Syndromic Surveillance and Case Identification for Varicella Among Recent Immigrants: New York City, 2023.

To determine utility of syndromic surveillance in improving varicella case detection during an outbreak among recent immigrants to New York City (NYC). During March through August 2023, the NYC Health Department received varicella reports from routine sources and syndromic surveillance from emergency department visits with varicella as a chief complaint or discharge diagnosis. Reports were reviewed to determine if individuals met criteria for confirmed or probable varicella cases and if cases were outbreak-associated. We calculated positive predictive value (PPV) and timeliness of syndromic surveillance reports and compared them with routine surveillance reports. The health department received 639 unique varicella reports. Of 513 varicella cases, 247 (48.1%) were from syndromic surveillance alone, 194 (37.8%) from routine sources alone, and 72 (14.0%) from both sources. PPV was higher for syndromic surveillance (89.1%) versus routine surveillance (74.7%). Among 310 outbreak-associated cases, 139 were identified through syndromic surveillance (44.8%); syndromic surveillance was the only reporting source for 75 (24.2%). Syndromic surveillance was more timely than routine reporting (median = 3 days; range = 1-27 vs 5 days; range = 0-52). NYC syndromic surveillance improved varicella case detection during this outbreak. (. Published online ahead of print January 30, 2025:e1-e4. https://doi.org/10.2105/AJPH.2024.307961).