Salmonella are bacteria that can cause food poisoning (gastroenteritis), typhoid fever, and bacteremia. All Salmonella infections start by ingestion of contaminated water or food; egg-associated salmonellosis is a major cause of food-borne illness. Typhoid fever is transmitted from human to human via contaminated food or water. Vaccines for typhoid fever are recommended for people traveling to India, for example, where the disease is endemic. The young, elderly and people with weakened immune systems are at risk for more severe illness.
Food Poisoning
Salmonella food poisoning can be transmitted by meat, poultry, eggs and even orange juice. The U.S. Centers for Disease Control and Prevention (CDC) estimates there are 2 million cases per year with 500 to 2,000 deaths.
Egg-associated salmonellosis is a major cause of food-borne illness in the US and several European countries. A strain of Salmonella (enteritidis) infects the ovaries of healthy hens and contaminates the eggs before the shells are formed. Consequently, normal-appearing grade A eggs that have been infected can cause gastroenteritis, if the eggs are eaten raw or undercooked.
A person infected with this strain of Salmonella usually has fever, abdominal cramps, and diarrhea beginning 12 to 72 hours after eating a contaminated food or beverage. The illness lasts four to seven days, and most persons recover without antibiotic treatment. The diarrhea, however, can be severe, and the person may require hospitalization.
Typhoid Fever
Typhoid fever is also called enteric fever. It may be caused by two different strains of Salmonella (typhi, or paratyphi). Humans with acute or chronic infections serve as the reservoir of infection and transmit the disease to other people usually via contaminated food, or water. It is rare in developed nations, but endemic in India, South America and Asia. According to Harrison's Principles of Internal Medicine, it is estimated that 13 to 17 million cases occur worldwide per year with 600,000 deaths.
Typhoid fever vaccine is recommended for travelers to these countries, unless contraindicated due to pregnancy or a weakened immune system.
After an incubation period of three to 21 days, the patient may experience chills, headaches, weakness and muscle pains. Prolonged fevers of 102F to 104F are the most prominent symptom of this illness. Patients can present with either diarrhea or constipation.
An early physical finding is a rash called "rose spots" on the chest and trunk; the rash is a salmon-colored. The gold standard diagnostic test is a culture, either stool, urine, bone marrow or blood, that is positive for Salmonella.
Bacteremia
In approximately 5 percent of patients with Salmonella food posioning, the organism will enter the bloodstream (bacteremia), especially if the patient is an infant, elderly, or immunocompromised (transplant recipient, or HIV-positive). Salmonellae target vascular sites to infect; consequently, an infection of the inside of the heart (endocarditis) and infection inside an artery (arteritis) may be rare complications, but can have devastating consequences such as heart valve perforation or ruptured aneurysm.
In typhoid fever, approximately 90 percent of blood cultures are positive during the first week of infection and 50 percent are still positive by week three.
Bacteremia is a life-threatening infection. Before antibiotics---specifically, chloramphenicol---was introduced in 1948, the mortality rate from typhoid fever was up to 15 percent. After chloramphenicol, mortality decreased to less than 1 percent.
References
- U.S. Centers for Disease Control and Prevention (CDC): Salmonella enteritidis
- "Harrison's Principles of Internal Medicine"; Dennis Kasper, M.D.; 2005
