is an acute infectious disease caused by the spore-forming bacterium bacillus anthracis. Anthrax most commonly occurs in wild and domestic animals including cattle, sheep, goats, camels, antelopes, and other herbivores, but it can also occur in humans when they are exposed to infected animals or tissue from infected animals.
Anthrax is most common in agricultural regions. These include South and Central America, Southern and Eastern Europe, Asia, Africa, the Caribbean, and the Middle East. When anthrax affects humans, it is usually due to an occupational exposure to infected animals or their products. It is rare to find infected animals in the United States.
As a biological weapon, anthrax may be inhaled by humans. It is also very cheap to produce, costing about $50 per kilogram. One test tube of feed stock (samples of anthrax) can produce a kilogram of anthrax in about 96 hours in a fermenter. Samples are relatively easy to find because it is a naturally occurring disease throughout the world. Anthrax is easy to deliver in the form of a weapon (crop dusting, air distribution systems, and enclosed spaces). Since HVAC air distribution systems may be a path of contamination, access to these areas should be secure.
Symptoms of disease vary depending on how the disease was contracted, but symptoms usually occur within 7 days. Once exposure to anthrax has been identified, timely medical treatment of the exposed individuals is recommended as the bacteria can be fatal.
There are three ways in which humans can be infected by Anthrax spores:
- Cutaneous (or through the skin): Most (about 95%) anthrax infections occur when the bacterium enters a cut or abrasion on the skin, such as when handling contaminated wool, hides, leather or hair products (especially goat hair) of infected animals. Skin infection begins as a raised itchy bump that resembles an insect bite but within 1-2 days develops into a vesicle and then a painless ulcer, usually 1-3 cm in diameter, with a characteristic black necrotic (dying) area in the center. Lymph glands in the adjacent area may swell. About 20% of untreated cases of cutaneous anthrax will result in death. Deaths are rare with appropriate antimicrobial therapy.
- Inhalation (or through the respiratory system): Initial symptoms may resemble the common cold. After several days, the symptoms may progress to severe breathing problems and shock. Inhalation anthrax can be fatal if treatment lags infection.
- Intestinal (or through eating contaminated products): The intestinal disease form of anthrax may follow the consumption of contaminated meat and is characterized by an acute inflammation of the intestinal tract. Initial signs of nausea, loss of appetite, vomiting, fever are followed by abdominal pain, vomiting of blood, and severe diarrhea. Intestinal anthrax may result in death in 25% to 60% of cases.
When questioned about anthrax the following points apply:
- There is extremely low risk of biological attack if the facility is outside of a major urban area. Hence, if you are tens of miles outside of a major city, you probably do not need to do much to be prepared other than have food, water, power, supplies, etc. stored up in case of long infrastructure outages due to biological attacks.
- The only true air filtration protection for anthrax is a HEPA filter. To be effective, this must be an air distribution system that takes outside air in through the filter and pushes this filtered air back out through the leak paths in the building - thus the HEPA system creates a slight positive overpressure in the facility. Such building positive pressure creates a balloon effect that helps keep contaminated air from entering the building. HEPA units that merely cleanse the recirculation air would provide little protection against anthrax laden air that is sucked into your facility, unless an area is provided with complete positive overpressure protection.
- A document already exists that may be used to combat airborne anthrax spores in a facility. The CDC Guidelines for the Control of Mycobacterium Tuberculosis has some excellent recommendations for control of this type of contaminant. Airborne tuberculosis in its respirable form is also 1-5 microns in size. When considering controls these guidelines provide sound mechanical system advice that may be applied to reduce the airborne level of infectious anthrax
- One additional point on filters bears mentioning. Although a HEPA filter is the only sure way of eliminating airborne spores, they may also be removed to a lesser degree by ASHRAE grade filters. MERV 14 and higher ASHRAE grade filters can remove more than 97%+ of the particles in the 1 to 5 micron range although they should not be considered a fail-safe alternative to HEPA filter application. A MERV 16 (commonly referred to as 95% DOP) filter is at least 99% efficient in this range.
- Additionally any filter in an HVAC system only performs when air is
moved through the system. To decrease numbers of particles per cubic
foot, increase the number of air changes to the space (thus moving more
air through the filter, decreasing the number of particles per cubic
foot with each pass). Given a particular particle size, and a filter
efficiency approaching 100%, the following chart demonstrates the
importance of increased air changes.
- The typical commercial building with a constant volume system offers 6-8 air changes per hour. VAV systems sometimes operate as low as 2-3 air changes per hour. During incidences of infectious control (flu season, etc.), increasing air changes can reduce the number of infectious airborne contaminant. If the system has a fan 'on' switch for constant flow volume, you can increase the number of air changes per hour, by moving this switch to 'on'. As an example, in the aforementioned chart increasing air changes from 6 to 15 will 'clean' the air to a 99% removal rate in 18 minutes as opposed to 46 minutes.
- Isolate any item suspected including mail or other items.
- Isolate individuals that may have been exposed.
- Call 911, or contact authorities, and state what has occurred.
- Notify building maintenance to turn off any ventilation systems.
- Ensure that all persons who may have been exposed wash their hands with soap and water.
- List all persons who may have been exposed and provide the list to public health authorities.
- Wait for the police and HAZMAT team to arrive. They will provide further directions.