A new sequential procedure for surveillance of Down's syndrome

Area of Science:

• Epidemiology
• Biostatistics
• Public Health Surveillance

Background:

• Down's syndrome risk is strongly linked to maternal age.
• Environmental factors may contribute additively to Down's syndrome risk across all maternal ages.
• Existing surveillance methods may not be sensitive enough to detect subtle, environmentally induced risk changes.

Purpose of the Study:

• To introduce and evaluate a new surveillance method for Down's syndrome.
• To specifically detect additive increases in Down's syndrome risk potentially caused by environmental factors.
• To compare the performance of the new method against the Poisson cumulative sum (cusum) method.

Main Methods:

• The proposed method utilizes registry data from successive time periods for a defined population.
• It assumes knowledge of Down's syndrome cases and total births across all maternal age groups.
• Average run lengths (ARLs) were calculated for a sample size of 14,500 births per period, using quarterly data from Norway (1978-1989).

Main Results:

• The new surveillance method demonstrated significantly faster detection of moderate additive increases in risk compared to the Poisson cusum.
• Retrospective application to Norwegian data indicated the method was close to an alarm in 1985 and signalled a strong alarm in 1986.
• These findings correlated with a known increase in Down's syndrome risk during that period, which the cusum method did not detect as sensitively.

Conclusions:

• The proposed registry-based surveillance method is highly effective for detecting changes in Down's syndrome risk.
• It offers improved sensitivity for identifying environmentally induced risk increases compared to the standard Poisson cusum method.
• This method provides a valuable tool for public health surveillance of congenital conditions.