Variability of pepper mild mottle virus in wastewater across the United States: A review of methodological, environmental, and demographic drivers

Wastewater-based surveillance has become a valuable public health tool, helping communities track disease trends at the population level. To make wastewater data meaningful, researchers often rely on biomarkers that indicate the presence of human waste. One of the most widely used is pepper mild mottle virus (PMMoV), a virus commonly found in human waste due to the consumption of pepper-based foods.

PMMoV has been widely adopted to normalize pathogen measurements, particularly during the COVID-19 pandemic. However, despite its popularity, there has been limited understanding of why PMMoV concentrations vary so widely between locations.

Carollo’s Aiswarya Rani Pappu and Scott Montgomery co-authored a recent peer-reviewed study examining this question. The paper, “Variability of Pepper Mild Mottle Virus in Wastewater across the United States,” was published in ACS ES&T Water.

What Drives PMMoV Variability Across the U.S.

The research team analyzed data from 46 studies spanning 360 monitoring sites in 34 states, revealing a wide range of PMMoV concentrations in domestic wastewater. Average values ranged from 3.6 to 10.3 log₁₀ genome copies per liter, underscoring the inconsistency of PMMoV signals nationwide.

The study found that methodological and demographic factors were the strongest drivers of variability. Sample preprocessing methods, especially debris removal, along with sampling location type and population characteristics such as median income and race, had the greatest influence on PMMoV concentrations.

In contrast, weather, seasonality, and sampling frequency played a smaller role. As the authors note, PMMoV levels appear to be influenced more by daily dietary patterns than by environmental conditions.

Implications for Wastewater-Based Epidemiology

One important finding from the research is that most existing PMMoV data comes from urban and suburban systems, leaving major gaps in understanding how the biomarker behaves in rural communities. This complicates the assumption that PMMoV can be applied uniformly as a global normalization tool.

Rather than calling for a single standardized method, the authors emphasize the importance of clear documentation of sampling and analytical practices. Doing so can help researchers better account for variability, improve normalization approaches, and strengthen data-driven public health models.

Strengthening the Future of Wastewater-Based Epidemiology

Ultimately, the study reinforces both the value and the limitations of PMMoV as a wastewater biomarker. While it remains a useful tool, the findings highlight the need for careful interpretation, improved transparency in methods, and more inclusive data collection, especially from underrepresented communities.

By clarifying the drivers of PMMoV variability, this work supports more accurate pathogen normalization and helps strengthen data-driven models used to predict disease prevalence and inform public health decisions.

Read the full article in ACS ES&T Water to explore the detailed analysis, nationwide dataset, and recommendations for improving wastewater-based surveillance using PMMoV.