Table 1. Foodborne Diseases Active Surveillance Network (FoodNet) Surveillance Area, by State and County, 1996–2011

How is incidence per 100,000 persons calculated?

Annual incidence is reported as cases per 100,000 persons. Incidence is calculated by dividing the total number of infections with each pathogen by the population in the FoodNet surveillance system for that year.

All sites, 1996 to 2011
Table 2a. Number of infections
Table 2b. Incidence per 100,000 persons

By site, 2011
Table 3a. Number of infections
Table 3b. Incidence per 100,000 persons

By age group, 2011
Table 4a. Number of infections
Table 4b. Incidence per 100,000 persons

Table 5. Top 10 Salmonella serotypes, 2011
Table 6. Shiga toxin-producing Escherichia coli serogroups (non-O157), 2011
Table 7. Vibrio and Vibrionaceae species, 2011

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.  The model is used to calculate the estimated change in incidence (relative rate) between 2011 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 by incidence of infection for each pathogen.

By pathogen

Compared with 1996-1998 period
Figure 1. Percent change
Figure 2. Relative rates
Figure 3. Relative rates

Compared with 2006-2008 period
Figure 4. Percent change

Summary (both comparison periods)
Table 8. Percent change

By Salmonella serotype

Compared with 1996-1998 period
Figure 5. Percent change
Figure 6. Relative rates
Figure 7. Relative rates

Compared with 2006-2008 period
Figure 8. Percent change

Summary (both comparison periods)
Table 9. Percent change

Overall change in incidence

Overall change for 2011
Table 10. Percent change
Figure 9. Relative rates

How is percentage of hospitalization calculated?

The percentage of hospitalization is calculated as follows:

Patients are considered to have been hospitalized if hospitalization occurs at any time within 7 days of the specimen collection date.

Results:

Overall, 2011
Table 11. Number and percentage of hospitalizations

Number and percentage of hospitalizations by age group, 2011
Table 12a. Persons <5 years
Table 12b. Persons 5-9 years
Table 12c. Persons 10-19 years
Table 12d. Persons 20-64 years
Table 12e. Persons >65 years

How is the case fatality ratio calculated?

The case fatality ratio is calculated as follows:

Patients' vital status is recorded at hospital discharge (if hospitalized) or at 7 days after the specimen collection date (if not hospitalized).

Results:

Overall, 2011
Table 13. Number of deaths and case fatality ratio

By age group, 2011
Table 14. Number of deaths and case fatality ratio