Salmonella Blog - Surveillance & analysis on salmonella news & outbreaks

Thank goodness for the AP and Mike Stobbe covering the CDC. He reports today that more Americans got food poisoning last year, with Salmonella cases driving the increase, the government reported Tuesday. Illness rates for the most common serious type of E. coli fell last year. There was a rise in cases caused by other strains of the bacteria, although that bump may just reflect more testing was done for them, the Centers for Disease Control and Prevention said.An unusually aggressive strain of E. coli is behind the current large outbreak of food poisoning in Europe, mostly in Germany. That strain has never caused an outbreak in the U.S.

The CDC estimates that 50 million Americans each year get sick from foodborne illnesses, including about 3,000 who die.

The report released Tuesday is based on foodborne infections in only 10 states, or about 15 percent of the American population. But it has information that other databases lack and is believed to be a good indicator of food poisoning trends.

More than 19,000 cases of food poisoning were reported in those states last year. That was up from 17,500 cases in 2009, and about 18,500 in 2008.

Last year, there were 4,200 hospitalizations and 68 deaths in those states.

One of the largest U.S. outbreaks last year involved salmonella tainted eggs that may have sickened as many as 56,000, according to a CDC estimate. That probably contributed to the increase seen in Tuesday's report, said Dr. Christopher Braden, a CDC epidemiologist.

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.

Symptoms of Salmonella infection

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).