It is generally accepted that a microbiological concentration
in the indoor air is similar to the outdoor values,
which means that the indoor/outdoor concentration ratio
(I/O) is close to 1. In our studies the I/O ratios for both
bacteria and fungi in most investigated rooms were lower
than this value, especially in the morning time. The situation
observed in the ventilated lecture hall (where I/O
ratios in the afternoons were lower than in the mornings)
is evidence of a proper ventilation system. Extremely high
values of I/O ratios in the afternoons for librarian lending
room and reading room, canteen, corridor and toilets can
be explained by the fact that all these places are most of
the time overcrowded with visitors. It is a main source of
microbiological contamination there.