Resistance to infections in extended space flight

Although much can be done to minimize the spread of micro-organisms from one individual to another, it is inevitable that an exchange of microflora will occur among individuals in an enclosed space. The chief sources of the microflora will be the respiratory tract, the gastrointestinal tract and the skin. Local care can deal with most problems of the skin, but potential problems in the respiratory and gastrointestinal tract cannot be dealt with as readily. Although many of the common pathogens can be eliminated by pre-flight procedures, the building up of normal flora represents potential hazards of substantial magnitude. The chief limitations of the effects of high concentrations of normal microbial flora are in the variety of host defensive mechanisms. Some of these have been reviewed, and it has been indicated that with respect to the bronchopulmonary defense mechanisms, the major defenses rest in the pulmonary alveolar macrophage system. This system has been shown to be adversely affected by a large variety of environmental circumstances, many of which will be operative in prolonged spaceflight. Similarly in the gastrointestinal tract, the large microbial load represents a source of micro-organisms and of waste products, which represent potential hazards. Methods for minimizing the latter effects include reducing the total microbial load or implanting a monoculture of a desired micro-organism which produces a minimum of the undesirable side effects. The solution to these problems requires sustained effort, and it is likely that solutions when found will have substantial application to medicine and public health in ground-based communities.