Todd Neale, Senior Staff Writer, MedPage Today
Published: September 29, 2011
The listeriosis outbreak stemming from tainted cantaloupes has sickened at least 72 individuals, killing 13 of them, according to the CDC.
“This is the deadliest outbreak of a foodborne disease that we’ve identified in more than a decade,” said CDC director Thomas Frieden, MD, MPH, on a conference call with reporters Wednesday.
Overall, 18 states have been affected as of Monday, with four different strains of Listeria monocytogenes implicated. State and federal health officials are continuing to investigate other listeriosis cases across the country that might be related to the outbreak.
Most of the infected individuals are older than 60 or have conditions that weaken the immune system, the CDC said in its most recent update. All but one of the patients with information on hospitalization have required admission.
The 13 confirmed deaths have occurred in New Mexico (four), Colorado and Texas (two each), and Kansas, Maryland, Missouri, Nebraska, and Oklahoma (one each). That figure is more than triple the four deaths reported last week. Three additional deaths could be related to the contaminated cantaloupe melons, the BBC reports.
Early on in the investigation, the Colorado Department of Public Health and Environment identified cantaloupes grown in the Rocky Ford region of the state as the likely source of the outbreak, which is unusual because Listeria has not previously been seen in cantaloupe.
Within days, the department pinpointed the exact source as whole cantaloupes grown at Jensen Farms’ production fields in Granada, Colo., which was later confirmed by the FDA.
The FDA said it is working with other agencies to determine how the contamination of the facility occurred, with consideration given to all environmental factors on the farm, including possible animal intrusions, water quality, and growing practices.
On Sept. 14, Jensen Farms recalled its Rocky Ford brand whole cantaloupes, reporting distribution to 17 states. In its update, the CDC said that the cantaloupes were shipped to at least 25 states, with the possibility of further distribution.
Even though the cantaloupes have been recalled, the CDC said that it expects to receive reports of more cases related to the outbreak through October because individuals can develop listeriosis up to two months after coming into contact with the bacteria.
The shelf life of cantaloupe is about two weeks, and all of the affected product was shipped from July 29 to Sept. 10.
The FDA said that it is collaborating with state health officials to check retail stores, wholesalers, and distributors to make sure they know about the recall and that they have taken steps to inform customers and remove affected product from shelves.
The agency said that consumers should throw away any of the recalled cantaloupes from Jensen Farms and should not try to wash the bacteria off of the fruit.
he CDC recommended that people at high risk for listeriosis — including older adults, immunocompromised individuals, and pregnant women — should not eat Rocky Ford cantaloupes from Jensen Farms, and that other individuals should not eat those cantaloupes if they want to reduce their risk of Listeria infection.
The agency noted that the bacteria can grow both at room temperature and in the refrigerator.
“For the public, it’s important to know that if you know the cantaloupe that you have is not [from] Jensen Farms, then it’s okay to eat,” Frieden said, “but if you’re in doubt, then throw it out.”
According to the CDC, there are about 800 reported cases of Listeria infection each year in the U.S., with three or four outbreaks. Typical sources include deli meats, hot dogs, and Mexican-style soft cheeses made with unpasteurized milk, although produce — including sprouts in 2009 and celery in 2010 — has been implicated as well.
Frieden said over the past decade there have been about 10 outbreaks of foodborne illness in which cantaloupes were the definite vehicle for infection, seven involving Salmonella and three involving norovirus.
He added that the number of multistate outbreaks of foodborne illness in general have increased substantially in recent years.
“This is a reflection at least of better quality monitoring and perhaps also of the increasing complexity and centralization of the food supply,” he said. “It’s not that food is getting riskier, but we’re getting better at identifying problems that have probably been there for a long, long time.”
FDA commissioner Margaret Hamburg, MD, added that “these kinds of outbreaks are a powerful reminder that, despite the fact that we have one of the safest food supplies in the world, it does remain vulnerable to contamination, and the American people remain vulnerable to foodborne illness.”
Listeria monocytogenes with flagella
New York Times:
LISTERIA Q & A
Q&A: Key Answers About Listeria in Fruit
On September 14, 2011, the FDA warned consumers not to eat cantaloupes shipped by Jensen Farms from Granada, Colorado due to a potential link to a multi-state outbreak of listeriosis. At that time Jensen Farms voluntarily recalled cantaloupes shipped from July 29 through September 10, and distributed to at least 17 states with possible further distribution. The CDC reported that at least 22 people in seven states had been infected as of September 14. On September 26, the CDC reported that a total of 72 persons had been infected with the four outbreak-associated strains of Listeria monocytogenes which had been reported to the CDC from 18 states. All illnesses started on or after July 31, 2011 and by September 26, thirteen deaths had been reported: 2 in Colorado, 1 in Kansas, 1 in Maryland, 1 in Missouri, 1 in Nebraska, 4 in New Mexico, 1 in Oklahoma, and 2 in Texas.
Health officials say as many as 16 people have died from possible listeria illnesses traced to Colorado cantaloupes, the deadliest food outbreak in more than a decade. The Centers for Disease Control and Prevention said that 72 illnesses, including 13 deaths, are linked to the tainted fruit.
Some questions consumers may have about listeria in cantaloupes.
Q: What is listeria?
A: Listeria is a hardy bacteria found in soil and water that can be carried by animals. It is often found in processed meats because it can contaminate a processing facility and stay there for a long period of time. It is also common in unpasteurized cheeses and unpasteurized milk. It is less common in produce like cantaloupe, but there have been a couple of other listeria outbreaks in fruits and vegetables in recent years. When a person contracts the disease, it can cause fever, muscle aches, gastrointestinal symptoms and even death. One in five people who have listeria can die.
Q: Am I at risk?
A: Listeria generally only affects the elderly, people with compromised immune systems, pregnant women and newborns whose mothers were infected before birth. The median age of victims in this outbreak is 78 years old. Healthy, younger adults and most children can usually consume listeria with no ill effects or mild illness.
Q: So can I eat cantaloupe?
A: You should avoid cantaloupe from Jensen Farms, the Colorado grower that distributed the tainted fruit.
Q: How do I know if I have a cantaloupe from Jensen Farms?
A: The recalled cantaloupe may be labeled “Colorado Grown,” ”Distributed by Frontera Produce,” ”Jensenfarms.com” or “Sweet Rocky Fords.” It may also be labeled “USA.” Not all of the recalled cantaloupes are labeled with a sticker, the Food and Drug Administration said, so it may be hard to tell. Neither the government nor Jensen Farms has released a list of retailers who sold the fruit, so health officials advise consumers ask retailers about the origin of their cantaloupe.
Q: I think I may have had one of the contaminated cantaloupes in my home. But I’m not sure. What should I do?
A: The government’s motto is “when in doubt, throw it out.” And if you think you had tainted fruit in your home, clean and sanitize all surfaces it may have touched.
Q: I scrub all of my fruits and vegetables before I eat them. So I am okay, right?
A: Scrubbing is never a bad idea, but it may not rid produce of all contaminants, especially on cantaloupe which has a thick, rough skin with a lot of places for pathogens to hide. Health officials think people may have been sickened when people cut into their cantaloupes, bringing listeria on the outside of the fruit to the inside. If you think you may have a tainted cantaloupe in your house, the best recourse is to throw it out.
Q: It looks like the cantaloupes weren’t even shipped to my state. Should I still be concerned?
A: The FDA said Jensen Farms shipped to 25 states, but it may have been resold in other states. Illnesses have been discovered in several states where cantaloupes weren’t shipped, including in Maryland where a person died.
Q: Why have there been so many deaths?
A: Listeria is less well-known than other pathogens like salmonella and E. coli, which cause many more illnesses in tainted food every year. But listeria is more deadly. One in five people who contract it can die.
Q: When is this outbreak going to be over?
A: FDA and CDC officials said Wednesday that they expect the number of illnesses and even deaths to rise through October. Listeria has an incubation period of a month or more, so people who ate contaminated fruit last week may not see illnesses until next month.
Listeria monocytogenes grown on Biorad RAPID’L.Mono Agar
- Listeria is a bacterial genus that contains six species. Named after the English pioneer of sterile surgery Joseph Lister, the genus received its current name in 1940. Listeria species are gram-positive bacilli. The major human pathogen in the Listeria genus is L. monocytogenes, which is usually the causative agent of the relatively rare bacterial disease, listeriosis. Listeria ivanovii is a pathogen of mammals, specifically ruminants, and has rarely caused listeriosis in humans.
The first documented case of Listeria was in 1924. In the late 1920’s, two researchers independently identified Listeria monocyctogenes from animal outbreaks. They proposed the genus Listerella in honor of surgeon and early antiseptic advocate Joseph Lister; however, that name was already in use for a slime mold and a protozoan. Eventually, the genus Listeria was proposed and accepted.
The genus Listeria currently contains seven species: L. grayi, L. innocua, L. ivanovii, L. monocytogenes, L. murrayi, L. seeligeri, and L. welshimeri. Listeria dinitrificans, previously thought to be part of the Listeria genus, was reclassified into the new genus Jonesia.
Listeria can be found in soil, which can lead to vegetable contamination. Animals can also be carriers. Listeria has been found in uncooked meats, uncooked vegetables, fruit such as cantaloupes, unpasteurized milk, foods made from unpasteurized milk, and processed foods. Pasteurization and sufficient cooking kill listeria; however, contamination may occur after cooking and before packaging. For example, meat-processing plants producing ready-to-eat foods, such as hot dogs and deli meats, must follow extensive sanitation policies and procedures to prevent listeria contamination. Listeria monocytogenes is commonly found in soil, stream water, sewage, plants, and food. Listeria are responsible for listeriosis, a rare but potentially lethal food-borne infection. The case fatality rate for those with a severe form of infection may approach 25%. (Salmonella, in comparison, has a mortality rate estimated at less than 1%). Although listeria has low infectivity, it is hardy and can grow in temperatures from 4 C (39.2 °F) (the temperature of a refrigerator), to 37 C (98.6 °F), (the body’s internal temperature). Listeriosis is a serious illness, and the disease may manifest as meningitis, or affect newborns due to its ability to penetrate the endothelial layer of the placenta.
Listeria monocytogenes, for example, encodes virulence genes that are thermoregulated. The expression of virulence factor is optimal at 37 degrees Celsius and is controlled by a transcriptional activator, PrfA, whose expression is thermoregulated by the PrfA thermoregulator UTR element. At low temperatures, the PrfA transcript is not translated due to structural elements near the ribosome binding site. As the bacteria infect the host, the temperature of the host melts the structure and allows translation initiation for the virulent genes.
Listeria monocytogenes is a Gram-positive, rod-shaped bacterium. It is the agent of listeriosis, a serious infection caused by eating food contaminated with the bacteria. The disease affects primarily pregnant women, newborns, and adults with weakened immune systems. Listeriosis is a serious disease for humans; the overt form of the disease has a mortality greater than 25 percent. The two main clinical manifestations are sepsis and meningitis. Meningitis is often complicated by encephalitis, a pathology that is unusual for bacterial infections.
Under the microscope, Listeria species appear as small, Gram-positive rods, which are sometimes arranged in short chains. In direct smears, they may be coccoid, so they can be mistaken for streptococci. Longer cells may resemble corynebacteria. Flagella are produced at room temperature, but not at 37 °C. Hemolytic activity on blood agar has been used as a marker to distinguish L. monocytogenes among other listeria species, but it is not an absolutely definitive criterion. Further biochemical characterization may be necessary to distinguish between the different listeria species.
As Gram-positive, nonsporeforming, catalase-positive rods, the genus listeria was classified in the family Corynebacteriaceae through the seventh edition of Bergey’s Manual. The 16S rRNA cataloging studies of Stackebrandt, et al. demonstrated that L. monocytogenes is a distinct taxon within the Lactobacillus-Bacillus branch of the bacterial phylogeny constructed by Woese. In 2001, the Family Listeriaceae was created within the expanding Order Bacillales, which also includes Staphylococcaceae, Bacillaceae and others. Within this phylogeny, there are six species of listeria. The only other genus in the family is Brochothrix.
Mechanism of infection
The majority of listeria bacteria are targeted by the immune system before they are able to cause infection. Those that escape the immune system’s initial response, however, spread through intracellular mechanisms and are, therefore, guarded against circulating immune factors (AMI).
To invade, listeria induces macrophage phagocytic uptake by displaying D-galactose in their teichoic acids that are then bound by the macrophage‘s polysaccharide receptors. Other important adhesins are the internalins. Once phagocytosed, the bacterium is encapsulated by the host cell’s acidic phagolysosome organelle. Listeria, however, escapes the phagolysosome by lysing the vacuole’s entire membrane with secreted hemolysin,now characterized as the exotoxin listeriolysin O. The bacteria then replicate inside the host cell’s cytoplasm.
Listeria must then navigate to the cell’s periphery to spread the infection to other cells. Outside the body, listeria has flagellar-driven motility, sometimes described as a “tumbling motility.” However, at 37 C, flagella cease to develop and the bacterium instead usurps the host cell’s cytoskeleton to move. Listeria, inventively, polymerizes an actin tail or “comet”,from actin monomers in the host’s cytoplasm with the promotion of virulence factor ActA. The comet forms in a polar manner and aids the bacteria’s migration to the host cell’s outer membrane. Gelsolin, an actin filament severing protein, localizes at the tail of listeria and accelerates the bacterium’s motility. Once at the cell surface, the actin-propelled listeria pushes against the cell’s membrane to form protrusions called filopodsor “rockets”. The protrusions are guided by the cell’s leading edge to contact adjacent cells, which then engulf the listeria rocket and the process is repeated, perpetuating the infection. Once phagocytosed, the listeria is never again extracellular: it is an intracytoplasmic parasite like Shigella flexneri and Rickettsia.
The Center for Science in the Public Interest has published a list of foods that have sometimes caused outbreaks of listeria: hot dogs, deli meats, raw milk, cheeses (particularly soft-ripened cheeses like feta, Brie, Camembert, blue-veined, or Mexican-style “queso blanco”), raw and cooked poultry, raw meats, ice cream, raw vegetables, some fruit such as cantaloupe, raw and smoked fish, and the green lip mussel.
Preventing listeria as a food illness requires effective sanitation of food contact surfaces. Alcohol is an effective topical sanitizer against listeria. Quaternary ammonium can be used in conjunction with alcohol as a food contact safe sanitizer with increased duration of the sanitizing action. Refrigerated foods in the home should be kept below 4 °C (39.2 °F) to discourage bacterial growth. Preventing listeriosis also can be done by carrying out an effective sanitation of food contact surfaces.
Modern relevance/future research
Listeria is an opportunistic pathogen: It is most prevalent in the elderly, pregnant mothers, and AIDS patients. With improved healthcare leading to a growing elderly population and extended life expectancies for AIDS patients, physicians are more likely to encounter this otherwise-rare infection (only 7 per 1,000,000 healthy people are infected with virulent listeria each year). Better understanding the cell biology of listeria infections, including relevant virulence factors, may help us better treat Listeriosis and other intracytoplasmic parasites. Researchers are now investigating the use of listeria as a cancer vaccine, taking advantage of its “ability to induce potent innate and adaptive immunity.”
Mixtures of bacteriophages have also proven effective in the treatment of Listeria.
Food Poison Alert
Presented By Marler Clark – The nation’s foremost law firm with a practice dedicated to representing victims of foodborne illness
Posted by Drew Falkenstein
Salmonella and cantaloupes
Salmonella and cantaloupe, and cantaloupe and other bugs like E. coli, have been bedfellows all too frequently. A 2005 article by Trevor Susslow, Linda Harris, and Tracy Parnell at UC Davis states that “[c]antaloupe has been associated with foodborne outbreaks involving Escherichia coli O157:H7 (DelRosario and Beuchat, 1995), Norovirus (Iversen et al.,1987), and numerous serovars of Salmonella, including Salmonella chester (CDC, 1991), Salmonella poona (CDC, 1991; FDA, 1991; California Department of Health Services, 2000, 2001, 2002), Salmonella oranienburg (Health Canada, 1998), and Salmonella saphra (Mohle-Boetani et al., 1999).
Common themes in these outbreaks were that the melons were cut and most had been subjected to temperature abuse. In some cases, melons were contaminated through inadvertent contact with raw meat (see Harris et al., 2003) or a human handler (Iversen et al., 1987), but in other cases, the contamination was thought to have been soil on the melon rind (Mohle-Boetani et al., 1999), packing house wash water, or shipping ice (Hedberg et al., 1994; Tauxe, 1997).
What are best consumer practices to reduce the risk of contaminating the meat of the melon by contact with surface bacteria? Note that contamination of the meat can occur during cutting, so it is important to (1) simply avoid cantaloupe during an outbreak and (2) take measures to clean the entire melon before preparing it for consumption. The same article by Parnell, Harris, and Susslow, says:
scrubbing with water resulted in reductions comparable to soaking in 200 ppm of total chlorine, while scrubbing in chlorine provided the greatest reduction. However, in the absence of chlorine, Salmonella spread from inoculated to uninoculated surfaces. Washing cantaloupes in a common batch-water system is strongly discouraged for packinghouses, processors, foodservice, and home consumers.
In agreement with current recommendations, consumers and food service industries should scrub melons with a clean brush under running water. It is important that these instructions also include advice on cleaning and sanitizing brushes prior to and after preparation as using a contaminated scrub brush may negate the benefits achieved with washing. Brushes can be cleaned either by washing in the dishwasher with a hot cycle or by soaking in a 200 ppm total chlorine solution made with 45 ml household bleach (5% sodium hypochlorite)/l water