Impact of the prevalence of different pathogens on the performance of sampling plans in lettuce products

Norovirus GII.17 Caused Five Outbreaks Linked to Frozen Domestic Bilberries in Finland, 2019

In March 2019, the Finnish Institute for Health and Welfare and Finnish Food Authority started an outbreak investigation after a notification of food business operators' recall of frozen bilberries due to a norovirus finding. A retrospective search was conducted in the food and waterborne outbreak notification system to identify the notifications linked to norovirus and consumption of bilberries in January-March 2019. Five outbreaks were found in which norovirus GII or GII.17 had been detected in patient samples. A pooled retrospective cohort study was performed for those four in which a questionnaire study had been done. A case was defined as a person with diarrhoea or vomiting within 2 days after consuming a meal studied at one of the outbreak locations. Of 79 participants, 45 (57%) cases were identified. Persons that had consumed foods containing unheated bilberries were three times more likely to get ill than those who had not consumed them (RR 3.1, CI 95% 1.2-8.1, p = 0.02). Norovirus GII.17 was found in 16/17 patient samples sent for further typing. Identical norovirus GII.17 was detected in frozen Finnish bilberries and patient samples. At the berry packaging premises, signs of norovirus GII contamination were found in packaging lines. A new procedure for extracting viral nucleic acid from food and environmental samples was used during the outbreak investigation. Consumption of industrially packed frozen berries as heated would be one of the means to prevent norovirus infections.

A systematic review and meta-analysis indicates a high risk of human noroviruses contamination in vegetable worldwide, with GI being the predominant genogroup

Human noroviruses (HuNoVs) are the most predominant viral agents of acute gastroenteritis. Vegetables are important vehicles of HuNoVs transmission. This study aimed to assess the HuNoVs prevalence in vegetables. We searched the Web of Science, Excerpta Medica Database, PubMed, and Cochrane databases until June 1, 2023. A total of 27 studies were included for the meta-analysis. Statistical analysis was conducted using Stata 14.0 software. This analysis showed that the pooled HuNoVs prevalence in vegetables was 7 % (95 % confidence interval (CI): 3-13) worldwide. The continent with largest number of studies was Europe, and the highest number of samples was lettuce. As revealed by the results of the subgroup meta-analysis, the prevalence of GI genogroup was the highest (3 %, 95 % CI: 1-7). A higher prevalence was seen in vegetables from farms (18 %, 95 % CI: 5-37), while only 4 % (95 % CI: 1-8) in retail. The HuNoVs prevalence of ready-to-eat vegetables and non-ready-to-eat vegetables was 2 % (95 % CI: 0-8) and 9 % (95 % CI: 3-16), respectively. The prevalence by quantitative real time RT-PCR was 8 % (95 % CI: 3-15) compared to 3 % (95 % CI: 0-13) by conventional RT-PCR. Furthermore, the HuNoVs prevalence in vegetables was 6 % (95 % CI: 1-14) in ISO pretreatment method and 8 % (95 % CI: 1-19) in non-ISO method, respectively. This study is helpful in comprehensively understanding the prevalence of HuNoVs contamination in vegetables worldwide.

Prioritization of vegetable-borne biological hazards in Argentina using a multicriteria decision analysis tool

Vegetables, especially those eaten raw, have been implicated in several foodborne disease outbreaks. Since multiple vegetable matrices and hazards are involved, risk managers have to prioritize those with the greatest impact on public health to design control strategies. In this study, a scientific-based risk ranking of foodborne pathogens transmitted by leafy green vegetables in Argentina was performed. The prioritization process included hazard identification, evaluation criteria identification and definition, criteria weighting, expert survey design and selection and call for experts, hazard score calculation, hazard ranking and variation coefficient, and result analysis. Regression tree analysis determined four risk clusters: high (Cryptosporidum spp., Toxoplasma gondii, Norovirus), moderate (Giardia spp., Listeria spp., Shigella sonnei), low (Shiga toxin-producing Escherichia coli, Ascaris spp., Entamoeba histolytica, Salmonella spp., Rotavirus, Enterovirus) and very low (Campylobacter jejuni, hepatitis A virus and Yersinia pseudotuberculosis). Diseases caused by Norovirus, Cryptosporidium spp. and T. gondii do not require mandatory notification. Neither viruses nor parasites are included as microbiological criteria for foodstuff. The lack of outbreak studies did not allow to accurately identify vegetables as a source of Norovirus disease. Information on listeriosis cases or outbreaks due to vegetable consumption was not available. Shigella spp. was the main responsible for bacterial diarrhea, but it has not been epidemiologically associated with vegetable consumption. The quality of the available information for all hazards studied was very low and low. The implementation of good practice guidelines throughout the entire vegetable production chain could prevent the presence of the identified hazards. The current study allowed the identification of vacancy areas and could help reinforce the need for performing epidemiological studies on foodborne diseases potentially associated with vegetable consumption in Argentina.

Meta-analysis of the prevalence of the main human pathogens in vegetables, with emphasis on lettuce

This meta-analysis aims to summarize the available information on the prevalence of the main human pathogenic microorganisms in vegetables, with emphasis on lettuce (Lactuca sativa). The database searches included scientific papers from 1980 to 2019, without language restrictions. Inclusion criteria were prevalence or incidence studies published in peer-reviewed journals reporting the total number of vegetable samples studied and the number of samples positive for the presence of the studied pathogens. The target pathogens were grouped into the following categories: bacteria, parasites and viruses. Results of different vegetable types, years of sampling, analyzed regions or species of microorganisms reported in the same article were considered as different studies. Therefore, each scientific article may contain several studies. Multilevel random-effect meta-analysis models were fitted to estimate the mean occurrence rate of pathogenic microorganisms and to compare them with different factors potentially associated with the outcome. Overall, the prevalence of bacterial, parasitic and viral pathogens in vegetables was relatively low. The mean prevalence of bacterial hazards was < 0.023, with the exception of S. aureus, whose prevalence was estimated at 0.096. The mean occurrence rates of parasites and viruses were 0.067 (95 % CI: 0.056-0.080) and 0.079 (95 % CI: 0.054-0.113), respectively. The prevalence of pathogenic E. coli and parasites increased as the year of publication of the scientific articles progressed, whereas the prevalence of the other bacterial pathogens and enteric viruses was steady. The types of vegetables evaluated did not affect pathogen prevalence. The prevalence of pathogenic microorganisms differed according to the continent of origin, except for E. coli O157:H7 and parasites. The prevalence of pathogens in vegetables is of public health importance, especially in vegetable types that are eaten raw, without thermal treatment to inactivate pathogens. This meta-analysis results show the need to apply proper sanitation methods to treat raw vegetables in order to avoid foodborne infections.

Extraction of human noroviruses from leafy greens and fresh herbs using magnetic silica beads

Consumption of leafy greens and to a lesser extent fresh herbs has been associated with several foodborne outbreaks including human norovirus (HuNoV). However, the extraction and detection of viruses from these matrices present multiple challenges such as low recovery yields and relatively high PCR inhibition. A new magnetic silica bead based (MSB) extraction protocol was developed and used to recover norovirus from leafy greens and fresh herbs. The performance results were compared to the ISO 15216-1:2017 standard. The HuNoV GII.4 and GI.5 recovery yields from spiked lettuce using the MSB extraction protocol range from 33 to 82%. There was a good correlation between murine norovirus (MNV) and HuNoV recovery yields from fresh herbs and leafy greens. No reverse-transcriptase quantitative polymerase chain reaction (RT-qPCR) inhibition was detected from leafy green extracts using the MSB methodology. The selected commercial RT-qPCR detection kit had a major impact on RT-qPCR inhibition levels detected in the ISO 15216-1:2017 RNA extracts. RNase treatment was used to estimate genome recovery from HuNoV with intact capsids. This treatment resulted in similar HuNoV and MNV recovery yields. Between 2019 and 2020, the MSB protocol was used to conduct a survey of HuNoV in domestic and imported leafy greens and fresh herbs sold at retail in Canada. All of the 280 samples tested were negative. Overall, the use of MSB was shown to be an efficient approach to recover HuNoV from leafy greens and certain types of fresh herbs and to conduct surveys.

A Potentiometric Electronic Tongue as a Discrimination Tool of Water-Food Indicator/Contamination Bacteria

Microorganism assessment plays a key role in food quality and safety control but conventional techniques are costly and/or time consuming. Alternatively, electronic tongues (E-tongues) can fulfill this critical task. Thus, a potentiometric lab-made E-tongue (40 lipid sensor membranes) was used to differentiate four common food contamination bacteria, including two Gram positive (Enterococcus faecalis, Staphylococcus aureus) and two Gram negative (Escherichia coli, Pseudomonas aeruginosa). Principal component analysis and a linear discriminant analysis-simulated annealing algorithm (LDA-SA) showed that the potentiometric signal profiles acquired during the analysis of aqueous solutions containing known amounts of each studied bacteria allowed a satisfactory differentiation of the four bacterial strains. An E-tongue-LDA-SA model (12 non-redundant sensors) correctly classified 98 ± 5% of the samples (repeated K-fold-CV), the satisfactory performance of which can be attributed to the capability of the lipid membranes to establish electrostatic interactions/hydrogen bonds with hydroxyl, amine and/or carbonyl groups, which are comprised in the bacteria outer membranes. Furthermore, multiple linear regression models, based on selected subsets of E-tongue sensors (12–15 sensors), also allowed quantifying the bacteria contents in aqueous solutions (0.993 ± 0.011 ≤ R2 ≤ 0.998 ± 0.005, for repeated K-fold-CV). In conclusion, the E-tongue could be of great value as a preliminary food quality and safety diagnosis tool.

Systematic Review and Meta-analysis: Salmonella spp. prevalence in vegetables and fruits

In this study, a systematic review and a meta-analysis were conducted to analyse recent worldwide information about the prevalence of Salmonella spp. in vegetables and fruits to estimate the effect of the different processes such as washing, cutting or disinfection, and place of sampling. A systematic search was conducted for articles from 2014 to 2020 published to date regarding prevalence of Salmonella spp. in vegetables and fruits, without excluding material by location, or author. It was possible to determine eight categories for vegetables and fruits in comparison with the meta-analysis which showed five categories due to data availability. Results showed prevalence for Salmonella spp. of 0.1%, 0.2%, 13.7%, 0.1%, and 0% for fruits, leafy vegetables, mixed vegetables related to ready-to-eat salads (RTE), tubercles, and tomatoes, respectively. Moreover, categories such as fruits, tubercles, and tomatoes as associated with different types of preparations and places of sampling (Retail stores, fresh products wholesale, street markets, distribution centers, farms, and processing plants) did not present a significant combined effect on the prevalence of Salmonella spp. Likewise, leafy, and mixed vegetables showed differences associated with a type of processing, where leafy fresh unprocessed vegetables had a significant positive effect on the prevalence of the pathogen regarding the RTE products. These findings may be useful for the construction of a quantitative model of risk assessment as a means to characterize the differences among the sort of vegetable, fruit, type of processing, and place of sampling.

Agricultural Detection of Norovirus and Hepatitis A Using Fecal Indicators: A Systematic Review

Fresh-produce consumers may be at risk of pathogen infection due to fecal contamination of the agricultural environment. Indicators of fecal contamination may be used as a proxy to evaluate the potential presence of human pathogens, such as norovirus and hepatitis A, on agricultural samples. The objective of this systematic review was to determine whether the presence of human norovirus or hepatitis A was associated with microbial indicators in agricultural samples including fresh produce, equipment surfaces, and hands. Four databases (Embase, PubMed, Web of Science, and Agricola) were systematically searched and fifteen articles met inclusion and exclusion criteria. After data extraction, individual indicator-pathogen relationships were assessed using Cohen's Kappa coefficient. The level of agreement between norovirus with adenovirus was 0.09 (n = 16, 95% CI -0.05, 0.23), indicating poor agreement using Landis and Koch's criterion. Similarly, the Kappa coefficient between norovirus with E. coli (κ = 0.04, n = 14, 95% CI -0.05, 0.49) or total coliforms (κ = 0.03, n = 4, 95% CI -0.01, 0.02) was also poor. The level of agreement between hepatitis A with adenovirus (κ = -0.03, n = 3, 95% CI -0.06, 0.01) or fecal coliforms (κ = 0, n = 1, 95% CI 0, 0) was also poor. There were moderate relationships between hepatitis A with E. coli (κ = 0.49, n = 3, 95% CI 0.28, 0.70) and total coliforms (κ = 0.47, n = 2, 95% CI 0.47, 0.47). Based on these limited results, common indicator organisms are not strong predictors of the presence of norovirus and hepatitis A virus in the agricultural environment.

Interaction between norovirus and Histo-Blood Group Antigens: A key to understanding virus transmission and inactivation through treatments?

Human noroviruses (HuNoVs) are a main cause of acute gastroenteritis worldwide. They are frequently involved in foodborne and waterborne outbreaks. Environmental transmission of the virus depends on two main factors: the ability of viral particles to remain infectious and their adhesion capacity onto different surfaces. Until recently, adhesion of viral particles to food matrices was mainly investigated by considering non-specific interactions (e.g. electrostatic, hydrophobic) and there was only limited information about infectious HuNoVs because of the absence of a reliable in vitro HuNoV cultivation system. Many HuNoV strains have now been described as having specific binding interactions with human Histo-Blood Group Antigens (HBGAs) and non-HBGA ligands found in food and the environment. Relevant approaches to the in vitro replication of HuNoVs were also proposed recently. On the basis of the available literature data, this review discusses the opportunities to use this new knowledge to obtain a better understanding of HuNoV transmission to human populations and better evaluate the hazard posed by HuNoVs in foodstuffs and the environment.

Suitability of centrifuge water for detecting the presence of Escherichia coli versus finished fresh-cut lettuce testing

Fresh produce causes most foodborne outbreaks in the USA, and it is also considered a hazardous food product in other areas of the world such as Europe. The outbreaks attributed to fresh produce increase the focus of producers on hygiene to minimize exposure to food hazards. The fresh produce industry has the urgent need to detect if there are production lots contaminated with pathogenic microorganisms before distribution. Although the industry is mostly using end-product testing for the detection of target microorganisms, previous studies have evaluated the suitability of different sampling points within the production line of a fresh-cut processing plant. In the present study, the centrifuge effluent water was assessed as an alternative sampling point to end-product testing. E. coli was selected as an index microorganism of the presence of pathogens. The presence of E. coli was assessed in centrifuge effluent water, and fresh-cut lettuce from a commercial fresh-cut produce processing line (n = 95). The rate of false positives and negatives, as well as the specificity, sensitivity, and efficiency of the alternative method were calculated. The mean population of E. coli in positive water samples was 0.86 log cfu/100 mL, while the mean population of E. coli in positive fresh-cut lettuce samples was 0.23 log cfu/g. The proportion of positive samples in centrifuge effluent water and lettuce was similar (≈20%), and most of the results in both matrices were coincident (81.1%). However, the alternative method was not reliable due to its low sensitivity, as only 47.6% of the lettuce samples positive for E. coli could be matched with positive water samples.

Irrigating Lettuce with Wastewater Effluent: Does Disinfection with Chlorine Dioxide Inactivate Viruses?

Reclaimed water obtained from urban wastewater is currently being used as irrigation water in water-scarce regions in Spain. However, wastewater can contain enteric viruses that water reclamation treatment cannot remove or inactivate completely. In the present study, greenhouse-grown baby lettuce ( L.) was irrigated with secondary treatment effluent from a wastewater treatment plant untreated and treated using chlorine dioxide (ClO). The effect of ClO treatment on the physicochemical characteristics and the presence of enteric viruses in irrigation water and lettuce was assessed. The presence of human noroviruses genogroups I and II (NoV GI and NoV GII), and human astroviruses (HAstV), was analyzed by real-time polymerase chain reaction (RT-qPCR). Additionally, to check for the loss of infectivity induced by the disinfection treatment, positive samples were re-analyzed after pretreatment with the intercalating dye PMAxx before RNA extraction and RT-qPCR. There were no significant differences in the proportion of positive samples and the concentration of enteric viruses between treated and untreated reclaimed water without PMAxx pretreatment ( > 0.05). A significantly lower concentration of NoV GI was detected in ClO-treated water when samples were pretreated with PMAxx ( < 0.05), indicating that inactivation was due to the disinfection treatment. Laboratory-scale validation tests indicated the suitability of PMAxx-RT-qPCR for discrimination between potentially infectious and ClO-damaged viruses. Although the applied ClO treatment was not able to significantly reduce the enteric virus load of the secondary effluent from the wastewater treatment plant, none of the lettuce samples analyzed ( = 36) was positive for the presence of NoV or HAstV.

Assessment of Salmonella spp. and Escherichia coli O157:H7 growth on lettuce exposed to isothermal and non-isothermal conditions

This study aimed to assess the growth of Salmonella and Escherichia coli O157:H7 on lettuce exposed to isothermal and non-isothermal conditions. Pathogens were inoculated on lettuce separately and stored under isothermal condition at 5 °C, 10 °C, 25 °C, 37 °C for both bacteria, at 40 °C for Salmonella and 42 °C for E. coli O157:H7. Growth curves were built by fitting the data to the Baranyi's DMFit, generating R2 values greater than 0.92 for primary models. Secondary models were fitted with Ratkowsky equations, generating R2 values higher than 0.91 and RMSE lower than 0.1. Experimental data showed that both bacteria could grow at all temperatures. Also, the growth of both pathogens under non-isothermal conditions was studied simulating temperatures found from harvest to supermarkets in Brazil. Models were analysed by R2, RMSE, bias factor (Bf) and accuracy factor (Af). Salmonella and E. coli O157:H7 were able to grow in this temperature profile and the models could predict the behavior of these microorganisms on lettuce under isothermal and non-isothermal conditions. Based on the results, a negligible growth time (ς) was proposed to provide the time which lettuce could be exposed to a specific temperature and do not present an expressive growth of bacteria. The ς was developed based on Baranyi's primary model equation and on growth potential concept. ς is the value of lag phase added of the time necessary to population grow 0.5 log CFU/g. The ς of lettuce exposed to 37 °C was 1.3 h, while at 5 °C was 3.3 days.

Occurrence of hepatitis A and E and norovirus GI and GII in ready-to-eat vegetables in Italy

Fresh vegetables and their ready-to-eat (RTE) salads have become increasingly recognized as potential vehicles for foodborne diseases. The EU Reg. 1441/2007 establishes microbiological criteria for bacterial pathogens for products placed on the market during their shelf-life (i.e. Salmonella spp., Listeria monocytogenes) for pre-cut fruits and vegetables (RTE) whilst it does not address the problem of contamination by enteric viruses. In this study we investigated the contamination by hepatitis A virus (HAV), hepatitis E virus (HEV) and norovirus (NoV) in 911 ready-to-eat vegetable samples taken from products at retail in Apulia and in Lombardia. The vegetable samples were tested using validated real-time PCR (RT-qPCR) assays, ISO standardized virological methods and ISO culturing methods for bacteriological analysis. The total prevalence of HAV and HEV was 1.9% (18/911) and 0.6% (6/911), respectively. None of the samples analysed in this study was positive for NoV, Salmonella spp. or Listeria monocytogenes. The detection of HAV and HEV in RTE salads highlights a risk to consumers and the need to improve production hygiene. Appropriate implementation of hygiene procedures is required at all the steps of the RTE vegetable production chain and this should include monitoring of emerging viral pathogens.

Risk Assessment for Foodborne Viruses

Risk is an inherent component of human existence, as is our creation of ways to avoid or minimize such risks. The formal process of assessing the likelihood and magnitude of risk, using that information to manage risk, and then communicating the process to others, forms the basis for risk analysis. This chapter provides an overview of the steps of risk analysis with a focus on risk assessment for foodborne viruses, particularly quantitative efforts that model and estimate the risks these viruses pose to human health. Most risk assessments in food and environmental virology performed in the last decade have focused on water, fresh produce, molluscan shellfish, and prepared foods. Recent examples of enteric virus risk modeling efforts are discussed in detail, as are several of the difficulties and intricacies of performing risk assessments for foodborne viruses compared to bacteria and other agents. This is a relatively new area of study, but one that will continue to grow as national and international agencies continue to adopt and require the methodology for food safety and the protection of human health.