Salmonella infection: transmission, disease characteristics, and outbreak investigation

Salmonella

Salmonellosis is an infection with bacteria called Salmonella. Salmonella germs have been known to cause illness for over 100 years. The bacteria were first isolated in 1885 by Theobald Smith from pigs. The genus name was derived from the last name of D.E. Salmon, who was Smith's director. In 1896 Salmonella infection was diagnosed in humans. Salmonella is the genus name for over 2,500 types of bacteria. Though each type is closely related each is distinctly identifiable by its specific protein. Salmonella bacteria are known to cause disease in humans, animals, and birds throughout the world. The major diseases caused by Salmonella are gastroenteritis and typhoid fever (Davis, 2010).

According to the CDC (2010) approximately 40,000 cases of salmonellosis are reported in the United States each year. Since many milder cases are not diagnosed or reported, some estimate that the actual number of infections may be thirty or more times greater. Salmonella serotype Typhimurium and Salmonella serotype Enteritidis are the most common in the United States. Salmonellosis is more common in the summer than winter. It is estimated that each year approximately 400 persons die with acute Salmonellosis (CDC, 2010).

Transmittal of Salmonella

Salmonellosis is spread to people by ingestion of Salmonella bacteria through contaminated food. Salmonella can contaminate almost any food type; however outbreaks of the disease have involved eggs, raw meat, egg products, fresh vegetables, cereal, pistachio nuts, tomatoes, and contaminated water. Contamination can come from animal or human feces that contact the food during processing or harvesting. Potential direct sources of Salmonella are pets, such as turtles, dogs, cats, most farm animals, and humans that are infected or are carriers of the organisms. Although typhoid and paratyphoid fevers can be transmitted by the same methods as salmonellosis, their most frequent manner of transmission is by the feces of infected people contaminating the water or food source of uninfected people (Davis, 2010).

Clinical Features/Signs and Symptoms

Most persons infected with Salmonella bacteria develop diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts 4 to 7 days, and most persons recover without treatment. However, in some persons, the diarrhea may be so severe that the patient needs to be hospitalized. Salmonella infection may spread from the intestines to the bloodstream and then to other body sites and can cause death unless the person is treated promptly with antibiotics. Older adults, infants, and those with impaired immune systems are more likely to suffer a severe illness as a result of Salmonella infection.

Persons with diarrhea usually recover completely, although it may be several months before their bowel habits are entirely normal. A small number of persons with Salmonella develop pain in their joints, irritation of the eyes, and painful urination. This is called Reiter's syndrome. It can last for months or years, and can lead to chronic arthritis which is difficult to treat. Antibiotic treatment does not make a difference in whether or not the person develops arthritis (CDC, 2010).

Preventative Measures

The key to the prevention of Salmonella is cleanliness. Hand washing with soap and hot water, especially after handling eggs, poultry, and raw meat is likely to reduce the chance for infections. Additionally, antibacterial soaps have also been recommended as well as using chlorine-treated drinking water, washing produce, and avoiding the ingestion of undercooked foods such as eggs, and meat. Furthermore, avoiding direct contact with animal carriers of Salmonella also may reduce the risk of infection. Human carriers of Salmonella should never work in the food-handling service industry and ideally should undergo gallbladder removal and antibiotic therapy for an attempt for a cure of the carrier state (Davis, 2010).

Public-health authorities that enforce restaurant cleanliness and employee hand washing have helped in general prevention. Public-health authorities also initiate recalls when products are contaminated with Salmonella or other contaminating organisms or toxins. Salmonella vaccines are available for poultry and animals; however human vaccines are available only for typhoid fever. Currently the CDC recommends only those going to developing countries where typhoid fever is endemic receive the vaccine (Davis, 2010).