The World Health Organization published in 2003 the Guide to the Prevention of Nosocomial Infections, an exhaustive research that places special emphasis on good ventilation and air filtration to dilute bacterial contamination, as well as the proper design of systems and maintenance of the filters, humidifiers, grids and other parts to prevent the spread of airborne diseases.
In addition, the American Association of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE), in the Legionellosis document, published in 1989, recognizes that heating, ventilation, air conditioning and refrigeration systems as well as their components, hot water services and watering facilities can amplify and disseminate aerosols in the form of many pollutants. Therefore, it is recommended to pay special attention in the design and execution of procedures of maintenance of all the components of these systems.
Nosocomial infections are defined as those contracted during a stay in a hospital or other health facility, which had not manifested or were in the incubation period at the time of the patient’s admission, including those manifested after the discharge of the patient. They are related to many factors such as the vulnerability of the patients, environmental factors and microbial agents and their resistance to the antibiotics.
The hospitals are an ideal environment for the spread of diseases for the reason that they have pathogens and the people who are sick or have low immune resistance are prone to fall the victims. Some studies estimate that between 5 and 10 percent of the people entering a hospital acquire an infection during their stay and they cause about 100 thousand deaths a year.
On the other hand, nosocomial infections imply millions of dollars in the expenditures to health institutions. The respiratory system diseases are the third most common type of infection, after urine and surgical wound infections and occupy specialists in HVAC systems as the air conditioning equipment plays a crucial role in its dissemination.
Legionella pneumophila was identified in 1977, one year after an outbreak of pneumonia caused the deaths of 34 people in the Legionaries Convention. This bacteria, according to studies since then, is found in small colonies in natural sources of water such as rivers, lakes and streams and it can survive in very different environmental conditions.
In order for its concentration to increase sufficiently and to cause risk to humans, appropriate temperature conditions are required for its multiplication, between 25 and 45 °C. It can be transmitted through the air with the evaporation of water droplets from cooling towers of air conditioning systems or to form aerosols in the shower given by the patients and then be inhaled by them, thereby, exposing them to risk of the infection. There is no evidence of person-to-person transmission as its contagion is by air.