46 Water & Sewerage Journal

Human norovirusin untreated andtreated sewage

Carlos JA Campos

NOROVIRUS CONTROL

Water Quality Scientist, Centre for Environment, Fisheries &Aquaculture Science (CEFAS)

Human noroviruses (NoV)have been responsible formillions of cases ofgastrointestinal disease inthe UK. These viruses makeheadlines every two to fouryears when new strainsemerge as the virus mutates,usually during the months ofOctober to March.In 2002/03, NoV outbreaksin hospitals cost the NHSaround £115 million1.

These viruses are excreted in highnumbers in the faeces of infectedindividuals and may directly orindirectly contaminate surface waters.For this reason, wastewater treatmentsare an important means for reducingNoV transmission in the environmentoutside the host and to prevent newcycles of human infection. It is thereforeimportant to characterise typicalconcentrations of NoV in untreatedsewage and treated effluents todevelop NoV risk-managementmeasures.

Research approachTo characterise the relative NoV riskfrom untreated and treated sewagedischarges, samples were taken fromthe different stages of the treatmentprocess at a full-scale sewage treatmentworks (STW) for NoV testing(genogroups I and II) using a PCRmethod during the period October2012 to January 2015. The treatmentprocess included screening, primary

settlement, activated sludge and UVdisinfection prior to discharge into anestuary. The activated sludge processis the Modified Ludzack-Ettinger (MLE)process, which is a two-stagebiological nitrification/de-nitrificationwith internal recirculation.

The N removal process consists of anaerobic zone, in which nitrificationoccurs, and an anaerobic zone in whichde-nitrification occurs. The nitrified flowis fed back to the low oxygen anoxiczones, which is de-nitrified by theinfluent flow from the primarysettlement tanks. Samples were alsotaken from the storm tank associatedwith the STW.

Norovirus prevalence/seasonalityDuring the study period, NoV wasfrequently detected in samples ofscreened influent (93 per cent of

samples positive for GI and 100 percent positive for GII), indicating thatNoV were frequently excreted from thelocal human population. However,there was extreme variability in theconcentrations detected. For GI,concentrations ranged 2.3log10 ordersof magnitude, while for GII they ranged2.9log10 orders of magnitude.The mean concentrations of GI and GIIin influent samples taken during thehigh-risk period were 925 genomecopies/ml and 10,025 copies/ml.In settled stormwater samples, meanNoV GI and GII concentrations were513 copies/ml and 3,174 copies/ml,respectively.

Mean concentrations of total NoV (GIand GII summed) in the influent werehigher in 2012/13 (13,914 copies/ml)than in 2014/15 (6,541 copies/ml).This variation between years indicatesthe general concentrations of NoV

As part of CEFAS’ recent research into norovirus risk, samples were taken atdifferent stages of the sewage treatment process at a full-scale works as well asthe associated storm tank

Water & Sewerage Journal 47

arriving at STW that reflect theproportion of human populationinfected and are probably associated tothe emergence of a new strain (GII.4Sydney2012) across England, causinga peak number of cases relative toprevious seasons2.

MLE effective in NoVreductionAll the physical and biological sewage-treatment processes are expected toremove or inactivate NoV to someextent. However, none of them wereobserved to reduce NoV to a similarextent. The concentrations of NoV GIIin influent (screened) were significantlyhigher than those in primary settledeffluents and in the activatedsludge tank.

The MLE process was tmore effectivethan primary settlement in removingNoV (see Figure 1). Other studies havefound higher efficiency of activatedsludge in reducing NoV than othertreatment processes, such as tricklingfilters. This is probably associated withthe short contact times between theviruses and the filter media and/orthe elution of viruses in the tricklingfilters relative to the longer contacttimes characteristic of suspendedgrowth processes.

Factors influencingnorovirus removalNoV GII removal increased as theconcentration of the virus in the influentalso increased (see Figure 2). Linearmodelling showed that an increase ininfluent concentrations by a factor of 10would correspond to an increase of0.5log10 virus removal. This indicatesthat there is large variation in STWperformance, with respect to NoVremoval within the range of normaloperating conditions of the STW, andtherefore large scope for enhancementof NoV removal in these types oftreatment processes.

It is possible that the PCR methodologyused for NoV measurementunderestimated the inactivation of thevirus during UV disinfection, becausePCR detects virus genome materialwhich may potentially still bedetectable for a period following virusinactivation. Therefore, further studiescomparing PCR and virus culturemethods applied to UV disinfection ofwastewater would help inform thispossibility. Based on the resultsobtained, the highest risk to publichealth is associated with stormoverflows, even during periods of low-virus prevalence, because theinfectious dose of the virus is very lowand its resistance to environmentalstressors is high. The public-healthsignificance of storm discharges hasbeen demonstrated by associationsbetween rainfall events, sewagebypasses and increased frequency ofhospital admissions for treatment ofgastrointestinal illness3 and reporting ofNoV outbreaks linked to consumptionof oysters harvested from areasimpacted by untreated sewage spills4.

References1. Lopman, BA; Reacher, MH; Vipond,IB; Hill, D; Perry, C; Halladay, T; Brown,DW; Edmunds, WJ; Saranji, J (2004).Epidemiology and cost of nosocomialgastroenteritis, Avon, England, 2002-2003. Emerging Infectious Diseases10(10): 1827–1834.

2. Allen, DJ; Adams, NL; Aladin, F;Harris, JP; Brown, DWG (2014).Emergence of the GII-4 norovirusSydney2012 strain in England, winter2012–2013. PLoS ONE 9(2): e88978.

3. Redman, RL; Nenn, CA; Eastwood,D; Gorelick, MH (2007). Pediaticemergency department visits fordiarrheal illness increased a6er releaseof undertreated sewage. Pediatrics120(6): e1472–e1475.

4. Wall, R; Dymond, N; Bell, A;Thornley, C; Buik, H; Cumming, D;Petersen, N (2011). Two New Zealandoutbreaks of norovirus gastroenteritislinked to commercially farmed oysters.New Zealand Medical Journal124(1347): 63–71.

Further readingCampos, CJA; Avant, J; Lowther, J; Till,D; Lees, D (2013). Levels of norovirusand E coli in untreated, biologicallytreated and UV-disinfected sewageeffluent discharged to a shellfish water.Journal of Water Resources andProtection 5: 978–982.

Campos, CJA; Lees, DN (2014).Environmental transmission of humannoroviruses in shellfish waters. Appliedand Environmental Microbiology80(12): 3552–3561.

ContactE: carlos.campos@cefas.co.uk

Figure1:RemovalofnorovirusgenogroupsI(GI)andII (GII) throughthesewagetreatmentprocess

Figure 2: Norovirus removal through the treatment process (log10 scale) as afunction of the concentrations in the influent