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Serotypes Profile of Salmonella Isolates from Meat and Poultry Products January 1998 through December 2010

Tables and figures are available in the PDF version of this document, beginning on page 6. 

Background
The Food Safety and Inspection Service (FSIS) issued the Pathogen Reduction; Hazard Analysis and Critical Control Point (PR/HACCP) Systems, Final Rule, which sets Salmonella performance standards for establishments that slaughter or produce selected classes of food animals or raw ground products (Federal Register, 1996). FSIS used the nationwide microbiological baseline studies prior to 1996 to establish the PR/HACCP performance standards for carcasses of cow/bulls, steers/heifers, market hogs, broilers, ground beef, ground chicken, and ground turkey. The performance standards and guidance describe the maximum number of Salmonella-positive samples acceptable per sample set. The number of samples in a sample set varies by product class. The maximum number of positive samples acceptable in a set establishes an 80% probability of an establishment passing when it is operating at the standard. Guidance on standards for turkey carcasses is available in the Federal Register (2005).

FSIS initiated the product-specific Salmonella limits in large establishments on January 26, 1998, small establishments on January 25, 1999, and very small establishments on January 25, 2000. FSIS inspection personnel randomly collect and submit product samples to one of three FSIS Field Service laboratories in Athens, GA; Alameda, CA; or St. Louis, MO for Salmonella analysis, according to procedures described in Appendix E, Federal Register (1996) to verify that establishments meet standards.

The FSIS Field Service laboratories report the analysis results, and the Salmonella-positive isolates become eligible for serotyping at the USDA Animal and Plant Health Inspection Service's National Veterinary Services Laboratories in Ames, IA. Salmonella testing and serotype data, along with complementary data from molecular and phenotypic analyses, provide an opportunity to examine the association among serotypes isolated on-farm, from meat and poultry products, and from human cases of salmonellosis.

Prior to 2006, there were two phases of the FSIS regulatory program for Salmonella in raw products: non-targeted and targeted testing. FSIS collected non-targeted or "A" set samples at establishments randomly selected from the population of eligible establishments with a goal of scheduling every eligible establishment at least once a year. Establishments that failed a set undergo targeted testing, which includes "B", "C", and "D" sets.

Beginning June 2006, FSIS began to schedule establishments based on new criteria that are risk-based, rather than random (FSIS, 2006). FSIS developed the new sampling program to focus FSIS resources on at-risk establishments with the most samples positive for Salmonella and the greatest number of samples with serotypes associated with human salmonellosis (CDC, 2006). Beginning with the second 2006 quarterly report, FSIS summarized serotype data from all sample sets.

Note: The restructuring of Salmonella set scheduling prohibits the comparison of results from 2006 onwards to previous years. For such comparisons, nationwide baseline study results provide valid estimates of the prevalence of certain pathogens of public health concern and allow for valid statistical comparisons over time.

From January 1998 through December 2005, FSIS serotyped Salmonella isolates for four carcass and three raw ground product classes. Starting in June 2006, FSIS began to serotype Salmonella isolates from turkey carcasses. Each of the eight tables presented in this report identifies the ten most commonly isolated Salmonella serotypes by calendar year in a specific carcass or raw ground product class. When more than one serotype ranks in tenth place, each serotype in tenth place is listed. The Agency believes that researchers can use this product-specific serotype information to support foodborne pathogen surveillance. FSIS will provide updates of serotype distribution results in future reports. In 2010, FSIS identified Kentucky, as the most common serotype isolated in combined chicken classes; Hadar was most common in the ground turkey class; Montevideo was most common in combined cattle classes; and Derby was most common in the market hog class (Figure 1).

FSIS reviews CDC data for the serotypes isolated from human cases of salmonellosis found in meat and poultry products and those causing human illness (CDC, 2011; CDC, 2006). Some of the more common serotypes isolated from meat and poultry products are rarely isolated from human patients. Conversely, some of the serotypes frequently responsible for human cases of salmonellosis occur in various meat and poultry products. Salmonellosis serotypes identified from human cases also occur in other food and non-food sources.

CDC identifies the ten most common serotypes associated with human infection in the United States: Enteritidis, Newport, Typhimurium, Javiana, 4,[5],12:i:-, Heidelberg, Saintpaul, Muenchen, Montevideo, and Infantis. Combined, these serotypes account for a majority (75.2%) of human infections in the Foodborne Diseases Active Surveillance Network  FoodNet) sites in 2010, (CDC, 2011). Figures 2-12 identify the percent of the top ten human serotypes in meat and poultry product classes with the exception of Javiana, which is uncommon. Year-to-year variation both within and between product classes, with respect to these more common human serotypes, can be observed. The dominant serotypes identified in 2010 in meat and poultry products (Kentucky, Hadar, and Derby) were not among the top ten serotypes identified in human surveillance data. As reported by the CDC in 2011, Enteritidis and Newport incidence was significantly higher, while the incidence of Typhimurium did not change significantly for 2006-2008.

Human illnesses attributable to Salmonella Newport began to rise in the late 1990's. Newport is detected in all FSIS commodities; most frequently in the cattle classes (Figure 5). In 2003, Newport peaked as the most commonly isolated serotype in ground beef. In 2010, the presence of Newport dropped significantly in ground beef. By 2010, this serotype reached zero in cow/bull (Table 3) and steer/heifer (Table 4), while only five Newport isolates were recovered in ground beef (Table 5).

CDC reported that a Salmonella serotype having the antigenic formula 4,[5],12:i:- has been increasingly recognized since the mid-1990's in human illness cases. In 2010, the serotype was the fifth most commonly identified serotype in U.S. human surveillance data. In 2010, 4,[5],12:i:- was the sixth most commonly identified serotype in broiler isolates (Table 1). FSIS laboratories did not report antigenic formulas until 2004. Prior to 2004, serotypes identified solely by antigenic formulas and classified as "monophasic" were included in the "unidentified" isolates category.

FSIS launched a Salmonella initiative in 2006 to decrease Salmonella contamination of poultry products and other meats. In 2010, the percent of samples from broiler carcasses positive for Salmonella was 6.7%, down from 7.2% in 2009, 7.4% in 2008, 8.5% in 2007, 11.4% in 2006, and a high of 16.3% in 2005. Comparing 2009 to 2010 data, FSIS verification testing showed an increase in the proportion of Salmonella Enteritidis in broilers and in ground chicken (Figure 4) and a decrease in the proportion of Salmonella Heidelberg in broilers. The testing did not indicate a significant change in the proportion of Salmonella Heidelberg in ground chicken (Figure 7).

Verification testing is a regulatory sampling program intended to assess the ability of meat and poultry establishments to comply with existing, product-specific performance standards. Serotype profile results are not intended to indicate serotype prevalence within a respective product class. Despite program limitations, FSIS believes that verification testing results presented in this report provide a good indication of relative serotype distributions in raw products for each product class for the 13 years following implementation of the PR/HACCP final rule in federally inspected meat and poultry establishments. FSIS continues to work with public health partners to better identify the proportion of human salmonellosis attributable to FSIS-regulated products.

Results
 

  • FSIS reports serotypes by product class and calendar year based on the date of sample collection from 1998 through 2010. Tables 1-8 include the number of isolates of each serotype and category, the percent of total serotyped isolates, and the percent of total samples collected.

  • The ten most common serotypes isolated from a specified product class during a given year are identified by name while less commonly identified serotypes are included in the "other serotypes" category. When there is more than one serotype in tenth place, FSIS lists all serotypes in tenth place.

  • FSIS includes entries classified as "not typed" and "unidentified" in the serotype profile. "Not typed" Salmonella entries were not serotyped. Unidentified entries include isolates in which a single specific serotype could not be determined. Prior to 2004, FSIS classified serotypes identified solely by antigenic formulas as monophasic, such as I4,[5],12:i:-, and included in the unidentified isolates category.

  • From 1998-2005, only "A" set samples were included in the report. Beginning with the second 2006 quarterly report, FSIS summarized data from all samples in the reports.

  • FSIS reported variants of serotypes separately. Tables 1, 2, 5, 6, 7, and 8 include data for each product class for combined variants in 2010. Tables 3 and 4 include one variant per serotype observed. Merging variants are most useful in facilitating comparisons of the proportion of Salmonella Typhimurium in product classes with human health surveillance data. FSIS combines and reports Typhimurium and Typhimurium 5- as Typhimurium in U.S. human health surveillance data (CDC 2006).

  • The figures display the percent of isolates identified out of total isolates serotyped for each product class. The y-axis, the serotype percentage, varies from graph to graph because the percent of different serotypes varies by commodity and year.


Note: The calendar year total for samples analyzed is not always the simple addition of the totals from all four quarters. On occasion, appealed sample results are removed from the totals for verification results.

Tables and Figures
All tables and figures are available in this 121-page PDF document.

References
CDC. 2006. PHLIS Surveillance Data, Salmonella Annual Summary. Available at: http://www.cdc.gov/ncidod/dbmd/phlisdata/salmonella.htm . Accessed 1 July 2011.

CDC. 2011. Vital Signs: Incidence and Trends of Infection with Pathogens Transmitted Commonly Through Food - Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 1996 - 2010. Available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6022a5.htm?s_cid=mm6022a5_w . Accessed on 1 July 2011.

Federal Register. 1996. Pathogen Reduction; Hazard Analysis and Critical Control Point (HACCP) Systems, Final Rule. Available at: http://www.fsis.usda.gov/OPPDE/rdad/FRPubs/93-016F.pdf. Accessed on 1 July 2011.

Federal Register. 2005. Generic E. Coli and Salmonella Baseline Results. Available at: http://www.fsis.usda.gov/OPPDE/rdad/FRPubs/02-046N.pdf. Accessed on 1 July 2011.

FSIS. 2006. Scheduling Criteria for Salmonella Sets in Raw Classes of Product. Available at: http://www.fsis.usda.gov/pdf/scheduling_criteria_salmonella_sets.pdf . Accessed on 1 July 2011.

Last Modified Aug 12, 2013