Salmonella spp.

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.

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.

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).

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.

In August and September, 1985, S. enteritidis was isolated from employees and patrons of three restaurants of a chain in Maryland. The outbreak in one restaurant had at least 71 illnesses resulting in 17 hospitalizations. Scrambled eggs from a breakfast bar were epidemiologically implicated in this outbreak and in possibly one other of the three restaurants. The plasmid profiles of isolates from patients all three restaurants matched.

The Centers for Disease Control (CDC) has recorded more than 120 outbreaks of S. enteritidis to date, many occurring in restaurants, and some in nursing homes, hospitals and prisons.

In 1984, 186 cases of salmonellosis (S. enteritidis) were reported on 29 flights to the United States on a single international airline. An estimated 2,747 passengers were affected overall. No specific food item was implicated, but food ordered from the first class menu was strongly associated with disease.

S. enteritidis outbreaks continue to occur in the U.S. (Table 1). The CDC estimates that 75% of those outbreaks are associated with the consumption of raw or inadequately cooked Grade A whole shell eggs. The U.S. Department of Agriculture published Regulations on February 16, 1990, in the Federal Register establishing a mandatory testing program for egg-producing breeder flocks and commercial flocks implicated in causing human illnesses. This testing should lead to a reduction in cases of gastroenteritis caused by the consumption of Grade A whole shell eggs.

Salmonellosis associated with a Thanksgiving Dinner in Nevada in 1995 is reported in MMWR 45(46):1996 Nov 22.

MMWR 45(34):1996 Aug 30 reports on several outbreaks of Salmonella enteritidis infection associated with the consumption of raw shell eggs in the United States from 1994 to 1995.

A report of an outbreak of Salmonella Serotype Typhimurium infection associated with the consumption of raw ground beef may be found in MMWR 44(49):1995 Dec 15.

MMWR 44(42):1995 Oct 27 reports on an outbreak of Salmonellosis associated with beef jerky in New Mexico in 1995.

The report on the outbreak of Salmonella from commercially prepared ice cream is found in MMWR 43(40):1994 Oct 14.

An outbreak of S. enteritidis in homemade ice cream is reported in this MMWR 43(36):1994 Sep 16.

A series of S. enteritidis outbreaks in California are summarized in the following MMWR 42(41):1993 Oct 22.

For information on an outbreak of Salmonella Serotype Tennessee in Powdered Milk Products and Infant Formula -- see this MMWR 42(26):1993 Jul 09.

Summaries of Salmonella outbreaks associated with Grade A eggs are reported in MMWR 37(32):1988 Aug 19 and MMWR 39(50):1990 Dec 21.

For more information on recent outbreaks see the Morbidity and Mortality Weekly Reports from CDC.