Evaluation of removal of noroviruses during wastewater treatment, using real-time reverse transcription-PCR: different behaviors of genogroups I and II

Abstract

Noroviruses, an important cause of gastroenteritis, are excreted by infected individuals and are therefore present in wastewater. We quantified norovirus genogroup I (GI) and GII in wastewater at different locations in France and evaluated removal by a range of treatment types, including basic (waste stabilization pond), current industry standard (activated sludge), and state-of-the-art (submerged membrane bioreactor) treatments. Noroviruses were quantified using real-time reverse transcription-PCR (rRT-PCR). Mengovirus was used as a virus extraction control, and internal controls were used to verify the level of GI and GII rRT-PCR inhibition. A total of 161 (81 influent and 79 effluent) samples were examined; GI and GII were detected in 43 and 88% of the influent samples, respectively, and in 24 and 14% of the effluent samples, respectively. Physicians in France report far more cases of GII than GI during outbreaks; thus, the frequent presence of GI was unexpected. The GI influent concentrations were more variable, the peak GI influent concentrations were higher than the peak GII influent concentrations at all four sites (up to 1 x 10(9) and 6 x 10(7) genome copies/liter, respectively), and the average positive influent concentrations of GI were higher than the average positive influent concentrations of GII. The maximum effluent breakthrough concentrations were 6 x 10(6) and 3 x 10(6) genome copies/liter for GI and GII, respectively, indicating that the four treatment systems studied decreased the norovirus contamination load in receiving waters.

FIG. 1.

Control procedure for sample processing and norovirus quantification. IC, internal control; NA, nucleic acid extract. The graphs indicate usage of rRT-PCR. Adapted from the study of Costafreda et al. (7).

FIG. 2.

Concentrations of norovirus GI and GII in influents and effluents. The concentrations of GI and GII are expressed in log₁₀ genome copies/liter for the four wastewater treatment plants studied during the periods from (a) December 2005 to March 2006 (MBR plant [A] and small AS plant [B]) and (b) December 2005 to December 2006 (large AS plant [C] and WSP plant [D]). The dashed lines indicate limits of detection. ○, influent; ▴, effluent.