Foodborne Disease Outbreaks, 2018

Background

Known pathogens are estimated to cause 9.4 million foodborne illnesses each year in the United States.1 Although relatively few of these illnesses occur in the setting of a recognized outbreak, data collected during outbreak investigations provide insight into the pathogens and foods that cause illness. Public health officials, regulatory agencies, and the food industry can use these data to inform efforts to prevent foodborne illness.

Findings

Outbreaks were reported by public health officials from 50 states, Washington, D.C., and Puerto Rico (Figure). The median reporting rate per million population was 5.22 outbreaks; rates ranged from 2.28 in Oklahoma to 16.83 in Kansas.

Etiologic agents

A single etiologic agent was confirmed in 471 (45%) outbreaks, resulting in 13,591 (68%) illnesses (Table 1).

Salmonella was the most common cause of confirmed, single-etiology outbreaks, accounting for 147 (31%) outbreaks and 4,792 (35%) illnesses. Among the 138 confirmed Salmonella outbreaks with a serotype reported, the most common serotypes were

1. Enteritidis (29 outbreaks, 21%)
2. Typhimurium (13, 9%)
3. Newport (12, 9%)
4. I 4,[5], 12:i:- (8, 6%)
5. Infantis (7, 5%)
6. Braenderup (6, 4%)

Norovirus was the next most common cause of confirmed, single-etiology outbreaks, accounting for 115 (24%) outbreaks and 3,969 (29%) illnesses. Cyclospora caused 31 confirmed, single-etiology outbreaks and Shiga toxin-producing E. coli (STEC) caused 29 confirmed, single-etiology outbreaks, of which 16 (55%) were caused by serogroup O157. Among all outbreaks, 252 (24%) reports did not include an etiologic agent.

Among confirmed, single-etiology outbreaks, the most outbreak-associated hospitalizations were caused by

1. Salmonella (984 hospitalizations, 67%)
2. STEC (231, 16%)
3. Norovirus (47, 3%)

Outbreaks caused by Clostridium botulinum resulted in the highest percentage of ill persons hospitalized (7 hospitalizations, 100%), followed by Listeria monocytogenes (38, 88%), hepatitis A virus (HAV) (19, 59%), and Enteroinvasive E. coli (28, 54%).

Among the 21 deaths reported, 19 (90%) were attributed to bacterial etiologies (Salmonella [7], STEC [6], Listeria [4], and Shigella [2]). Two deaths were attributed to HAV.

Food categories implicated

A confirmed or suspected food source was reported for 453 (43%) outbreaks. In 267 (59%) of these outbreaks, the food could be classified into a single category (Table 2a).

The categories most commonly implicated were

1. Mollusks (49 outbreaks, 18%)
2. Fish (46, 17%)
3. Chicken (35, 13%)
4. Beef (26, 10%)

The most outbreak-associated illnesses were from

1. Beef (961 illnesses, 10%)
2. Chicken (761, 8%)
3. Vegetable row crops (624, 6%)
4. Pork (548, 6%)

Etiologic agents and food category pairs

The pathogen-food category pairs responsible for most outbreaks with a single confirmed etiologic agent were Vibrio parahaemolyticus in mollusks (24 outbreaks), ciguatoxin in fish (20), Cyclospora in herbs (18) and scombroid toxin (histamine) in fish (18) (Table 2b).

The pathogen-food category pairs responsible for the most illnesses in outbreaks with a single confirmed etiologic agent were Salmonella in chicken (497 illnesses), Salmonella in beef (488), STEC in vegetable row crops (388), and Cyclospora in herbs (308).

The pathogen-food category pairs responsible for the most hospitalizations in outbreaks with a single confirmed etiologic agent were STEC in vegetable row crops (152 hospitalizations), Salmonella in beef (132), Salmonella in chicken (95), and Salmonella in pork (60).

Deaths were reported for the following pathogen-food category pairs: STEC in vegetable row crops (5 deaths), HAV in crustaceans (2), Salmonella in chicken, STEC in beef, and Salmonella in fruits (1 each).

Location of food preparation

Among the 925 outbreaks and 15,391 illnesses with a reported single location where food was prepared, 631 outbreaks (68%) and 7,797 associated illnesses (51%) were attributed to foods prepared in a restaurant (Table 3).

Among these, sit-down dining restaurants were the type of restaurant most commonly reported (445 outbreaks, 48%).

Multistate outbreaks with first identified illness onset during 2018

These outbreaks involved a median of six and a half states (range 2–37).

Forty-one multistate outbreaks were caused by Salmonella; the most frequent serotypes were Typhimurium (5 outbreaks) and Newport (4). Thirteen multistate outbreaks were caused by STEC, nine of which were due to serogroup O157. The remaining multistate outbreaks were caused by Listeria (4 outbreaks), Vibrio parahaemolyticus (4), Cyclospora (2), Campylobacter (1), norovirus (1), multiple etiologies (1), and an unknown etiology (1).

The confirmed food sources for multistate Salmonella outbreaks were chicken (2 outbreaks), eggs (2), alfalfa sprouts, beef, cake mix, chicken salad, English cucumber, ground beef, ground turkey, melon, pasta salad, puffed wheat cereal, tahini, turkey, and whey powder (1 each). In addition, pork (4 outbreaks), chicken (2), onions (2), frozen pizza, frozen waffles, raw tuna, and sushi (1 each) were suspected sources. A food was not identified for 12 multistate outbreaks caused by Salmonella.

The confirmed food sources for multistate STEC outbreaks were romaine lettuce (3 outbreaks), ground beef (2), chicken salad, flour, and iceberg lettuce (1 each). Ground beef (2 outbreaks) and leafy greens (1) were suspected sources. Two multistate STEC outbreaks did not have a food identified.

Queso fresco type cheese was the suspected source in one multistate Listeria outbreak and three multistate Listeria outbreaks did not have a food identified.

The confirmed food sources for multistate Vibrio parahaemolyticus outbreaks were raw oysters (3 outbreaks) and crab (1).

Salad mix containing lettuce and carrots and vegetable trays were suspected sources in multistate outbreaks caused by Cyclospora (1 outbreak each), chicken liver was the confirmed source in one multistate Campylobacter outbreak, oysters were the confirmed source in one multistate norovirus outbreak, and raw oysters were the confirmed source in a multistate outbreak caused by multiple etiologies.

One multistate outbreak had an unknown etiology and an unknown food source.

Multistate outbreaks spanning multiple years

Ten multistate outbreaks investigated during 2018 in which the last outbreak-associated illness occurred in 2018 were not included in the 2018 tally because the first outbreak-associated illness occurred before 2018.

Six were caused by Salmonella; the confirmed food sources were chicken, dried coconut, frozen shredded coconut, kratom, shell eggs, and sprouts; all had the first illness onset in 2017.

The remaining four outbreaks were caused by Listeria. The confirmed food sources were country style deli ham (first illness onset in 2012) and ready-to-eat pork products (2017). One outbreak caused by Listeria had pasteurized cheese as the suspected source (2017) and in one Listeria outbreak no food was identified (2015).

Multistate outbreaks spanning multiple years may be identified more frequently in recent years due to the increased use of whole genome sequencing technology, especially for Salmonella and Listeria, which enhances the ability to link cases with a long duration between onset of illness.

Recalls

Twenty-seven outbreaks resulted in product recalls.

The foods recalled after being implicated in outbreaks for which the exposure occurred in a single state were cheddar flavored crackers, chicken enchiladas, chicken wings, jarred tuna, meatballs, pasteurized apple juice, raw milk, raw oysters, and shell eggs (1 outbreak each).

In multistate outbreaks, recalled products included ground beef (3 outbreaks), raw oysters (2), cake mix, cantaloupe and watermelon, chicken, chicken salad, eggs, flour, ground turkey, pasta salad, puffed wheat cereal, salad mix, tahini, vegetable trays, and whey powder (1 each).

The data

Figure

_{^*Cut points for outbreak rate categories determined using quartiles. Legend differs for each map.}

_{^†Reported outbreaks in each state. Puerto Rico reported eight outbreaks and Washington, D.C., reported eight outbreaks (not shown).}

_{^‡Includes the 67 multistate outbreaks (i.e., outbreaks in which exposure occurred in more than one state) with a confirmed or suspected etiology assigned as an outbreak to each state involved. In total, 68 multistate outbreaks involved a median of six and a half states (range: 2–37).}

_{^§Reporting agencies are to consider an etiology confirmed if it meets confirmation criteria; otherwise, it is considered suspected. Etiologic agents that are not listed in confirmation criteria or that are not known to cause illness are sometimes reported as confirmed or suspected etiologies.}

Table 1

_{Abbreviations: CE = confirmed etiology, SE = suspected etiology}

_{^*Etiology reported to FDOSS by the reporting site as confirmed or suspected. If at least one etiology was laboratory-confirmed, the outbreak was considered to have a confirmed etiology. If no etiology was laboratory-confirmed, but an etiology was reported based on clinical or epidemiologic features, the outbreak was considered to have a suspected etiology.}

_{^†Salmonella serotypes causing more than five outbreaks were Enteritidis (31 outbreaks), Typhimurium (14), Newport (13), unknown serotype (9), I 4,[5],12:i:- (8), Braenderup (7), Infantis (7), and Saintpaul (6). Serotypes reported here include both confirmed and suspected etiologies.}

_{^‡Campylobacter jejuni (19 outbreaks), Campylobacter unknown species (11), and Campylobacter coli (1), and Campylobacter multiple species (1).}

_{^§STEC serogroups O157 (19 outbreaks), unknown serogroup (8), O26 (7), O103 (2), O121 (1), O61 (1), and multiple serogroups (1). Serogroups reported here include both confirmed and suspected etiologies}

_{^¶Shigella sonnei (6 outbreaks), Shigella flexneri (3), and Shigella unknown species (1).}

_{^**The denominator for the etiology percentages is the single etiology total. The denominator for the single etiology, multiple etiologies, and unknown etiology is the total. Because of rounding, numbers might not add up to the single etiology total or the total.}

_{^††If at least two etiologies are confirmed in an outbreak, it is considered a confirmed multiple etiology outbreak; otherwise it is considered a suspected multiple etiology outbreak.}

_{^‡‡An etiologic agent was not confirmed or suspected based on clinical, laboratory, or epidemiologic information.}

Table 2a

_{^*Interagency Food Safety Analytics Collaboration (IFSAC) food categorization scheme}

_{^†Bivalve mollusks (48 outbreaks) and non-bivalve mollusks (1).}

_{^‡Unpasteurized dairy products (9 outbreaks), and pasteurization unknown (4), pasteurized dairy products (3).}

_{^§Bulbs (2 outbreaks).}

_{^¶Solanaceous seeded vegetables (4 outbreaks), legumes (2), and vine-grown seeded vegetables (1).}

_{^**Leafy vegetables (11 outbreaks) and stem vegetables (2).}

_{^††Sub-tropical fruits (3 outbreaks), fruits not further classified (1), melons (1), pome fruits (1), and small fruits (1).}

_{^‡‡Grains (5 outbreaks), grains and beans not further classified (2).}

_{^§§Seeds (1 outbreak).}

_{^¶¶The denominator for the food category percentages is the "food reported, attributed to a single food category" total. The denominator for the "food reported attributed to a single food category", "food reported, not attributed to a single food category", and "No food reported" is the total. Because of rounding, numbers might not add up to the "food reported, attributed to a single food category" total or the total.}

Table 2b

Most common pathogen-food category pairs^* resulting in outbreaks, outbreak-associated illnesses, hospitalizations, and deaths — Foodborne Disease Outbreak Surveillance System, United States, 2018

_{^*Pathogen-food category pairs are limited to outbreaks with an identified food vehicle and a single, confirmed etiology.}

_{^†Interagency Food Safety Analytics Collaboration (IFSAC) food categorization scheme.}

Table 3

_{^*The denominator for the location percentages is the single location total. The denominator for the single location, multiple locations, and unknown location is the total. Because of rounding, numbers might not add up to the single location total or the total.}

Table 4

About the data

Suggested citation

Centers for Disease Control and Prevention (CDC). Surveillance for Foodborne Disease Outbreaks, United States, 2018, Annual Report. Atlanta, Georgia: U.S. Department of Health and Human Services, CDC, 2026.