A 3 year old boy presents with a 1 day history of loose stools, fever, abdominal cramping, headache, and myalgia. He has no blood in the stool. A careful history reveals that he has several pet tules. Which of the following is most likely the causative agent of his diarrhea?: (A) Chlamydia psittaci, (B) Entamoeba histolytica, (C) Salmonella spp, (D) Staphylococcus aureus
Answer is C. Salmonella spp., including S. enteritidis and S. typhimurium, produce a gastroenteritis or enterocolitis. Patients with decreased gastric acidity, sickle cell disease, defects in immunity, or children younger than 4 years have a more severe course of disease. Salmonella spp. are carried in nature by animal reservoirs such as poultry, tules, cattle, pigs, and sheep. The incubation period is 8-48 hours after ingestion of contaminated food or water. Chlamydia psittaci produces an interstitial pneumonitis accompanied by headache, backache, and a dry, hacking cough. A pale, macular rash is also found on the trunk (Horder's spots). Patients at risk include pet shop workers, pigeon handlers, and poultry workers. Entamoeba histolytica produces a diarrhea (frequently bloody or heme-positive), right lower quadrant crampy abdominal pain, and fever. Patients frequently have weight loss and anorexia. There is usually a history of travel outside the U.S. Most cases are chronic. Complications include liver abscesses. Staphylococcus aureus produces a self-limited gastroenteritis due to the production of preformed, heat-stable enterotoxins. The incubation period is 16 hours. The toxins enhance intestinal peristalsis and induce vomiting by a direct effect on the CNS. Ref: Ray C.G., Ryan K.J. (2010). Chapter 33. Enterobacteriaceae. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.