MERGINET.News for November/December, 1999
Biological Agents as Weapons:
Medical Implications Part 2 Countermeasures & Decontamination
by Ken Miller, M.D., Ph.D.
[Note: Part 1 of this series from MERGINET.News, October 1999 discusses methods of delivery and identification for the most common biological weapon agents. Also to be noted are Specific Biological Agents and Biological Agents with Weapon Potential.]
A few pre-attack countermeasures may be possible: Protection of food and water sources and control of rodents and insects which may transmit some of the biological agents, for example. Protection of food and water is more practical in a military contingency than in a civilian one. Truly effective defense against terrorism would mean restricting common freedoms. This presents significant problems for emergency planners and is one reason terrorism continues to be effective.
Among the post-attack countermeasures are:
- Hygiene & Sanitation will prevent further spread of the agent from contaminated areas.
- Collective protection. This term is used for holding people in shelters with filtered positive-pressure ventilation. It is a military tactic but it has also been reported that the HEPA (high-efficiency particulate air) filters in HVAC (heating, ventilation, and air-conditioning) units of commercial buildings could effectively protect occupants from an aerosol attack if other sites of air entry are blocked.
- Shelter-in-place. The population is specifically instructed to stay indoors as a temporary measure of protection. It's most effective for a fast-moving toxic cloud, when people near the release point have insufficient time to evacuate, or when there is a finite duration exposure. Shelter-in-place may be harmful for long-term or continued release of a toxic agent if the:
- Outcome of the release cannot be reasonably predicted
- Cloud is prevented from dispersing
- Agent is flammable or highly reactive.
It should be concluded as soon as the cloud or aerosol passes as verified by monitoring, and is more readily done in chemical than biological agent releases. Structures should then be opened and ventilated and the population evacuated. The international news media showed examples of this during Operation Desert Storm in reference to protecting Israeli civilians from potential chemical or biological attack from Iraqi SCUD missiles.
- Vaccines. Some are available to protect from infection by selected biological agents. However, they must be administered well in advance of exposure and require periodic revaccination. They are practical only for military personnel based on an anticipated threat. Some can be used post-exposure.
- Antibiotics can also be effective if administered orally after exposure but before symptoms occur. Intravenous antibiotics, with supportive therapy are therapeutic once infection has occurred. However, some more aggressive biological agents cause a fast moving disease so early treatment is essential.
Once multi-system illness occurs fatalities remain high even with treatment. Should a biological agent attack be carried out effectively, a larger number of people could be exposed. Some fraction large or small will become ill. This could potentially overwhelm the supply of common antibiotics used prophylactically or therapeutically.
- Personal Protective Equipment (PPE). The military issues PPE, called the "battledress overgarment" (BDO). It consists of a hood, a full face mask with air-purifying respirator, butyl rubber gloves and booties, and a carbon-infiltrated overgarment. The BDO is designed to protect soldiers from chemical and biological agents. The carbon in the BDO adsorbs chemical agents.
During the decontamination of casualties, the military adds a butyl rubber apron over the BDO for the decon team. Comparable PPE in the fire service are the Levels A (vapor and splash), B (splash), and C (protective equipment).
Since the inhalation exposure route presents the greatest risk of fatal disease from biological agents, respiratory protection is critical while the aerosol is present. Once the aerosol has dissipated, contaminated surfaces may still present an infectious risk, but not necessarily one as great as inhalation.
If a biological terrorist attack is immediately identified, Level A and B protection will allow for rescue of victims and their collection for decontamination. Level A protection would provide maximum safety during the rescue of non-ambulatory victims from a contaminated environment.
Unlike chemical agents, where off-gassing of vapor is still a hazard after the agent has dispersed, the respiratory protection of Level B could still be adequate when only a biological agent is suspected. However, it's unlikely that the agent/s would be identified at the scene, so Level A protection would be the safest choice.
The BDO seems to be an enhanced Level C protection system; it incorporates full skin protection with a full face air-purifying respirator using a HEPA filter filtering one to 1.5 micron size particles as well as a canister to filter organic agents.
When caring for decontaminated victims out of the hot zone, universal precautions should be sufficient. When caring for symptomatic victims days after the attack, universal precautions with HEPA or N95 masks, as with any other infectious disease exposure like tuberculosis, will be effective.
Only two biological agents used historically cause disease that can be transmitted person-to-person: pneumonic plague and smallpox. Both are transmitted by respiratory aerosol from coughing or respiratory secretions suctioning, bag-valve-mask ventilation, intubation so respiratory protection with a well-fitted HEPA or N95 mask or HEPA air-purifying respirator and universal precautions will be effective protection.
Drainage from skin lesions produced by brucellosis, anthrax, and viral hemorrhagic fevers can potentially transmit disease person-to-person, but universal precautions are sufficient. In all cases, good washing of the hands and exposed skin and decontamination or disposal of equipment after patient care will reduce the risk of rescuer infection.
Biological agents may be encountered in several forms:
- Slurry Mix
- Thick Droplets
- Dry Powder
- Vectors infected insects or rodents, which then infect people
Casualties may present in several ways:
- Exposed & Contaminated some ambulatory, some non-ambulatory
- Exposed, Unaware, No Symptoms during incubation
The actions rescuers will take will depend on these presentations.
Chemical and biological terrorism present two potentially major complicating realities not commonly encountered in industrial and transportation hazardous materials incidents. The large number of people who may be contaminated and the fact that some of them will self-triage and self-transport to local hospitals. Also, some chemical agents require that respiratory support and specific antidotes be administered during and immediately following decon a situation requiring coordination between HazMat and EMS. The problem with the self-triaged contaminated victims is that they may contaminate and disable close-by emergency departments, making subsequent triage and transport decisions at the incident more difficult.
The challenge of mass decon can also contribute to the chances of victims' self-transporting. The longer it takes to set up and operate mass decon, the greater the probability that ambulatory victims will seek their own care. Probably the most practical and rapid approach to mass decon is to set up sequential - two to three elevated masterstreams, deck guns, or 1½- to 1¾-inch handlines operated on a fog pattern and low pressure and walk the ambulatory victims through the water curtain while still clothed. Ladder pipes with a 2½-inch gated-Y with two 2½-inch nozzles attached operated at hydrant pressure or up to 50 psi at the nozzle seems to work. At the end of this decon corridor, tarps could be set up for privacy. Ambulatory victims may then undress and wash with soap and water and then dry and redress in large trash bags with holes cut out for the head and arms.
Since a suspected terrorist incident constitutes a crime scene, all clothing removed from victims will be evidence. This means the clothing needs to be bagged, tagged for later victim identification (like triage tags) and set aside in a secure location until the Federal Bureau of Investigation (FBI) the lead law enforcement agency determines its disposition. Such mass decon tactics will work for biological agents and toxins and for many, but not all chemical agents.
The consensus seems to be that dilution of any biological agent by the method described above is so great that it's not necessary to contain runoff. Rescuers working in this decon corridor would be protected in Level B PPE, which for many departments is considered equivalent to structural turnout gear with SCBA.
In the case of a biological agent release, non-ambulatory victims would have to have been incapacitated by the dispersing mechanism, such as a bomb or secondary event, since the resulting disease takes time to develop and incapacitate. Unlike chemical agents, symptoms are not immediate.
For non-ambulatory victims, rescue may require Level A protection. Contaminated victims would be taken to the decon corridor where personnel in Level B or Level C (if appropriate air-purifying respirator canisters are available) protection can perform decon by systematic clothing removal and containment, soap and water (or just lots of water) wash-down probably in two stages drying, and covering.
Sodium or calcium hypochlorite in dilute solution 0.5 percent in military manuals may be used as an oxidant for chemical and as a disinfectant for biological agent decon in the initial step but isn't essential. It's better to proceed with water or soap and water decon than to wait for the availability of hypochlorite. Open wounds must be irrigated with sterile saline at each stage of decon as well.
Managing Victims with Delayed Symptoms
What about the biological agent release when victims may not know they've been exposed? This is entirely likely if a terrorist uses a biological agent dispersed with a nondestructive aerosol mechanism. Victims won't know they're victims until they start getting sick hours to days later. The key is that once the agent has dissipated, these victims are no more a hazard to rescuers than any other patient with an infectious disease. Most likely, they'll have been self-decontaminated through the use of their usual hygiene. Contaminated clothing may still have the organism on it, but its threat is greatly reduced if it's not re-aerosolized.
Only pneumonic plague and smallpox can be transmitted person-to-person once infected, through respiratory secretions. In general, universal precautions with respiratory protection will be adequate protection if these two diseases are suspected or if pulmonary symptoms are the predominant problem.
- Medical Management of Biological Casualties, U.S., Army Medical Research Institute of Infectious Diseases, second edition, Aug. 1996.
- NATO Handbook on the Medical Aspects of NBC Defensive Operations, Part II--Biological, Departments of the Army, Navy and Air Force, Feb. 1996.
- Franz, DR, et al, "Clinical Recognition and Management of Patients Exposed to Biological Warfare Agents, JAMA, 278(5):399-411, 1997.
- Metropolitan Medical Strike Team Field Operations Guide, U.S. Department of Health and Human Services, Office of Public Health and Science [YEAR?]
- Proceedings, National Disaster Medical System Annual Conference, Denver, Mar. 1998.
Reprinted by Permission from Fire Engineering