EHEC: Current State of Knowledge Concerning Illnesses in Humans

13-Jun-2011 - Germany

Current State of Knowledge Concerning Illnesses in Humans

Using information obtained from the various surveillance systems at the Robert Koch Institute, the observation is confirmed that the number of new EHEC infections is on the decline. On the one hand, the Sentinel surveillance system in the emergency reception centres of the affected hospitals is showing that the daily number of patients with bloody diarrhoea – the first indication of a possible EHEC infection – as well as the percentage of affected women in the regions in question are reducing continuously. On the other hand, mathematical models of the delay in reporting are showing that despite the late receipt of reports, a decline in the trend can be observed in regard to both the date on which the illness was contracted as well as the date of hospitalization. This decline could be attributable to a change in the consumption behaviour of the general public in regard to cucumbers, tomatoes and leaf lettuce (which is also likely to have indirectly reduced the consumption of sprouts) or to the drying up of the infection source.

Earlier Epidemiological Studies

In cooperation with national and regional health and food authorities, the RKI has been examining the outbreak of haemolytic uraemic syndrome (HUS) in northern Germany since 20 May 2011. By means of the epidemiological studies, which built on one another, it was possible to narrow down the cause of the outbreak to an increasing extent.

The first two case control studies were restricted for methodical reasons to those exposures which were capable of explaining a majority of the cases. Epidemiological analyses showed here that the affected patients had consumed raw tomatoes, cucumbers and leaf lettuce significantly more frequently than healthy study participants. These results were complemented by a case control study among canteen customers which led to the result that the consumption of food from the salad bar was clearly associated with the illness. As it was not possible to narrow down the number of suspect vegetable varieties through these studies or from information gained from the field of food safety, the RKI initiated additional studies.

Recipe-Based Restaurant Cohort Study

By means of a “recipe-based restaurant cohort study” it became possible today, for the first time, to narrow down the cause of the outbreak with a high degree of epidemiological certainty to the consumption of sprouts. The recipe-based cohort study could only be conducted now because a sufficient number of restaurant customers had first to be identified and made available in order to guarantee the sufficient statistical resilience of the analysis.

With the help of this recipe-based restaurant cohort study, the RKI took the following approach when recording the consumption of raw fruit and vegetables in order to be less dependent on the memory capacity of the patients and control persons questioned. Five groups (travel groups, clubs etc) with a total of 112 participants, 19 of whom took ill after a group visit to a restaurant, were investigated in regard to the foods they consumed in the restaurant. The restaurant visitors were not only questioned, it was also established on the basis of the order lists and invoice data which menus the travel group members had ordered. At the same time, the kitchen staff of the restaurant concerned were questioned in detail about the menus they had prepared and which amounts of which ingredients the menu contained. Parallel to this, photos taken by the travel groups were evaluated in order to determine which foods and garnishings were on the plates. This information was evaluated using a cohort approach which enabled the retrospective calculation of the relative risk of disease for restaurant customers. The latest analyses showed here that customers who consumed sprouts were 8.6 times more at risk (95% CI 1.5 - ∞) of contracting EHEC/HUS than customers who had not eaten these foods. It was also possible to establish in this way that of the total number of cases included in the study, 100% had eaten sprouts.

Findings from the Case Control Studies on the Consumption of Sprouts

Even during the first intensive questioning of patients in Hamburg (20.5./21.5), a wide variety of foods of animal and vegetable origin were considered, including sprouts. During this explorative questioning, only 3 out of 12 patients stated that they had eaten sprouts. Because the patients questioned were particularly aware about and conscious of what they ate, a relevant underestimation of sprouts did not seem likely. It is a methodical requirement and standard procedural method only to include to the extent possible those exposures which are potentially capable of explaining a large part of the outbreak from an epidemiological point of view. If a too great number of exposures are included, the risk of erroneously positive connections increases. Sprouts were not pursued further initially for this reason. Sprouts were taken into consideration in subsequent detailed RKI surveys. A total of 16 (30%) of the 54 patients who were able to provide information on bean sprout consumption in detailed interviews stated that they had eaten sprouts during the assumed infection period.

In another in-depth “raw fruit and vegetables case control study” started on 29 May 2011, which had the goal of enabling more precise differentiation between foods of vegetable origin, 27 persons from Lübeck, Bremerhaven and Bremen who had contracted HUS were allocated individually to 3 non-infected persons on the basis of their age, sex and place of residence. The result here was that 6 (25%) of 24 persons who had fallen ill stated that they had eaten sprouts during the assumed infection period, as opposed to 7 (9%) of 80 of those who had not taken ill and gave the same information. Although this connection is statistically significant in univariate analysis (OR=4.35 and 95% KI 1.05-18), it is not in multivariate analysis which means that the validity of this result is limited. As in the previous case control studies, the consumption of other foods of vegetable origin, such as tomatoes, cucumber and leaf lettuce, was reported more frequently in this raw fruit and vegetable study by persons who had taken ill than by comparative persons who had not, but the connection in this study was not statistically significant. These results match up with the RKI case control studies already published in as much as the vegetable varieties mentioned are often consumed together.

Current State of Knowledge of the Food Chain

Up to now it has not been possible to detect contamination with the EHEC pathogen O104:H4 in any food on the market. Despite the intensive efforts of all of the authorities involved in the affected "Bundesländer", as well as the RKI, BfR and BVL, it has not yet been possible to clearly identify the source of entrance of the EHEC pathogen O104:H4 into the food chain.

According to the current state of knowledge, supply channels and interactions also indicate that the EHEC infection has spread from a horticulture company in Lower Saxony and that these activities match up with the geographic distribution of many of the case clusters.

To support the investigation of the causes and consequences of the outbreak in several parts of the country, the national and regional governments have decided to set up a task force at the BVL which includes experts from several "Bundesländer", the Federal Office of Consumer Protection and Food Safety, the Federal Institute for Risk Assessment and the Robert Koch Institute with the support of experts from the European food safety authority EFSA and the European Commission.

The mandate of this task force is to make an analysis across the "Bundesländer" of the epidemiological findings via individual outbreak clusters using the information on the related supply chains which is available at the competent authorities of the "Bundesländer". Clusters are for example hotels, restaurants, canteens in which people have eaten before taking ill.

The distribution channels of sprouts from the horticulture company in Lower Saxony can account up to now for 26 of 55 case clusters and individual infections with EHEC O104:H4 in five affected federal states. The state of Lower Saxony has provided extensive information from its food surveillance activities to this end. According to the latest information available at the moment, it cannot be excluded that the responsible pathogen was introduced to the horticulture company by humans. Introduction via water, pre-suppliers or seed is also conceivable. This is currently being investigated by checking supply relations and conducting lab tests .

Other sources of entrance to the farm cannot currently be discarded either. The authorities in Lower Saxony and the BfR have taken extensive samples at the farm in question over the last few days but have not yet fully completed their analysis. Even though no evidence of the pathogen responsible for the outbreak can be confirmed to date, the amount of substantial evidence that has accumulated in the meantime is so incriminating that the federal institutions and state authorities must assume that the EHEC outbreak started here.

The national and regional governments will continue to investigate and analyze distribution channels to find out whether contaminated seed is being used for the production of sprouts in other companies, or otherwise marketed.

Because the bean sprout seed used can also be a possible source of entrance, other bean sprout producing businesses must also be regarded as potential distributors of EHEC O104:H4.

The survival and proliferation of EHEC on sprouts favours a wide distribution of the pathogen along the supply chains from the producing companies to the consumer.

For this reason, the RKI, BVL and BfR are advising against the consumption of raw sprouts until they can be excluded as a possible source of contamination.

This latest statement supersedes the previous warnings of the RKI and BfR not to consume cucumbers, tomatoes and leaf lettuce because the latest available information and knowledge indicate that it is highly likely that the horticulture company is the source of the EHEC infections.

Conclusions

1. The Federal Institute for Risk Assessment (BfR), Federal Office of Consumer Protection and Food Safety (BVL) and Robert Koch Institute (RKI) have come to the joint conclusion that the existing general recommendation not to consume cucumbers, tomatoes and leaf lettuce in northern Germany no longer has to be complied with.

2. As a precaution over and above customary hygiene measures, BfR, BVL, and RKI are recommending that sprouts should not be consumed raw. Households and catering businesses are advised to destroy any sprouts that may still have in stock along with any other foods with which they may have come in contact.

3. BfR, BVL and RKI are also recommending that all foods originating from a horticultural farm business in Lower Saxony be taken out of circulation.

4. BfR, BVL and RKI are recommending that the customary rules of hygiene be adhered to strictly when handling foods and dealing with patients.

This latest statement supersedes the previous warnings of the BfR and RKI not to consume cucumbers, tomatoes and leaf lettuce.

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