How are incidence trends examined in FoodNet?
FoodNet uses a main-effects, log-linear Poisson regression (negative binomial) model to estimate changes in
the incidence of infection. The model adjusts for the increase in the number of FoodNet sites since 1996 and
for variation in the incidence of infections among sites. The average annual incidence for 1) 1996–1998 (1997–
1998 for Cryptosporidium), the first years of surveillance, and 2) a more recent 3-year period (2006–2008) are
used for comparisons. Prior facts and figures on FoodNet surveillance data from 2008 and 2009 used the
preceding 3 years, a moving period, for comparison; this report initiates use of 2006–2008 as a stable
comparison period. The model is used to calculate the estimated change in incidence (relative rate) between
2010 and the comparison periods, with 95% confidence intervals (CI). In the figures that report percent
change, the percent change for the current year is calculated by comparison with the appropriate comparison
period and graphed along with the 95% confidence interval. In the figures that report relative rate, the relative
rate for each year is graphed. Trends in STEC non-O157 and Cyclospora infection were not evaluated because
of sparse data.
FoodNet also uses the negative binomial model to measure overall trends in incidence. In this model, data for
Campylobacter, Listeria, Salmonella, STEC O157, Yersinia, and Vibrio, the bacterial pathogens for which >50%
of illnesses are estimated to be transmitted by food, are combined, weighting them equallyweighting by
incidence of infection for each pathogen.
Results:
By pathogen
Compared with 1996-1998 period
Figure 1. Percent change  PDF 41KB
Figure 2. Relative rates (graph 1) PDF 29KB
Figure 3. Relative rates (graph 2) PDF 21KB
Compared with 2006-2008 period
Figure 4. Percent change PDF 28KB
Summary (both comparison periods)
Table 8. Percent change PDF 61KB
By Salmonella serotype
Compared with 1996-1998 period
Figure 5. Percent change PDF 27KB
Figure 6. Relative rates (graph 1) PDF 41KB
Figure 7. Relative rates (graph 2) PDF 37KB
Compared with 2006-2008 period
Figure 8. Percent change PDF 25KB
Summary (both comparison periods)
Table 9. Percent change PDF 64KB
Overall change in incidence Overall change for 2010
Table 10. Percent change PDF 41KB
Figure 9. Relative rates PDF 37KB
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