[Communicable disease problems of sewage with special reference to human pathogenic viruses]

Summarizing, it can be said that the epidemiological hygienic risk originating from community waste water can be controlled. This risk appears to be considerably lower when directly handling waste water than indirectly by contact with water contaminated by waste water. The sewage treatment technologies presently in use reduce the contents of viruses, bacteria, protozoa and worm eggs to a varying extent. Owing to the fluctuating concentrations in the inflow to the sewage treatment plant, a proportion of these microbes or proliferation stages of parasitic worms must always be expected not to be eliminated. The pathogens held back in the treatment plant burden primarily the sewage sludge. The various processes of sludge stabilisation influence their number and degree of infectiousness to a varying extent (2, 3, 6). The most important risks of infection which waste water entails, originate from contaminations of raw water and above all of treated drinking water. Statistics from the United States indicate that the above-mentioned bacteria, protozoa and part of the viruses have caused drinking water epidemics (23, 24). Attention has to be paid to bacteria and viruses because some of them prove harmful already in very low doses. Moreover, the occurrence of protozoa should be investigated more intensely. Apart from changes in pathogenicity and low infectious doses, also the fact should be duly considered that these microorganisms are likely to increasingly invade our waste waters, as millions of people yearly head for southern climates. There they fall easily prey to infections which overwhelmingly remain inapparent clinically, and discharge pathogens frequently for a very long period without revealing any symptoms. Also in connection with methods of virus analysis, improved meanwhile the constant efforts for improved indicator systems in the identification of pathogenic organisms must be continued so that epidemiological hygienic problems can be better evaluated and solved.