Salmonella

CASE 1

• A cook at a local restaurant prepared ice cream using recipe that called for evaporated milk, sugar, vanilla, and raw eggs. The first batch of the newly prepared ice cream was eaten by the restaurant owner and his family. Thirty-six to 72 hours after eating the ice cream, the owner, her husband, two of their three children and the owner's elderly father all developed nausea, abdominal cramps, and diarrhea. At that point, they removed the remaining ice cream from the restaurant kitchen.

• The youngest child (age 3) and the owner's father developed fever (temperatures above 39 degrees) along with the diarrhea. The elderly father was hospitalized for 4 days to receive intravenous rehydration and antibiotic therapy. His blood culture, taken at the time of admission, grew Salmonella enteritidis.

• The youngest child was taken to the hospital and was treated with an oral antibioticfor 3 days. Before antibiotic therapy, a stool culture was obtained, and it grew S. enteritidis 24 hours later. Three weeks later, the child developed fever with pain and swelling in the right knee. An aspirate of the right knee effusion grew S. enteritidis. The patient was then treated with a prolonged course of amoxicillin and recovered completely.

• The three other family members who were not febrile continued to have cramps and diarrhea, but these symptoms resolved without specific treatment after 4-5 days. However, they were unable to go to work or to school during this period of illness.

Questions:

1. What was the source of the Salmonella in this small outbreak? The cook? The milk? Or the eggs?
2. What animal sources are commonly associated with S. enteritidis (i.e., non-typhoid Salmonella) infection?
3. What factors led to more severe illness in certain families and not in others?
4. How does Salmonella interact with the intestinal mucosa in order to facilitate its entry into cells and growth?
5. Is it necessary or helpful to treat this infection with antibiotics? When are antibiotics necessary?
6. What media was used to isolate Salmonella from the stool sample of the child? What is selective media?
7. Salmonella and Shigella are both lactose-negative Gram-negative bacilli. What indicator in the culture media may distinguish them at a glance?
8. What are the obvious problems that complicate making a non-typhoid Salmonella vaccine?

CASE 2

• A 38 year old man has had daily stepwise increasing fever during the past week. The fever is accompanied by increasing abdominal pain, headache, joint pains, and malaise. Although he had a few loose stools at the onset of the illness, he has been constipated more recently. He was treated empirically for malaria on the fourth day of illness but did not improve. On the 8th day of his illness, he becomes bedridden and delirious. His family brings him to the hospital for treatment.

• Physical examination reveals a temperature of 39.4 degrees and a pulse rate of 80/minute. He has a dry cough. The rest of the examination is unremarkable except for a slightly tender liver and diffuse abdominal tenderness.

• A white blood cell count is 3,300. There are mild increases in the liver injury tests (AST and ALT). Blood, urine and fecal cultures are all negative.

Questions:

1. What is the likely cause of this illness?
2. What was the most likely source of the causative organism? An animal? Another human?
3. How did the pathogen enter the body of the affected individual?
4. What were the initial tissues to become infected? How and where did the organism spread from there?
5. Are negative cultures unusual in patients with this infection? If the organism can easily be cultivated on several different artifical media, why do you think it is difficult to culture from a patient?
6. What serious complications can occur with this disease?
7. Are there effective vaccines against the disease? What do they consist of?
8. What simple precautions and public health measures can prevent the spread of this disease?