A dramatic 22-fold increase in Novirhabdovirus (typically a rare fish virus) was detected in Greater Boston, with a 6.6-fold surge in the uncommon Picornavirus ampivirus also reported in Boise, signaling unusual viral activity in urban wastewater this week.
This week’s national wastewater surveillance is highlighted by two prominent and atypical viral events: a pronounced 22-fold elevation of Novirhabdovirus in Greater Boston and a 6.6-fold escalation in Picornavirus ampivirus at Boise. These sharp increases stand out amidst more typical seasonal activity, marking a shift in surveillance focus from the consistently high levels of enteric viruses to the sudden emergence of rarely detected agents. Such relative changes are particularly noteworthy given their historical rarity, especially in major urban centers.
Several urban sites—specifically Greater Boston, Boise, and Kansas City—continued to report high absolute concentrations of common enteric viruses, such as Rotavirus A, Astrovirus (other), and both genogroups of Norovirus. However, these pathogens remain within expected elevated ranges for this summer period and are not showing significant changes versus recent baselines. Notably, both Novirhabdovirus and Sapporo virus reached unusually elevated levels at urban sites, raising the need for further investigation into possible sources, particularly given Novirhabdovirus's usual association with aquatic environments rather than human wastewater.
With respect to priority respiratory viruses, SARS-CoV-2 was again detected at low-to-moderate levels in Greater Boston, Boise, and Kansas City, with no evidence of a major surge or novel urban emergence this week. There is no actionable signal for Influenza A/B or RSV in current wastewater data, with both viruses remaining undetected or at non-elevated concentrations nationally. This stability is consistent with seasonal expectations during summer months, offering reassurance for those concerned about respiratory virus resurgence.
Rare or atypical detections this week largely center on urban sites, which elevates their significance. The marked appearance of Novirhabdovirus and Picornavirus ampivirus—viruses that are generally undetectable in human wastewater—suggests potential environmental or cross-species exposures. While these viral signals could represent transient or non-human sources, their abrupt rise in large population centers warrants targeted environmental review and, if relevant, assessment of urban aquatic systems or recreational waters.
In light of ongoing detections of common gastrointestinal viruses, the public is advised to maintain vigilant hygiene practices (especially proper handwashing and safe food handling). Routine vaccinations for rotavirus and influenza (when in season) remain the most effective preventive strategies for at-risk populations. Municipal leaders and health officials in affected cities should continue to monitor for clinical clusters, particularly if unusual pathogens persist or increase.
It is important to note that some surveillance sites are experiencing data delays—most notably Milan, MO (13 weeks behind), and several others including Riverside, CA are 1–3 weeks behind. These lags may temporarily limit the ability to detect or interpret emerging trends in some regions. Continued timely submission of wastewater samples will be critical for maintaining comprehensive situational awareness.