Which environmental surveillance marker indicates poliovirus circulation when analyzing sequence data?

• A. Sequence analysis shows lineage and divergence of PV sequences.
• B. Environmental surveillance relies solely on virus isolation, not sequencing.
• C. AFP case reports alone establish environmental circulation.
• D. Sewage samples cannot detect polio.

Answer: (B)

The key idea is that, in environmental surveillance, the signal of poliovirus circulation in sequence data is shown when the PV sequences form a related lineage and accumulate divergence over time. This pattern demonstrates ongoing transmission and genetic evolution within the community detected through sewage sampling and subsequent sequencing. Sequencing lets us connect detections across samples, identify how closely new isolates relate to known strains, and track how the virus is changing as it spreads.

Relying only on virus isolation misses these genetic relationships and evolution, so it doesn’t by itself prove circulation over time. AFP case reports are important for identifying poliomyelitis disease risk but do not by themselves prove environmental circulation. And sewage testing is indeed capable of detecting poliovirus; saying it cannot would be incorrect.