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 rates 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 prevalence rate (12.3 per 10,000). We investigated the accuracy of this report.

METHODS

All children born to Colorado residents during 1989-1991 and reported to CRCSN as having DS went through an active medical record review to eliminate false-positive cases. To adjust for case underascertainment, we used capture-recapture methods to estimate the number of cases missed during surveillance activities. After eliminating false-positive cases and adjusting for case underascertainment, we estimated a new prevalence rate.

RESULTS

A total of 198 children born to Colorado residents during 1989-1991 were reported to CRCSN as having DS. Of these, 151 (76%) were definite cases, 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 number of definite DS cases in Colorado was 155 (95% CI = (153-160)) and the new prevalence rate for 1989-1991 was 9.6 per 10,000 live-born infants.

CONCLUSIONS

Identifying false-positive cases and applying capture-recapture methods can help identify problems with birth defects surveillance efforts and provide direction for improvements. In Colorado, these techniques identified a problem of false-positive and inconclusive reports of DS. Case underascertainment was discovered not to be a problem.