Biology

Mr. McDowell

E. Coli and Spinach: On the Trail of an Outbreak

Think of it as the ultimate connect-the-dots puzzle. It began back on Aug. 2, when the first case of E. coli infection tied to this recent outbreak was diagnosed, and has taken investigators on a circuitous journey through 21 states that seems to end somewhere in the spinach fields of Salinas, Calif.


“By no means has the actual farm been identified,” cautions Dean Cliver, a professor of food safety at the University of California at Davis. And he’s not convinced it ever will be, since so many factors—both on the farm and in the processing plants—have the potential to cause the bacterial infection. He points out that in previous outbreaks of E. coli linked to spinach and lettuce, there has never been a firm association with a specific farm.
But the experts are determined to do everything they can in an attempt to get to the root of the problem. The first step in the process occurs when doctors initially come across a new case of a food-borne illness, like the current E. coli infection. “Organisms from the feces of infected people are cultured and sent to the CDC [Centers for Disease Control and Prevention] to be subjected to a genetic fingerprint,” explains Don Schaffner, a food microbiologist and spokesman for the Institute of Food Technologists. “As early on as finding two cases with the same fingerprint, you can be fairly certain that the same thing made them sick.”
And that’s where epidemiologists come in. It’s their job to start compiling food histories of all those found to be infected with the same strain—in this case, E. coli 0157:H7. And the more people who are infected, the easier it will be to find the common link. Because E. coli can be spread by eating contaminated vegetables, meat and unpasteurized dairy products, a pattern of consumption of a specific food has to emerge before the source of the bacteria can be identified. “If there were only two cases and both people had eaten hamburgers and spinach salads, it would be harder to narrow the focus,” says Schaffner.
The detective process, however, is not an easy one. While food histories quickly revealed that spinach appeared to be the common link in this current outbreak, that was only the beginning. Of the 114 known cases, the CDC, as of Monday, has information on food consumption from 73 people, and it has determined that more than 60 of them ate spinach. Whenever possible, the brand names and even UPC codes from the bags of spinach consumed are being used to help trace the source of the infection. “To date, all brands implicated appear to originate from fields in California, and the bulk of epidemiological evidence links to [producer] Natural Selection,” says Dr. David Acheson, of the Center for Food Safety and Applied Nutrition at the Food and Drug Administration.
But Dr. Acheson is quick to point out that those conclusions are still speculative and that it’s too soon to rule out other brands and farms located in states besides California. That’s why the current FDA advisory calls for consumers to avoid all fresh spinach—bagged, loose, organic and conventional—and all brands under which it might be marketed.
And while the information about brand names helps investigators narrow their focus, it’s only the tip of the iceberg. Even if it’s eventually determined that the contaminated produce was bagged by Natural Selection, more detective work will be required. Natural Selection grows spinach (both organic and conventional) on 150 farms, and the produce is processed and bagged under several different brands, including Earthbound Farm, Dole, River Ranch, Ready Pac and President’s Choice.
Trace-back investigations are necessary to determine exactly which brands were consumed, which facilities those bags were processed in, and which farms grew the spinach. And even if they manage to find the farm, investigators will still have to pinpoint the actual cause of the contamination on that farm—a process akin to seeking a needle in a haystack. “Problems can occur in many areas—irrigation water, farm worker hygiene, animals in the environment, so it’s going to take long hours of detective work,” says microbiologist Schaffner.
Monday, investigators from the FDA and the California Department of Health Services followed the spinach trail by heading onto a number of suspect farms in the Salinas Valley to begin collecting samples. FDA officials report that they’ve also obtained samples from Natural Selection’s facilities and that they will be doing the same from other firms. They’ll be looking for any evidence of E. coli contamination—especially any that matches the genetic fingerprint of the strain that has now infected 114 people, and killed at least one. To date, no E. coli contamination has been found.

E. coli: The raw and the cooked
Eating undercooked beef, especially hamburger, can increase your risk of infection with Escherichia coli (E. coli) bacteria. E. coli are a broad group of bacteria that live in the intestinal tract of healthy people and animals. Most of the bacteria are harmless and play an essential role in absorbing certain vitamins. But a few strains of E. coli are responsible for serious food-borne infections.
A particularly virulent strain of E.coli, called E. coli O157:H7,can cause severe, bloody diarrhea, kidney failure and even death. Most cases of E. coli O157:H7 have been traced to undercooked ground meat. Although it's not always possible to prevent food poisoning, knowing how E. coli spreads and how to handle food safely can help you avoid getting sick.

Dissecting the bad bugs

Not all disease-causing E. coli bacteria are created equal. One strain, enterotoxigenic E.coli, is a leading cause of diarrhea in children in developing nations. It's also responsible for most cases of traveler's diarrhea and is an increasing source of food-borne infection in industrialized countries.
Enterotoxigenic E.coli bacteria spread in contaminated food — including raw fruits and vegetables, raw seafood, and unpasteurized dairy products — and in contaminated water. Signs and symptoms, which include watery diarrhea and abdominal cramping, usually last just a few days. The infection normally clears on its own without treatment, and most adults and children have no lasting ill effects.
But E. coli O157:H7 is different. It produces a toxin that damages the lining of the small intestine, leading to intense abdominal cramps and severe, bloody diarrhea. You may have 10 or more bowel movements a day, some consisting almost entirely of blood. The marked loss of fluids and electrolytes causes dehydration and fatigue.
Nevertheless, many people recover completely from the infection in five to 10 days. But others, especially older adults, children under the age of 5 and people with weakened immune systems, may develop a serious complication called hemolytic uremic syndrome. This syndrome damages the lining of the tiny blood vessels in the kidneys, sometimes leading to kidney failure.
Even with the best of care, including blood and platelet transfusions and kidney dialysis, a few children die every year of hemolytic uremic syndrome. Others may have lifelong kidney problems or require long-term dialysis. Still others develop further complications such as high blood pressure, seizures, blindness and paralysis.

How E. coli spreads

You develop an E. coli infection when you accidentally ingest the bacteria. These are the most common sources of infection:
  • Contaminated food. E. coli bacteria exist naturally in the intestine of many animals, including cattle. Meat can become contaminated with fecal matter containing the bacteria when cattle are slaughtered or processed. The problem is particularly serious in modern feedlots, where animals spend their lives in crowded, filthy conditions. Although beef in general may be contaminated, ground meat is a special concern because grinding combines meat from different animals and transfers bacteria from the meat's surface to its interior. The bacteria also can spread from one surface to another, which means that bacteria on a cow's udder or on equipment can end up in milk. Pasteurization kills the bacteria, but raw milk can be a source of infection. Other foods that may become contaminated with the bacteria include dry cured sausage, salami, alfalfa sprouts, lettuce, and unpasteurized apple juice and apple cider.
  • Contaminated water. Runoff from feedlots can contaminate ground and surface water, including water used to irrigate crops. Drinking or inadvertently swallowing untreated water from lakes and streams can cause infection. So can eating unwashed raw fruits and vegetables. And although public water systems use chlorine, ultraviolet light or ozone to kill E. coli, some outbreaks have been linked to contaminated municipal water supplies. Private wells are a greater cause for concern. If you have a private well, have it tested once a year for pathogens, including E. coli. Your state health department can help you find a laboratory certified to conduct the tests.
  • Person-to-person contact. E. coli bacteria can easily travel from person to person, especially when infected adults and children don't wash their hands properly. Family members of young children with the infection are especially likely to become sick themselves. Children can shed the bacteria in their stools for up to two weeks after symptoms improve.

Keeping E. coli at bay

It's not always possible to avoid food poisoning, but common-sense precautions can go a long way toward preventing infection with E. coli O157:H7 bacteria.
  • Cook all ground meat, hamburger or roast beef thoroughly. Meat, especially if grilled, is likely to brown before it's completely cooked, so use a meat thermometer to ensure that meat is heated to at least 160 F at its thickest point. If you don't have a thermometer, cook ground meat until no pink shows in the center.
  • To prevent the growth of bacteria in your kitchen, thoroughly wash anything that comes in contact with raw meat, including your hands, counters and utensils. Use hot, soapy water, bleach or disinfecting wipes. Never put cooked hamburgers on the same plate you used for raw patties.
  • Order beef cooked medium or well-done when eating out. Be persistent about getting what you ask for, even if it means sending your food back more than once.
  • Drink pasteurized milk, juice and cider. Any boxed or bottled juice kept at room temperature is likely to be pasteurized, even if the label doesn't say so.
  • Wash raw produce thoroughly, using plenty of running water and a scrub brush or a vegetable wash. Children, older adults and people with weakened immune systems should avoid alfalfa sprouts.
  • Avoid drinking untreated water from lakes and streams and swallowing water when swimming — even pool water, which can be contaminated with feces.
  • Make sure that family members, including children, wash their hands after using the bathroom, changing diapers and before eating.

You're sick: Now what?

Most E. coli infections — even those caused by E. coli O157:H7 — aren't life-threatening. But the bacteria can cause serious and even fatal illness in some people. If you're at high risk of hemolytic uremic syndrome, see your doctor at the first sign of profuse or bloody diarrhea. If you're not at risk, seek medical advice if your symptoms are severe or persistent. You should have your stool checked for E. coli bacteria.
Most cases of traveler's diarrhea clear up on their own in a few days, although doctors sometimes prescribe a short course of the antibiotic rifaximin (Xifaxan), which reduces the number of E. coli bacteria in the gut. When it comes to more severe infections such as O157:H7, however, no current treatments can cure the infection, relieve symptoms or prevent complications.
Anti-diarrheals can make O157:H7 worse by preventing your body from eliminating the toxins. And antibiotics increase the risk of hemolytic uremic poisoning. For most people with O157:H7 infection, rest and plenty of fluids to prevent dehydration are the best option.