Bad Bug Book:
Foodborne Pathogenic Microorganisms and Natural Toxins Handbook
1. Name of the Organism:
Salmonella is a rod-shaped, motile bacterium -- nonmotile exceptions S. gallinarum and S. pullorum--, nonsporeforming and Gram-negative. There is a widespread occurrence in animals, especially in poultry and swine. Environmental sources of the organism include water, soil, insects, factory surfaces, kitchen surfaces, animal feces, raw meats, raw poultry, and raw seafoods, to name only a few.
2. Nature of Acute Disease:
S. typhi and the paratyphoid bacteria are normally caused septicemic and produce typhoid or typhoid-like fever in humans. Other forms of salmonellosis generally produce milder symptoms.
3. Nature of Disease:
Acute symptoms -- Nausea, vomiting, abdominal cramps, minal diarrhea, fever, and headache. Chronic consequences -- arthritic symptoms may follow 3-4 weeks after onset of acute symptoms. Onset time -- 6-48 hours. Infective dose -- As few as 15-20 cells; depends upon age and health of host, and strain differences among the members of the genus. Duration of symptoms -- Acute symptoms may last for 1 to 2 days or may be prolonged, again depending on host factors, ingested dose, and strain characteristics. Cause of disease -- Penetration and passage of Salmonella organisms from gut lumen into epithelium of small intestine where inflammation occurs; there is evidence that an enterotoxin may be produced, perhaps within the enterocyte.
4. Diagnosis of Human Illness:
Serological identification of culture isolated from stool.
5. Associated Foods:
Raw meats, poultry, eggs, milk and dairy products, fish, shrimp, frog legs, yeast, coconut, sauces and salad dressing, cake mixes, cream-filled desserts and toppings, dried gelatin, peanut butter, cocoa, and chocolate.
Various Salmonella species have long been isolated from the outside of egg shells. The present situation with S. enteritidis is complicated by the presence of the organism inside the egg, in the yolk. This and other information strongly suggest vertical transmission, i.e., deposition of the organism in the yolk by an infected layer hen prior to shell deposition. Foods other than eggs have also caused outbreaks of S. enteritidis disease.
6. Relative Frequency of Disease:
It is estimated that from 2 to 4 million cases of salmonellosis occur in the U.S. annually.
The incidence of salmonellosis appears to be rising both in the U.S. and in other industrialized nations. S. enteritidis isolations from humans have shown a dramatic rise in the past decade, particularly in the northeast United States (6-fold or more), and the increase in human infections is spreading south and west, with sporadic outbreaks in other regions.
Reported cases of Salmonellosis in the U.S. excluding typhoid fever for the years 1988 to 1995. The number of cases for each year varies between 40,000 and 50,000. From Summary of Notifiable Diseases, United States MMWR 44(53): 1996 (October 25).
S. typhi and S. paratyphi A, B, and C produce typhoid and typhoid-like fever in humans. Various organs may be infected, leading to lesions. The fatality rate of typhoid fever is 10% compared to less than 1% for most forms of salmonellosis. S. dublin has a 15% mortality rate when septicemic in the elderly, and S. enteritidis is demonstrating approximately a 3.6% mortality rate in hospital/nursing home outbreaks, with the elderly being particularly affected.
Salmonella septicemia has been associated with subsequent infection of virtually every organ system.
Postenteritis reactive arthritis and Reiter's syndrome have also been reported to occur generally after 3 weeks. Reactive arthritis may occur with a frequency of about 2% of culture-proven cases. Septic arthritis, subsequent or coincident with septicemia, also occurs and can be difficult to treat.
8. Target Populations:
All age groups are susceptible, but symptoms are most severe in the elderly, infants, and the infirm. AIDS patients suffer salmonellosis frequently (estimated 20-fold more than general population) and suffer from recurrent episodes.
9. Foods Analysis:
Methods have been developed for many foods having prior history of Salmonella contamination. Although conventional culture methods require 5 days for presumptive results, several rapid methods are available which require only 2 days.
10. Selected Outbreaks:
For information on recent outbreaks see the Morbidity and Mortality Weekly Reports from CDC.
12. Other Resources:
A Loci index for genome Salmonella enteritidis is available from GenBank.