Polyethylene glycol (PEG) methods are superior to acidification for secondary concentration of Adenovirus and MS2 in water
The most common and cost-effective approach to concentrating viruses from water samples involves virus adsorption and elution procedures, followed by secondary concentration. There is a lack of consistency in how secondary concentration methods are practiced and some methods may have better recovery for particular groups of viruses. Secondary concentration methods typically involve precipitation and the most common methods employ organic flocculation (OF) by acidification at a pH of 3.5, or precipitation by polyethylene glycol (PEG) in combination with NaCl. In this study, the recovery of coliphage MS2 using the plaque assay and human adenovirus strain 41 (HAdV41) using cell-culture and qPCR assays were evaluated by OF and PEG secondary concentration of spiked samples of wastewater, surface water, and groundwater. Recovery of MS2 and HAdV41 by PEG precipitation was significantly higher than OF (p<0.0001) when viruses were detected by culture based methods and marginally better when HAdV41 was enumerated by qPCR (p<0.019). The recovery of HAdV41 by qPCR ranged from 75.3% to 94.4% (n=36). The mean recovery of MS2 by OF was 4.4% (0.9%-7.7%; n=14) and ranged from 57.1% to 87.9% (n=28) for the PEG methods. Poor recovery of MS2 by OF was attributed to inactivation or poor stability at acidic conditions as MS2 were not recovered in the supernatant following OF and centrifugation. The inconsistency and lack of justification for method selection in many studies calls for a systematic study to inform guidance and standardization with respect to the application of concentration methods for various water types and viral pathogens.