynch (17) . The air pressure differentials were measured between the room and the anteroom and between the room and the hallway. The average in the aerosol count per m3 where larger when there were greater movement of people and doors, however the aerosol score decreased as the air pressure differential increased. The authors indicate a negative air pressure differential of 20 Pa when there is heavy traffic between areas. In this context, there is a need for routine monitoring of the pressure differential between the areas, for example, by testing with the observation of the direction of smoke flow or specific gauges (18) .
Other parameters shown in Figure 2  and creating air flow patterns (19) .
The need for negative air pressure in isolation rooms is strongly evidenced in the literature, aiming to reduce the risk of exposure microorganisms transmitted by aerosol infected people to uninfected people (especially other patients or professionals). The advent of diseases such as severe acute respiratory syndrome, avian flu and drug resistant tuberculosis raises concern for health authorities in relation to the isolation of patients (11,18) .

Discussion
In the selected technical papers for this review, there is a consensus of the need for negative pressure air in cleaning and decontamination areas of the MD in CSD. This directive corresponds to the norms of the RDC ANVISA 15/2012 (7) , where it is stated that in class II CSD a negative differential ambient air pressure (minimum 2,5Pa) should be kept between adjacent areas. However, it was found that both the national and international technical documents do not cite scientific references that prove, with conclusive evidence, the risk of environmental exposure to aerosols for both the MD and for professionals. The classification of CSD as level one, related to the risk of adverse health events by exposure to ambient air (9) , states that this risk is not scientifically proven, but based on expert opinions, which reinforces the need for research to generate data for the support of laws, rules and recommendations.
As mentioned in the introduction of this study, microorganisms in the air of the CSD environment can be related to two issues: inhalation by professionals and depositing of them on the clean material in the preparation area. Regarding the last issue, considering that the MD will be sterilized before use and that this Also there is no consensus on the number of air changes per hour in isolation rooms (4) .
The release of aerosols also occurs in other sectors of the health system. In the study of Verde and collaborators (20) , the goal was to characterize the air pollution levels in different areas of the hospital (emergency room, surgical ward and operating room).
After finishing the procedure, it was detected an increase in the concentration of bacteria in the air. However, the contamination level returned to baseline values (collected in the empty operating room) after cleaning procedures.
Bronchoscopy is a procedure recognized for its potential to generate aerosols, by stimulating coughing patient leading to the contamination of the environment and professionals. In the study by Lavoie and collaborators (21) , although it is not the main goal of the authors, sizes and aerosol concentrations were compared in two bronchoscopy rooms, (one with negative differential air pressure and one without). After statistical analysis, it was shown statistically significant increase in the average concentration of aerosols per m3 in a non-negative differential room during the performance of bronchoscopy, and there was no significant increase in the room with differential. These or dirt adhered to products) (7) . Despite using the same principle, the equipment currently available are modern, of different dimensions and efficiency when compared to the washer used in the study included in this review (14) , and the fact that they are usually operated capped. A limitation of this study was the definition for the recovery of only one microorganism (Pseudomonas aeruginosa) and it was rated as partially conclusive.
In the studies included in this review (13,16) , it was shown that using pressurized water cleaning devices generate more aerosol when compared to conventional methods (brushing and low pressurization of water).
Considering the guiding question of this review and the fact that these experiments were not performed in a CSD environment they were classified as partially conclusive.
On CSD, the pressurized water guns are used for crude dirt cleaning. Compressed air guns are used for drying products with lumen and complex conformation (22) .
About the size of the particles, it was evidenced in this review that the aerosol generated after the use of pressurized water surface cleaning devices were smaller than 5μm (13,16) . In the study of Bollin and collaborators (15) , there are reports that Legionella pneumophila aerosols generated by the tap were larger than the ones in the shower, however, there is no detailed description of the sizes. Particles larger than 10μm are more likely to remain on the surface of the upper airways and not penetrate into the lower lung regions. However, the smaller the particle size, the easier it is its moving until the alveoli (23) . Researchers say less than 5μm aerosols can be easily inhaled and it moves slowly with speed lower than 1m / h (24) .
The size of the aerosol is the factor that most influences in its biological properties and displacement.
The permanence of aerosols in ambient air undergoes action of physicochemical processes such as evaporation, interaction with other particles, transportation, gravity, temperature, relative humidity and air currents, among others. There are reports that aerosols remain suspended in the same environment for years (25) .
Therefore, there is evidence of air pollution in the CSD cleaning area; however, data on the permanence in the air and displacement of aerosols to adjacent areas is lacking. A limitation of the studies included in this review was the lack of control of environmental factors where the experiments were carried out, which may have underestimated or overestimated the recovery of aerosols.
In a study of this review the contamination of water and air by Legionella pneumophila was evaluated and it was identified that the strains detected in aerosols were of the same subtype of the samples of shower water and hot tap water (15) . This study has limitations regarding the collection of data because there has been no standardization of the number of samples, time and air collection instrument, furthermore, the authors collected water samples a week before the air samples, which resulted in its classification as an inconclusive study. water (26) . Infection by these bacteria generates concern especially for immunosuppressed people. In a retrospective study in elderly care institutions (27) ,  (19) .
There were no scientific evidence on occupational diseases related to the cleaning activity in CSD. Greater emphasis is given to accidents with sharp objects, chemical or ergonomic exposure. The use of PPE in CSD is problematic due to the compliance to the use and discomfort reported by the professionals working in this sector (28) . Nurses should the responsibility to raise awareness and motivate the CSD team of the obligation and benefits of using PPE.
Considering the occupational health of the CSD workers, the environment temperature control contributes to the comfort of the professional (10) . The control of this parameter, and the relative humidity is possible through thermo hygrometer installation. However, maintenance of air quality with microbiological approach, based on the values recommended by ASHRAE (19) , it is impractical in the reality of the CSD. In this sector there is no full control of conditions of environmental contamination, as carried out in a controlled production structure, found in the pharmaceutical industry, considering that microorganisms can be released both by professionals (eg, movement of people, sneezing, coughing, expiration, speech) and by the activities carried out there.