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Abstract:
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A small proportion of passengers travelling on cruise ships in the U.S. experience acute gastroenteritis (AGE) illness. We estimated AGE outbreak frequencies, outbreaks per 1,000 voyages, outbreaks per 10 million travel-days, and AGE illness per 100,000 travel-days during 2008-2014, based on reports submitted to CDC by cruise ships in U.S. jurisdiction. Our study objective was to project 2015-2050 AGE illness rates using 2008-2014 by applying exponential smoothing method. Since (2008-2014) rates did not show a significant trend, we applied the single exponential smoothing technique, where the (n+1)th value was estimated by taking a weighted average of past n values. We gave higher values to weights for the most recent terms, assigning weights using the geometrical series r(1-r)t where r is the smoothing constant in the range 0 < r < 1, and t is the past tth value. Since the rates also showed a non-significant trend, so we used double exponential smoothing technique. From observed AGE rates per 100,000 travel-days, we projected 2015-2050 (5-yr interval) rates as 24.2, 23.3, 22.5, 21.7, 20.9, 20.0, 19.2, and 18.4. We will use Markov model and other methods to project and compare.
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