Wastewater surveillance reveals hidden scale of mpox rpidemic, challenging official figures

In a recent study published in the International Journal of Infectious Diseases, researchers evaluated the correlation between monkeypox virus (MPV) detection in wastewater and MPV-associated hospitalizations in Poland.

Study: Mpox virus detection in the wastewater and the number of hospitalized patients in Poznan metropolitan area, Poland. Image Credit: CI Photos / Shutterstock

Background

Wastewater-based epidemiology (WBE) is a valuable approach for estimating the extent of an epidemic and the genomic diversity of causative pathogens. WBE may be used to complete the data obtained via clinical monitoring and increase the accuracy of estimations and surveillance reports. WBE is based on polymerase chain reaction (PCR)-based qualitative and quantitative detection of pathogens.

WBE enables monitoring pathogen transmission among populations when conventional epidemiological techniques may not be readily available due to inadequate access to healthcare facilities and diagnostics, overwhelming diagnostic laboratory capability, society’s hesitance to undergo diagnostic testing, and the increased availability of self-testing kits. WBE also enables the tracking of asymptomatic cases and enigmatic pathogen transmission.

MV nucleic acids have been identified in drainage systems of five Dutch districts, eight wastewater treatment plants (WTP) located in California, five WTPs in Florida, WTPs in France, and airport infrastructure in Italy. However, data on the correlation between MPV detection in wastewater and associated hospitalizations are limited.

About the study

In the present study, researchers monitored for MPV in sewage from WTPs in the Poznan metropolitan region of Poland and correlated this with the number of hospitalizations.

Weekly samples were obtained from two WTPs, the Left-Bank wastewater treatment plant and the Central wastewater treatment plant in Poland, between July and December 2022 (week 27 to week 48). Nucleic acids were extracted from the concentrated wastewater samples for MPV deoxyribonucleic acid DNA detection using real-time PCR.

The team analyzed pepper mild mottle virus (PMMoV, wastewater indicator virus) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) levels in the wastewater using quantitative reverse transcription-PCR (RT-qPCR). Samples with cycle threshold (Ct) values <40 were considered MPV-positive. In addition, the ratio of Ct values obtained for MPV and PMMoV was calculated to assess MPV transmission among Poznan individuals.

The lower the ratio, the higher the quantity of detectable MPV DNA in wastewater. The Poznan University of Medical Sciences Department and Clinic of Infectious Diseases, Hepatology, and Acquired Immunodeficiencies (DCIDHA) provided weekly counts of MPV-associated hospitalizations.

Results

MPV DNA was identified in week 29.0, week 43.0, and week 47.0 at the Central WTP and between weeks 37.0 and 38.0 and weeks 40.0 and 43.0 at the Left-Bank WTP (i.e., mainly between mid-September and October-end at the Left-Bank WTP) at 38 cycles on average. MPV/PMMoV ratios ranged between 1.5 (during week 42.0 at the Left-Bank WTP) and 1.8 (at week 43 at the Left-Bank WTP).

There was some reduction in MPV DNA between weeks 37 and 40, followed by a swift elevation during week 41.0 and the subsequent week at the Left-Bank WTP. The population health authorities documented 22 MPV cases between July and December 2022, and most hospital admissions were reported between mid-July and mid-August.

MPV detection did not correlate with the hospitalization count in Poland. Of note, chlorination was performed on inactive sewage from DCIDHA prior to release in the public drainage systems. Thus, MPV-associated hospitalizations showed no significant impact on MPV DNA detection in the Central WTP. All MPV-positive samples were associated with non-hospitalized MPC cases among the public, in the author’s opinion. Additionally, MPV detection at the Left-Bank WTP between mid-September and mid-October showed no correlation with the reported MPV case counts, indicating several undetected MPV infections among Poznan individuals.

The current MPV outbreak, caused by MPV of West African origin, in most cases, presents with mild infections with symptoms such as rash, fever, and enlarged lymph nodes, or unusual symptoms including none or a few viral lesions, restricted to genital and perianal regions. Therefore, MPV-infected individuals might not seek care, and the infection may not be documented. A few patients may also avoid seeking help because of the societal stigma that surrounds MPV, resulting in underreporting of MPV infections and biased reports by health officials concerning the extent of the MPV epidemic.

Overall, the study findings highlighted the detection of MPV DNA in wastewater when no MPV infection cases were documented. However, MPV detection in wastewater did not correlate with MPV-associated hospitalizations. The findings underpinned the idea that WBE could determine the scale of an epidemic. However, the MPV epidemic is underestimated since public health authorities have not identified many MPV-infected individuals.

Written by

Pooja Toshniwal Paharia

Dr. based clinical-radiological diagnosis and management of oral lesions and conditions and associated maxillofacial disorders.