Monitoring H1N1 Activity in Maryland Using Syndromic Surveillance

Background: In April 2009, cases of novel influenza A virus (H1N1) were identified across the United States, prompting states to increase surveillance activities to detect cases of the novel virus. Maryland used its electronic syndromic surveillance system to monitor H1N1 activity throughout the state and inform decision-makers.

Methods: Through the surveillance system, emergency department visits for influenza-like illness (ILI) and over-the-counter sales of respiratory medications were reviewed closely on a daily basis throughout the initial H1N1 response. The Maryland Department of Health and Mental Hygiene (DHMH) used its syndromic surveillance system as a tool to enhance case finding efforts as well as to monitor levels of ILI across the state. Daily reports were provided to state executives to enhance situational awareness and inform decision-making.

Results: Emergency department visits for ILI spiked during the initial H1N1 outbreak. A statistically significant increase in ILI occurred for 10 consecutive days from April 26, 2009 to May 6, 2009. The peak of emergency department visits for ILI occurred on April 30, 2009, on which there was a 4.5 fold increase compared to the same date in 2008.

Discussion: Syndromic surveillance proved to be a vital tool in supporting decision-makers by providing timely and ongoing situational awareness of the initial H1N1 outbreak. This data indicated that although there was a large increase in emergency department visits for ILI during the initial outbreak, hospitals were not completely overwhelmed. DHMH is continuing to monitor this data closely to maintain situational awareness of ILI activity in Maryland.