E. coli O104:H4 – How Big Is The Iceberg?

“I believe the HUS cases are the real tip of the iceberg.”

– Dr. Michael T. Osterholm, PhD, MPH, Director of the University of Minnesota’s Center for Infectious Disease Research and Policy (CIDRAP), the publisher of CIDRAP News.

One puzzling aspect of the E. coli O104:H4 outbreak has been the very high number of cases of hemolytic uremic syndrome (HUS) and the large number of deaths in comparison to the total number of reported infections.

The World Health Organization, as of July 7th, reported a total of 3,941 cases worldwide, including 909 cases of HUS and 52 deaths. This tally actually dropped from the previously reported total (on July 1st) of 4,137 cases. The change was due to a redefinition of outbreak-related cases issued by the European Union.

Determining the actual number of outbreak victims in a foodborne disease investigation is rarely easy. I’ve wondered for some time how many mild and/or asymptomatic illnesses have gone unreported. On July 5th, I gave voice to my suspicion that many cases of E. coli O104:H4 have gone unreported, saying, “It’s likely that an unknown number of milder gastrointestinal illnesses also can be blamed on this outbreak strain.”

It is now clear that my hunch was well-founded. The European Centre for Disease Prevention and Control (ECDC) and the European Food Safety Authority (EFSA) have released an updated “Risk Assessment”which includes the following paragraph:

“The most significant development since June 29 relates to the preliminary results of the screening of children and staff in a school in Kreis Paderborn (Paderborn county), Germany, where three cases of HUS STEC and one case of non-HUS STEC infection have been identified since 13 June 2011 and onwards. In 22 of the 30 children tested (including the three HUS STEC cases, and the non-HUS STEC case), the epidemic strain of E. coli was isolated, indicating a significant level of asymptomatic infection. Asymptomatic carriage of STEC infection was also found in three kitchen workers at the school, in four guardians in four different child care centres in the district, and in three staff members of a supplying catering company. Further investigations of this cluster are ongoing.”

So, how big is the E. coli O104:H4 iceberg? Let’s do the math. First, we must decide on our multiplier. Let’s look at the two extreme cases.

The conservative estimate. The ECDC/EFSA report of asymptomatic cases documented a total of 22 children and 10 adults who were carriers of E. coli O104:H4 in its investigation of the Kreis Paderborn cluster of illnesses. Of these 32 carriers, only 4 developed active illnesses – including 3 cases of HUS. This gives us a multiplier of 8 (i.e., each reported case represents 8 actual infections).
The opposite extreme. In January 2011, CDC released its latest estimates of foodborne disease illness in the USA. The report details the multipliers that the authors developed for each pathogen to extrapolate actual illnesses from the numbers of reported illnesses. For non-O157 strains of enterohemorrhagic E. coli – the category into which E. coli O104:H4 falls – this multiplier is 106.8 (see Table 2 of report).

Taking these two multipliers and applying them to the most recent numbers reported by the World Health Organization, we arrive at the following:

The conservative estimate: 3,941 reported cases worldwide x 8 = 31,528 estimated symptomatic and asymptomatic infections.
The opposite extreme: 3,941 reported cases worldwide x 106.8 = 420,899 estimated symptomatic and asymptomatic infections.

The truth, no doubt, lies somewhere in between these two extremes.

Why is this important? Simply, the more people who have been infected – especially those who show no symptoms of illness – the more likely that E. coli O104:H4 will establish itself as thoroughly as E. coli O157:H7 already has done.

As for the “most probable source” of the outbreak, the Egyptian fenugreek seeds have been tracked forward to 25 countries so far – Austria, Belgium, Bulgaria, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Italy, Latvia, Lithuania, Luxembourg, the Netherlands, Norway, Poland, Portugal, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.

As for the German outbreak investigation, the Federal Office of Consumer Protection and Food Safety has released its final Task Force report.

The German investigation may be complete, and the present outbreak winding down, but this is not the last we’ve heard from E. coli O104:H4.

Note to Anne: Home-Sprouting Seeds Is Not Safe Alternative

Whenever I speak with my husband’s 80-something Auntie Anne, I know that the subject will eventually turn to recipes and food safety. From grav lax to ganache, I’m her “go-to” gal. The last time we spoke, the topic was sprouts.

“I understand,” Anne said, “that sprouts in the supermarket are risky, and I don’t buy them anymore. But why can’t I buy the seeds at a health food store and sprout them myself?”

I explained that the seeds she finds in the health food store might be contaminated with Salmonella or E. coli.

“Then why,” she asked, ” can people eat the seeds without becoming sick?”

Putting aside the question as to how many people actually eat raw alfalfa seeds, arugula seeds, or mung beans, Anne’s question was a reasonable one. And the answer is in the arithmetic.

When a pathogenic microbe such as Salmonella, E. coli O157:H7 or E. coli O104:H4 is found in a batch of seeds, the level of contamination is typically very low. Researchers at the California Department of Health Services reported in 2001 (Journal of Food Protection, Vol. 64, No. 8, 2001, Pages 1240–1243) that they found Salmonella in contaminated batches of alfalfa seeds at levels as low as 0.07 per 100g – just a single live Salmonella in 3.15 pounds (1.4Kg) of seeds – and as high as 1.8 per 100g (or about one live Salmonella in 2 ounces of seeds).

If the level of pathogens in/on contaminated seeds is so low, why are sprouts such a problem? It’s all in the way the sprouts are produced.

Typical growing conditions for sprouts:- Moist, warm temperatures (typically, 70-80ºF)
Typical growing conditions for Salmonella and E. coli:- Moist, warm temperatures (optimally, 95-100ºF, but grow well in the 70-80ºF range)

And that’s the problem. The conditions required for sprouting seeds also encourage abundant growth of bacteria, including Salmonella and E. coli. A single Salmonella or E. coli cell can produce more than one million offspring during the first 10 hours of sprouting.

This risk is not just theoretical. Some of the German outbreak victims ate raw sprouts that they produced at home.

Another question I have been asked is how long pathogens such as Salmonella and E. coli can survive on or in seeds used for sprouting. The answer, in a word, is “years.”

The same study that documented the number of Salmonella present in the alfalfa seeds also mentioned that Salmonella had remained viable in the seeds after two years of storage at room temperature in the dark.

E. coli O157:H7 is just as rugged. In 1995, two Japanese sprouting facilities purchased radish seeds from the same US distributor. Between May and December 1996, more than 9,400 people in Japan became infected with a single outbreak strain of E. coli O157:H7, and 12 people died. Most of the outbreak victims were school children. The source of the infection was traced to radish sprouts produced in one of the two Japanese sprouting facilities.

Eight months later, in 1997, Japanese health authorities investigated another spurt of E. coli O157:H7 illnesses. The second series of illnesses was traced to radish sprouts produced in the second Japanese sprouting facility. The outbreak strain was identical to the 1996 outbreak strain. Clearly, this strain of E. coli O157:H7 survived on or in the US-produced radish seeds for more than a year.

It’s too soon for anyone to have determined the long-term survival of E. coli O104:H4; however, I would be astonished if it was very different from the others.

To summarize:

The ideal conditions for sprouting seeds and for growing bacteria overlap.
Bacteria will multiply into the millions per gram during the sprouting process.
Salmonella and E. coli can survive for 1-2 years – or longer – on or inside the dry seeds.

Finally, my advice to Auntie Anne – and to anyone else who is interested: Do not eat raw sprouts.

Well-Traveled Fenugreek Seeds Behind E. coli Outbreaks

A single batch of fenugreek seeds from Egypt is the ‘most likely common link’ between the 2011 German and French E. coli O104:H4 outbreaks, according to a Technical Report issued today by the European Food Safety Authority (EFSA).

The European Union has withdrawn Egyptian seeds from the market, and has temporarily banned the import of certain types of seeds and beans from Egypt. Member States have been instructed to insure that all lots of fenugreek seeds obtained from the implicated Egyptian exporter between 2009 and 2011 are withdrawn, sampled and destroyed. Further import of Egyptian seeds and beans for sprouting are suspended until October 31, 2011.

Between them, the two outbreaks have accounted for 896 cases of hemolytic syndrome and an additional 3,241 cases of bloody diarrhea in 16 countries since May 1st, 2011 – 4,137 reported cases in all. Fifty people have died – 48 in Germany, one in Sweden and one in the USA. It’s likely that an unknown number of milder gastrointestinal illnesses also can be blamed on this outbreak strain.

Although the EFSA has concluded that Egyptian fenugreek seeds are the most likely culprit, Egypt’s Ministry of Agriculture was quite correct in stating last week that the implicated seeds were shipped to Holland, not to Germany, France or the UK. Here’s what happened.

On November 24, 2009, a consignment of fenugreek seeds (Lot #48088) departed by boat from the Egyptian port of Damietta. The boat arrived at Antwerp (Belgium) and the consignment – still packed in a sealed customs’ container – was sent by barge to Rotterdam (the Netherlands), where it cleared customs.

The sealed container then was trucked to Germany, where the German Importer (unidentified in the EFSA report) redistributed most of the seeds (now identified as Lot #6832) and retained 75 kg in storage. In October 2010, the German Importer received another lot (Lot #8266) of seeds from the same Egyptian exporter.

The German Importer of the fenugreek seeds supplied approximately two-thirds of the 2009 shipment to a distributor in Germany (also unnamed in the report).

The Distributor, in turn, sold 75 kg of the seeds to the German sprout producer – Gärtnerhof Bienenbüttel – implicated in the German E. coli O104:H4 outbreak. The German Importer also supplied approximately 400 kg of the same batch of seeds to a UK seed supplier/repacker (identified in French reports as Thompson & Morgan).

Thompson & Morgan repackaged the seeds in 50g packages (now identified as Lot #DRG1041132/10) and supplied them to a distributor in France, who resold the seeds to about 200 French garden centers. One 50g packet of the seeds was the source of the contaminated sprouts that caused the French outbreak cluster in the Bordeaux region. In addition to the seeds that were supplied to France, UK-packaged seeds from the implicated lot were also shipped to Luxembourg, the Netherlands and Switzerland.

It’s likely that at least some contaminated seeds are still either on the market or in the hands of consumers who produce their own sprouts. Trace-forward investigations have determined that the seeds were distributed by the German Importer as follows:

10 500 kg were received by a single large distributor in Germany, who redistributed the seeds to 70 companies (54 in Germany and 16 in 11 other European countries;
3 550 kg were received by 9 other companies in Germany;
400 kg were received by one company in the UK;
250 kg were forwarded via an Austrian distributor and received by one company in Austria; and
375 kg were received by one company in Spain.

Contaminated seeds may also have been exported from Egypt to other countries. Play it safe – do not eat raw sprouts.