Evaluation of Chlorine Treatment Levels for Inactivation of Human Norovirus and MS2 Bacteriophage during Sewage Treatment

Abstract

This study examined the inactivation of human norovirus (HuNoV) GI.1 and GII.4 by chlorine under conditions mimicking sewage treatment. Using a porcine gastric mucin-magnetic bead (PGM-MB) assay, no statistically significant loss in HuNoV binding (inactivation) was observed for secondary effluent treatments of ≤25 ppm total chlorine; for both strains, 50 and 100 ppm treatments resulted in ≤0.8-log unit and ≥3.9-log unit reductions, respectively. Treatments of 10, 25, 50, and 100 ppm chlorine inactivated 0.31, 1.35, >5, and >5 log units, respectively, of the norovirus indicator MS2 bacteriophage. Evaluation of treatment time indicated that the vast majority of MS2 and HuNoV inactivation occurred in the first 5 min for 0.2-μm-filtered, prechlorinated secondary effluent. Free chlorine measurements of secondary effluent seeded with MS2 and HuNoV demonstrated substantial oxidative burdens. With 25, 50, and 100 ppm treatments, free chlorine levels after 5 min of exposure ranged from 0.21 to 0.58 ppm, from 0.28 to 16.7 ppm, and from 11.6 to 53 ppm, respectively. At chlorine treatment levels of >50 ppm, statistically significant differences were observed between reductions for PGM-MB-bound HuNoV (potentially infectious) particles and those for unbound (noninfectious) HuNoV particles or total norovirus particles. While results suggested that MS2 and HuNoV (measured as PGM-MB binding) behave similarly, although not identically, both have limited susceptibility to chlorine treatments of ≤25 ppm total chlorine. Since sewage treatment is performed at ≤25 ppm total chlorine, targeting free chlorine levels of 0.5 to 1.0 ppm, these results suggest that traditional chlorine-based sewage treatment does not inactivate HuNoV efficiently. HuNoV is ubiquitous in sewage. A receptor binding assay was used to assess inactivation of HuNoV by chlorine-based sewage treatment, given that the virus cannot be routinely propagated Results reported here indicate that chlorine treatment of sewage is not effective for inactivating HuNoV unless chlorine levels are above those routinely used for sewage treatment.

Human Norovirus Replication in Human Intestinal Enteroids as Model to Evaluate Virus Inactivation

“…For chlorine, our data showed that complete inactivation of 3 different GII.4 strains could be achieved with concentrations as low as 50 ppm. These results are consistent with a recent report indicating that treatment with chlorine concentrations <50 ppm were not sufficient to inactivate human norovirus in secondary effluents from water treatment plants ( 31 ). In conclusion, our inactivation data demonstrate that chlorine, but not alcohol, completely inactivates human norovirus and that evaluation of inactivation strategies based only on detection of viral RNA does not always reflect the effectiveness of the treatment.…”

Free Chlorine Disinfection Mechanisms of Rotaviruses and Human Norovirus Surrogate Tulane Virus Attached to Fresh Produce Surfaces

“…Similar trends were found with HuNoV GI.1, and GII.4 treated with high CTs of free chlorine lost its ability to bind to PGM-MBs. 48,49 and chlorine treatment at C 0 ≤ 25 ppm did not cause binding loss of HuNoV to PGM-MBs. 48 In addition to protein damage, free chlorine penetrates inside the TV virions to damage its genome at least partially.…”

Waterborne Norovirus outbreak at a seaside resort likely originating from municipal water distribution system failure

“…Drinking water from municipal supplies fed by lake or groundwater has already been identified in the past as the source of waterborne NoV outbreaks in Italy [27–29] and NoV is now considered one of the pathogens causing the largest number of affected consumers in drinking waterborne outbreaks [12]. NoV can persist in water longer than 15 days [30] and it is resistant to chlorine disinfection when free chlorine levels or pre-treatment processes are inadequate [31, 32]. Moreover, microfiltration filters labelled as certified by NSF Standards 53 or 58 (with a pore size ranging from 0.05 to 5 µm) are not effective in removing viruses and can even decrease chlorine concentration in filtered water [33].…”