Foodborne Diseases, NIAID Fact Sheet: NIAID


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Article title: Foodborne Diseases, NIAID Fact Sheet: NIAID
Conditions: Foodborne Diseases, Enterohemorrhagic Escherichia Coli Infection, EHEC, Salmonellosis, Campylobacter, Shigellosis
Source: NIAID

Foodborne Diseases

September 2000
Overview
Enterohemorrhagic Escherichia Coli Infection
Salmonellosis
Campylobacter Infections
Shigella Infections
NIAID Research on Foodborne Diseases
For More Information



Overview

Infectious diseases spread through food - so-called foodborne illnesses - are a common, distressing, and sometimes life-threatening problem for millions of people in the United States and around the world. Scientists estimate that the 76 million foodborne illnesses that occur each year in the United States account for 325,000 hospitalizations and 5,000 deaths. Persons infected with foodborne organisms may have no symptoms or can develop symptoms ranging from mild intestinal discomfort to severe dehydration, bloody diarrhea, and death.

Foodborne illness is also extremely costly. Researchers estimate that the yearly cost of all foodborne diseases in this country is $5 to $6 billion in direct medical expenses and lost productivity. Infections with the bacteria Salmonella and Campylobacter alone account for $1 billion in direct and indirect medical costs.

Some basic ways to help protect yourself from being infected by most foodborne diseases include:
  • Wash your hands carefully before preparing food.
  • Thoroughly cook beef and beef products, especially hamburger.
  • Thoroughly cook poultry and eggs.
  • Wash fruits and vegetables thoroughly, especially those that will not be cooked.
  • Don't drink unpasteurized milk and juices and untreated surface water.
  • Wash your hands, utensils, and kitchen surfaces with hot soapy water after they touch raw meat or poultry.
  • Wash your hands carefully after changing infant diapers or cleaning up animal feces.
The National Institute of Allergy and Infectious Diseases (NIAID), a component of the National Institutes of Health, works with other research institutions to conduct and support basic, clinical, and applied research aimed at understanding, detecting, treating, and preventing foodborne diseases. Those described below are among the most common and serious.

Enterohemorrhagic Escherichia Coli Infection

Escherichia coli, commonly called E. coli, is just one of many bacteria that can cause diarrhea. While harmless strains of E. coli normally can be found widely in nature, including the intestinal tracts of humans and other vertebrates, disease-causing types are a frequent cause of both intestinal and urinary-genital tract infections. Several different types of harmful, or pathogenic, E. coli can cause diarrheal disease. A particularly dangerous type is referred to as enterohemorrhagic E. coli, or EHEC. In 1982, scientists identified the first such strain in the United States. Since then, EHEC strains have been associated with foodborne outbreaks traced to undercooked hamburgers, unpasteurized apple juice or cider, salad, salami, and unpasteurized milk. Recent outbreaks have also been traced to contaminated well water and improperly disinfected swimming pools.

The strain of EHEC most commonly found in the United States is designated O157:H7. Others, including O26:H11 and O111:H8, also have been found in this country, and can cause human disease. EHEC strains produce toxins (poisons) that are structurally similar and have effects like those produced by Shigella dysenteriae bacteria. These toxins can damage the lining of the intestine, cause anemia, stomach cramps and bloody diarrhea, and a serious complication called hemolytic uremic syndrome (HUS), which can lead to kidney failure. In North America, HUS is the most common cause of acute kidney failure in children, who are particularly susceptible to this complication.

Cattle are known to carry EHEC, but other domestic and wild animals and birds also can harbor these bacteria. Heat destroys EHEC and its toxins. To avoid infection from E. coli:
  • Eat only thoroughly cooked beef and beef products.
  • Cook ground beef patties to an internal temperature of 160 degrees Farenheit
  • Avoid unpasteurized juices.
  • Thoroughly wash uncooked fresh fruits and vegetables.

Salmonellosis

Salmonellosis is an infection caused by Salmonella bacteria. Salmonella infections are increasing in the United States. The disease causes acute intestinal distress with sudden onset of headache, fever, abdominal pain, diarrhea, nausea, and sometimes vomiting.

These symptoms, along with loss of appetite, can last for several days. Dehydration (extreme loss of body water), especially among infants, can be severe. Salmonella is an invasive organism that can escape from the intestine and be spread by the blood to other organs. It can become a chronic infection in some people, who may have no symptoms yet can spread the disease to others. While most people recover successfully from salmonellosis, a few will experience long-term symptoms such as arthritis. Salmonellosis can be a very serious or even deadly infection in those who are very young, elderly, or have weakened immune systems.

Many types of Salmonella cause disease in both animals and people. While the prevalence of different types of Salmonella species vary from country to country, in the United States Salmonella typhimurium and Salmonella enteritidis are the two most commonly reported. An antibiotic-resistant strain of Salmonella typhimurium, called Definitive Type 104 (DT104), first emerged in the United Kingdom in 1984 and was recently detected in the United States. Now it is the second most prevalent strain (after enteritidis) of Salmonella found in humans. This strain poses a major new threat because it is resistant to several antibiotics normally used to treat people with Salmonella infections including ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline.

Salmonellosis occurs worldwide, but it is most often reported in North America and Europe. The U.S. Centers for Disease Control and Prevention (CDC) estimates that 1.4 million people in the United States are infected each year with Salmonella. Only a small proportion of infected people are tested and diagnosed, with as few as 2 percent of cases reported to CDC. Salmonellosis may occur in small, localized outbreaks in the general population or in large outbreaks in hospitals, restaurants, or institutions for children or the elderly.

To avoid Salmonella infections:
  • Don't drink unpasteurized milk.
  • Don't eat undercooked poultry and poultry products such as eggs.
  • Avoid contact with infected domestic and wild animals, including poultry, pigs, cattle, and pets such as turtles, iguanas, chicks, dogs, and cats.
In addition, other types of food prepared on surfaces contaminated by raw chicken or turkey can, in turn, become contaminated with the bacteria. Less often, the illness stems from food contaminated by a food worker.

Campylobacter Infections

Campylobacteriosis is caused by species of the Campylobacter bacteria. Its symptoms include inflammation of the small intestine, diarrhea, nausea, vomiting, tiredness, and fever. CDC estimates that Campylobacter is the leading cause of diarrheal disease in the United States, causing 2.5 million cases per year. While some infections have no symptoms, others may result in arthritis and, rarely, febrile convulsions or meningitis. Campylobacter jejuni, C. fetus, and C. coli are the usual causes of campylobacteriosis in people.

Campylobacter organisms cause between 5 and 14 percent of all diarrheal illness worldwide. In industrialized countries, illness is more common in children younger than 2 years of age. In developing countries, older children and young adults have the highest incidence of infection. Most frequently, cattle and poultry are the sources of human infection, but puppies, kittens, pigs, sheep, rodents, and birds may also serve as reservoirs.

Most people get campylobacteriosis by handling raw poultry or eating raw or undercooked poultry meat. Large outbreaks due to Campylobacter are usually associated with drinking unpasteurized milk or contaminated water. Animals can also be infected, and some people have gotten infected by contact with the infected stool of an ill dog or cat.

A small number of people with Campylobacter may develop Guillain-Barré Syndrome (GBS), the leading cause of acute paralysis in this country. GBS develops two to four weeks after Campylobacter infection and usually after diarrheal symptoms have disappeared. People with GBS suffer from progressive paralysis of the limbs that lasts for several weeks, and in more severe cases, develop respiratory failure requiring prolonged hospitalization.

Shigella Infections

Shigellosis, also called bacillary dysentery, causes bloody diarrhea, fever, nausea, vomiting, and cramps. CDC estimates that more than 400,000 cases occur every year in the United States. Four main species of Shigella cause disease: Shigella dysenteriae, S. flexneri, S. boydii and S. sonnei. S. dysenteriae type 1, like EHEC, produces Shiga toxin and can lead to life threatening hemolytic uremic syndrome.

Outbreaks of shigellosis frequently occur in tropical or temperate climates, especially under conditions of severe crowding and poor sanitation such as occurs in refugee settings, where personal hygiene is poor. S. sonnei is the most common of the Shigella species in developed countries, including the United States. While outbreaks have occurred in primate colonies, the only significant carriers are people. Shigella organisms are generally transmitted via the fecal-oral route. Like EHEC, the infectious human dose can be as few as 10 organisms. Infected food workers can cause outbreaks in eating establishments.

NIAID Research on Foodborne Diseases

Basic research is helping researchers to better understand how the organisms that can be spread by contaminated food or water cause disease in humans. NIAID-supported researchers are studying the bacterial genes that play a role in colonization and pathogenesis of these organisms. For example, genes have been identified that appear to be involved in the signaling of immune system cells that cause inflammation, and which may contribute to the development of diarrhea.

Other NIAID-sponsored research focuses on methods by which the organism grows and interacts in host cells. Scientists have discovered that some intestinal bacteria recognize when they are in a human host and respond by activating a particular set of virulence genes that enable the organism to colonize the host and cause disease. Future studies will define new ways to intervene, whether by prevention or treatment, in the disease process.

In recent studies of EHEC and Shigella infections, NIAID-sponsored scientists have identified a gene in both types of bacteria that allows the organisms to resist the usually lethal effects of stomach acid. The great majority (85 percent, as shown in recent NIAID studies) of EHEC infections are caused by acid-resistant bacteria. The remaining 15 percent are caused by bacteria that have defects in a certain control gene common to all intestinal bacteria. This gene turns on other genes and results in acid resistance. Isolating a gene that confers such a biological advantage is an important step toward improved treatment and prevention.

In other studies on EHEC, NIAID-sponsored investigators are further defining the mechanisms by which the toxins produced by EHEC and Shigella result in the kidney damage leading to hemolytic uremic syndrome. The primary goal of this research is to enhance understanding of physiological mechanisms underlying the progression of kidney vascular disease. Researchers are developing antitoxins that may be useful in preventing the development of hemolytic uremic syndrome in children who become infected. Researchers also are exploring vaccine approaches that would prevent EHEC and Shigella infections of animals or people.

Preliminary tests of live, attenuated Shigella flexneri vaccine candidates have resulted in the discovery of two new toxins that may contribute to the diarrhea associated with Shigella species. Studies are under way to clarify the mechanism by which these toxins bring about fluid loss. The findings will provide crucial information on how to improve attenuated vaccines to prevent shigellosis.

The NIAID enteric diseases program also supports basic and clinical research on other pathogens including Vibrio cholerae, Helicobacter pylori, Yersinia, Listeria, Clostridia, Bacteroides, Staphylococcus and effects of toxins on the intestinal tract.

The complete DNA sequence of several of these foodborne pathogens have been or are being determined with NIAID support. Scientists anticipate that this new information will speed the discovery of new targets for treatment interventions and vaccine strategies against this group of important human pathogens.

NIAID supports an Enteric Pathogens Research Unit to carry out research on the mucosal immune response to infection with intestinal pathogens. Because foodborne pathogens universally affect the intestinal mucosa, these studies will provide information needed to engineer vaccines or develop treatment for diseases caused by these organisms. The research includes clinical trials of vaccine candidates and the use of adjuvants, delivery systems, or dosing schedules that will help scientists determine how best to enhance the immune response to vaccines.

In addition to the organisms mentioned above, NIAID conducts research on other gastrointestinal pathogens such as Norwalk viruses, rotaviruses, and hepatitis A virus. Scientists at the NIAID Laboratory of Infectious Diseases devised the first method for detecting Norwalk virus particles and for measuring Norwalk virus-specific antibodies (disease-fighting proteins). Current studies are trying to produce new vaccines including edible vaccines against Norwalk virus and hepatitis A. NIAID scientists also developed a recently licensed inactivated vaccine for hepatitis A virus infection.

As foodborne and waterborne diseases continue to have a major impact on health in the United States and elsewhere in the world, and with the emergence of drug-resistant strains of many organisms including Salmonella, biomedical research will continue to play a critical role in understanding the disease process, and in preventing and controlling these infections.

For More Information

Centers for Disease Control and Prevention
National Center for Infectious Diseases
Division of Bacterial and Mycotic Diseases
Atlanta, GA 30333
1-888-232-3228
http://www.cdc.gov/ncidod/dbmd/diseaseinfo/foodborneinfections_g.htm

Food and Drug Administration
Center for Food Safety and Applied Nutrition
200 C Street SW
Washington, DC 20204
1-800-532-4440
http://vm.cfsan.fda.gov/list.html



NIAID is a component of the National Institutes of Health (NIH). NIAID conducts and supports research on HIV and AIDS, malaria, tuberculosis and other infectious diseases, as well as allergies and immunology. NIH is an agency of the U.S. Department of Health and Human Services.

Prepared by:
Office of Communications and Public Liaison
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892

Public Health Service
U.S. Department of Health and Human Services



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