Question

The patient was a previously healthy 11-year-old female who came to the emergency department (ED) in mid-September with a 2-day history of bloody diarrhea. Three days previously he had the onset of fever, headache and lower abdominal pain. Her diarrhea began as watery and became increasingly bloody. She denied any recent travel but reported that her brother also had blood diarrhea. In her history, she said that she had eaten a hamburger at school picnic prior to the onset of disease, as well as having consumed spinach. There was no family history of inflammatory bowel disease or bloody stools. On physical examination, the patientÕs vital signs were normal and the physical findings were unremarkable except for severe abdominal pain. Her stool was hemoccult positive and showed 2+ white blood cells (WBCs). A complete blood count was within normal limits except for a WBC of 14,900/ul, with an absolute neutrophil count of 12,500/ul. She was given morphine in the ED for her abdominal pain. An abdominal ultrasound ruled out acute appendicitis but revealed thickened bowel loops consistent with colitis. During the first week of her hospital course she continued to have bloody diarrhea and severe abdominal pain. Her final stool submitted to the laboratory on hospital day 7 was consistent with a blood clot. During her hospital course she developed low urine output and hematuria, with a serum creatinine of 2.1 mg/dl on hospital day 5. Her renal symptoms were treated with fluids and her renal function was closely monitored. In addition, on hospital day 6 she had a platelet count of 16000/ul and a hemoglobin level of 7.2mg/dl. She received a unit of packed red blood cells on the 6th, 7th and 11th hospital days. By discharge on the 13th hospital day her serum creatinine, blood urea nitrogen, and platelet count had returned to normal and her hemoglobin had stabilized at 10.2mg/dl. Culture of her stool on sorbitol MacConkey agar was positive.

1. What organism is infecting this patient?

2. What two virulence factors does this organism produce, and what are their roles in the gastrointestinal disease seen in the patient?

3. How do you think this patient became infected? How would you prove a specific source was responsible for infection with this organism?

4. Give at least two reasons why large outbreaks caused by this organism are being recognized with increasing frequency.

Answer 1

1. What organism is infecting this patient?

The patient is infected with E. coli O157:H7 the symptoms as well as the positive result using Sorbitol MacConkey Agar confirms this. Since this pathogenic E.Coli strain cannot ferment sorbitol it uses peptone to grow whihc alter the pH of the medium and the pH indicator highlights the difference between the pathogenic microorganism from the normal E.Coli.

2. What two virulence factors does this organism produce, and what are their roles in the gastrointestinal disease seen in the patient?

The two main virulence factors produced by this organism are Shiga toxin 2 and adhesin intimin.

Shiga toxin stops protein synthesis in the cell that it enters and adhesin intimin is an attaching and effacing protein which is the reason for the lesions in the gut lining (LEE - Locus of entrrocyte effacement).

Shiga toxins is the main reason for HUS (Haemolytic uremic syndrome).

3. How do you think this patient became infected? How would you prove a specific source was responsible for infection with this organism?

The patient could have been infected though the hamburger she had in the picnic as the major cause for infection is due to consuming contaminated meat products or even spinach which are eaten raw or under-cooked. We can prove the specific source to be the food that she had in her school picnic as her brother too had similar symptom. If the brother had not attended the school picnic then he could have infected his sister through the common oral-faecal route due to sharing of common toilet areas and not following good handwashing techniques.

4. Give at least two reasons why large outbreaks caused by this organism are being recognized with increasing frequency.

Two reasons why large outbreaks are being recognised with increasing frequency:

Contaminated Food being the major reason for the cause of infection - increasing number of food chain or restaurants which have a common raw material supplier. Especially ground beef which is a major vehicle for carrying the pathogenic microorganism. Outbreak investigations by state and local health departments and identifying the transmission route and vehicle for transmission have helped to recognise the outbreaks.

Studying the epidemiology of the particular strain of E Coli too has helped in the identification of the outbreak and trace it back to the source.