The San Diego County influenza surveillance system, has disclosed detection of H5 influenza RNA in wastewater.  The County operates a closed sewage system that suggests that the presence of viral RNA could be derived from discarded contaminated animal products or an ongoing human or animal infection or the unlikely expedient of contamination from wild bird droppings.

The presence of H5 influenza RNA was reported to the California Department of Public Health, the California Department of Food and Agriculture and the California Department of Fish and Wildlife for further investigation.

Wastewater assay represents an early warning system for the presence of influenza viruses and other pathogens circulating in animal or human populations in a given area facilitating an early response.  It is noted that surveillance of sewage detected H5N1 in water in Texas counties concurrent with the emergence of bovine influenza-H5N1. This was attributed to disposal of contaminated milk.