HF183 is a DNA marker that is found in a type of gut bacteria known as Bacteroides spp.

HF183 is specific to human fecal contamination, meaning that when managers detect HF183, they know the fecal source is not from dogs or birds or another animal source that poses a lesser health risk than human fecal contamination.

HF183 is a relatively new indicator of fecal contamination compared to more established indicators of fecal contamination like Enterococcus and E. coli. Scientists already have established the relationship between Enterococcus and E. coli levels and human health risk, which has enabled robust beach water-quality testing programs to be built around measuring Enterococcus and E. coli.

The limitation of these established fecal contamination indicators is that they are not human-specific, meaning that they cannot distinguish between human and nonhuman sources like HF183 can.

HF183 was discovered in 2000 and first used in southern California during a landmark 2003 study examining different, then-experimental methods for detecting fecal contamination from different animal sources. The study – which included participation by the SMC – found that DNA-based methods like HF183 offer a consistently effective way to distinguish among different sources of bacteria. The finding was significant because fecal contamination indicators in use at the time were not able to distinguish human from nonhuman sources.

Since the 2003 study, researchers have further validated HF183 as a management tool for reliably detecting human-specific fecal sources. Today, HF183 is a foundational management tool that has become widely implemented to document human fecal contamination in waterways across southern California.