Oregon Wastewater Surveillance

Highly Pathogenic Avian Influenza A (H5N1) Viruses. Highly Pathogenic Avian Influenza A, also known as ‘bird flu’, is widespread in wild birds worldwide and is currently causing outbreaks in poultry and U.S. dairy cows (https://www.cdc.gov/bird-flu/situation-summary/).   

In Oregon we measure flu A and flu B viral RNA in wastewater samples. Therefore, if H5N1 (a type of flu A) were present it would be included in the flu A measurement. However, we do not specifically measure H5N1 separately from other flu A viral RNA.  

In response to H5N1 concerns the CDC has a new influenza A dashboard at https://www.cdc.gov/nwss/wastewater-surveillance/Flu-A-data.html. Sites are categorized as having minimal to high levels of influenza A, compared to other time periods in the 2023-24 flu season at the same site. Oregon data is represented on this map, however, sites labeled “insufficient data” either did not have at least 10 samples positive for influenza A between October 1 and March 2, submitted fewer than 6 total samples between Oct 1 and Jan 1, or have not submitted data in the last two weeks. Using these CDC NWSS parameters, only 7 Oregon sites are eligible for listing on the new dashboard.  

Units of wastewater concentrations. The CDC recommends reporting the concentration of virus (COVID-19, flu, RSV, etc.) in units of “viral RNA copies per day/person”.  Viral RNA refers to the # of RNA molecules in the sample (the RNA specific to the target virus), and is sometimes abbreviated to ‘copies’. This approximates the number of virus, or remnants of virus, in the wastewater. The concentration represents how many copies were in the wastewater in one day of flow and is divided by the number of people in the collection boundary.  

What does log mean? In reporting wastewater surveillance viral concentration, log base 10 is conventionally used to express the concentration of virus present. The reason that the log of the viral concentration is used is because of the large range of concentrations possible. The convention is to use log to compress this range for intuitive understanding. For example, a low COVID-19 log value is 5.6 RNA copies per day/person, while a high value is 8.5. These values correspond to the following ‘unlogged’ values: 

Log 5.6 = 10^5.6 = 398,107 viral RNA per day/person 

Log 8.5 = 10^8.5 = 316,227,766 viral RNA per day/person