Surveillance

How does it work?

Enteric bacterial pathogens are isolated from human clinical cases

Molecular subtyping, pulsed-field gel electrophoresis (PFGE), is performed by participating laboratories using standardized methodology, equipment, and software.

Molecular subtyping results are entered into electronic databases at the provincial and federal (NML) laboratories.  Participating members are certified and have a direct link to the federal databases.

Participating laboratories post clusters of cases with matching PFGE patterns in their jurisdictions to the PulseNet Canada discussion board on the Canadian Network for Public Health Intelligence .  Members view and respond to postings on a daily basis.

Database managers at NML search for clusters of indistinguishable patterns in more than one province; results are report to the participating lab(s), PHAC epidemiologists, and are posted to the discussion board. 

What diseases/pathogens are involved?

PulseNet Canada performs molecular subtyping on all E. coli O157:H7 cases and most cases of Salmonella in close to real-time.  Additionally, PulseNet has the capability for molecular subtyping of Listeria monocytogenes, Campylobacter, Shigella, and Vibrio.

Source of information: Public Health Agency of Canada (Disease Surveillance On-Line)

E. coli O157:H7

WORLDWIDE DISTRIBUTION:  This category of E. coli was first recognized in 1982, when an outbreak of bleeding colitis (inflammation of the large intestine) occurred in the United States. These infections are now an important public health problem in North America, Japan, Europe, South Africa, southern South America and Australia.

SYMPTOMS: Diarrhea ranges in severity from mild with no blood in the stools to severe with stools that are virtually all blood. There is little or no fever associated with this infection. Most people recover without antibiotic treatment within 5 to 10 days after exposure.  Children < 5 years of age and the elderly are susceptible to a complication called "hemolytic uremic syndrome"(HUS), in which the red blood cells are destoyed and the kidneys fail. HUS is a life-threatening condition usually treated in an intensive care unit. Blood transfusions and kidney dialysis are often required.

PERIOD OF COMMUNICABILITY: A person is capable of transmitting the infection for as long as the bacteria are present in stools, usually 1 week or less in adults and up to 3 weeks in 33% of infected children.

HOW IT IS TRANSMITTED: Transmission occurs by eating contaminated food, most frequently undercooked beef, especially ground beef. Unpasteurized or raw milk has also been identified as a source of contamination. Person-to-person transmission may occur in families, child care centres and nursing homes. Waterborne transmission can occur: one outbreak was associated with swimming in a crowded lake, and one was associated with drinking contaminated unchlorinated municipal water.

Salmonella

WORLDWIDE DISTRIBUTION: The types most often reported as the cause of human illness in Canada are S. typhimurium and S. enteritidis although over 2000 types, or species, of Salmonella are known.Occurrence is worldwide. It is estimated that only 1% of all infections are ever clinically recognized. The incidence rate of infection is highest among infants and young children. About 60-80% of all cases occur sporadically; however, large outbreaks in hospitals, institutions for children, restaurants, nursing homes and the community are common and usually arise from food contaminated at source or during handling by an ill person or carrier, although person-to-person transmission can occur.

SYMPTOMS: Symptoms usually appear 12-48 hours after consumption of contaminated food or beverages. Symptoms include sudden onset of headache, abdominal pain, diarrhea, nausea and sometimes vomiting. Dehydration, especially among the young, the elderly and those with impaired immune systems, can be severe, and the person may become ill enough to be hospitalized. In these patients, the infection may spread to the bloodstream; occasionally, the bacteria may localize in any tissue of the body, producing abscesses and causing, for example, pneumonia. The infection can result in death unless the person is treated promptly with antibiotics.

PERIOD OF COMMUNICABILITY: An infected person remains infectious throughout the illness, and may continue to excrete the bacteria for a while after symptoms have stopped, making good personal hygiene very important.

HOW IT IS TRANSMITTED: Most types of Salmonella live in the intestines of animals and birds. Infection is acquired by the ingestion of organisms in food contaminated by the stool of an infected animal or person. The most common food sources include raw and undercooked eggs and egg products, raw milk and raw milk products, contaminated water, meat and meat products, poultry and poultry products and raw fruits and vegetables. Pets are another common source of infection. The bacteria can be carried by iguanas, turtles, tortoises, chicks, and sometimes cats and dogs. Farm animals may become infected through the ingestion of feeds and fertilizers prepared from contaminated meat scraps, tankage, fish meal and bones. Fecal-oral transmission from person-to-person is important when diarrhea is present, especially in institutional settings.

Shigella

WORLDWIDE DISTRIBUTION:  Shigellosis is caused by bacilli belonging to the Shigella family.The most common subtypes are S. sonnei, S. flexneri, S. boydii, S. dysenteriae 1 (shigae), S. dysenteriae (schmitzii).  Occurrence is worldwide. It accounts for >600,000 deaths/year, with 2/3 of all deaths occurring in children under 10 years of age. Outbreaks are common, particularly among homosexual men and in areas of overcrowding where sanitation is poor, such as jails, institutions for children, daycare centres, mental hospitals and crowded refugee camps. In general, S. flexneri, S. boydii, and S. dysenteriae 1 account for most cases in developing countries. In developed countries, S. sonnei is most common and S. dysenteriae is the least common. Multi-antibiotic resistant strains have appeared worldwide, resulting from wide spread use of antibiotics.

SYMPTOMS:  The incubation period is usually quite brief, lasting for 12-96 hours. The illness is characterized by diarrhea accompanied by fever, nausea, vomiting, and cramps. In typical cases, the stools may contain blood and mucus, resulting from tiny abscesses on the intestinal wall. Convulsions may be an important complication in children. The severity of illness and the case-fatality rate is influenced by several factors: age of the patient, presence of underlying disease, and the type of Shigella. S. dysenteriae 1causes the most severe illness and the most severe complications with a death rate as high as 20%.

PERIOD OF COMMUNICABILITY:  An infected person is capable of transmitting the bacteria as long as the bacteria remain in the feces.

HOW IT IS TRANSMITTED:  The bacteria is transmitted via the fecal-oral route. Person-to-person transmission is most common among children and in circumstances where hygiene practices are poor. In these cases, persons do not wash their hands thoroughly after using the toilet. Subsequently, the infection is transmitted by direct physical touching of the hand(s) or indirectly through contaminated food. Contaminated fecal matter can infect open sources of water and food. Flies can transmit enough of the bacteria from waste products to infect items of food.

Campylobacter

WORLDWIDE DISTRIBUTION:  Campylobacteriosis is caused by the bacteria, Campylobacter jejuni and Campylobacter coli.  Statistics show that, globally, 5-14% of reported cases of diarrhea are caused by infection with Campylobacter. In industrialized countries the illness affects predominantly children older than 5 years of age and young adults. In developing countries, the persons most affected are infants and children under 2 years.

SYMPTOMS:  Symptoms occur 2-10 days after initial exposure and are characterized by diarrhea, abdominal pain, malaise, fever, nausea and vomiting. The symptoms can vary from mild to severe. Relapses can occur. Blood and mucus may be present in liquid stools. Complications include typhoid-like syndrome, arthritis, febrile convulsions, meningitis (the bacteria infects the membrane which lines the surface of the brain) and Guillaume-Barre syndrome (an illness which causes progressive weakness and paralysis; recovery is often slow and the condition may lead to death in some cases).

PERIOD OF COMMUNICABILITY:  An infected person can pass the infection on throughout the illness, which usually lasts from several days to several weeks.

HOW IT IS TRANSMITTED: A person becomes infected by eating undercooked pork or chicken, contaminated food or water, or unpasteurized millk. The bacteria can transfer from a primary source, such as chicken, to contaminate other foods or surfaces, including cutting boards, knives, and plates. A person may also become infected from close contact with infected puppies or kittens, farm animals or infected infants.

Listeria monocytogenes

WORLDWIDE DISTRIBUTION:  Listeriosis is caused by the bacterium, Listeria monocytogenes. The bacteria are found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Livestock become contaminated after eating contaminated silage or water. Unpasteurized milk, or foods made from unpasteurized milk may also contain the bacterium.Occurrence is worldwide. Cases usually occur sporadically; however, several outbreaks have been recognized in recent years.

SYMPTOMS: The incubation period ranges from 3 to 70 days, with the median incubation estimated at 3 weeks. A person with listeriosis usually has fever, muscle aches, and sometimes, nausea and vomiting. The bacteria may infect the brain and the membrane lining the brain causing meningoencephalitis. The onset of meningoencephalitis may be sudden, with fever, intense headache, nausea, and vomiting. Complications include endocarditis (the bacteria infects the membrane lining the cavities of the heart), and internal and external abscesses. Infected pregnant women may have minimal symptoms, characterized by a mild flu-like illness. An infected pregnant woman may unknowingly pass on the illness to her unborn child in utero. Infection during pregnancy may lead to premature delivery, infection of the newborn or stillbirth. The infant may develop meningitis. Thirty percent of infant infections are fatal. If onset of illness occurs within the first four days of life, the case-fatality rate is 50%.

PERIOD OF COMMUNICABILITY:  Infected persons may retain the bacteria in their stools for several months. Mothers of infected babies mayretain the bacteria in vaginal discharges and urine for 7-10 days after delivery.

HOW IT IS TRANSMITTED:  A person contracts listeriosis by eating food contaminated with the bacterium, L. monocytogenes. The bacteria is found in soil and water. Livestock become infected after ingesting silage or water contaminated with the bacteria. Vegetables can be contaminated from the soil or from manure used as a fertilizer. The bacterium has been found in raw foods, such as uncooked meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and coldcuts. Unpasteurized milk or food made with unpasteurized milk may contain the bacterium.
The following persons are most likely to become infected with the bacteria:

• pregnant women are about 20 times more likely than other healthy adults to get listeriosis;
• newborns;
• persons with weakened immune systems;
• persons with cancer, diabetes or kidney disease;
• persons with AIDS are almost 300 times more likely to get listeriosis than persons with normal immune function;
• persons who take glucocorticosteroid medication;
• the elderly.