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BACKGROUND: Florida’s Respiratory Syncytial Virus (RSV) surveillance historically relies on laboratory data including that supplied by the National Respiratory and Enteric Virus Surveillance System (NREVSS). NREVSS RSV season baselines are determined by the calculation of percent positive; 10% or more positive laboratory tests for RSV for two consecutive weeks signals season onset, falling below 10% positive for two consecutive weeks signals RSV season end. Ongoing NREVSS challenges include: facility recruitment, retention, reporting delays, missed reports, and hand data entry. Florida’s statewide syndromic surveillance (SS) system is ESSENCE-FL which is easily accessible and provides timely access to emergency department (ED) and urgent care center (UCC) visit data. Timely monitoring of Florida’s unique statewide and regional RSV seasons is important for real-time decision-making and has implications for the pre-approval of prophylactic treatment. This analysis compares RSV laboratory data (including NREVSS data) to ED and UCC data to establish SS RSV seasonal thresholds.
METHODS: Laboratory data season onset and offset weeks between week 1, 2010 and week 50, 2014 were identified using the laboratory data seasonal thresholds. Corresponding proportions of all visits from children<5 with a discharge diagnosis of RSV were identified using ESSENCE-FL. SS RSV seasonal thresholds were calculated by averaging SS RSV activity levels for the weeks when laboratory data signaled season onset and end between week 1, 2010 and week 50, 2014. For season onset, the SS RSV threshold was identified as the first week where >= 0.5% of all ED visits were from children <5 with a discharge diagnosis of RSV. To signal RSV season end, the SS threshold was determined as the first week (after season onset) where the proportion of all ED visits from children <5 with a discharge diagnosis of RSV was <=0.65%. The identified SS RSV thresholds were then compared to laboratory data to evaluate their sensitivity and specificity.
RESULTS: Trend analysis determined that SS-identified RSV ED visits increased sharply during the same weeks that laboratory data signaled season onset. When compared to corresponding laboratory data, SS RSV thresholds had 97% sensitivity and 77.6% specificity.
CONCLUSIONS: NREVSS is the established system to determine RSV season start and end. However, advances in electronic surveillance systems, like SS, could offer greater efficiency while maintaining accuracy, by reducing reporter delays. The methods described here may enable other states to characterize their own state-specific SS RSV thresholds and help create national SS RSV thresholds.