Abstract
BACKGROUND: Sensitive surveillance for acute flaccid paralysis (AFP) allows for rapid detection of polio outbreaks and provides essential evidence to support certification of the eradication of polio. However, accurately assessing the sensitivity of surveillance systems can be difficult due to limitations in the reliability of available performance indicators, including the rate of detection of non-polio AFP and the proportion of adequate stool sample collection. Recent field reviews have found evidence of surveillance gaps despite indicators meeting expected targets. METHODS: We propose two simple new approaches for AFP surveillance performance indicator analysis to supplement standard indicator analysis approaches commonly used by the Global Polio Eradication Initiative (GPEI): (1) using alternative groupings of low population districts in the country (spatial binning) and (2) flagging unusual patterns in surveillance data (surveillance flags analysis). Using GPEI data, we systematically compare AFP surveillance performance using standard indicator analysis and these new approaches. RESULTS: Applying spatial binning highlights areas meeting surveillance indicator targets that do not when analyzing performance of low population districts. Applying the surveillance flags we find several countries with unusual data patterns, in particular age groups which are not well-covered by the surveillance system, and countries with implausible rates of adequate stool specimen collection. CONCLUSIONS: Analyzing alternate groupings of administrative units is a simple method to find areas where traditional AFP surveillance indicator targets are not reliably met. For areas where AFP surveillance indicator targets are met, systematic assessment of unusual patterns ('flags') can be a useful prompt for further investigation and field review.