Using active medical record review and capture-recapture methods to investigate the prevalence of Down syndrome among live-born infants in Colorado

Background: In a 1994 comparison of Down Syndrome (DS) birth prevalence rat es between 17 states (CDC '94), the average rate for the 17 states was 9.2 per 10,000 live-born infants. Colorado residents had the highest birth prev alence rate (12.3 per 10,000). We investigated the accuracy of this report. Methods: All children born to Colorado residents during 1989-1991 and repor ted to CRCSN as having IDS went through an active medical record review to eliminate false-positive cases. To adjust for case underascertainment, we u sed capture-recapture methods to estimate the number of cases missed during surveillance activities. After eliminating false-positive cases and adjust ing for case underascertainment, we estimated a new prevalence rate. Results: A total of 198 children born to Colorado residents during 1989-199 1 were reported to CRCSN as having IDS. Of these, 151 (76%) were definite c ases, 25 (13%) were false-positive cases, and 22 (11%) were inconclusive. A log-linear capture-recapture model applied to the definite cases resulted in an estimate of three missing cases. Therefore, the estimated total numbe r of definite DS cases in Colorado was 155 (95% Cl = (153-160)) and the new prevalence rate for 1989-1991 was 9.6 per 10,000 liveborn infants. Conclusions: Identifying false-positive cases and applying capture-recaptur e methods can help identify problems with birth defects surveillance effort s and provide direction for improvements. In Colorado, these techniques ide ntified a problem of false-positive and inconclusive reports of IDS. Case u nderascertainment was discovered not to be a problem. Teratology 64:S14-S19 , 2001. (C) 2001 Wiley-Liss, Inc.