Secular trends in 1,192 diarrheal outbreaks in the Israel Defence Forces between 1988-2011.

Background: In the military, outbreaks of infectious diarrhea pose a significant health problem. In this descriptive analysis of data collected by the IDF on all infectious diarrhea outbreaks between 1988-2011, we analysed temporal, seasonal, and unit-type trends in 1,192 diarrheal outbreaks in the Israel Defence Forces (IDF) over a 24-year period, and described the long-term trends in seasonality and the effects of strategic preventive measures on outbreak frequency among populations at risk.

Results: We found two distinct phases in annual outbreak occurrence. The mean annual number of outbreaks during the period 1988-1996 was 75.8 (14.50) but dropped to 34.0 (8.13) during the period 1997-2011 (P < 0.0001). Overall, a downward trend continued through the 1990's, while from 2000 onwards outbreak counts fluctuated annually. A significantly higher number of outbreaks occurred during the summer season, throughout the study period. The greatest number of outbreaks occurred in deployed units, although the proportion of outbreaks in this unit type decreased over time. Accordingly, the proportion of outbreaks in training units more than doubled during the study window. When we looked at outbreak size, summer outbreaks increased in magnitude over time, and during all periods outbreaks were larger, on average, in training units than in deployed units.

Conclusions: The changing patterns in diarrheal outbreaks in the Israel Defence Forces require maintenance of a higher level of vigilance than ever before. Lack of a clear peak period require the use of all available preventive measures throughout the year. This is especially true in training units, where the increased number of outbreaks coincides with increased trainee volume, regardless of season.