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What It Measures

NREVSS tracks the percentage of respiratory specimens that test positive for specific viruses, including RSV (respiratory syncytial virus), influenza, parainfluenza, human metapneumovirus, and others.

How It Works

Participating laboratories across the country report the number of tests performed and the number of positive results for various respiratory viruses each week.

What It Tells You

Unlike syndrome-based surveillance (ILINet, NSSP), NREVSS confirms which specific virus is causing illness. The percent positivity rate shows what proportion of people who were tested actually had a specific virus.

Limitations

Only covers samples sent for lab testing, which is a small fraction of all respiratory illness.
Testing patterns change over time and vary by region.
Not all viruses are tested at all labs.