The Recovery of Viruses from Drinking-Water by Means of an in-Line Electropositive Cartridge Filter

Abstract

Efficient, fast and relatively inexpensive techniques, which will consistently give high recoveries of viruses from one hundred or more litres of water, are still sought for the monitoring of drinking-water systems. A technique using electropositive absorbent filters showed promise if sample volumes were limited to 100 ℓ. Investigation of this recovery method was warranted, as the use of an in-line cartridge filter would constitute an ideal monitoring tool if the filter could be inserted at set points in a distribution system, removed under sterile conditions after the filtration of a known volume of water, and returned to a specialized virological laboratory for elution and virus isolation. In the present study, tests were carried out to determine the efficiency of positively charged AMF-Cuno Virosorb cartridge filters in processing 100 ℓ of tap water continuously seeded with varying dosages of different viruses. Viruses were desorbed by the cycling of a 3 g/ℓ beef extract solution in 50 mM glycine - NaOH at pH 9.5 for 5 min, followed by immediate neutralization with 1 mol/ℓ HCl. In order to avoid a second concentration step, the 1 ℓ eluent was converted into growth medium by the addition of dehydrated Dulbecco's modified Eagle medium with decontamination by filtration through a 147 mm diameter 0.22 µm membrane. In eleven tests where the average poliovirus 1 seed was 22 × 106 TCID50 per 100 ℓ, virus recoveries were 75.9% ± 25.9%. In subsequent tests the virus seed was progressively reduced by one log at a time until the theoretical dosage was between one and ten TCID50 virus per 100 ℓ tap water. Virus could always be isolated from at least one to ten Nunc flasks which had been changed to the Virosorb eluent medium. Comparisons are given of the efficiency of the technique for the recovery of poliovirus types 1 and 2, reovirus type 1, the SA 11 rotavirus and coliphages.