TUBERCULOSIS SPREAD AND INFECTION

The most prominent way to spread an air borne infection is from person to person via close contact with infected people or patients, or exposure over long periods of time in a small poorly ventilated room. Simple talking, singing, sneezing or coughing in close proximity to others will spread a sufficient amount of aerosols to infect them. Infection is also spread by inhaling MTB in aerosols made during medical procedures in treatment of pulmonary or extrapulmonary TB ( TB infections’ other than in the lungs ). TB infection is usually benign and the initial infection can go unnoticed, however, the infection can still be detected with a skin test. The TB lesions or positive skin test will usually take 4 to 12 weeks to show up. Lesions in the lungs which usually heal will seldom leave any residual changes. About 95% of those infected and that have healed, will still be in the latent phase of the disease and still will have a lifetime risk of reactivation of TB. The other 5% progress directly to TB infections. The risk of progressive TB is greatest within the first year or two after infection. The potential for infants, adolescents and young adults to develop a serious disease is greater. All this is the reason why early diagnosis and treatment is so important.

If active TB is not treated, about _ of those infected will die within the first two years. However, early treatment almost always results in a cure, even though reactivation is still possible in future years.

Diagnosis of TB can be via a positive skin test, chest X rays, positive smear test of the persons sputum, or fatigue and fever as well as weight loss could occur in the early stages. Advanced stages could show up as coughing, chest pain, coughing or spitting up blood.

Treatment is via antibiotics and is given in spite of the fact that 90% of the diseased people will heal. It is to reduce the cross contamination of others as well as reduce the risk of progression, that a therapy regime is started immediately. The least costly treatment is a regime of three drugs for 6 months. If the patient stays on the regime then progression to a drug resistant strain is reduced. Typically Latin Americans, Asians and Africans have shown the highest rate of drug resistant strains.

Many of the drugs used for the TB therapy may be carcinogenic as well as cause liver changes. Also, hepatitis, enlarged mammary glands, fetus problems, various nervous system reactions, and lymphoma can all be started with these drugs. Lesions in the lungs

Action - The idea that one could get TB and treat it without any other problems, is a misnomer, because:

1 - Treatment drug therapy can create other physical problems or sicknesses.

2 - Having the TB lesions in the lungs for the rest of your life, that could reactivate as a future disease, when one gets rundown or HIV.

3 - There is a 50/50 chance that if TB is not detected, death could happen within two years.

Ultimately, the risk of hepatitis, cancer, death, reproductive effect, or other adverse reactions must be weighed against the risk of not using the most effective drugs in fighting TB. The more obvious alternative is to prevent skin test conversions within all means possible. This thinking highlights the need to understand and implement occupational exposure controls as well as patient isolation from other uninfected patients, especially in settings where active infections are recognized. It also demands action in high risk populations, even where infection may or may not be recognized.

Tuberculosis as an indoor air quality problem - A thorough study of airborne health hazards generally requires much knowledge, including the following:

1 - Knowledge of the health effects of the disease

2 - Determination of the airborne concentration of contaminants,

3 - A comparison to safe airborne levels of these contaminants established in current standards, guidelines and codes.

Periodic surveillance of air quality is often performed using sampling methods for specific airborne contaminants generated by specific industrial processes. Chemical vapors are very familiar to us and only pose a risk when we cannot smell them or they are such that there presence is extremely dangerous, especially when in high concentrations. Just like these chemicals TB can be suspended in a mist of vapor, this mist can be termed a bioaerosol when speaking of TB.

Understanding the physical form and method of generation of any airborne contaminant, including bioaerosols, is fundamental in evaluating and controlling the hazards they pose. Most bioaerosols are generated from an environmental source except TB, therefore, TB is a communicable disease. Environmentally generated bioaerosols involving mechanical processes or heating and ventilating systems, are generally easier to control than are activities of human beings such as coughing. Coughing is an undesirable symptom, from an exposure standpoint, of active TB. These bioaerosols have been tested to be about 1 to 10 microns in size. Since particle size is the most important parameter for characterizing the behavior of all aerosols, this information is the important framework for understanding how exposure occurs and how air cleaning controls should be chosen.

The infectious dose of TB is a measure of infectability, which depends upon the route of exposure, if this route is not directly to, or from, the host, then the amount of infection carried is diminished. Case histories demonstrate that the numbers of TB bacilli generated from a coughing person are indeed orders of magnitude higher than that required for infection. The American Thoracic Society has made the following statements with regard to airborne generation rates:

The key factors that effect the aerosol survival are visible light, ultraviolet light and photoreactivation, ultraviolet light and pigmentation. Those characteristics of TB which influence aerosolization and survival include the following:

Although bioaerosol testing for most agents is common place in the industrial and commercial environments the TB test is much more problematic. TB infectious agents, if airborne, are present in far fewer numbers than a normal fungi or other bioaerosols. Also the infectious agents are far less likely to survive the rigors of air sampling devices.

It is entirely appropriate to present means of diagnosing indoor air quality problems other than air sampling because examining the performance of a ventilating system usually precedes air sampling for air contaminants in indoor air quality investigations.

Tuberculosis remediation -The easiest and best way to limit the infection possibilities between people or between patient to patient or between patient to health care worker is by dilution. That is, a system has to gather the dirty air, clean and disinfect it and reintroduce this clean air back into the space.

The existing heating and ventilating system is not designed to collect and kill the TB. These systems contain dust particles and heat or cool the air, as well as introduce fresh air into the space. Dilution ventilation of indoor air with outside air is the standard way to help indoor air quality problems.

HVAC systems for buildings are designed to provide good air quality and thermal comfort at reasonable energy costs. Good air quality implies adequate oxygen, removal of carbon dioxide, and removal of contaminants. Acceptable indoor air quality has been defined by the American Society of Heating, Refrigeration, and Air Conditioning Engineers, Inc. (ASHRAE) as air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80% or more) of the people exposed do not express dissatisfaction (ASHRAE 62-1989).

Dilution ventilation is used in all areas of buildings and hospitals to reduce infection risk. Source capture of contaminants will work well in infectious isolation rooms, however, this is an impossibility in all other areas of any building.

Nonetheless, there are circumstances where dilution ventilation must be used because the source capture of contaminant cannot be controlled by local exhaust ventilation. Only because it is not feasible to design local exhaust ventilation systems for TB patients, dilution ventilation is used to reduce over time the room average concentrations of droplet nuclei in a room.

A simple 35% reduction in concentrations was shown to happen at the introduction of the first 2 air changes to a space. 6 air changes reduced the totals by 50%. More air changes only reduce the concentrations to a 60% level. This therefore is the most prudent start to an infection control program.

NQ SYSTEMS FUNCTION

The patented airflow off the top of a NQE unit will distribute clean air at the ceiling while gathering the dirty air at the floor. This procedure will assure the best air in the breathing zone of both healthcare workers as well as the patients and the people in the other spaces.

Airflow patterns are critical to the proper functioning or the system.

This capture process must be as close to the source or host with the active TB.

TUBERCULOSIS CONTROLS WITH NQ

The recommended way to control TB as an air borne infection, is via two important measures:

The first, administrative measures, is quite obvious to most healthcare workers, it is to keep people away from the infection, but what happens when the person with that infection needs to be tested or cared for. Or the worker is in a business that has contact with people that are unknown if they have TB or not. The healthcare worker needs to not only protect himself or herself, but to also protect other patients from getting the infection as well. This brings us to the second point, a hierarchy of engineering control measures.

The use of the facility HVAC systems is typically quite expensive and in fact may not give as good a result as a recirculation system mounted directly in the space. The reasons that the facility HVAC system may not be as good are:

The most important principle to remember is: . . . . "one can filter the air with the most modern concepts or equipment, BUT, if the air does not get to all corners of the room then it is worthless and not effective."

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