Concentration of enteroviruses, adenoviruses, and noroviruses from drinking water by use of glass wool filters

Abstract

Available filtration methods to concentrate waterborne viruses are either too costly for studies requiring large numbers of samples, limited to small sample volumes, or not very portable for routine field applications. Sodocalcic glass wool filtration is a cost-effective and easy-to-use method to retain viruses, but its efficiency and reliability are not adequately understood. This study evaluated glass wool filter performance to concentrate the four viruses on the U.S. Environmental Protection Agency contaminant candidate list, i.e., coxsackievirus, echovirus, norovirus, and adenovirus, as well as poliovirus. Total virus numbers recovered were measured by quantitative reverse transcription-PCR (qRT-PCR); infectious polioviruses were quantified by integrated cell culture (ICC)-qRT-PCR. Recovery efficiencies averaged 70% for poliovirus, 14% for coxsackievirus B5, 19% for echovirus 18, 21% for adenovirus 41, and 29% for norovirus. Virus strain and water matrix affected recovery, with significant interaction between the two variables. Optimal recovery was obtained at pH 6.5. No evidence was found that water volume, filtration rate, and number of viruses seeded influenced recovery. The method was successful in detecting indigenous viruses in municipal wells in Wisconsin. Long-term continuous filtration retained viruses sufficiently for their detection for up to 16 days after seeding for qRT-PCR and up to 30 days for ICC-qRT-PCR. Glass wool filtration is suitable for large-volume samples (1,000 liters) collected at high filtration rates (4 liters min(-1)), and its low cost makes it advantageous for studies requiring large numbers of samples.

FIG. 1.

Effect of pH on efficiency of glass wool concentration of poliovirus in tap water. Recovery within the pH range of 6.0 to 7.5 was evaluated in two experiments, each with two filtration trials per pH level. Each histogram (hatched bars) represents the combined results of experiments 1 and 2 (four replicates). Experiment 1 was performed by seeding 6.39 × 10⁷ genomic copies in 20 liters; experiment 2 was done with 1.14 × 10⁸ genomic copies seeded in 20 liters. Recovery at pH 8.0 and 9.0 was evaluated in two additional separate experiments of four replicates each, i.e., experiment 3 (gray bar), performed at pH 8 with 3.13 × 10⁶ genomic copies seeded in 10 liters, and experiment 4 (black bar), performed at pH 9 with 7.64 × 10⁶ genomic copies seeded in 10 liters. Error bars represent 1 standard deviation.

FIG. 2.

Effect of pH on efficiency of glass wool concentration of adenovirus 41 in tap water (5.25 × 10³ genomic copies were seeded into 20 liters). Two filtration trials were conducted at each pH value.