*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

In a recent study posted to the medRxiv* preprint server, researchers determine the nucleic acid content of several types of viruses in samples collected from wastewater treatment plants in an attempt to correlate this information with clinical data on disease occurrence in the community.

Study: Respiratory virus concentrations in human excretions that contribute to wastewater: A systematic review. Image Credit: APIWAN BORRIKONRATCHATA / Shutterstock.com

Background

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Viral nucleic acids, which can be in the form of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), enter wastewater from various human excretions, including urine, mucus, stool, sputum, and saliva. Thus, wastewater surveillance of respiratory viruses might be a viable tool for public health officials to identify community or population-level infection trends.

Throughout the coronavirus disease 2019 (COVID-19) pandemic, wastewater-based epidemiology (WBE) helped support public health efforts to monitor the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This information subsequently supported the use of this surveillance approach to monitor respiratory syncytial virus (RSV) and influenza transmission rates within the community, as these levels have similarly reflected the clinical incidence rates of these viruses.

About the study

In the present study, researchers collected and synthesized published scientific literature on concentrations and shedding patterns of respiratory viruses across all human excretion types that enter wastewater. The screened studies examined RSV, rhinovirus, parainfluenza virus, human influenza A and B viruses, metapneumovirus, and seasonal coronaviruses including HKU1, OC43, 229E, and NL63.

The primary study outcome was estimating the concentration of viral nucleic acids in five human excretion types that were quantified as viral genome copies per unit (mass/volume) of excretion.

The team extensively searched three databases including Web of Science, PubMed, and Scopus for each respiratory virus between June 2022 and August 2022. The search string comprised two fields, with the first searching for the respiratory virus name and its common variations. The second field remained constant and searched for five excretion types.

Next, the researchers uploaded study records into Covidence, a web-based software that screened, deduplicated, and extracted data for the meta-analysis. Data sets from longitudinal and cross-sectional studies were considered separately, with viral nucleic acid concentrations from cross-sectional studies graphed separately from concentrations from longitudinal studies. A weighted average was also used to combine viral positivity rates from cross-sectional studies for each excretion type.

Study findings

The final data for this review comprised 220 data sets from 50 articles that met inclusion criteria and documented information on the respiratory virus concentrations in five human excretion types.

A total of 195 of the 220 datasets only determined positivity rates of respiratory viruses in human excretions. Conversely, 14 and 11 of the 220 studies quantified viral nucleic acid concentrations or examined their longitudinal shedding patterns in excretions, respectively.

While many datasets evaluated respiratory viruses in excretions, the focus primarily remained on three excretion types of mucus, saliva, and sputum. The availability of data on respiratory virus detection in stool was less and even more sparse in urine.

In fact, no studies examined the presence of rhinovirus, seasonal coronaviruses, and parainfluenza virus in urine, whereas just one study assayed both RSV and metapneumovirus in urine. These findings indicate that stool and urine are the most underexamined human excretions, especially in the context of respiratory viruses. This is comparable to several studies that have detected influenza in the urine samples of infected subjects.

Data availability was found to vary with each respiratory virus, with only 20 excretion datasets available for both metapneumovirus and rhinovirus. Conversely, 75 excretion datasets were available for influenza.

Furthermore, positivity rates for each virus, except human coronaviruses, were highest in mucus, followed by sputum and saliva. Accordingly, the positivity rate of human coronavirus was the highest in mucus.

Finally, the researchers found comparing respiratory viral concentrations across five excretion types challenging due to the quantification methods used in the included studies and units reported.

Conclusions

The current review highlights a lack of studies examining respiratory virus concentrations in human excretions. Since a major proportion of this data documented the presence or absence of respiratory viruses in excretions in a cross-sectional study design, there remains a need for more longitudinal data, which could help estimate the number of people in the community infected with the virus and shedding it into wastewater.

*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Neha Mathur

Neha is a digital marketing professional based in Gurugram, India. She has a Master’s degree from the University of Rajasthan with a specialization in Biotechnology in 2008. She has experience in pre-clinical research as part of her research project in The Department of Toxicology at the prestigious Central Drug Research Institute (CDRI), Lucknow, India. She also holds a certification in C++ programming.