Tuesday, February 24, 2015

CDC Report - Attribution of Foodborne Illnesses, Hospitalizations, and Deaths

The CDC issued a report that attributes foodborne illness cases to different foods. Calculations, based on known cases over the period from1998 to 2008, are used to estimate the number of cases caused by each disease causing agent as well as to attribute to one of 17 food types.

There are some big assumptions that are made in the report that I feel limits what headlines will report. 1) It applies known outbreaks to apply to sporadic cases. Because of this, it underestimates the number of cases caused by organisms that have illnesses which tend to be more sporadic in nature, such as Campylobacter. 2) Along those same lines, mass distributed product where a single contamination event results in a large number of illnesses, such as in bagged produce, outweighs foods that may are considered high risk for contamination. 3) In the cases where mixed food caused an illness, the blame is put on the item commodity that they determined to have caused the biggest
proportion of illnesses, rather than the real risk. 4) Some organisms don't even show up, such as Taxoplasma spp.. even though that organism is claimed to be one of the major pathogens associated with meat....(although owning multiple cats is probably a bigger risk).

The headlines from some of the major news outlets give the impression that certain foods are risky.

Philly.com - U.S. Officials Pinpoint Common Sources of Foodborne Illnesses
Reuters - U.S. government report outlines foods most prone to pathogens
Time - Here’s What Foods Are Most Likely To Have E. Coli or Salmonella

 It is hard to get a real sense of real risk there is no calculation associated with the units consumed. Without this, many will jump on items that show to have a caused a higher percentage of the number of illnesses caused, but not the real risk.

My takeaways:
  • Produce - Because of the way that produce is processed and distributed, a contamination event involving produce will impact many and thus gets seen as having a big impact in this report.  However, if we look at the number of units sold, produce is a much smaller risk than it appears to be in this report when compared to other commodities.  Not to say that there is not work that needs to be done, especially in preventing contamination events that can impact thousands of units.  However, people should not be discouraged from produce due to the potential for foodborne illness.
  • Dairy - raw milk should be considered the highest risk dairy product, and on the further processed side, cheese accounts for many of the cases of Listeria recently seen.
  • Mollusks - raw shellfish is a high risk item, especially when you consider the small number of people that eat raw shellfish (compared to produce)
  • Poultry - because it has a natural association with Salmonella and Campylobacter, there have been outbreaks.  Looking at USDA monitoring records, while the levels of Salmonella in whole chicken are low, for ground poultry and parts, it is higher.  So while the industry is working to lessen the prevalence of these pathogens in poultry products, elimination is unlikely.
  • Meat - ground meat is the primary source of STEC E.coli.  USDA testing indicates that about 0.5% of ground meat tested was positive. 
  • As for pathogens, Salmonella is a pathogen that seems to find its way to the consumer via a number of different food products.  As for Campylobacter, it has a high prevalence on chicken, but we don't necessary see the cases; probably, because most cases are sporadic. In recent outbreaks, raw milk has been the culprit.
Has the number of foodborne illness cases dropped recently?  While that seems to be the case, it is hard to tell in this report.  And if policy decisions are going to be made on this report, even using weighting the data from the last five years, there may be some issues.  For example, our ability to determine the agent (detection of Campylobacter as an example) has improved dramatically in the last few yeas.  Additionally, issues that occurred 2 to 5 years ago may not be as big as an issue today  Granted it is difficult to trend when working with  minimal data.  However, considerations must be taken if these calculations are used to set policy.

CDC - Emerging Infectious Diseases

Volume 19, Number 3—March 2013
Attribution of Foodborne Illnesses, Hospitalizations, and Deaths to Food Commodities by using Outbreak Data, United States, 1998–2008
John A. Painter(http://wwwnc.cdc.gov/eid/article/19/3/11-1866_article#comment) , Robert M. Hoekstra, Tracy Ayers, Robert V. Tauxe, Christopher R. Braden, Frederick J. Angulo, and Patricia M. Griffin
Author affiliations: Author affiliation: Centers for Disease Control and Prevention, Atlanta, GA, USA
Each year, >9 million foodborne illnesses are estimated to be caused by major pathogens acquired in the United States. Preventing these illnesses is challenging because resources are limited and linking individual illnesses to a particular food is rarely possible except during an outbreak. We developed a method of attributing illnesses to food commodities that uses data from outbreaks associated with both simple and complex foods. Using data from outbreak-associated illnesses for 1998–2008, we estimated annual US foodborne illnesses, hospitalizations, and deaths attributable to each of 17 food commodities. We attributed 46% of illnesses to produce and found that more deaths were attributed to poultry than to any other commodity. To the extent that these estimates reflect the commodities causing all foodborne illness, they indicate that efforts are particularly needed to prevent contamination of produce and poultry. Methods to incorporate data from other sources are needed to improve attribution estimates for some commodities and agents.

[Selections from the text]
During 1998–2008, a total of 13,352 foodborne disease outbreaks, causing 271,974 illnesses, were reported in the United States (Technical Appendix 1 Table 1[PDF - 723 KB - 8 pages](http://wwwnc.cdc.gov/eid/article/19/3/11-1866-techapp1.pdf)). Of those outbreaks, 4,887 (37%), causing 128,269 (47%) illnesses, had an implicated food vehicle and a single etiology; 298 of those outbreaks were excluded because information about the vehicle was insufficient to categorize the ingredients. We also did not include the 3% of outbreaks that had multiple etiologies reported.
We applied percentages derived from outbreak-associated illnesses for each etiology to the 9.6 million estimated annual illnesses assessed and attributed ≈4.9 million (≈51%) to plant commodities, ≈4.0 million (≈42%) to land animal commodities, and ≈600,000 (≈6%) to aquatic animal commodities (Table 1(http://wwwnc.cdc.gov/eid/article/19/3/11-1866-t1.htm)). Produce commodities (fruits-nuts and the 5 vegetable commodities) accounted for 46% of illnesses; meat-poultry commodities (beef, game, pork, and poultry) accounted for 22%. Among the 17 commodities, more illnesses were associated with leafy vegetables (2.2 million [22%]) than any other commodity. The high estimate for illnesses attributable to leafy vegetables was many times higher than the low estimate (Figure 2, panel A), which indicates that leafy vegetables were frequently found in complex foods. After leafy vegetables, the commodities linked to the most illnesses were dairy (1.3 million [14%]), fruits-nuts (1.1 million [12%]), and poultry (900,000 [10%]). Norovirus comprised 57% of all illnesses.
Most bacterial illnesses were attributed to dairy (18%), poultry (18%), and beef (13%) commodities (Table 1(http://wwwnc.cdc.gov/eid/article/19/3/11-1866-t1.htm)). Most chemical illnesses were attributed to fish (60%, most caused by the marine biotoxin ciguatoxin). Most parasitic illnesses were attributed to mollusks (33%) and fruits-nuts (26%); this reflects the fact that 1 simple food outbreak was caused by Giardia intestinalis (mollusks) and 1 by Cryptosporidium spp. (fruits-nuts). Most viral illnesses were attributed to leafy vegetables (35%), fruits-nuts (15%), and dairy (12%). Of the 20 outbreaks associated with simple foods and caused by norovirus transmitted by dairy, 14 (70%) were transmitted by cheese products.
More illnesses were attributed to leafy vegetables (22%) than to any other commodity; illnesses associated with leafy vegetables were the second most frequent cause of hospitalizations (14%) and the fifth most frequent cause of death (6%). Previous studies have shown that produce-containing foods were the food source for approximately half of norovirus outbreaks with an identified simple food vehicle during 2001–2008 (8) and the second most frequent food source for E. coli O157 outbreaks during 1982–2002 (9). Outbreaks of E. coli O157 infections transmitted by spinach (10) and lettuce (11) and Salmonella spp. infections transmitted by tomatoes (12,13), juice (14,15), mangoes (16), sprouts (17,18), and peppers (19,20) underline concerns about contamination of produce consumed raw.
More deaths were attributed to poultry (19%) than to any other commodity, and most poultry-associated deaths were caused by Listeria or Salmonella spp. From 1998 through 2002, three large listeriosis outbreaks were linked to turkey delicatessen meat contaminated in the processing plant after cooking (2123). A risk-ranking model for listeriosis among ready-to-eat foods identified delicatessen meat as the highest risk food (24).
[Assumptions and Limitations]
  • We assumed that using the number of outbreak-associated illnesses rather than number of outbreaks would enable better assignment of illnesses to commodities. Our choice had the potential to bias the results toward large outbreaks. However, large outbreaks often represent system failures that have resulted in smaller, undetected outbreaks; investigation may determine the source for illnesses that otherwise might have been considered sporadic.
  • We further assumed outbreak illnesses represented all illnesses and weighted the results for each agent by number of all foodborne illnesses attributed to each agent (1). Unweighted outbreak data may be biased toward seafood outbreaks caused by marine biotoxins (e.g., scombroid) that are frequently reported but cause relatively few illnesses. For some agents, foods implicated in outbreaks might not well represent foods responsible for sporadic illnesses. For example, outbreak data underrepresent poultry (8%) and overrepresent dairy (67%) as sources of Campylobacter spp. infection; studies of sporadic infections implicate consumption of poultry but not dairy as a major risk factor (33). Campylobacter spp. are estimated to be the third most common bacterial cause of foodborne illness, but relatively few outbreaks are detected (1). For pathogens for which outbreaks are uncommon or do not reflect major modes of transmission, methods that incorporate data from nonoutbreak sources are needed.
  • We also assumed that, for a given agent, when an outbreak was associated with a complex food, the likelihood that any commodity was the source was proportional to the frequency of illnesses for outbreaks associated with simple foods associated with that commodity.
  • A limitation of our study is the absence of outbreaks caused by some agents. None caused by Toxoplasma spp. or Vibrio vulnificus were reported. The attributable risk for Toxoplasma infection is highest for meat (49%) and mollusks (16%) (36); most foodborne V. vulnificus infections are linked to oysters (37).
  • Other limitations of our study included the choice not to use the credible interval for the estimated number of illnesses, hospitalization, and deaths (1); the lack of published estimates for the number of illnesses caused by chemical etiologies; and the fact that the quality of outbreak data is dependent on the quality and quantity of investigations reported.

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