SUMMARYThe results of a three year study of the viruses isolated from sewage by means of five tissue culture types are reported. The enteroviruses identified demonstrated a seasonal pattern which was similar to that of clinical isolates. Echoviruses and coxsackieviruses displayed a changing pattern of dominant serotypes in both sewage and clinical isolates; echovirus 6, 19, 3 and coxsackievirus B4, B5, A9 successively became the most common serotypes. The poliovirus in sewage was all vaccine-like in character. Reovirus, type 2 was abundant; adenovirus, of several serotypes, were the least often identified.

A novel method for the concentration of Cryptosporidium oocysts from water has been developed, based upon the precipitation of calcium carbonate. A 10 l water sample is treated by adding solutions of calcium chloride and sodium bicarbonate and raising the pH value to 10 with sodium hydroxide. Crystals of calcium carbonate form and enmesh particles in the Cryptosporidium oocyst size range. The crystals are allowed to settle, the supernatant fluid is discarded and the calcium carbonate precipitate dissolved in sulphamic acid. The sample can be concentrated further by centrifugation. Recoveries of oocysts from seeded samples of deionized, tap and river water were in excess of 68%.

A flow cytometric method for the routine analysis of environmental water samples for the presence of Cryptosporidium oocysts has been developed. It uses a Coulter Epics Elite flow cytometer to examine water samples and to separate oocysts from contaminating debris by cell sorting. The sorted particles are then rapidly screened by microscopy. The method has been evaluated and compared with direct epifluorescence microscopy on 325 river, reservoir and drinking water samples. The technique was found to be more sensitive, faster and easier to perform than conventional epifluorescent microscopy for the routine examination of water samples for Cryptosporidium.

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