Correlation between microbial source tracking markers and pathogens at beaches and estuaries in southern California

Fecal indicator bacteria (FIB) have historically been used to assess public health risks associated with contact water recreation, and microbial source tracking (MST) has been introduced to distinguish human-associated fecal pollution from natural sources of animal feces. While MST can identify human-associated fecal pollution, without interpretation it cannot differentiate between small amounts of fresh fecal contamination and large amounts of decayed pollution, which can present vastly different health risks. This study examined the ratio of HF183 and pepper mild mottle virus (PMMoV) as an indicator of the age of fecal contamination. The correlation was also assessed between these two individual markers, the HF183:PMMoV ratio, and two enteric viruses, norovirus genogroup II (NoV GII) and human adenovirus (HAdV). A total of 364 samples were collected under varying weather conditions over two years at impacted and reference surface water sites in southern California, including estuaries and adjacent ocean locations. The mean concentrations of MST markers and enteric viruses were higher during the rainy season compared to the dry season, especially at the impacted sites. NoV GII showed seasonality with higher detections and concentrations during the rainy season, while HAdV did not show such seasonal trends. The HF183:PMMoV ratio demonstrated a stronger correlation with enteric viruses than either marker alone, but when seasonal and weather effects were factored out, the HF183:PMMoV ratio and PMMoV had a stronger relationship with the concentration of enteric viruses. The results of this study indicate that the HF183:PMMoV ratio is a more reliable indicator of human fecal pathogens than the two individual markers by themselves. SYNOPSIS: The HF183:PMMoV ratio is a reliable and robust indicator for recreational water quality.