Foodborne Illness Outbreaks at Retail Food Establishments 

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CDC – Each year, state, tribal, local, and territorial health departments (hereafter referred to as health departments) report hundreds of foodborne illness outbreaks to CDC (1). During 2009–2015, health departments reported 5,760 foodborne illness outbreaks (2). A majority of these outbreaks occurred in retail food establishments (e.g., restaurants or caterers), defined as operations that store, prepare, package, serve, or vend food directly to the consumer or otherwise provide food for human consumption (2,3).

Health departments typically are responsible for regulating and ensuring food safety in retail food establishments, primarily through routine inspections to identify and correct violations of their jurisdictions’ food safety regulations. The U.S. Food and Drug Administration (FDA) Food Code underlies a majority of jurisdictions’ food safety regulations. The FDA Food Code is a model set of science-based, comprehensive food safety recommendations intended to reduce foodborne illness risk in retail food establishments (4). For example, the Food Code includes recommendations to limit opportunities for food workers to contaminate food, such as washing hands, using gloves, and prohibiting ill or infectious workers from working with food when they are experiencing specified symptoms. Although the Food Code represents recommendations for food safety, adoption of its provisions, in whole or in part, is voluntary and at the discretion of state and local governments (4).

Health departments also are typically responsible for investigating suspected foodborne illness outbreaks in retail food establishments to control and stop the outbreak. Health departments provide epidemiologic and laboratory data from their foodborne outbreak investigations to CDC through the National Outbreak Reporting System (NORS). The data reported include the etiologic agent; food vehicle; outbreak setting; and number of illnesses, hospitalizations, and deaths associated with an outbreak (5). These data have led to discoveries of new and emerging foodborne illness agents and specific agent–food pairs (6).

In addition to epidemiologic and laboratory data reported to NORS, certain health departments also provide data to CDC from the environmental health component of their investigations, often called the environmental assessment, through the National Environmental Assessment Reporting System (NEARS) (7). Since 2014, when NEARS began data collection, 29 health departments have voluntarily reported environmental assessment data from foodborne illness outbreak investigations to NEARS. The data collected describe how the retail food service environment contributes to the introduction or transmission of agents that lead to outbreaks. NEARS collects data on food preparation policies and practices, the processes used in preparing food items suspected in the outbreak, and workers’ food preparation practices (3,8,9). These environmental health data can be used in combination with epidemiologic and laboratory data to gain a comprehensive understanding of an outbreak and identify gaps in the establishments’ food safety policies and practices.

This report summarizes selected data reported to NEARS for foodborne illness outbreaks that occurred during 2017–2019, the most recent years for which final data are available. The findings describe the outbreaks, the establishments where the outbreaks occurred, and food safety policies of those establishments, with an emphasis on policies focused on identifying and managing ill workers. Contamination of food by ill food workers is a top contributing factor to foodborne outbreaks in retail food establishments (3,8); therefore, identifying gaps in these establishments’ ill worker policies is important to outbreak prevention. Health departments responsible for ensuring food safety in retail food establishments can use the findings in this report to assess their food safety priorities and guide their outbreak investigations and routine (i.e., preventive) inspections.

Methods

Description of the System and Case Definition

In 2014, NEARS was launched to collect environmental assessment data during foodborne illness outbreaks associated with retail food establishments (6,7). CDC defines a foodborne illness outbreak as an incident in which two or more persons experience a similar illness resulting from ingesting a common food (10); a majority of health departments have a similar definition. Identified outbreak agents are classified as confirmed if they were laboratory confirmed according to CDC laboratory and clinical guidelines (10); otherwise, they are classified as suspected.

Participating Sites

For this report, NEARS data were submitted by Alaska; California; Connecticut; Delaware; Fairfax County, Virginia; Georgia; Harris County, Texas; Indiana; Iowa; Jefferson County, Colorado; Kansas City, Missouri; Maricopa County, Arizona; Massachusetts; Michigan; Minnesota; New York; New York City, New York; North Carolina; Oregon; Rhode Island; South Carolina; Southern Nevada Health District; Tennessee; Washington; and Wisconsin. These health departments reported environmental assessment data from at least one foodborne illness outbreak occurring in a retail food establishment.

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Data Sources, Collection, and Availability

Data collected and entered into NEARS are from three sources: observations or determinations made by the environmental health professional conducting the investigation, interviews with the managers of establishments with outbreaks, and the epidemiology or laboratory counterparts at health departments Follow link to: (Box 1). After each foodborne illness outbreak investigation is completed, participating health departments voluntarily report their environmental health investigation data to CDC through the NEARS online data management system on CDC’s website. Not all data elements are collected during all investigations; therefore, denominators vary throughout the results. Data on foodborne illness outbreaks reported to NEARS included in this report are publicly available at https://stacks.cdc.gov/view/cdc/127053.

Variables Included

For this report, data were collected and presented on three sets of variables: characteristics of foodborne illness outbreaks, characteristics of establishments linked with outbreaks, and ill worker policies of establishments linked with outbreaks.

• Outbreak characteristics. Characteristics include the outbreak agent and contributing factors. FDA and CDC have identified three groups of outbreak contributing factors (11):
  • contamination of food with a foodborne illness agent,
  • proliferation or growth of microbial agents in food (proliferation can mean an increase in the number of bacteria, the production of toxins, or both), and
  • survival of foodborne illness agents after a process (e.g., cooking) that should have eliminated or reduced them.
• Outbreak establishment characteristics. Characteristics include those that have been hypothesized or found to be associated with retail food establishment food safety. These characteristics include ownership (independent or chain, defined in NEARS guidance as an establishment that shares a name and operations with at least one other establishment) and number of meals served daily (12–15).
• Outbreak establishment ill worker policies. Policies assessed include those designed to limit opportunities for food workers to contaminate food by prohibiting workers who are ill or infectious from working with food (4). The report also assessed whether these policies were written. The Food Code recommends written plans and procedures (4). Specifically, data were presented on whether establishments provided paid sick leave to workers and whether establishments with outbreaks had policies addressing four components of the Food Code relating to ill or infectious workers. This report assessed whether establishments had policies that
  • required workers to tell a manager when they are ill,
  • specified the five symptoms of foodborne illness workers need to report to their manager (i.e., vomiting, diarrhea, jaundice, sore throat with fever, and lesion with pus),
  • restricted (i.e., prevented from handling food) or excluded (i.e., prevented from working) ill or infectious workers, and
  • specified the five symptoms requiring worker restriction or exclusion from work activities.

Data Analysis

CDC calculated descriptive statistics on characteristics of foodborne illness outbreaks and characteristics and policies of establishments linked with outbreaks. Data cleaning, management, and analysis were conducted using SAS (version 9.4; SAS Institute) and Microsoft Excel for Microsoft 365 MSO (version 2022; Microsoft Corporation). This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.*

Results

During 2017–2019, a total of 800 foodborne illness outbreaks associated with 875 retail food establishments were reported to NEARS by the 25 participating state and local health departments. Among the 800 outbreaks, 216 (27.0%) occurred in 2017, 306 (38.3%) in 2018, and 278 (34.8%) in 2019. Of these outbreaks, 725 (90.6%) involved one establishment and 75 (9.4%) involved multiple establishments. Twenty-eight (3.5%) were multistate outbreaks. Investigators conducted an interview with a manager in 679 (84.9%) outbreaks.

Outbreak Characteristics

Investigations identified an etiologic agent in 555 (69.4%) outbreaks. Of these agents, 157 (28.3%) were suspected and 398 (71.7%) were confirmed. A majority of identified agents were viral (48.1%) and bacterial (46.8%); parasitic (2.3%) and toxic or chemical (2.5%) agents accounted for the remainder. The most common agent was norovirus, accounting for 47.0% (65.1% of which were laboratory confirmed), followed by Salmonella, accounting for 18.6% (87.4% of which were laboratory confirmed) Follow link to: (Table 1).

Investigators identified at least one contributing factor in 500 (62.5%) outbreaks. Outbreaks can have more than one contributing factor, and 819 contributing factors were identified altogether. Of the 500 outbreaks with an identified contributing factor, 426 (85.2%) had at least one contamination factor, 129 (25.8%) had at least one proliferation factor (i.e., conditions allowed pathogens in food to grow), and 71 (14.2%) had at least one survival factor (i.e., pathogens survived processes designed to kill or reduce their numbers) Follow link to: (Table 2).

The top five contributing factors to foodborne illness outbreaks were all contamination related (Box 2). The most common contributing factor was other mode of contamination (excluding cross-contamination) by a worker who was suspected to have an infectious illness (104 [20.8%]). Other sources of contamination included contaminated raw food (88 [17.6%]), bare-hand contact with ready-to-eat (RTE) food by a food worker suspected to have an infectious illness (72 [14.4%]), cross-contamination of ingredients (68 [13.6%]), and other unspecified source of contamination (62 [12.4%]) (Table 2). Contributing factors associated with ill workers (i.e., bare-hand contact with RTE food, gloved-hand contact with RTE food, and other contamination by workers suspected of having an infectious illness) were identified in 205 (41.0%) outbreaks. The most common proliferation contributing factor was improper or slow cooling of hot food (53 [10.6%]), and the most common survival contributing factor was insufficient time or temperature during cooking or heat processing (33 [6.6%]).

Outbreak Establishment Characteristics

A majority of establishments with outbreaks were independently owned (473 of 725 [65.2%]) and served ≤300 meals (upper range = 8,500 meals) daily (440 of 725 [60.7%]) Follow link to:  (Table 3). Most were restaurants (712 of 875 [81.4%]), and 84.0% (735 of 875) served complex food items. Complex food items require a kill step (i.e., a process, such as cooking, that reduces or eliminates foodborne illness pathogens) and holding beyond same-day service, or a kill step and a combination of holding, cooling, reheating, and freezing. The most common menu type was American (485 of 875 [55.4%]). A majority (624 of 875 [71.3%]) of establishments received at least one critical violation on their last routine inspection before the outbreak.

Outbreak Establishment Policies

Most managers interviewed (665 of 725 [91.7%]) said their establishment had a policy requiring food workers to notify their manager when they were ill, and the policy was written (439 of 665 [66.0%]) Follow link to:  (Table 4). Approximately 75% (504 of 665 [75.8%]) had policies that required ill food workers to tell managers their symptoms; 452 (68.0%) specified vomiting or diarrhea (each) as symptoms workers needed to tell managers about. Fewer policies mentioned sore throat with fever (328 [49.3%]), lesion with pus (265 [39.8%]), and jaundice (182 [27.4%]). Only 23.0% (153) of policies listed all five symptoms workers needed to tell managers about.

Of the managers interviewed, most (620 of 725 [85.5%]) said that their establishment also had a policy restricting or excluding ill food workers from working, and these policies were written (387 of 620 [62.4%) Follow link to: (Table 5). A majority (431 of 620 [69.5%]) said these policies specified symptoms that would prompt restriction or exclusion. Nearly two thirds of policies specifically mentioned vomiting (406 [65.5%]) and diarrhea (410 [66.1%]) as symptoms that would require restriction or exclusion. Fewer policies mentioned sore throat with fever (283 [45.6%]), lesion with pus (231 [37.3%]), and jaundice (165 [26.6%]). Only 17.8% (129) of policies listed all five symptoms that would require restriction or exclusion.

Only 16.1% (117 of 725) of establishments had policies that included the four recommendations of the FDA Food Code that were assessed. These recommendations were to have a policy that required workers to tell a manager when they are ill, a policy that specified all five symptoms workers need to tell a manager about, a policy that restricted or excluded ill or infectious workers from working, and a policy that specified all five symptoms requiring restriction or exclusion. Fewer than half (316 of 725 [43.6%]) of managers said their establishments provided paid sick leave to any workers.

Discussion

During 2017–2019, norovirus was the most common cause of outbreaks in retail food establishments reported to NEARS, and the most common contributing factor was “other” contamination by a food worker suspected to have an infectious illness. Examples include non–cross-contamination sources such as aerosolized vomitus and outbreaks where investigators could not determine if the food worker was wearing gloves during food preparation. At least one of three contributing factors associated with suspected infectious workers (bare-hand contact with RTE food, gloved-hand contact with RTE food, and other contamination by a suspected infectious worker) was reported in 41.0% of the outbreaks. These findings are similar to those from the 2014–2016 NEARS surveillance period and in national outbreak data reported to NORS (3).

One way to help prevent foodborne illness in retail food establishments is to adopt comprehensive food safety policies. Such policies have been linked to improved food safety outcomes (e.g., increased frequency of equipment cleaning and proper date marking) (16). Establishment policies might also mitigate the size of outbreaks. Outbreak establishments with cleaning and glove use policies had smaller norovirus outbreaks than those without such policies. Moreover, the form of the policy was associated with outbreak size; outbreak establishments with written policies had smaller outbreaks than those with only verbally communicated policies (17).

Ill workers continue to play a substantial role in retail food establishment outbreaks (3,8,16), and comprehensive ill worker policies will likely be necessary to mitigate this public health problem. Restaurants with policies requiring workers to report illness to managers were less likely to have employees who worked while ill (18). Most outbreak establishments with manager interview data had written or verbally communicated policies requiring ill workers to tell managers when they were ill (91.7%) and restricting or excluding ill workers (85.5%) from working. However, managers indicated that their ill worker policies did not include all of the five symptoms of illness itemized in the FDA Food Code (i.e., vomiting, diarrhea, jaundice, sore throat with fever, and lesion with pus). Vomiting and diarrhea, two of the most common symptoms of foodborne illness, were specified most often (range = 65.5%–66.1% of establishments with outbreaks). However, approximately one third of establishments did not specify these two symptoms. Policies might need to be comprehensive to be effective; only 16.1% of outbreak establishments with manager interview data had all four components of ill worker policies that were assessed.

Although research suggests that written policies are more effective than verbally communicated policies (17), the existence of written policies alone is unlikely to markedly reduce incidence of foodborne illness outbreaks in retail establishments. Policy implementation and compliance are also important. Recent FDA modeling data indicated that high compliance with policies excluding ill food employees substantially decreased predicted illnesses (19). Moreover, policies that are regulatory requirements might have greater likelihood of effectiveness. For example, states with a regulatory requirement to exclude ill employees from working had lower norovirus outbreak rates than states without this requirement (20). A lack of regulatory requirements might reduce the likelihood of officials thoroughly assessing policy components during inspections. In contrast, policies assessed during inspections are likely prioritized for implementation and enforcement.

Food workers report numerous reasons for working when ill, such as loss of pay and perceived social pressure (18). NEARS data demonstrate that fewer than half of establishments with outbreaks provided paid sick leave to at least one food worker. Research suggests that paid sick leave might improve food safety outcomes. Expanded paid sick leave in a restaurant chain reduced the incidence of working while ill among front-line food service workers (21), and supportive paid sick leave regulations were found to be associated with decreased foodborne illness rates (22). A multilayered approach addressing implementation and enforcement might be required to prevent ill employees from working. Such an approach not only includes adoption and enforcement of comprehensive written ill worker policies but also enhances training, management plans to continue operations when a worker is absent (e.g., on-call staffing), and adoption of a food safety culture where absenteeism due to illness is not penalized (17,18,23).

Approximately half of the outbreaks reported to NEARS were caused by a bacteria, including Salmonella, that either exist at unsafe levels in foods (e.g., Escherichia coli O157:H7 in ground beef) or have contaminated food at a certain point in the food production chain. Bacteria on food can be eliminated or reduced through a kill step (e.g., cooking). However, if contaminated food does not go through a kill step or the kill step is inadequate (e.g., undercooking), the bacteria can survive and proliferate, particularly when the food is not maintained at adequate temperatures. Moreover, the majority of establishments with outbreaks engaged in complex processes that might have increased the likelihood of pathogen proliferation or survival because these processes involve riskier food preparation practices (e.g., reheating, cooling, and holding). Taken together, these findings are a reminder that following Food Code guidance on cross-contamination prevention and proper cooking, reheating, holding, and cooling of food is important to prevent bacterial illness (4).

Limitations

The findings in this report are subject to at least six limitations. First, data are reported voluntarily by a limited number of state and local health departments. Although these health departments represent geographically diverse areas, the foodborne illness outbreaks reported to NEARS might not be representative of all U.S. outbreaks. Second, not all outbreaks are identified, reported, or investigated; therefore, the extent to which the outbreaks reported to NEARS represent all outbreaks that occurred in the reporting areas is unknown. Third, outbreak investigation procedures and practices vary across state and local health departments, possibly resulting in systematic differences in data collection. Fourth, manager interview data were based on managers’ recall of policies and practices. For example, managers were asked to list symptoms in their establishments’ ill worker policies from memory. Although this interview method was chosen so that findings were more reflective of conditions and practices in the establishment, written policies in place might have been more comprehensive than captured in the data. Fifth, manager interviews might also be subject to social desirability bias, in which respondents overreport socially desirable conditions (e.g., the existence of food safety policies in their establishments). Finally, these data were collected before the COVID-19 pandemic. Evidence suggests that retail food establishments changed at least some of their practices during the pandemic (21), and certain changes might be permanent. Thus, the data reported might not be representative of current practices.

Future Directions

Future NEARS analyses will focus on stratifying data by etiologic agent to identify the contributing factors of outbreaks linked with specific agents (e.g., Salmonella) and foods (e.g., poultry and vegetables). Regression modeling can be used to assess risk factors associated with specific agents. Root cause analyses of norovirus outbreaks, in particular, might be useful in identifying policies and practices to reduce outbreaks associated with retail establishments. Future analyses also will identify longitudinal trends in NEARS data, such as whether the percentage of establishments with outbreaks that have comprehensive ill worker policies has changed since 2014 when NEARS was launched. Finally, matching NEARS environmental health data with NORS epidemiologic and laboratory data will enable the examination of associations between establishment policies and practices and outbreak size. An analysis of this type found that the existence of certain food safety policies in establishments with outbreaks (environmental health data) were linked with smaller norovirus outbreaks (epidemiologic data) (17). These types of findings can help guide and develop outbreak prevention efforts.

Conclusion

NEARS provides important environmental data on retail food establishments that have had foodborne illness outbreaks. These data increase knowledge about the environmental context of outbreaks and contribute to generating and testing hypotheses about outbreak causes and prevention. The analyses identified primary contributing factors to outbreaks and gaps in establishment policies related to ill workers. The findings in this report can help public health authorities and the retail food establishment industry develop data-driven, effective approaches to preventing foodborne illness outbreaks (7).

Acknowledgments

Laurie Williams, Food and Drug Administration; Yasmine Sharifai, National Center for Environmental Health, CDC; National Environmental Assessment Reporting System health department staff members. Eight health departments (California; Harris County, Texas; Minnesota; New York City; New York; Rhode Island; Southern Nevada Health District; and Tennessee) received funding through a CDC grant award under CDC-RFAEH05-013.

Corresponding author: Erin D. Moritz, Division of Environmental Health Science and Practice, National Center for Environmental Health, CDC. Telephone: 404-498-2756; Email: emoritz@cdc.gov.

¹Division of Environmental Health Science and Practice, National Center for Environmental Health, CDC, Atlanta, Georgia; ²Oak Ridge Institute for Science and Education, Oak Ridge, Tennessee; ³Bureau of Environmental Surveillance and Policy, New York City Department of Health and Mental Hygiene, New York, New York; ⁴Environmental Health Services, Baltimore County Department of Health, Baltimore, Maryland

Conflicts of Interest

All authors have completed and submitted the International Committee of Medical Journal Editors form for disclosure of potential conflicts of interest. No potential conflicts of interest were reported.

* See e.g., 45 C.F.R. part 46.102(l)(2), 21 C.F.R. part 56; 42 U.S.C. §241(d); 5 U.S.C. §552a; 44 U.S.C. §3501 et seq.

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