Aeromedical evacuation of biological warfare casualties: A treatise on infectious diseases on aircraft

Military Medicine, Nov 2000 by Withers, Mark R

A basic understanding of the transmission and isolation of infections would be essential to the safe and effective aeromedical evacuation (AE) of biological warfare (BW) casualties. First, the airframe as microbial environment is considered, and relevant preventive and disinfecting measures are discussed. A survey of past infectious disease transmission on civilian aircraft (including tuberculosis, influenza, measles, smallpox, and viral hemorrhagic fevers) is presented, and the communicability and stability of likely BW agents is described. A brief history of U.S. military aeromedical evacuation (as it relates to contagious diseases and U.S. Air Force BW doctrine) is also outlined. Special containment procedures (especially as used by the U.S. Army Aeromedical Isolation Team) are described. Finally, international legal and regulatory aspects of the AE of BW casualties are considered, and some unanswered questions and suggestions for future research are offered. It is concluded that, given adequate foresight, expertise, and resources, the AE of even contagious BW casualties could be safely and effectively accomplished.

Introduction

he aeromedical evacuation (AE) of biological warfare (BW) casualties has never been attempted or, fortunately, reT quired. The operational decision to evacuate BW casualties would be a complex one depending on many factors, not the least of which would be the specific BW agent in question. Unlike nuclear and chemical weapons, some biological agents continue to represent a potential threat to medical personnel even after external decontamination. Theater medical facilities might be rapidly overwhelmed by the influx of large numbers of BW casualties in a short time, making rapid evacuation highly desirable. But events could easily overwhelm the ability of medical personnel to understand and manage the situation, making orderly movement, treatment, and isolation difficult and rendering AE unfeasible.

Although considerable basic and applied research, as well as public media attention, has been directed toward the possibility of the use of BW weapons by countries antagonistic to the United States, very little has been published in the medical or military literature specific to the AE of BW casualties. A recent search of the MEDLINE electronic database (for the period 1966 to 1998) queried the intersection of the key words "biological warfare" and "aeromedical evacuation" (or just "evacuation"). This search yielded but a single article.' Moreover, standard textbooks of flight medicine simply reiterate hospital infection precautions if they address infectious disease concerns at all.2

A comprehensive understanding of all possible aspects of the AE of BW casualties would encompass expertise in such diverse areas as disaster medicine, air transport medicine, critical care medicine, isolation and containment of highly communicable diseases, international aviation law and diplomacy, the ergonomics and aerobiology of aircraft interiors, and the operational requirements and constraints of the U.S. Air Force and other military and civil services. An aeromedical evacuation system integrating all of these elements does not exist at present. This article does not purport to be exhaustive or definitive. We will draw together what is known about the transmission of infectious diseases onboard aircraft and sketch out areas of ignorance with an eye toward stimulating discussion and suggesting future research. We will explore and highlight elements of the current understanding of possible BW scenarios, military AE plans and capabilities, and emerging U.S. military doctrine as they apply to the feasibility of the AE of BW casualties.

Definitions: Transmission, Precautions, Isolation, Quarantine, and Containment

There are three primary routes for the transmission of human pathogenic microorganisms: direct, indirect, and airborne.3 Direct transmission may be by direct contact (body-to-body by touching or sex) or large droplet transmission. In the latter, large "wet" droplets (>5 Jm) are generated from the source patient by coughing, sneezing, or talking or by certain procedures (suctioning, bronchoscopy). These microbe-bearing droplets are propelled a short distance (generally not more than about 1 m) through the air and are deposited on a susceptible person's conjunctiva or mucosa before they can fall to the floor. Indirect transmission may be vehicle-borne- food-borne, water-borne, and via certain medical routes (contaminated drugs, fluids, devices). It may also be vector-borne-the familiar routes of arthropod, rodent, and other vermin transmission. In airborne transmission, dissemination occurs by airborne droplet nuclei or dust particles of 5 um diameter or less. These partially evaporated droplet nuclei or particles are actually suspended in midair rather than flying through it, as with the larger wet droplets. They contain the infectious agent and may be widely dispersed by air currents and inhaled deeply into the bronchioles of a susceptible host. Depending on environmental factors, the area of transmissibility may be confined to a single room or spread over a larger distance from the source patient. Airborne transmission probably represents the mechanism whereby the largest number of aircraft occupants could be infected during the shortest exposure.4 The direct (including large-particle aerosol) and airborne (small-particle aerosol) routes are the most relevant to BW casualty management. Table I lists typical examples of infections transmitted by the three routes.