Diarrhea Case 6

A 45-year-old man presents to a physician because of severe chronic diarrhea accompanied by a 18 kg (40 Ib) weight loss. The diarrhea began several years ago, and has become steadily worse. It is often accompanied by excessive flatulence, and the man notes that his stools usually float. The man additionally has felt generally poorly and sometimes has experienced joint symptoms. Intestinal biopsy demonstrates

Iarge numbers of foamy macrophages distending the lamina propria. A periodic acid-Schiff (PAS) stain shows granules within the macrophages.

Q 1

Which of the following is the most likely diagnosis?

/ A. Celiac sprue

/ B. Intestinal lymphangiectasia

/ C. Lactase deficiency

/ D. Tropical sprue

/ E. Whipple disease

Q2

This patient disease has been etiologically related to infection with which of the following?

/ A. Bartonella

/ B. Borrelia

/ C. Francisella

/ D. tropheryma

/ E. Vibrio

Q3

Excessive flatulence suggests which of the following problems :

/ A. Colon obstruction

/ B. GI hypermotility

/ C. GI hypomotility

/ D. Malabsorption

/ E. Small intestinal obstruction

Q 4

BIood studies on this patient demonstrate a microcytic hypochromic anemia. The nutrient whose deficiency would most likely account for the patient's anemia is primarily absorbed in which of the following sites?

/ A. Colon

/ B. Duodenum

/ C. Esophagus

/ D. IIeum

/ E. Stomach

Q 5

This patient's illness is most effectively treated with which of the following?

/ A. Antibiotics

/ B. Chemotherapy

/ C. Radiation therapy

/ D. Steroid therapy

/ E. Surgery

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Diarrhea Case 6 Answers

A1

The correct answer is E. This patient has Whipple disease, which is a rare illness characterized by diarrhea, often severe malabsorption, and weight loss. The condition most commonly affects men aged 30 to 60. The disease may present either abruptly or insidiously. If it develops insidiously, non-gastrointestinal manifestations may bring the patient to medical attention. These may include pleuritic pain, pleural effusion, anemia, joint problems, cardiac problems, neuropsychiatric problems, eye problems, or hepatic dysfunction.

All of the other diseases listed can also cause chronic diarrhea.

Celiac sprue (choice A) shows villous atrophy on biopsy, and is related to gluten sensitivity.

Intestinal lymphangiectasia (choice B) shows dilated lymphatic channels on biopsy.

Lactase deficiency (choice C) is due to an enzymatic abnormality and is characterized by a histologically normal intestinal epithelium.

Tropical sprue (choice D) usually shows moderate broadening and shortening of villi, and an often intense inflammatory reaction.

A2

The correct answer is D. Electron microscopy of the intestinal mucosa shows that the PAS-positive granules in macrophages in Whipple disease are actually bacterial forms. The causative organism is Tropheryma whippelii, and, if necessary, its DNA can be identified with PCR technology. This is necessary because attempts to culture the organism have not, to date, been successful. At the moment, this test is available only through reference laboratories. In patients who have extraintestinal manifestations, macrophages containing the bacteria may be found in extraintestinal sites.

Bartonella(choice A) species can cause cat scratch disease, trench fever, and disseminated infections.

Borrelia(choice B) causes Lyme disease.

Francisella(choice C) causes tularemia.

Vibrio(choice E) causes cholera and other diarrheal illnesses.

A3

The correct answer is D. When a patient complains of excessive flatulence, the first step is to ask them to describe the amount and frequency of the flatulence, since some people with normal intestinal gas production have unrealistic expectations about the possibility of completely eliminating flatulence. In cases in which excessive flatulence really is present, you should think of gastrointestinal disorders that can cause malabsorption, since many cases of excessive flatulence are related to bacterial digestion of unabsorbed nutrients (notably carbohydrates) with resultant gas production as a by-product. These disorders may include a wide variety of underlying conditions including pancreatic disease, liver disease, genetic enzymatic abnormalities of the intestinal mucosa, and acquired intestinal tract disease.

Colonic obstruction (choice A), small intestinal obstruction (choice E), and GI hypomotility (choice C) can also cause gas to be retained in the bowel and be visible on abdominal x-ray films, but do not, by themselves, increase gas production.

GI hypermotility (choice B) often accompanies acute diarrheal illness, but the excessive flatulence that may also be present in that setting is secondary to malabsorption rather than the hypermotility.

A4

The correct answer is B. Microcytic, hypochromic anemia suggests iron deficiency. Patients with Whipple disease frequently develop anemia related to poor duodenal absorption of either folate (producing a macrocytic anemia) or iron. Other substances absorbed in the duodenum include water, calcium, fats, sugars, proteins, many vitamins, magnesium, and sodium.

The colon (choice A) absorbs water and electrolytes.

The esophagus (choice C) does not absorb nutrients.

The ileum (choice D) can absorb bile salts, vitamin B12, and chloride.

The stomach (choice E) can absorb water and alcohol.

A5

The correct answer is A. The symptoms of Whipple disease often dramatically improve after antibiotic therapy, although the therapy must often be continued for prolonged intervals to prevent relapse and the microscopic intestinal changes may not resolve for 2 years. Many antibiotics are effective, including chloramphenicol, tetracycline, ampicillin, penicillin, and trimethoprim-sulfamethoxazole. The other therapies listed in the choices are not usually employed with Whipple disease.

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Diarrhea Case 5

An 11-month-old girl who attends a day care center develops vomiting and severe, watery diarrhea. The child is taken to an emergency department on the third day of the illness, because the mother is concerned that she has not been able to hold any food or liquids down without vomiting. Physical examination demonstrates an obviously ill child with listless behavior, Ioss of skin turgor, dry mucous membranes, and weight 3 pounds less than 1 week previously. Her blood pressure is 64/40 mm Hg.

Q 1

Which of the following is the most common cause of viral gastroenteritis in children under the age of three?

/ A. Astrovirus

/ B. Calicivirus

/ C. Enteric adenovirus

/ D. Norwalk virus

/ E. Rotavirus

Q 2

In the United States, this virus tends to cause illness during which of the following periods?

/ A. Predominately fall months

/ B. Predominately spring months

/ C. Predominately summer months

/ D. Predominately winter months

/ E. Year-Iong with no seasonal preference

Q 3

The virus is predominately spread by which of the following routes?

/ A. Contaminated blood

/ B. Contaminated food

/ C. Contaminated water sources

/ D. Direct fecaI-oral route

/ E. Inhaled aerosols

Q 4

This child's poor skin turgor, dry mucus membranes, significant weight loss, and low blood pressure all suggest which of the following?

/ A. Dehydration

/ B. Disseminated intravascular coagulation

/ C. IIeus

/ D. Sepsis

/ E. Starvation

Q 5

In 1989, the FDA Iicensed a live attenuated vaccine against the causative agent of this disease for use in infants. It was later withdrawn for

which of the following reasons?

/ A. Data suggested a link between the vaccine and intussusception in some infants during the first 1-2 weeks following vaccination.

/ B. It was questioned if there was association between the vaccine and the development of autism.

/ C. Seizures occurred in a significant number of recipients.

/ D. The vaccine was not widely used because it was too expensive.

/ E. The vaccine was thought to be associated with the development of arthritis in recipients.

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Diarrhea Case 5 Answers

A1

The correct answer is E. The most common cause of severe dehydrating diarrhea in infants and young children is Group A rotavirus. The peak incidence of infection occurs from 3 to 15 months. After age three, severe diarrhea is rare, but mild disease can occur. This virus accounts for about half of the cases of diarrhea requiring hospitalization in children in the United States. Rotaviruses are in the Reoviridae family and have a genome consisting of 11 double-stranded RNA segments. The other agents listed can also cause viral gastroenteritis in children and/or adults.

A2

The correct answer is D. In temperate climates, rotavirus has a winter seasonal pattern. In the United States, epidemics occur from November to April. In tropical climates, disease caused by rotavirus occurs year round.

A3

The correct answer is D. Rotavirus is a notoriously contagious virus, and the infective dose is thought to be as small as 10-100 infectious viral particles. While the initial yearly source of the virus may be from contaminated estuary waters (choice C), the vast majority of cases are spread from person to person via direct contact with stool on diapers, objects such as toys, or fingers. While not always necessary, the presence of rotavirus can be confirmed by using enzyme immunoassay on stool specimens. Day care centers are notorious sources of minor epidemics of the virus, and day care workers should be encouraged to be very careful. Reasonable precautions include removal of kids with diarrhea from the day care environment, prompt diaper changing before the children have a chance to touch the stool, and routine use of fresh disposable gloves during diapering.

Contaminated blood (choice A) and inhaled aerosols (choice E) are not usual routes of infection.

Contaminated food (choice B), typically contaminated by food handlers who have recently changed an infected child's diapers, is an uncommon source of infection.

A4

The correct answer is A. These findings strongly suggest that the child is severely dehydrated and in need of intravenous fluid replacement. Approximately 500,000 children are seen in emergency room and outpatient clinic visits for rotavirus infection yearly, and of these, about 50,000 hospitalizations (usually to correct dehydration) and 20 deaths (usually caused by failure to correct the dehydration in a timely fashion) occur yearly in the United States. World-wide, rotavirus infection is thought to cause around 600,000 deaths, primarily in young children. This child with severe dehydration should at least be given IV fluids, and might require hospitalization.

Disseminated intravascular coagulation (choice B) would cause multiple petechiae and purpura, and does not usually complicate rotavirus infection.

Ileus (choice C) is a paralyzed bowel, which is the opposite of the problem seen in gastroenteritis.

Sepsis (choice D) is not usually diagnosed in viral infections, but is seen in severe bacterial infections, often with bacteremia.

Three or four days of not eating is not long enough to induce starvation (choice E).

A5

The correct answer is A. The live attenuated rotavirus vaccine was a virus mixture of reassorted strains that were primarily animal viruses except for one human-virus gene segment. The vaccine had a 49-68% efficacy against any diarrhea due to rotavirus and a 61-100% efficacy against severe disease. However, during the first 11 months of use, post-licensure studies identified intussusception, a form of intestinal obstruction in which a segment of the bowel prolapses into a more distal segment, as an uncommon but potentially life-threatening side effect. Follow up studies estimated that 1 additional case of intussusception occurred for every 5,000- 10,000 vaccinees. The vaccine has currently been withdrawn from use in the US.

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Diarrhea Case 4

A 17-year-old boy is seen in an emergency department with severe acute abdominal symptoms that suggest appendicitis. The patient had a similar episode previously that led to an appendectomy, but the appendix was free of inflammation at pathologic examination. On questioning,

the boy reports having had intermittent diarrhea with moderate chronic abdominal pain for several years, which he had been afraid to tell anyone about after having had a "normaI" appendix removed. On physical examination, the boy is noted to be thin, with short stature, and have a palpable fullness in the right lower quadrant of his abdomen. UItrasound examination of the abdomen shows some thickening of bowel mesentery, but no distinct masses. Colonoscopy demonstrates sharply demarcated segments of diseased bowel with patchy mucosal ulcersseparated by adjacent normal bowel involving both the distal ileum and right side of the colon.

Q 1

Which of the following is the most likely diagnosis?

/ A. Colon cancer

/ B. Crohn disease

/ C. Hirschsprung disease

/ D. Pseudomembranous colitis

/ E. UIcerative colitis

Q 2

Which of the following findings on right colon mucosal biopsy would be most suggestive of the patient's likely diagnosis?

/ A. Absence of nerve cell bodies in submucosa

/ B. Bacteria-Iaden pseudomembrane

/ C. Crypt abscesses

/ D. Neoplastic epithelial cells

/ E. Small granulomas

Q 3

The patient is treated initially with corticosteroids, and then these are tapered and he is switched to a maintenance therapy with sulfasalazine.

Sulfasalazine is an unusual medication that combines which of the following?

/ A. A histamine derivative and a beta blocker

/ B. A Iipoxygenase inhibitor and a penicillin derivative

/ C. A mast cell degranulation inhibitor and an anticoagulant

/ D. A salicylate derivative and a sulfonamide derivative

/ E. A serotonin antagonist and a proton pump inhibitor

Q 4

Several years later, the patient develops recurrent urinary tract infections with mixed flora bacteria isolated from the urine. This pattern

suggests that which of the following may have developed?

/ A. BIadder stone

/ B. Fistula

/ C. Kidney stone

/ D. Systemic immunosuppression

/ E. Urethral strictures

Q 5

At a still later date, the patient develops chronic lower back pain and is diagnosed with ankylosing spondylitis. Which HLA type has been

associated with this extracolonic manifestation?

/ A. HLA-B27

/ B. HLA-B35

/ C. HLA-Cw6

/ D. HLA-DR3

/ E. HLA-DR5

Q 6

Examination of the patient's legs reveals necrotic ulcers with ragged bluish-red overhanging edges together with areas containing plaques

with pustules. Which of the following is the most likely diagnosis?

/ A. Eruptive xanthomata

/ B. Lupus vulgaris

/ C. Raynaud's phenomenon

/ D. Psoriasis

/ E. Pyoderma gangrenosum

____________________________________________________________________________

Diarrhea Case 4 Answers

A1

The correct answer is B. This patient most likely has Crohn disease, as indicated by his chronic abdominal complaints and the distal small intestinal and colonic ulceration with skip lesions (normal bowel separating involved areas). In addition to the distal small intestine and colon, Crohn disease can affect the perianal area, entire small intestine, stomach, and esophagus. Crohn disease may present with chronic diarrhea with systemic complaints, acute abdomen, or extraintestinal manifestations. The peak incidence for onset of symptoms occurs between 14 to 24 years. Crohn disease is thought to be due to a genetic predisposition that leads to an autoimmune reaction in the intestine that may be triggered in response to an environmental, dietary, or infectious agent. About 1 in 6 people with Crohn disease have a relative with Crohn disease, or, less commonly, ulcerative colitis.

Colon cancer (choice A) would be highly unlikely in a 17-year-old, and usually causes a single mass lesion or stricture.

Hirschsprung disease (choice C) causes megacolon in young children.

Pseudomembranous colitis (choice D) is due to overgrowth of Clostridium difficile and is usually seen following treatment with broad-spectrum antibiotics.

Ulcerative colitis (choice E) usually extends from the rectum proximally and does not have skip lesions.

A2

The correct answer is E. Microscopic features of Crohn disease include transmural inflammation, small granulomas (most characteristic, but only present in about 50% of cases), and variable degrees of inflammation.

Absence of nerve cell bodies in submucosa (choice A) suggests Hirschsprung disease.

A bacteria-laden pseudomembrane (choice B) suggests pseudomembranous colitis;

Crypt abscesses (choice C) suggest ulcerative colitis.

Neoplastic epithelial cells (choice D) suggest colon cancer or neoplastic polyps.

A3

The correct answer is D. Acute exacerbations of Crohn disease can be treated with corticosteroids, but then the patient is usually switched to maintenance therapy with immunomodulating drugs, such as azathioprine and 6-mercaptopurine, or sulfasalazine or related drugs. Sulfasalazine has a sulfapyrine component, which is a sulfonamide derivative and a 5-aminosalicyclic acid (5-ASA) component, which is a salicylate derivative. Most of the drug activity appears to be related to the 5-ASA component, and most of the toxicity is related to the sulfapyrine, so alternatives to sulfasalazine, such as mesalamine, are being developed that preserve the 5-ASA activity without retaining the sulfapyrine component. The other answers are distracters.

A4

The correct answer is B. The patient has probably developed a fistula between the intestine and the bladder. Fistulas are a relatively common complication of Crohn disease. Surgery is used to correct recurrent intestinal obstruction and intractable fistulas, but may be unsatisfactory because of disease recurrence.

The other choices do not commonly complicate Crohn disease and would not specifically predispose for mixed flora infections.

A5

The correct answer is A. Ankylosing spondylitis is one of the seronegative spondyloarthropathies. It should be suspected in any young person complaining of chronic lower back pain and can be confirmed by radiographs or CT scans of sacroiliac joints. The disease usually progresses to involve the whole vertebral column, producing ankylosis and respiratory failure secondary to restrictive lung disease. HLA-B27 positivity has been associated with Crohn disease patients who develop extracolonic manifestations including ankylosing spondylitis, sacroiliitis, uveitis, and primary sclerosing cholangitis.

You should associate HLA-B35 (choice B) with vitiligo, duodenal ulcer, and subacute thyroiditis.

You should associate HLA-Cw6 (choice C) with psoriasis.

You should associate HLA-DR3 (choice D) with celiac disease, Goodpasture syndrome, type I diabetes mellitus, and systemic lupus erythematosus.

You should associate HLA-DR5 (choice E) with juvenile rheumatoid arthritis and pernicious anemia.

A6

The correct answer is E. Pyoderma gangrenosum can precede the onset of chronic inflammatory bowel disease. It is treated by systemic and topical corticosteroids. It may also be associated with myeloproliferative disorders and rheumatoid arthritis.

Xanthomata (choice A) may be located on the tendons on the back of the hands, the Achilles tendon and patellar tendon, buttocks, and back. They are usually yellow papules up to 5 mm in diameter. They suggest familial hypercholesterolemia.

Lupus vulgaris (choice B) is a progressive form of cutaneous tuberculosis occurring in a person with a moderate or high degree of immunity. The two types are the plaque form (a tiny reddish-brown, flat plaque that extends gradually) or the ulcerative form (scarring and ulceration over the areas of necrosis).

Raynaud's phenomenon (choice C) presents as cold and cyanotic digits along with atrophy of the finger pulp and, in severe cases, gangrene. It is an exaggerated physiological response wherein the fingers turn white, and then when rewarmed, will turn blue, and then red as part of rebound hyperemia. It may be associated with underlying connective tissue diseases such as systemic sclerosis.

Psoriasis (choice D) presents as a thick plaque-like scale that is usually silver or salmon-pink in color. It is usually well defined on the extensor surfaces of elbows or knees. It is often associated with asymmetrical arthropathy mainly involving the terminal interphalangeal joints.

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Diarrhea Case 3

A 25-year-old woman is hospitalized for multiple injuries to her arms and legs from an automobile accident. She is treated with several intravenous broad-spectrum antibiotics because of significant concern that her wounds are becoming infected with a mixed flora of organisms. She responds over the next several days to the antibiotics with an initial decrease in fever. However, on the fourth day after her accident, she develops severe diarrhea with fever, vomiting, cramping abdominal pain, tenesmus, abdominal distension, and fluid losses severe enough to require IV fluids.

Q1

Proctoscopic examination demonstrates discrete yellow plaques up to 2 cm diameter which are scattered over the colonic mucosa. Which of the following would most likely be demonstrated on colonic biopsy?

/ A. Acid fast bacteria

/ B. Neoplastic polyps

/ C. Parasitic eggs

/ D. Pseudomembrane formation

/ E. Small granulomas

Q2

Which of the following organisms has been implicated in this disease?

/ A. Clostridium botulinum

/ B. Clostridium difficile

/ C. Clostridium perfringens

/ D. Clostridium septicum

/ E. Clostridium tetani

Q 3

Which of the following tests would be most helpful in confirming the diagnosis?

/ A. CT scan

/ B. MRI scan

/ C. "Scotch tape" test

/ D. Specific toxin in stool

/ E. Stool for ova and parasites

Q 4

This patient should not undergo barium contrast studies because of the increased risk in her disease of which of the following

/ A. AIIergic reaction

/ B. Gut perforation

/ C. Predisposition for cancerous transformation

/ D. Secondary appendicitis

/ E. Trapping of dye in diverticula

Q 5

Which of the following drugs is most likely to be effective in this case?

/ A. 3rd generation cephalosporin

/ B. Amoxicillin

/ C. Ampicillin

/ D. CIindamycin

/ E. Vancomycin

____________________________________________________________________________

Diarrhea Case 3 Answers

A1

The correct answer is D. This patient's history and proctoscopic examination are typical of severe pseudomembranous colitis (also sometimes called antibiotic associated colitis). Patients with milder disease may have only diarrhea. On pathologic examination, pseudomembranes composed of fibrin, neutrophils, necrotic material, and bacteria are seen overlying partially disrupted glands with prominent submucosal edema.

Acid fast bacteria (choice A) would suggest tuberculosis or atypical mycobacterial infection.

Neoplastic polyps (choice B) are seen as isolated findings or as part of familial polyposis syndromes.

Pseudomembranous colitis is not related to parasitic infection (choice C).

Small granulomas (choice E) could suggest either Crohn disease or tuberculosis.

A2

The correct answer is B. The clostridia are gram-positive, anaerobic, spore-forming rods that can produce a variety of nasty diseases. This patient's disease, pseudomembranous colitis, is due to bacterial gut overgrowth with Clostridium difficile, usually in the aftermath of broad-spectrum antibiotic therapy. Both children and adults may become infected. Probably in most cases, the patients already had small numbers of the organisms in their guts before antibiotic therapy, although isolated examples of transmission within wards have also been documented.

Clostridium botulinum(choice A) causes botulism.

Clostridium perfringens(choice C) and Clostridium septicum(choice D) cause gas gangrene.

Clostridium tetani(choice E) causes tetanus.

A3

The correct answer is D. Clostridium difficile produces toxins A and B, which can now be rapidly identified in stool samples. This is the best confirmatory test following proctoscopy, as the results will be back much faster than the pathology report on a tissue sample. The toxins cause necrosis of the superficial gut mucosa that, in turn, leads to pseudomembrane formation. True infection of the gut wall by the bacteria does not occur. (The bacteria like to live in and eat the necrotic material and fibrin of the pseudomembrane.)

CT scan (choice A) and MRI scan (choice B) are expensive tests that will not contribute to the diagnosis.

The "Scotch tape" test (choice C) involves using tape to collect pinworm eggs from the perirectal skin.

Clostridium difficile is a bacterium rather than a larger parasite, so stool for ova and parasites (choice E) would not be helpful.

A4

The correct answer is B. In addition to the immediate risks related to hypotension, dehydration, and electrolyte imbalance in these sometimes critically ill patients, complications that can incur include colonic perforation (which may be induced by barium contrast studies) and toxic megacolon.

Pseudomembranous colitis does not alter allergic reactions (choice A), predispose for appendicitis (choice D) or cancer (choice C), or induce formation of diverticula (choice E).

A5

The correct answer is E. Clostridium difficile is resistant to most antibiotics, which is why it tends to cause a bowel bacterial overgrowth when broad-spectrum antibiotics are used. The two antibiotics to which it is usually sensitive, and that are consequently most often used to treat pseudomembranous colitis, are vancomycin and metronidazole. The other agents listed in the choices are frequently reported causes of pseudomembranous colitis.

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Diarrhea Case 2

A 32-year-old woman goes to an emergency department because she has developed severe, watery diarrhea. On questioning, she reports that three days previously, she spent the weekend along the Gulf of Mexico, and ate at a raw oyster bar. About 36 hours later, she developed vomiting and an abrupt, painless, watery diarrhea. The volume of diarrhea has been copious, and she has subsequently developed intense thirst, oliguria, muscle cramps, and weakness. At the time of being seen in the emergency department, she is noted to have marked loss of tissue turgor, sunken eyes, and wrinkling of the skin of her fingers. Laboratory studies demonstrate hemoconcentration and severe metabolic acidosis with potassium depletion.

Q 1

Which of the following is the most likely cause of the woman's problems?

/ A. Amoeba infection

/ B. Bacterial infection

/ C. Food poisoning

/ D. Irritable bowel syndrome

/ E. Viral infection

Q 2

An organism cultured from the patient's stool is subsequently characterized as an oxidase-positive, gram-negative curved rod with polar

flagella that shows "shooting star" mobility and grows best on TCBS medium. Which of the following is the most likely pathogen?

/ A. Escherichia

/ B. Pseudomonas

/ C. Salmonella

/ D. Shigella

/ E. Vibiro

Q3

This organism is most likely classified as which of the following types ?

/ A. O1

/ B. O2

/ C. O5

/ D. O105

/ E. O139

Q 4

In the United States, approximately what percentage of patients who acquire this infection subsequently die?

/ A. 1% or less

/ B. 5-10%

/ C. 20-30%

/ D. 50-70%

/ E. 90% or more

Q 5

The patient responds with IV fluids, and is very much better within 24 hours. While this woman did not require antibiotic therapy, which of the

following antibiotics is used for this disease?

/ A. First generation cephalosporin

/ B. Metronidazole

/ C. Penicillin

/ D. Tetracycline

/ E. Third generation cephalosporin

____________________________________________________________________________

Diarrhea Case 2 Answwers

A1

The correct answer is B. This patient is severely ill and dehydrated. Severe watery diarrhea that persists is most likely to be due to a bacterial infection.

Amoeba infection (choice A) usually produces a bloody diarrhea that does not have the watery characteristic of cholera.

Food poisoning (choice C) usually begins within the first eight hours after ingestion of contaminated food, and is often over within 24 hours.

Irritable bowel syndrome (choice D) is usually a chronic, but relatively mild, problem.

Viral infection (choice E) can cause gastroenteritis, but it is not usually as debilitating as this patient's disease.

A2

The correct answer is E. The features noted are those of Vibrio cholerae, the causative organism of the severe diarrheal disease, cholera. The diarrhea is the result of the action of the cholera enterotoxin, which acts by ADP-ribosylating adenylate cyclase, leading to increased cyclic AMP with secondary increased efflux of Cl^- and H₂O. World-wide, cholera is usually spread by fecally contaminated water, but in areas such as Europe and the United States, where the general level of hygiene, sewage control, and water supply is good, the occasional cases seen are often the result of contaminated food. Some of the shellfish from the Gulf of Mexico naturally contain the organism, and ingestion of these shellfish in raw or poorly cooked form has caused cholera.

Escherichia(choice A) is oxidase-negative.

Pseudomonas(choice B) is an oxidase-positive, gram-negative rod that characteristically produces the blue pigment, pyocyanin.

Salmonella(choice C) is a motile, gram-negative rod that is a non-lactose fermenter that produces H₂S.

Shigella(choice D) are non-motile gram-negative rods.

A3

The correct answer is A. Vibrio cholera serogroup O1 is the major cause of epidemic cholera, and up until 1992 was the only cause. Since then, the O139 serogroup (choice E) has been an important pathogen in India and Bangladesh, but has not yet become important outside Asia. No other serotypes are known to cause epidemic cholera.

A4

The correct answer is A. The mortality of cholera varies markedly depending upon the general health of the individuals who become infected and the availability of adequate medical care. In extreme situations, such as in refugee camps with little sanitation, little food, and no available medical facilities, case fatality rates of 25-50% are encountered. In Europe, the Americas, and more recently Asia, case fatality rates in most situations are kept at 1% or less. A major reason for the decreased fatality rates in most parts of the world is that the World Health Organization has been encouraging endemic areas to pre-plan for epidemics and have available large numbers of previously prepared packages of oral rehydration salts.

A5

The correct answer is D. Most patients with cholera in this country who have disease severe enough to cause significant dehydration are rehydrated initially with IV fluids, and are then switched to oral fluids several hours later. In countries with more likelihood of having an epidemic and poorer medical availability, packages of oral rehydration salts to which water is added are commonly (and very effectively) used to treat cholera. Antibiotics are often not employed in milder cases. In severe cases, antibiotic therapy can reduce the volume and duration of the diarrhea experienced by the patient. The usual antibiotic of choice is tetracycline, although some resistant strains are emerging. Useful alternative drugs include ciprofloxacin, erythromycin, doxycycline, and furazolidone. No vaccine against cholera is presently available in the United States, although two vaccines (which are not completely effective) are available elsewhere in the world. The other agents listed in the choices are not used to treat cholera.

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