Table of Normal Values for Case Studies ________________________________________________________________________

CASE 1

This 8-year-old boy developed spiking fevers 1 week prior to hospital admission. The fever was treated with acetaminophen. He also complained of right ankle pain and tenderness that was attributed to summer sports activities although he did not have any known injury to the leg. Two days prior to admission he saw the doctor for ankle tenderness. The white blood cell count and X-rays of the leg were normal. He was thought to have a viral syndrome and was sent home. On the day of his admission to the hospital, he developed severe pain and tenderness in the right leg and a fever of 39.4ºC. X-rays were again negative.

An ankle aspiration revealed fluid with large numbers of white cells (3,350 WBC/mm3). A bone scan showed an abnormal area in the tibia. Bacterial cultures of blood, fluid from the ankle joint, and tibial aspirate were all positive for the same organism, which on Gram stain appears as gram-positive cocci.

1. Which organisms would be consistent with the Gram stain and the case presentation?

2. The organism was subsequently found to be both catalase and coagulase positive. What is this organism?

3. Where in nature is this bacterium found? How do people become infected?

4. This patient has osteomyelitis and septic arthritis. Name two ways in which bacteria may invade bone and joints to cause these infections. How is this type of infection managed?

5. What other types of infections does this organism cause?

CASE 2

This 15-year-old male has a history of sickle cell disease. He had a progressive, productive cough for 4 days and a spiking fever for 2 days prior to hospital admission. On admission, his temperature was 41.1ºC, his respiratory rate was 40/min, his pulse rate was 120 beats/min, and his blood pressure was 80/40 mmHg. He was alert and in mild respiratory distress. Chest examination was notable for decreased breath sounds. Initial laboratory studies included a hematocrit of 13.6% and a white blood cell (leukocyte, WBC) count of 52,400/mm3 with 86% neutrophils. A sputum Gram stain was non-diagnostic. A chest X-ray revealed a right lower lobe infiltrate. A blood culture was subsequently positive for gram-positive cocci in pairs (diplococci).

1. What is the clinical diagnosis in this patient?

2. What is the likely organism causing this illness? What is the major virulence factor of this organism?

3. Patients with sickle cell disease are at increased risk for bacterial infections with what types of organisms? Why?

4. How might this infection have been prevented?

CASE 3

The patient was a 23-year old female with an autoimmune connective tissue disorder who presented with fever, left foot and right upper quadrant pain, nausea, and vomiting. An exploratory laparotomy was performed during which 300 ml of greenish, non-odorous purulent material was aspirated from the peritoneum. An appendectomy was performed as well. The aspirate of the peritoneum revealed moderate polymorphonuclear leukocytes (PMN) and few gram-negative cocci. Aspirate of the fourth metatarsal joint revealed numerous PMNs, but few organisms were seen. An admission blood culture and joint and peritoneal aspirates grew the same organism, which was gram-positive, mucoid and beta-hemolytic.

1. When colonies are mucoid, this usually indicates the presence of which virulence factor?

2. Which three types of infections does this patient have?

3. On the basis of Gram stain and the infections observed, to which genus does this organism belong?

4. What further characteristics of this organism would be helpful in determining its identity?

The medical technologist returned the organism to the incubator after performing the tests suggested by you in your response to question 4, noting that the colonies were very mucoid. She took the culture out of the incubator about 6 hours later to show the infectious disease resident, telling her "you should see how mucoid this organism is!" When she showed the resident the plate, the colonies were no longer mucoid.

5. Explain this observation.

6. What organism is this?

CASE 4

This 6-year-old female presented with a 1-week history of a febrile illness with a sore throat and headache. She was given oral ampicillin by her local physician. One day prior to hospital admission, the patient awakened with pain and swelling in the right ankle. On hospital admission, she was noted to have a new systolic heart murmur thought to be consistent with mitral regurgitation (insufficiency of the mitral valve). The presumptive diagnosis was acute rheumatic fever.

1. The patient had a sore throat that preceded her acute rheumatic fever. Although we do not have the results of a throat culture taken during the sore throat, which pathogen would probably have grown from such a culture? How can a bacitracin disc help in the identification of this organism?

2. How is pharyngitis with this bacterium related to the subsequent development of rheumatic fever?

3. Which type of hemolysis is seen when this organism is streaked on sheep blood agar? Which types of hemolysins does this bacterium make?

4. Which serologic test may be useful in helping to confirm the diagnosis of rheumatic fever in this patient?

5. Which cell wall protein is believed to play a major role in the pathogenesis of rheumatic fever? Explain its role specifically.

6. What has happened to the incidence of rheumatic fever in the United States?

7. What is scarlet fever? Is it related to rheumatic fever?

CASE 5

This 2-year-old boy experienced an upper respiratory infection 2 weeks prior to hospital admission. Four days prior to admission, anorexia (loss of appetite) and lethargy were noted. The patient was seen in the emergency room 3 days prior to admission. At that time he had a fever of 39.9ºC. Physical examination revealed a clear chest, exudative pharyngitis (sore throat), and enlarged cervical lymph nodes. A throat culture was taken, and a course of penicillin was begun. The child's condition worsened, and he became increasingly lethargic. He developed respiratory distress on the day of admission. It was noted that the throat culture from 3 days prior to admission had not grown any group A streptococci. On examination, the child had a fever of 38.9ºC and had an exudate in the throat that was described as a yellowish thick membrane which bled when scraped. The patient's medical history revealed that he had received no immunizations.

1. The patient was admitted to the hospital and treatment was begun. Special cultures of the pharynx were requested that subsequently grew the suspected pathogen. What was the pathogen? Which types of media are used to isolate this organism?

2. To cause disease, does this organism invade the bloodstream? If not, in what way does it cause disease? Which special test is necessary to prove that this organism is capable of producing disease?

3. How can this disease be prevented?

4. How is this disease treated?

CASE 6

The patient was a 6-week-old male who was transferred to the University hospital with a 10-day history of choking spells. The child's spells began with repetitive coughing, progressing to his turning red and gasping for breath. In the prior 2 days, he also had three episodes of vomiting in association with his choking spells. His physical examination was significant for a pulse of 160 beats/min and respiratory rate of 72 (both highly elevated). The child's chest X-ray was clear. There was no evidence of tracheal abnormalities. His white cell count was 15,500/mm3 with 70% lymphocytes. A nasopharyngeal swab was diagnostic.

1. What was the organism infecting this child?

2. Why is a nasopharyngeal swab the specimen of choice for making this diagnosis?

3. Why did this patient have a predominance of lymphocytes?

4. Are this child's clinical course and chest radiograph consistent with his infection? Explain your answer.

5. What is the epidemiology of this infection, and how might it be prevented.

CASE 7

The patient was a 55-year-old male with a 2-month history of fevers, night sweats, increased cough with sputum production, and a 25-lb weight loss. The patient denied intravenous (i.v.) drug use or homosexual activity. He has had multiple sexual encounters, “sips” a pint of gin a day, was jailed 2 years ago in New York City, and has a history of gunshot and stab wounds. His physical examination was significant for bilateral anterior cervical and axillary adenopathy (swollen lymph nodes) and a temperature of 39.4ºC. His chest radiograph showed paratracheal adenopathy and bilateral interstitial infiltrates. His laboratory findings were significant for a positive HIV serology and a low absolute CD4 lymphocyte count. An acid-fast organism grew from the sputum and bronchoalveolar lavage fluid from the right lung.

1. Which organisms can be positive on acid-fast stain.

2. Given his medical history, which organism is this likely to be? How does the finding that the patient is HIV positive affect this decision?

3. Which factors in his medical history do you think are important in his contracting this infection with acid-fast bacteria?

4. What is a PPD test? What is its value in this patient? What additional tests would you order with a PPD test?

CASE 8

This 34-year-old man was well until 3 days prior to admission, when he noted the onset of fever, weakness, fatigue, headache, sore throat, and a cough productive of white sputum. One day prior to admission he awakened with burning chest pain that was made worse by coughing and by deep breathing. He developed shortness of breath and was seen at the University infirmary, where he appeared acutely ill with a fever. A chest radiograph demonstrated bilateral infiltrates consistent with pneumonia. An arterial blood gas analysis was notable for significant hypoxemia (pO2, 48 mmHg). The patient's shortness of breath increased markedly, and he was transferred to the hospital, where he was found to be cyanotic and febrile to 39.8ºC and to have a respiratory rate of 44/min with labored respirations. His sputum was grossly bloody with apparent clumps of tissue. Examination of the sputum revealed a grossly bloody background, numerous neutrophils, and sheets of gram-positive cocci in clusters. Despite appropriate antibiotic therapy and maximal intensive car support, the patient died. His illness occurred during January.

1. The sputum Gram stain is most consistent with which bacterial pathogen?

2. In addition to the bacterial infection noted above, the nonspecific symptoms that began this illness and the time of year in which he became ill suggest a viral illness as well. Which viral illness is most likely?

3. How is the presence of these two processes related?

4. Which other bacterial causes of pneumonia can complicate this viral infection?

CASE 9

This 30-year-old dairy farmer was in good health until the day prior to admission, when he felt chilled and feverish. He developed nausea, vomiting, diarrhea, and lower abdominal discomfort and presented to the emergency room, where he was noted to be lethargic. His vital signs included temperature of 40ºC, blood pressure of 100/60 mmHg in the supine position and 80/69 mmHg sitting, and a pulse of 80 beats/min. His physical examination was remarkable for lower abdominal tenderness. A rectal examination revealed occult blood in the stool. The patient was lethargic but had no focal neurological deficits. Of note, his 3-year-old daughter had been discharged from the hospital 2 days previously with a similar history.

The patient was treated with i.v. fluids and antibiotics, and his condition improved. A stool examination was fecal leukocytes was positive, and a stool culture was diagnostic. Biochemical examination of the organism revealed it to be a lactose nonfermenter on MacConkey agar, H2S negative, urease negative, and nonmotile.

1. Which organisms would be in your differential diagnosis of bloody diarrhea with fecal leukocytes?

2. On the basis of the biochemical reactions, which organism do you think it is?

3. How is dehydration in patients with diarrhea usually treated? Why could this therapy not be used in this case?

4. This patient's wife and another child also had this infection. Was this individual's vocation, dairy farming, important in the epidemiology of this infection in his family? Explain your answer.

CASE 10

The patient was a 19-year-old female with a history of urinary tract infection (UTI) 4 months prior to admission for which was treated with oral ampicillin. Five days prior to admission she began to note nausea without vomiting. One day later she developed left flank pain, fevers, and chills and noted increased urinary frequency. She noted foul-smelling urine on the day prior to admission. She presented with a temperature of 38.8ºC, and physical examination showed tenderness on the left side. Urinalysis was notable for >50 white blood cells per high-power field, 3-10 red blood cells per field, and 3+ bacteria. Urine culture was subsequently positive for >100,000 CFU of a gram-negative, lactose fermenting rod/ml; this bacterium was beta-hemolytic on sheep blood agar.

1. What do the urinalysis findings indicate?

2. Why were the numbers of organisms in her urine quantitated on culture?

3. Which gram-negative rods are lactose fermenters?

4. The isolate was indole positive. How does this information help in its identification?

5. This bacterium was resistant to ampicillin. What in this patient's history might explain this observation?

6. Urinary tract infections are more frequent in women than men. Why?

CASE 11

The patient was a 32-year-old male who presented to the emergency room with a 3-day history of fever to 40ºC, malaise, and back pain. Laboratory tests revealed a WBC of 4,700/mm3 and abnormal liver functions. Blood cultures were done and were subsequently reported as negative. He developed anorexia and jaundice in addition to fevers and malaise. He denied a history of intravenous drug use, sexual contact (for 2 months), and transfusions. Five weeks ago he was visiting friends in New York City, and they ate raw oysters. Recent telephone contact with one of the friends revealed that he had a similar illness.

On examination the patient was mildly icteric (jaundiced). There was no rash or lymphadenopathy. The abdominal examination revealed a tender liver, which was slightly enlarged. Laboratory tests showed an AST level of 2,501 U/liter, an alkaline phosphatase level of 298 U/liter, a bilirubin level of 2.2 mg/dl, and a lactate dehydrogenase level of 1,102 U/liter. Blood was sent for diagnostic testing. Over the next month his symptoms resolved and the liver function test results returned to within normal limits.

1. A number of liver function tests were performed on this patient. What did they reveal? What was the differential diagnosis?

2. What was the etiology of his illness? How did he contract this infection?

3. What is the spectrum of disease associated with this organism?

4. How is this infection typically diagnosed?

5. How can infections with this agent be prevented?

CASE 12

The patient was a 19-year-old female. She was seen in the walk-in medicine clinic with complaints of right knee and right shoulder pain, nausea, and vomiting. On physical examination, she had a swollen right knee and decreased range of motion of her right shoulder. She also had a thick vaginal discharge. Her temperature was 38.4ºC, and she had a WBC count of 15,700/mm3. She gave a history of having two recent sexual partners. Blood, vaginal, and joint fluid cultures were performed. A Gram stain of joint fluid showed numerous PMNs but no organisms were seen. Both the vaginal and joint fluid cultures were positive for the agent of infection.

1. What was the etiologic agent of her infection? What in her history supports this conclusion?

2. For what other agents should the patient be examined? Explain your answer.

3. This patient had a systemic infection. What phenotypic characteristics are found in isolates of this organism which cause systemic infections?

4. What should be done about her sexual partners?