What is the clinical evidence from this study?

Study design: Observational. Population: Human norovirus (HuNoV) GII infection. Intervention: Wastewater monitoring of HuNoV GII RNA vs. Clinical specimen positivity rates. Primary outcome: Correlation between HuNoV GII RNA concentrations in wastewater solids and clinical HuNoV positivity rates (Kendall's tau 0.74, p=<10^-7).

August 7, 2023Open Access

Human norovirus (HuNoV) GII RNA in wastewater solids at 145 United States wastewater treatment plants: comparison to positivity rates of clinical specimens and modeled estimates of HuNoV GII shedders

Q: What are the key findings of this study?

Concentrations of Human norovirus GII RNA in wastewater solids were strongly positively correlated with national clinical test positivity rates (Kendall's tau = 0.74, p < 10^-7).

Key Result

Concentrations of Human norovirus GII RNA in wastewater solids were strongly positively correlated with national clinical test positivity rates (Kendall's tau = 0.74, p < 10^-7).

Study Design

Type

Observational

Multicenter

Yes

Structured PICO

Population

Wastewater solids samples from 145 wastewater treatment plants across the United States, serving approximately 10.9% of the US population, monitored for Human norovirus GII RNA over up to five months.

Exposure

Measurement of Human norovirus (HuNoV) GII RNA in wastewater solids using digital droplet RT-PCR.

Comparator

Liquid wastewater influent (for adsorption comparison) and clinical HuNoV positivity rates.

Outcome

Concentration of HuNoV GII RNA in wastewater solids and its correlation with clinical HuNoV positivity rates.surrogate

Wastewater monitoring of HuNoV GII RNA in settled solids correlates with clinical positivity rates, providing a low-bias tool for tracking norovirus community spread.

Main Result

Effect estimate: Kendall's tau 0.74

p-value: p=<10^-7

Limitations

Clinical positivity rate data may not perfectly reflect actual community infection occurrence as specimens are typically from individuals with severe symptomatic illness.
Sentinel laboratories reporting to CDC NREVSS are not necessarily in the exact same states or sewersheds as the wastewater data.
The study was limited to HuNoV GII, although HuNoV GI also contributes to disease occurrence.
The mass-balance model relies on assumptions about shedding rates and peak shedding, which vary widely among individuals.

Abstract

BACKGROUND: Human norovirus (HuNoV) is a leading cause of disease globally, yet actual incidence is unknown. HuNoV infections are not reportable in the United States, and surveillance is limited to tracking severe illnesses or outbreaks. Wastewater monitoring for HuNoV has been done previously and results indicate it is present in wastewater influent and concentrations are associated with HuNoV infections in the communities contributing to wastewater. However, work has mostly been limited to monthly samples of liquid wastewater at one or a few wastewater treatment plants (WWTPs). OBJECTIVE: The objectives of this study are to investigate whether HuNoV GII preferentially adsorbs to wastewater solids, investigate concentrations of HuNoV GII in wastewater solids in wastewater treatment plants across the county, and explore how those relate to clinical measures of disease occurrence. In addition, we aim to develop and apply a mass-balance model that predicts the fraction of individuals shedding HuNoV in their stool based on measured concentrations in wastewater solids. METHODS: We measured HuNoV GII RNA in matched wastewater solids and liquid influent in 7 samples from a WWTP. We also applied the HuNoV GII assay to measure viral RNA in over 6000 wastewater solids samples from 145 WWTPs from across the United States daily to three times per week for up to five months. Measurements were made using digital droplet RT-PCR. RESULTS: HuNoV GII RNA preferentially adsorbs to wastewater solids where it is present at 1000 times the concentration in influent. Concentrations of HuNoV GII RNA correlate positively with clinical HuNoV positivity rates. Model output of the fraction of individuals shedding HuNoV is variable and uncertain, but consistent with indirect estimates of symptomatic HuNoV infections in the United States. IMPACT STATEMENT: Illness caused by HuNoV is not reportable in the United States so there is limited data on disease occurrence. Wastewater monitoring can provide information about the community spread of HuNoV. Data from wastewater can be available within 24 h of sample receipt at a laboratory. Wastewater is agnostic to whether individuals seek medical care, are symptomatic, and the severity of illness. Knowledge gleaned from wastewater may be used by public health professionals to make recommendations on hand washing, surface disinfection, or other behaviors to reduce transmission of HuNoV, or medical doctors to inform clinical decision making.

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