Automated Monitoring of Asthma Using the BioSense System

Background
In 2005, approximately 22.2 million persons had asthma and there were approximately 4000 asthma related deaths in the U.S.  The CDC BioSense System currently receives data from >400 hospital emergency departments (EDs; 427 send patient chief complaints and 175 send physician diagnoses), and captures about 12% of all U.S. ED visits.  We analyzed these data to determine its potential utility for asthma surveillance.  

 Methods
We analyzed asthma final diagnoses (ICD-9: 493.0-493.9) and chief complaints indicators for the 2007 calendar year.  We summarized data on date, demographics, and geographic location. 

 Results
Of 13.4 million ED visits, 278,070 (2.1%) had either a chief complaint or final diagnosis of asthma; these visits represented 239,315 patients (average 1.2 visits per patient). Forty-nine percent of the asthma visits were identified by an asthma chief complaint, 38% by an asthma diagnosis, and 13% had both. The 20-49 year age group comprised 39% of asthma visits. Among 19 metropolitan areas with ≥2 BioSense hospitals, the two largest asthma clusters were attributed to poor ambient air quality.  The first was characterized by 225 asthma chief complaints over three days in September 2007 among 48 hospitals in one metropolitan area.  The second included 138 final diagnoses over three days among five hospitals in San Diego, California in October associated with wildfires.  Seasonal increases were observed in the fall and were most prominent among final diagnoses.

Discussion
Asthma is a common reason for ED visits that can be readily monitored using chief complaints and final diagnoses.  These results suggest that BioSense may be an important and timely source of information on asthma that could be used to track morbidity and inform public health interventions.