Meta-Analysis of the Reduction of Norovirus and Male-Specific Coliphage Concentrations in Wastewater Treatment Plants

Human norovirus (NoV) is the leading cause of foodborne illness in the United States and Canada. Wastewater treatment plant (WWTP) effluents impacting bivalve mollusk-growing areas are potential sources of NoV contamination. We have developed a meta-analysis that evaluates WWTP influent concentrations and log(10) reductions of NoV genotype I (NoV GI; in numbers of genome copies per liter [gc/liter]), NoV genotype II (NoV GII; in gc/liter), and male-specific coliphage (MSC; in number of PFU per liter), a proposed viral surrogate for NoV. The meta-analysis included relevant data (2,943 measurements) reported in the scientific literature through September 2013 and previously unpublished surveillance data from the United States and Canada. Model results indicated that the mean WWTP influent concentration of NoV GII (3.9 log(10) gc/liter; 95% credible interval [ CI], 3.5, 4.3 log(10) gc/liter) is larger than the value for NoV GI (1.5 log(10) gc/liter; 95% CI, 0.4, 2.4 log(10) gc/liter), with large variations occurring from one WWTP to another. For WWTPs with mechanical systems and chlorine disinfection, mean log(10) reductions were -2.4 log(10) gc/liter (95% CI, -3.9, -1.1 log(10) gc/liter) for NoV GI, -2.7 log(10) gc/liter (95% CI, -3.6, -1.9 log(10) gc/liter) for NoV GII, and -2.9 log(10) PFU per liter (95% CI, -3.4, -2.4 log(10) PFU per liter) for MSCs. Comparable values for WWTPs with lagoon systems and chlorine disinfection were -1.4 log(10) gc/liter (95% CI, -3.3, 0.5 log(10) gc/liter) for NoV GI, -1.7 log(10) gc/liter (95% CI, -3.1, -0.3 log(10) gc/liter) for NoV GII, and -3.6 log(10) PFU per liter (95% CI, -4.8, -2.4 PFU per liter) for MSCs. Within WWTPs, correlations exist between mean NoV GI and NoV GII influent concentrations and between the mean log(10) reduction in NoV GII and the mean log(10) reduction in MSCs.