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Salmonella is a bacterium that causes one of the most common enteric (intestinal) infections in the United States – Salmonellosis. In some states (e.g. Georgia, Maryland), salmonellosis is the most commonly reported cause of enteric disease, and overall it is the second most common bacterial foodborne illness reported (usually slightly less frequent than Campylobacter infection).
The reported incidence of Salmonella illnesses is about 14 cases per each 100,000 persons (MMWR Weekly, 2006), amounting to approximately 30,000 confirmed cases of salmonellosis yearly in the U.S. (CDC, 2005, October 13). In 2005, just over 36,000 cases were reported from public health laboratories across the nation, representing a 12 percent decrease compared with the previous decade, but a 1.5 percent increase over 2004 (CDC, 2007).
As only about 3 percent of Salmonella cases are officially reported nationwide, and many milder cases are never diagnosed, the true incidence is undoubtedly much higher (Mead, 1999). The CDC estimates that 1.4 million cases occur annually (CDC, 2005, October 13). Approximately 600 deaths are caused by Salmonella infections in the U.S. every year, accounting for 31 percent of all food-related deaths (CDC, 2005, October 13; MMWR Weekly, 2001).
Theobald Smith, research-assistant to Daniel E. Salmon, discovered the first strain of Salmonella – Salmonella cholerae suis – in 1885. Since that time, the number of strains (technically termed serotypes or serovars) of Salmonella known to cause salmonellosis has increased to over 2,300. Salmonella typhi, the strain that causes typhoid fever, is uncommon in the U.S., while Salmonella enterica serotype Typhimurium and Salmonella enterica serotype Enteritidis have been the most frequently reported illnesses since 1993. Salmonella enterica serotypes Newport, Mississippi and Javiana have been increasingly identified as the source of illness (MMWR Weekly, 2006).
Symptoms of Salmonella Infection
An infectious dose of Salmonella is small, probably from 15 to 20 cells. Typically, non-typhoidal Salmonella produces a self-limiting febrile gastrointestinal illness that is indistinguishable from that caused by other bacterial enteric pathogens. Dehydration is the principal clinical concern. The incubation period – the time between ingestion of Salmonella bacteria and the onset of illness – varies from six to 72 hours (Mayo Clinic, 2007, April 12; MMWR Recomm Rep, 2001).
Salmonella can cause three different kinds of illness: gastroenteritis, typhoid fever, and bacteremia.
Symptoms of Salmonella gastroenteritis include diarrhea, abdominal cramps, fever, nausea, and/or vomiting. In mild cases diarrhea may be non-bloody, occur several times per day, and not be very voluminous; in severe cases it may be frequent, bloody and/or mucoid, and of high volume.
Fever generally occurs in the 100°F to 102°F (38°C to 39°C) range. Vomiting is less common than diarrhea. Headaches, myalgias (muscle pain), and arthralgias (joint pain) are often reported as well. Whereas the diarrhea typically lasts 24 to 72 hours, patients often report fatigue and other nonspecific symptoms lasting 7 days or longer.
Complications of Salmonella Infection
Typhoid fever, also known as enteric fever, is caused by Salmonella serotype typhi. The onset of symptoms usually occurs between 5 and 21 days after ingestion of Salmonela typhi bacteria. Symptoms may include constipation, cough, sore throat, headache, and a rash on the infected individual’s chest, as well as the slowing of the heartbeat and enlargement of the liver and spleen (Mayo Clinic, 2007, April 12).
Bacteremia is characterized by infection of tissues surrounding the brain and spinal cord (meningitis) and infection within the bloodstream (sepsis). This condition occurs when Salmonella enter and circulate within an infected individual’s bloodstream, and is accompanied by few symptoms (Mayo Clinic, 2007, April 12).
Salmonella is one of the most common enteric (intestinal) infections in the United States. Salmonellosis (the disease caused by Salmonella) is the second most common foodborne illness after Campylobacter infection. It is estimated that 1.4 million cases of salmonellosis occur each year in the U.S.; 95% of those cases are foodborne-related. Approximately 220 of each 1000 cases result in hospitalization and eight of every 1000 cases result in death. About 500 to 1,000 or 31% of all food-related deaths are caused by Salmonella infections each year. Salmonellosis is more common in the warmer months of the year.
Salmonella infection occurs when the bacteria are ingested, typically from food derived from infected food-animals, but it can also occur by ingesting the feces of an infected animal or person. Food sources include raw or undercooked eggs/egg products, raw milk or raw milk products, contaminated water, meat and meat products, and poultry. Raw fruits and vegetables contaminated during slicing have been implicated in several foodborne outbreaks.
By Lonny Stark
May 17, 2006
E. coli O157:H7 — Although it doesn’t typically cause a fever, this bacteria inflicts more severe abdominal cramps as well as bloody diarrhea. In extreme cases, it may cause anemia, profuse bleeding, and kidney failure. E. coli is present in the feces of cattle, so contaminated beef is the most common cause of infection.
Salmonella — Found in the intestines of birds, reptiles and mammals, this nasty bacteria causes all kinds of gastrointestinal distress in humans, including abdominal cramps and diarrhea. It can also cause a fever, and in those with weakened immune systems, it may invade the bloodstream and bones. Any improperly handled foods may be contaminated by Salmonella, but in recent years eggs have often been the cause of human infection.