Sorry to hear your son was ill, Carl. I'm confident he will make a full recovery.

I know that there is little I can say which will change your mind about who or what was at fault. But it could have come from anywhere. Posted some info :-
CampylobacteriosisCampylobacteriosis is a zoonotic disease which means it is transmissible between
humans and animals. Campylobacteriosis is caused by the bacteria, Campylobacter jejuni and, occasionally, C. coli. This agent is found in mammals and birds, both domestic and wild, and humans. The bacteria is spread from feces or products of abortion to other animals and people by ingestion. Campylobacter jejuni may persist for several weeks at low temperatures in natural water sources. It is destroyed by routine disinfection.
Campylobacteriosis in AnimalsAnimals with this disease may show signs of diarrhea, blood in the feces, poor appetite
and dehydration. Diarrhea is common in puppies. Nonhuman primates and calves may
also develop diarrhea. It is a common cause of abortion in sheep. Campylobacter jejuni may be present in unpasteurized milk. Many animals, especially primates, may shed this organism but have no signs of disease. All nonhuman primates at this institution are considered to be potential shedders of the organism.
Campylobacteriosis in PeopleCampylobacteriosis is one of the most common causes of diarrhea in humans in the
United States. Human campylobacteriosis is usually associated with ingestion of
contaminated poultry, contaminated drinking water or unpasteurized (raw) milk. The
agent is ingested, invades the intestinal tract and causes diarrhea. Large numbers of
organisms may be shed in diarrheic stools. Ingestion of a small number of organisms may result in disease. The incubation period in people is from two to five days. The principal symptoms in people are diarrhea, abdominal pain, vomiting (33% of patients) and blood in their feces (50-90% of patients). Fever is often accompanied by a general malaise, headache and muscle and joint pain. The feces are liquid and frequently contain mucous and blood. The patient usually recovers in a week to ten days without treatment. Some people have severe symptoms which may be mistaken for appendicitis. Septicemia, meningitis, arthritis or abortion has occurred on rare occasions. The bacteria may be shed in the feces of untreated people for weeks to months.
Full article :
http://www.research.cornell.edu/care/Documents/OHP/CAMPY.pdf