RESULTS:
Postflight microbial levels were generally 20-80% higher than preflight levels. However, the in-flight measurements were more useful in evaluating the microbial levels of crew exposure during the mission. Four slight drops in the microbial load were experienced during the first part of the mission, but this was followed by a rapid increase as the mission proceeded. The last in-flight levels increased as much as 200-400 percent over the first in-flight levels.

In-flight monitoring of the air proved to be a useful means of identifying microbial changes that occurred during missions. A slight drop in the level of microorganisms in the air was common during the early stages of the missions. This would indicate that the filtration system was adequate to clean the air at that time. However, as the mission progressed, the filtration system was no longer able to clear the air; the levels of contamination increased as the mission proceeded. This may have been due to the clogging of the filters with debris. It is logical to assume that longer missions and larger crews would increase the levels of contamination even more.

A number of potentially pathogenic fungi were isolated. The fungi have become increasingly important with the advent of the reusable spacecraft. Although the fungi are relatively slow growers, they are also very resistant to adverse conditions and remain viable for long periods of time. They remain dormant under adverse conditions but resume growth when conditions become more favorable. They pose a threat to the health of the crewmembers as 1) agents of infection, 2) allergens, and 3) producers of toxic metabolites. In addition, they are able to synthesize a vast array of enzymes enabling them to deteriorate practically every organic compound known.