CDC Wastewater Viral Activity Level Maps: Why Are They Bluer?

My favorite statistical podcast is actually about virology. The hosts of This Week in Virology (TWiV) are superb data communicators, and they often highlight statistical virtues or shortcomings of the virology and infectious disease papers they discuss. In TWiV 1352, recorded on August 26, 2026, Dr. Daniel Griffin used a statistical term that was new to me, saying that the Centers for Disease Control and Prevention (CDC) had “bluewashed” COVID-19 heat maps. Heat maps indicate activity level by color; a common map palette moves from blue (low level) through green and yellow to red (high level). The CDC changed the categories in the SARS-CoV-2 Wastewater Viral Activity Level Map in August 2026 (see Table 1). Some of the states that would have been in the “Moderate” category according to the previous classification are now in the “Low” category, and some of the states that would have previously been in the “Low” category are now classified as “Very Low.” With the new classification,…