I want to find the original full  report that University of Arizona
professor Charles Gerba filed in 1975 on the little known phenomenon
of bacterial and viral aerosols due to toilet flushing.

The report in question is a paper that was published in the journal
Applied Microbiology, 1975, Volume 30 (no. 2, August) on pages
229-237.  "Microbiological hazards of household toilets: droplet
production and the fate of residual organisms." by Gerba CP, Wallis C,
Melnick JL.

The authors found that large numbers of bacteria and viruses were
adsorbed onto the porcelain of toilet bowls.  However, each time the
toilet was flushed, a number of these microorganisms would be released
into the water.  The action of flushing would cause droplets of water
to be sprayed around.  These droplets were found to contain bacteria
and viruses, which were deposited by the spray onto other surfaces in
the bathroom.  The authors concluded that "there is a possibility that
a person may acquire an infection from an aerosol produced by a
toilet."

If you want to see a copy of this paper, you will have to obtain it
from a library that stocks Applied Microbiology.  Your public library
should be able to arrange this for you, or alternatively you could try
contacting the library of a nearby university to see if it could help
you.

In the meantime, here are a couple of articles about Gerba's work,
which might also be of interest.

On Germ Patrol, At the Kitchen Sink, By WENDY MARSTON     February 23,
1999   NY Times: http://www.siprep.org/scien/biology/loyd/web_pages/Starr3eHandouts/Bacteria%20LabWeb_files/On%20Germ%20Patrol%20NYT.htm

Does flushing the toilet cause dirty water to be spewed around the
bathroom?
16-Apr-1999  from The Straight Dope:
http://www.straightdope.com/classics/a990416.html

Search strategy: Medline database at http://www.nlm.nih.gov with
search terms "Gerba" and limited to publication year 1975
For the other articles, I searched on Google using: Gerba + toilet +
aerosol + 1975:
://www.google.com/search?q=Gerba+toilet+aerosol+1975&hl=en&lr=&ie=UTF-8&oe=UTF-8&start=10&sa=N

tehuti-ga knows his stuff. Cheers.