During spaceflight, there will be the transfer of microbes between crew members. Several bacterial associated diseases were experienced by the crew in Skylab 1. The microbial contamination in the Skylab was found to be very high. "Staphylococcus aureus" and "Aspergillus" spp have commonly been isolated from the air and surfaces during several space missions. The microbes do not sediment in microgravity which results in persisting airborne aerosols and high microbial densities in-cabin air in particular if the cabin air filtering systems are not well maintained. During one mission an increase in the number and spread of fungi and pathogenic streptococci were found.