Pathogen Airlift
In this time of extreme concern to take care of health, and in the face of the cyclical pandemic of the AH1N1 strain of influenza, it is vital that the people responsible for HVAC systems ensure the well-being of the occupants, contributing to create a healthy environment.
Recent studies show that air plays an important role in the transmission of infections, evidencing that certain diseases are transmitted by air, as was the experience in 2003 with the epidemic of Severe Acute Respiratory Syndrome (SARS), where it was discovered that the spread of the virus was by contact and airway, through the ventilation system in an apartment building.
This leads us to wonder about the role that the ventilation system plays in the spread of pathogens, such as viruses, bacteria, fungi or yeasts capable of causing diseases.
Figure 1. Particles Produced by People
When an individual coughs, sneezes or speaks, it emits particles of saliva and mucosa containing pathogens. These aerosolized particles are of various sizes, some of them can measure less than 10 microns in diameter and therefore, can reach the alveolar region, when inhaled by an individual (see figure 1).
Larger "droplet" particles quickly settle on surfaces. In contrast, smaller particles tend to get suspended in the air. In addition, the particles undergo an evaporation process, in which they reduce their size, leaving the "droplet nucle" (droplet nucle), which makes them small enough to continue suspended in the air.
Because of this, if particles containing the pathogen are inhaled by a susceptible individual, and deposited at a suitable site, for example in the respiratory tract, infection and disease can develop. Even while breathing, during exhalation particles can be projected up to one meter away, while when sneezing, particles can reach several meters (see Figure 2).
Figure 2. Dispersion of Particles Inhaled by the Human Respiratory System Aerodynamic Diameter (microns) Probable Region of Deposit 9.0 Filtered by the nose 6.0 – 9.0 It is deposited in the larynx 4.6 – 6.0 It is deposited in the trachea and primary bronchi 3.3 – 4.6 It is deposited in the secondary bronchi 2.15 – 3.3 It is deposited in the terminal bronchi 0.41 – 2.15 It is deposited in the alveoli 0.41 They can be exhaled
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Once the particles are emitted into the environment, the main factors that determine how they move are: their size and the air currents that move them.
The standards related to energy saving are:
The core of the droplet changes over time, depending on environmental conditions. Moisture in the air alters the rate of evaporation and therefore its size. Droplets in dry air evaporate quickly reducing in size and fall by gravity more slowly. This change in size affects how the particle responds to airflow patterns and their settlement (see Figure 3).
Airborne particles can be respirable (inhaled) or non-respirable, as in the case of certain skin or eye infections, nosocomial infections in wounds or gastrointestinal viruses (see box Ways of Contagion).
Forms of contagion 1. Contact•Direct transmission: Transmission occurs as a result of physical contact directly between the infected person and another person. For example between a patient and a doctor.
• Indirect transmission: Transmission occurs through the transfer of microorganisms through contact with an intermediate object, usually inanimate, within the patient's environment. The pathogen enters the body through the mouth, nose, eyes or a wound.
3. By airTravelage occurs by the spread of microorganisms in the form of an aerosol. Particles smaller than 5 microns can remain suspended in the air indefinitely. When an individual coughs, sneezes or speaks, it emits particles of saliva or mucous membrane that contain the pathogen. Airborne transmission occurs by the dissemination of the "droplet nucleus" following the aerosol evaporation process or by small particles such as squamous cells or dust that are already small enough to be suspended. Contagious microorganisms that are dispersed in this way can travel great distances due to drafts and can be inhaled by individuals who have not had direct contact with the infected person despite being in different rooms. Means of transmission: sneezing, coughing, talking, aerosol injected and distributed by the HVAC system, aerosols by contaminated water such as cooling towers, showers, deficiencies in the HVAC system.
Note: All infectious agents that cause diseases when airborne, can cause infections by direct contact or by large droplets. If the pathogen has part of its life in the respiratory tract, it is likely to present itself in aerosols generated and projected into the air when breathing, talking, coughing, sneezing or singing.
2. Large dropletsTransmission occurs by large droplets of saliva (larger than 5 microns) generated when a person sneezes, talks, or coughs. Many of these droplets are larger than 5 microns so they do not remain suspended in the air and are deposited on surfaces quickly. For a contagion to be generated, you must be one meter away from the infected person. Means of propagation: contact with the hand, with an infected fluid, transmission by insects.
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Currently aerosol contagion or airborne transmission is recognized for many pathogens such as viruses (Varicella zoster), bacteria (Mycobacterium tuberculosis) and fungi (Aspergillus spp.). Additionally, although the main mode of transmission of MRSA (MRSA) is by hand contact between people, especially in hospitals or health care facilities, airway transmission plays an important role in airway MRSA infections. However, in these times the debate continues about the way in which the influenza virus is transmitted.
In theory, the influenza virus can be transmitted by direct contagion, large droplets, or through aerosols (airborne), modes that are not exclusive. But there is also a tendency to diminish the importance of aerotransmission.
Are we underestimating the spread of influenza by air?
In the past, the medical community has emphasized transmission by large droplets or direct contact as the primary mode of propagation, diminishing the role of airborne transmission. However, some recently published papers suggest that the submicron Influenza A virus may be airborne.
Dr. Tellier in his study published by the CDC (U.S. Centers for Disease Control and Prevention) in November 2006, entitled "Summary of Influenza A Virus Transmission," states that there is evidence that area-related transmission of influenza can be an important form of transmission. which has obvious implications for contingency planning in the event of a pandemic.
"Despite extensive research, it has not found a single study that proves that large droplet transmission is predominant and that aerosol transmission is little or none."
His paper presents epidemiological observations and animal experiments demonstrating the importance of airborne transmission of influenza. Among his observations is the well-known outbreak described by Moser on an Alaskan Airlines plane, where five crew members and 49 passengers were traveling, who remained for 4.5 hours on hold in Homer, Alaska, including two to three hours in which a ventilation system was not working properly.
A passenger with severe symptoms of fever and cough was diagnosed with the Influenza A H3N2 virus, remained on the plane near the jacket closet and bathroom for 4.5 hours along with 30 other passengers. The rest of the travelers and crew periodically got off and off the plane.
Subsequently, 72% of the passengers and crew presented symptoms of influenza and of these, 91% were confirmed by laboratory tests with this disease.
Although there is currently no solution to solve the problem, if we can count on the technology to combat it, ultraviolet light is one of them.
On the other hand, observations of the effect of ultraviolet light in preventing this virus among tuberculosis patients during the 1957-58 influenza pandemic suggest airborne transmission. At a veterans hospital located in California, the proportion of individuals infected with influenza during two successive outbreaks was substantially lower in the department that had germicidal ultraviolet lamps, compared to the department that did not have them installed (2% vs. 19%).
Following this line, the Department of Health and Humanitarian Services of the United States, issued the Provisional Guide for the Planning of the Use of Medical Masks and Respirators in case of an Influenza Pandemic, a document in which it states that the proportional contribution and clinical importance of the possible modes of transmission of influenza (large droplets, airborne and direct contact) remains unclear and could depend on the strain of the virus.
Another West Virginia University study, published in January 2009, confirmed the presence of the influenza virus in air samples obtained from a hospital emergency room. The study was conducted during the 2008 flu season. Blachere and his colleagues took samples from a hospital emergency department. Measuring instruments, for particles of different sizes, stationary and portable were used on 6 different occasions in a variety of locations, including waiting and examination rooms. In three different days the Influenza A virus was found, of which 53% of the detected particles were within the fraction of respirable particles (less than 4 microns in diameter). The results were positive in the measuring instruments located in waiting rooms, reception and those used by the medical team. One more piece of evidence suggests that the influenza virus can be transmitted by air.
It is clear that although the mode of influenza transmission is complex and poorly understood, aerotransmission is an important factor, especially in hospitals and health care centers.
The 1918 flu pandemic that killed more than 50 billion people worldwide occurred slightly during the spring and returned in six months in a much more deadly form. The pandemics of the last 100 years: the Spanish Flu (1918), asian flu (1957) and the Hong Kong flu (1968), share a common denominator: subsequent waves with more force.
Figure 4. Particle Diameter (microns) Particle Diameter (Microns) Source: W.J. Kowalski, P.E, Airborne Respiratory Diseases and Mechanical Systems for Control of Microcrobs.
Isolation rooms in hospitals
In the study on the role of ventilation in the transmission of infectious agents in the environment, a specialist named Li and colleagues concluded, after analyzing 200 medical studies published between 1960 and 2005, that there is enough evidence to demonstrate the association between ventilation, controlling the direction of airflow in buildings and the transmission of infections such as measles, tuberculosis, chickenpox, anthrax, influenza, smallpox and SARS, so it is possible to reduce the risk of aerosol infection by altering ventilation parameters (see Figure 4).
Controlling airborne infections in hospitals requires certain considerations. When hospital rooms are connected through corridors, corridors, stairs or elevator shots, a pressure differential produced by differences in the temperature of air, wind or mechanical ventilators, can generate currents that move from one room to the other. These currents are modified when opening and closing doors and windows, because when opening a window you can change the pressure of the surrounding rooms or corridors. This highlights the importance of keeping the doors and windows of an insulation room closed.
Estimated time in which a particle travels 3 meters
Size in microns
Time
1-3
Indefinitely
10
17 minutes
20
4 minutes
100
10 seconds
Note: Weather may be affected by air turbulence
Currently, CDC guidelines recommend that people with highly contagious diseases (tuberculosis, etc.) should be isolated in a single room with certain characteristics. The use of filtration reduces airborne concentrations below their infectious dose and, in case of air recirculation, HEPA filtration (99.97% minimum particle efficiency of 0.3 microns) should be used.
It is also advisable to dilute the contaminant following the ventilation rate guidelines per area. Therefore, if the insulation room was built after 2001, there must be 12 air changes per hour, those built previously can use six air changes per hour, the important thing is the composition of the air.
It is also of the utmost importance that the insulation rooms remain under negative pressure to control exfiltrations by means of poorly sealed windows or doors, this is achieved through an extractor unit with HEPA filters, or through the air conditioning system when the injection air is less than that extracted. A minimum pressure differential of 2.5 Pa is recommended. (0.01" col. of water) in relation to corridors.
The flow of the air must move from the place where the health personnel are to the patient, that is, directional flow from the clean area to the contaminated one by placing the return or extractor near the patient. Preferably the air should be drawn to the outside and the room should have a sensor to alert in case there is a loss of negative pressure.
Some procedures, such as bronchoscopy or intubation, generate aerosols, potentially increasing the spread of "droplet nuclei" so the use of respiratory protection, for example, N-95, is recommended for all health personnel.
In times of epidemic, hospitals could be flooded with patients with contagious diseases, such as influenza, so it is very important to determine the number of isolation rooms when planning hospitals.
In case the negative pressure cannot be obtained with the ventilation system of the hospital, then portable or fixed extractor units can be used to convert a normal room into an isolation room. These units must be equipped with HEPA filters and optionally ultraviolet (short wave-C) germicidal lamps (see Figure 5 and 6).
The standards related to energy saving are:
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The standards related to energy saving are:
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HVAC system: critical element for the control of pathogens in closed places?
Microorganisms tend to proliferate in environments where there is air, dust and water, so an HVAC system (ventilation, heating and air conditioning) requires routine maintenance and monitoring to provide efficient Indoor Air Quality and minimize the conditions that favor the proliferation and distribution of pathogens.
According to the EPA, an HVAC system that is properly designed, installed, with proper operation and maintenance, is essential to providing a healthy environment. On the contrary, lack of maintenance can generate and spread contaminants.
The Federal Commission for the Protection against Sanitary Risks (Cofepris) of the Ministry of Health, states that the "air conditioning system has specifications for cleaning and maintenance, for example, washing of the equipment, replacement of filters, which must be verified through specific records that allow the control and evaluation of its operation". But a clean system is not unique to hospitals or clinics.
Because 90% of the time we spend indoors, it forces us to maintain adequate Indoor Air Quality for the protection and safety of occupants, reduce absenteeism and increase productivity.
According to the World Health Organization (WHO) points to the possibility that the new strain of influenza AH1N1 can mutate to a more virulent form. In addition, the WHO warns that if the virus interacts like H5N1, avian influenza, which is already found in several countries, it could be devastating. Are we ready?
Recommendations for raising the immune system of a building
Filtration. Manage an adequate level of filtration in conjunction with correct installation, operation and maintenance.
Ultraviolet Lamps for Air Conditioning. Ultraviolet light destroys the DNA of viruses and bacteria preventing microorganisms from reproducing. Disinfecting the air passing through the HVAC system significantly reduces the number of pathogens that recirculate through the building.
Use of purifiers or extractors with HEPA filters. For purification, recirculation and extraction of air.
Dilution by ventilation. Its effectiveness will depend on the changes of air per hour and distribution.
Pressurization. For example, isolated rooms must remain under negative pressure and rooms of immunocompromised patients under positive pressure.
Temperature and humidity control. It influences how quickly saliva dries and droplets change in size, in addition to growth and fungus.
Maintenance of all components of the HVAC system (injection ducts, return ducts and handler).
An outbreak of Serratia marcescens in a hospital in the United Arab Emirates, in the Neonatal Intensive Care department, caused 36 babies to be infected and another 5 to lose their lives, confirming that the source of contamination was the air conditioning ducts.
It seems that microbes or germs are opportunistic, the truth is that we share the environment with them, so it will be safer to take a proactive attitude. There is evidence that viruses such as influenza could be transmitted by airlift and although there is no single solution to solve this type of problem, fortunately there is technology, which without the intention of replacing infection control measures, it can be successfully applied by engineers, architects, building and maintenance managers, to combat the spread of airborne pathogens, making proper use of the ventilation system. The time to prepare us is now.
