Quantifying the sensitivity of scent detection dogs to identify fecal contamination on raw produce.

Consumption of raw produce commodities has been associated with foodborne outbreaks in the United States. In a recent Centers for Disease Control and Prevention report outlining the incidence of food-related outbreaks from 1998 to 2008, produce of all kinds were implicated in 46% of illnesses and 23% of deaths. Methods that quickly identify fecal contamination of foods, including produce, will allow prioritization of samples for testing during investigations and perhaps decrease the time required to identify specific brands or lots. We conducted a series of trials to characterize the sensitivity and specificity of scent detection dogs to accurately identify fecal contamination on raw agricultural commodities (romaine lettuce, spinach, cilantro, and roma tomatoes). Both indirect and direct methods of detection were evaluated. For the indirect detection method, two dogs were trained to detect contamination on gauze pads previously exposed to produce contaminated with feces. For the direct detection method, two dogs were trained to identify fecal contamination on fresh produce. The indirect method did not result in acceptable levels of sensitivity except for the highest levels of fecal contamination (25 g of feces). Each dog had more difficulty detecting fecal contamination on cilantro and spinach than on roma tomatoes. For the direct detection method, the dogs exhibited >75% sensitivity for detecting ≥0.25 g of feces on leafy greens (cilantro, romaine lettuce, and spinach) and roma tomatoes, with sensitivity declining as the amount of feces dropped below 0.025 g. We determined that use of a scent detection dog to screen samples for testing can increase the probability of detecting ≥0.025 g of fecal contamination by 500 to 3,000% when samples with fecal contamination are rare (≤1%).

A novel approach to enhance food safety: industry-academia-government partnership for applied research.

An independent collaborative approach was developed for stimulating research on high-priority food safety issues. The Fresh Express Produce Safety Research Initiative was launched in 2007 with $2 million in unrestricted funds from industry and independent direction and oversight from a scientific advisory panel consisting of nationally recognized food safety experts from academia and government agencies. The program had two main objectives: (i) to fund rigorous, innovative, and multidisciplinary research addressing the safety of lettuce, spinach, and other leafy greens and (ii) to share research findings as widely and quickly as possible to support the development of advanced safeguards within the fresh-cut produce industry. Sixty-five proposals were submitted in response to a publicly announced request for proposals and were competitively evaluated. Nine research projects were funded to examine underlying factors involved in Escherichia coli O157:H7 contamination of lettuce, spinach, and other leafy greens and potential strategies for preventing the spread of foodborne pathogens. Results of the studies, published in the Journal of Food Protection, help to identify promising directions for future research into potential sources and entry points of contamination and specific factors associated with harvesting, processing, transporting, and storing produce that allow contaminants to persist and proliferate. The program provides a model for leveraging the strengths of industry, academia, and government to address high-priority issues quickly and directly through applied research. This model can be productively extended to other pathogens and other leafy and nonleafy produce.

Escherichia coli O157:H7 in feral swine near spinach fields and cattle, central California coast.

We investigated involvement of feral swine in contamination of agricultural fields and surface waterways with Escherichia coli O157:H7 after a nationwide outbreak traced to bagged spinach from California. Isolates from feral swine, cattle, surface water, sediment, and soil at 1 ranch were matched to the outbreak strain.

Incidence and tracking of Escherichia coli O157:H7 in a major produce production region in California.

Fresh vegetables have become associated with outbreaks caused by Escherichia coli O157:H7 (EcO157). Between 1995-2006, 22 produce outbreaks were documented in the United States, with nearly half traced to lettuce or spinach grown in California. Outbreaks between 2002 and 2006 induced investigations of possible sources of pre-harvest contamination on implicated farms in the Salinas and San Juan valleys of California, and a survey of the Salinas watershed. EcO157 was isolated at least once from 15 of 22 different watershed sites over a 19 month period. The incidence of EcO157 increased significantly when heavy rain caused an increased flow rate in the rivers. Approximately 1000 EcO157 isolates obtained from cultures of>100 individual samples were typed using Multi-Locus Variable-number-tandem-repeat Analysis (MLVA) to assist in identifying potential fate and transport of EcO157 in this region. A subset of these environmental isolates were typed by Pulse Field Gel Electrophoresis (PFGE) in order to make comparisons with human clinical isolates associated with outbreak and sporadic illness. Recurrence of identical and closely related EcO157 strains from specific locations in the Salinas and San Juan valleys suggests that transport of the pathogen is usually restricted. In a preliminary study, EcO157 was detected in water at multiple locations in a low-flow creek only within 135 meters of a point source. However, possible transport up to 32 km was detected during periods of higher water flow associated with flooding. During the 2006 baby spinach outbreak investigation, transport was also detected where water was unlikely to be involved. These results indicate that contamination of the environment is a dynamic process involving multiple sources and methods of transport. Intensive studies of the sources, incidence, fate and transport of EcO157 near produce production are required to determine the mechanisms of pre-harvest contamination and potential risks for human illness.

Multistate shigellosis outbreak and commercially prepared food, United States.

In 2000, shigellosis traced to a commercially prepared dip developed in 406 persons nationwide. An ill employee may have inadvertently contaminated processing equipment. This outbreak demonstrates the vulnerability of the food supply and how infectious organisms can rapidly disseminate through point-source contamination of a widely distributed food item.

A multistate outbreak of Escherichia coli O157:H7 infection linked to consumption of beef tacos at a fast-food restaurant chain.

We investigated a multistate outbreak of Escherichia coli O157:H7 infections. Isolates from 13 case patients from California, Nevada, and Arizona were matched by pulsed-field gel electrophoresis subtyping. Five case patients (38%) were hospitalized, and 3 (23%) developed hemolytic uremic syndrome; none died. The median age was 12 years (range, 2-75 years), and 10 (77%) were female. Case-control studies found an association between illness and eating beef tacos at a national Mexican-style fast-food restaurant chain (88% of cases versus 38% of controls; matched OR, undefined; 95% confidence interval, 1.49 to infinity; P=.009). A trace-back investigation implicated an upstream supplier of beef, but a farm investigation was not possible. This outbreak illustrates the value of employing hospital laboratory-based surveillance to detect local clusters of infections and the effectiveness of using molecular subtyping to identify geographically dispersed outbreaks. The outbreak investigation also highlights the need for a more efficient tracking system for food products.

Industry practices and compliance with U.S. Food and Drug Administration guidelines among California sprout firms.

Since 1995, raw vegetable sprouts have been implicated as the vehicle of infection in 15 foodborne outbreaks involving Salmonella and 2 foodborne outbreaks involving Escherichia coli O157:H7. To reduce the numbers of sprout-related outbreaks, the U.S. Food and Drug Administration (FDA) published Guidance for Industry: Reducing Microbial Food Safety Hazards for Sprouting Seeds in 1999. Between October 2000 and April 2001, 61.5% (16 of 26) of the known commercial sprout firms in California were enrolled in a survey to evaluate the industry practices of California sprouting operations and to determine compliance with FDA guidelines. A standardized questionnaire was used to collect data on firm demographics and seed disinfection practices. Additionally, free chlorine levels in seed disinfection solutions were measured, and 48-h spent irrigation water samples were collected from each firm. The irrigation water was screened for Salmonella and E. coli O157:H7 with FDA-recommended test kits. Free chlorine levels in the treatment solutions ranged from 50 to 35,000 mg/liter (ppm), with a median of 14,000 mg/liter (ppm). Free chlorine levels were higher for firms producing alfalfa sprouts than for those producing only mung bean or soybean sprouts (P=0.03). Levels of free chlorine tended to be higher for firms using a calcium hypochlorite treatment solution than for firms using a sodium hypochlorite treatment solution (P=0.067). All 32 irrigation water samples screened for Salmonella tested negative. Of the irrigation water samples tested for E. coil O157:H7, 75% (24 of 32) tested negative, and 25% (8 of 32) tested presumptive positive. The eight presumptive positive samples were found to be negative after further testing. These results indicate that producers of alfalfa sprouts are generally achieving the FDA-recommended calcium hypochlorite level of 20,000 mg/liter (ppm), whereas mung bean sprout producers are not.

Alfalfa seed decontamination in a Salmonella outbreak.

Based on in vitro data, the U.S. Food and Drug Administration recommends chemical disinfection of raw sprout seeds to reduce enteric pathogens contaminating the seed coats. However, little is known about the effectiveness of decontamination at preventing human disease. In 1999, an outbreak of Salmonella enterica serotype Mbandaka occurred in Oregon, Washington, Idaho, and California. Based on epidemiologic and pulsed-field gel electrophoresis evidence from 87 confirmed cases, the outbreak was linked to contaminated alfalfa seeds grown in California's Imperial Valley. Trace-back and trace-forward investigations identified a single lot of seeds used by five sprout growers during the outbreak period. Cases of salmonellosis were linked with two sprout growers who had not employed chemical disinfection; no cases were linked to three sprout growers who used disinfection. This natural experiment provides empiric evidence that chemical disinfection can reduce the human risk for disease posed by contaminated seed sprouts.

An outbreak of food-borne illness associated with methomyl-contaminated salt.

CONTEXT: On January 5, 1999, the California Department of Health Services was notified of the repeated occurrence (December 21, 1998, and January 2, 1999) of gastrointestinal tract illness among patrons at a Thai restaurant in central California. OBJECTIVE: To identify the source of the outbreak. DESIGN: Case-control study; microbiological and toxicological laboratory testing of samples of food, stool, and vomitus. SETTING: Thai food restaurant in central California. PARTICIPANTS: Patrons of the restaurant. A case (n = 107) was defined as dizziness, nausea, or vomiting occurring in a person who ate at the restaurant between December 20, 1998, and January 2, 1999, with onset of symptoms within 2 hours of eating. A control (n = 169) was a person who ate at the restaurant during the same period but reported no symptoms. MAIN OUTCOME MEASURES: Odds ratios (ORs) of illness associated with food exposures; ORs of shifts during which illness occurred associated with certain cooks; laboratory results. RESULTS: The median latency period was 40 minutes from beginning eating to first symptom and was 2 hours to onset of diarrhea. The median duration of symptoms was 6 hours. Twenty-six persons (24%) visited the emergency department or were treated by a physician; no person required hospitalization. Patients reported nausea (95%), dizziness (72%), abdominal cramps (58%), headache (52%), vomiting (51%), chills (48%), and diarrhea (46%). Fifty-one cases (48%) included dizziness, lightheadedness, or a feeling of disequilibrium as the initial symptom. Illness was statistically associated with several foods and ingredients, but no single dish or ingredient explained a substantial number of cases. The analysis of food exposures included salt added by cooks, as estimated by using the amount of salt in the recipe for each dish and the amount of each dish eaten by respondents. This association was stronger with increasing levels of salt: ORs for illness among persons who consumed more than 0.42 to 0.84, more than 0.84 to 1.25, and more than 1.25 tsp of salt added to foods in the kitchen were 1.9 (95% confidence interval [CI], 0.6-5.7), 3.0 (95% CI, 1.0-8.8), and 4.0 (95% CI, 1.3-13.5) compared with persons who consumed less than 0.42 tsp (P value for trend =.004). Methomyl, a highly toxic carbamate pesticide, was identified in a sample of vomitus (20 ppm) and in salt taken from containers in the storeroom (mean, 5600 ppm) and the stovetop (mean, 1425 ppm). The oral toxic dose causing illness in 50% of those exposed to methomyl was estimated to be 0.15 mg/kg of body weight (estimated range, 0.09-0.31 mg/kg of body weight). The presence of cook A was associated with shifts during which cases of illness occurred (OR, 10.4; 95% CI, 1.2-157.4). CONCLUSION: This outbreak of gastrointestinal illness was associated with the consumption of food seasoned with methomyl-contaminated salt. To allow rapid assessment for further investigational and control measures by health officials, physicians should report suspected outbreaks of illness to public health departments, however trivial the symptoms or cause may seem.