Viruses in Sewage

One of the infectious causative agents of epidemic gastroenteritis are noroviruses, of which there are five genogroups, each including several genotypes; GGI (including Norwalk and Southampton genotypes), GGII (Hawaii and others), GGIII (Jena), GGIV (Alphatron) and GGV (found in mice). Inadequate or failing treatment of sewage leads to the insufficient removal of viruses and the discharge of this sewage may significantly enhance the concentration of viruses in the environment, potentially leading to virus-contaminated drinking or recreational water. Lodder & Husman (2005) investigated the contamination present in the Waal and Maas Rivers in the Netherlands and compared this to raw and treated sewage from the Apeldoorn pumping-engine station, Netherlands, and to norovirus stool sample specimens. They used molecular methods for enumeration and sequencing of the virus particles as well as cell culture for enumeration of plaque forming units. The River Waal is a tributary of the River Rhine and is composed of rain and melt water and approximately 30 million people depend upon it for drinking water, while the River Maas is made of just rainwater and approximately 5 million people depend upon it for drinking water.

Lodder & Husman (2005) found that each river was positive for the presence of F-specific and somatic phages, noroviruses, rotaviruses, reoviruses and enteroviruses and seven norovirus genotype strains were found out of a total of 38 clones. Four different norovirus genotypes were found in the River Maas; QueensArms, Mexico, Lordsdale and the Maas/Waal strain, while five norovirus genotypes were found in the River Waal; Southampton, Rotterdam, Lordsdale, Leeds and the Maas/Waal strain. The average virus concentrations were lower in treated sewage than raw sewage, except for rotaviruses, and virus removal at the treatment plant was 1.6, 1.1, 1.4, 1.3, 1.8 and 0.2 log₁₀ units for F-specific phages, somatic phages, enteroviruses, reoviruses, noroviruses and rotaviruses, respectively. Each sewage sample contained at least one strain of norovirus; the raw sewage samples contained six norovirus genotype strains while the treated sewage samples contained five norovirus genotype strains and Southampton, Mexico and Lordsdale genotypes were present in both.

This study highlights the need for more rigorous procedures aimed at removing viruses from sewage at treatment plants. Viruses can be effectively removed or inactivated by slow sand filtration and soil passage, however they are more resistant to UV and coagulation combined with sedimentation. This shows that consumption of drinking water or exposure to surface waters through recreation or shellfish could pose a risk if it coincides with failed treatment, however the screening period of the rivers was not extensive as it spanned only November through to April, when Noroviruses are known to be more prevalent so further investigation needs to determine whether the risk still occurs in the summer.

Lodder, W. & Husman, A. (2005) Presence of Noroviruses and other enteric viruses in sewage and surface waters in the Netherlands. Applied and Environmental Microbiology. 71, 1453-1461