CASE 9

A large cruise ship (operated by a company that shall remain unnamed) leaves Miami for a two-week cruise around the Caribbean. On the third day out of port, five passengers experience the sudden onset of nausea and abdominal cramps, followed by periods of watery diarrhea. Four of the ill passengers also experience vomiting, and most of them have headaches, myalgias, and/or abdominal pain. By the mext morning, 37 more passengers have become ill with the same symptoms, and all but one of those who became ill the day before are still acutely symptomatic. Most of the victims are adults. The ship's doctor examines all of the sick passengers. Vital signs are generally normal, except that about 1/2 of the patients have a low-grade fever (typically 38 C). The physical examination is unremarkable. The ship's physician has a microscope and examines several stool smears, but she sees no signs of red blood cells, leukocytes, ova, or cysts. The ship does not have a medical lab, so no other tests are done. The next day, 86 more passengers have become sick with the same symptoms and most of those who were infected earlier are still symptomatic. At this point the company decides to cancel the cruise and take the passengers to the nearest port where they can get more extensive medical care. The ship arrives at an appropriate port about eight hours later. By then, a few more passengers have become ill, but some of those who became ill on the first or second day of the outbreak now appear to be recovering on their own. Lab tests done for the passengers who are still sick confirm that their stool samples do not contain red blood cells, leukocytes, ova, or cysts. Routine cultures for bacterial gastrointestinal pathogens are all negative.

Question 9.1: What is the most likely causative agent?

Question 9.2: What are the genetic and structural characteristics of this causative agent?

Question 9.3: How is this disease transmitted?

Question 9.4: How common is this disease?

Question 9.5: How can outbreaks like this be prevented?

Question 9.6: How is this causative agent detected for diagnosis?

CASE 10

A 43-year-old man in the advanced stages of AIDS begins to experience watery diarrhea and intermittent abdominal pain, along with nausea, anorexia, and fever. The diarrhea persists over a period of four weeks, with no signs of letting up. In fact, the diarrhea is often profuse, with the patient producing 15-20 liters of fluid (as many as 30-40 stools) per day. The patient experiences weight loss, wasting, and increased diffuse abdominal pain along with the persistent diarrhea. Near the end of the four-week period, additional symptoms appear. The patient develops a mild jaundice, has repeated incidents of nausea and vomiting, and is still febrile. The physical examination reveals pain and tenderness in the right epigastrium. Palpation of the right upper quadrant elicits marked tenderness and stoppage of inspired breath, along with a guarding response. Microscopic examination of stool samples reveals the presence of structures that might be relatively small cysts or oocysts. These structure stain red when an acid-fast stain is applied to the fecal smear.

Question 10.1: What is your preliminary diagnosis?

Question 10.2: What tests should you do?

Question 10.3: How did the causative agent produce the symptoms seen here?

Question 10.4: How is this disease transmitted?

Question 10.5: How is this organism identified by the lab?

CASE 11

A 57-year-old woman is hospitalized for her fourth episode of unexplained Gram-negative bacteremia. The only other pertinent medical history was that the patient had recently begun treatment with corticosteroids for asthmatic bronchitis. Paradoxically, her cough got worse with this therapy and she started to experience abdominal pain and diarrhea. Likewise, the other episodes of bacteremia also followed the initiation of steroid therapy.

The patient was a resident of Michigan who had lived in rural Eastern Kentucky as a child and teenager. She was treated with antibiotics for the microorganism causing her bacteremia. Because a CT scan of the patient's abdomen showed a thickened intestinal wall, the patient underwent a small intestinal biopsy that revealed the presence of helminthic parasites attached to the mucosa. Subsequent examination of a stool specimen revealed numerous immature larvae. More developed larvae were also identified in the patient's sputum.

Question 11.1: What is the most likely causative agent?

Question 11.2: What is the life cycle of this causative agent?

Question 11.3: What was the role of the corticosteroid in this case?

Question 11.4: What is the geographic distribution of this pathogen?

Question 11.5: How is this disease treated?

Question 11.6: What precautions should be taken when caring for a victim of this disease?

CASE 12

A family with one child (a three-year-old boy) has been working with an international relief agency in Central America for a little over a year. They are stationed in a very remote and very impoverished village. The local people grow most of their own food and, as is common in the area, they often use human feces as a fertilizer on the local soil. The family's son has been accepted by the local children, so he often plays outdoors with them and can speak the local dialect quite well. The family was in good health when they arrived in Central America and, until recently, they had not experienced any major medical problems. A few weeks ago, the son started to experience abdominal pain and diarrhea. The pain has slowly worsened over time and the diarrhea, which is often bloody, has not abated. Moreover, the boy has become anorexic, is very weak, and is losing weight. The family then takes their son to the nearest substantial medical facility, in a small city about 200 miles from the village in which they have been working. The physicians take a history, do a physical examination, and collect stool and blood specimens for analysis. They find that the boy has no history of unexplained skin lesions or other cutaneous symptoms. The tests show that the patient has mild eosinophilia. The stool sample is examined microscopically and found to contain bile-stained, lemon-shaped eggs that are approximately 20 x 50 (m in size and have distinctive-looking polar plugs.

Question 12.1: What is the most likely causative agent?

Question 12.2: What is the life cycle of this causative agent?

Question 12.3: What are the usual consequences and possible complications of this disease?

Question 12.4: How is this disease transmitted?

Question 12.5: How is this pathogen identified by the lab?

Question 12.6: How is this disease treated and prevented?

CASE 13

A 44-year-old man has experienced intermittent low-volume diarrhea for the past month. He has noted no blood in the stool. During this time he has been feeling poorly and has lost 4 kg. Vital signs show T 38.9 C, P 80, R 14, and BP 100/65 mm Hg. The physical examination finds generalized non-tender lymphadenopathy. He has some tan to yellowish plaque-like areas on the lateral aspects of the tongue. The chest and abdominal examinations are normal. Active bowel sounds are present and there are no masses palpable and no abdominal tenderness. The rectal examination reveals external hemorrhoids. The stool is negative for occult blood.

A colonoscopy is performed, and the only finding is an area of mildly erythematous mucosa involving the cecum. Biopsies are taken.

Question 13.1: What is the most likely causative agent?

Question 13.2: What additional historical or laboratory findings are most likely to be present in this patient?

Question 13.3: How is this infection usually diagnosed?

Question 13.4 How is this infection treated?

Question 13.5 What are possible complications?