Highly Resistant Salmonella: Poultry, Antibiotics, Borders, Risk

If you’re a strain of Salmonella, it’s a very good week. If you’re a human, not so much.

There are two stories occurring simultaneously that underline the rising danger of drug-resistant organisms in the food supply, and the porousness of networks for detecting the dangerous bugs in time.

First, the Centers for Disease Control and Prevention and the Food and Drug Administration are tracking a US-wide outbreak of Salmonella Heidelberg that so far has killed one person and sickened 77 others that the agencies know of. (There are likely to be many more victims; most cases of foodborne illness are never reported to authorities.) The cases are scattered across 26 states, and apparently have been occurring since the second week of March, with the largest number so far in Michigan and Ohio (10 each), Texas (9), Illinois (7), California (6, including the death) and Pennsylvania (5).

The strain is “resistant to many commonly prescribed antibiotics,” according to the CDC, and may be traveling on ground turkey. The FDA on Friday issued a “public health alert” regarding fresh and frozen ground turkey, but neither agency has yet been able to pin the outbreak to a single product, processing plant or company. The CDC says that routine samples processed by NARMS (National Antimicrobial Resistance Monitoring System), a surveillance system shared by CDC,  FDA and the USDA, has retrospectively found the outbreak strain in four samples that were purchased between the beginning of March — before the earliest known case was reported — and the end of June. Three of the four trace back to a single processing facility that the agencies have not yet named. (See Update at end.)

Meanwhile, worse is coming. A multi-national team of scientists say in a paper released today by the Journal of Infectious Diseases that they have identified a clone of a different serotype, Salmonella Kentucky, that has become resistant to fluoroquinolones such as Cipro, the drug usually used to treat Salmonella infections. Comparing data from different countries’ surveillance systems, the researchers discovered that it has been causing human illnesses since 2002 in Europe, the Middle East and the US. It appears to have originated in Egypt in the late 1990s, and its primary vehicle is chicken.

The authors say the first clue to the emergence of this highly resistant strain (technically, Salmonella enterica serotype Kentucky ST198-X1) was illnesses among French people who had traveled in north Africa, starting with a single tourist who took a cruise on the Nile in 2002. That was followed by an outbreak that spread through hospitals in Slovakia starting in 2003. All of these cases were notable, because the Kentucky serotype is unusual in humans, though it had been commonly found in poultry since the 1930s. Making the infections more unusual was how resistant they were: not only to the fluoroquinolones, but also to amoxicillin, streptomycin, spectinomycin, gentamicin, sulfamethoxazole, and tetracyclines.

To test the strain’s current distribution, the authors called on countries where there are national surveillance systems for foodborne illnesses that incorporate laboratory analysis of whatever organisms are recovered: France, the United Kingdom, Denmark and the US. Between 2000 and 2008, they found, all of those databases recorded increasing amounts of the Kentucky strain, and higher percentages of Kentucky isolates that were multi-drug and  ciprofloxacin resistant. An important point: In the earlier years, the Kentucky cases were all associated with travel to north Africa; but more recently, infections occurred among people who had never left  their home countries, suggesting local spread.

Where did it come from? The authors say there’s really no question: They found the same strain in chickens and turkeys in Ethiopia, Morocco and Nigeria, all areas where fluoroquinolones are used in poultry farming.

Chickens themselves, though, are no longer the only vehicles. The highly resistant Kentucky strain has also been found in the US on spices that were imported from North Africa. You’ll recall that this summer’s massive outbreak of E. coli O104 in Europe arose from fenugreek seeds imported from Egypt, raising questions of whether the plants from which the seeds came had been contaminated by manure bearing the resistant organism. It’s tempting to wonder whether the same did not happen here.

Fluoroquinolones are just one of the drugs given to animals in intensive farming that are fundamentally identical to drugs given to humans. The World Health Organization, among other bodies, has been warning for years that using fluoroquinolones in this manner would make them not useful for human Salmonella infections, and the appearance of the highly resistant Kentucky strain appears to prove them right.

The authors have no doubt where it came from. In a statement distributed by the Infectious Diseases Society of America (which is the owner of JID, though publication is handled by the Oxford Journals) first author Simon Le Hello of France’s Pasteur Institute said: “We hope that this publication might stir awareness among national and international health, food, and agricultural authorities so that they take the necessary measures to control and stop the dissemination of this strain before it spreads globally.”

There’s another very intriguing aspect of this troubling Kentucky strain. I’ll take that up in a future post.

UPDATE: About 10 minutes after I hit the button on this, the Associated Press published a bulletin that Cargill Inc. will recall 36 million pounds of ground turkey because of the US outbreak and death. The recall appears to have been prompted by sleuthing by ferocious food-safety lawyer Bill Marler, who identified the plant Thursday afternoon.

Cite: Le Hello, S. et al. International Spread of an Epidemic Population of Salmonella enterica Serotype Kentucky ST198 Resistant to Ciprofloxacin.
Journal of Infectious Diseases. Released online.

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Image: PHIL, CDC


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