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					Case 191
The patient is a 30 year-old female who presents with polyuria and dysuria. Her medical history is significant for
crack cocaine addiction and a history of sexually transmitted diseases. She reports having unprotected sex with two
partners since her recent release from jail. Her physical examination is unremarkable with normal vital signs and
without flank pain or costovertebral or abdominal guarding. Analysis of a clean catch urine specimen is notable for
positive leukocyte esterase and nitrate tests. Examination of a wet mount of vaginal secretions reveals "clue cells".
Organisms cultured from a urine specimen can be seen in Figure 1.

1. Explain the purpose of the leukocyte esterase and nitrate tests.
How you would interpret the results of these tests in this patient?
          Leukocyte Esterase: Positive= Presence of pus in her urine, ie. white blood cells
          Nitrate Test: Positive= Presence of bacteriuria (Nitrate to Nitrite); Negative does not mean the absence of
an infection.
          Interpretation: She has bugs and is trying to fight them.

2. What types of genital tract infections can be detected by examining wet mounts of vaginal secretions?
          Types: Fungal, Bacterial, Yeast, and Clue cells
          Bacterial types: Trichomoniasis Vaginalis, Gardnerella Vaginalis, and Candida
The "clue cells" found in her specimen are suggestive of which of these infections?
          Bacterial vaginosis
          Clue Cells: Epithelial cells coated with bacteria, giving the cell a granular appearance. In contrast normal
epithelial cells have a distinct margin under phase contrast.
How would you establish this diagnosis definitively?
          Three of the first four:
          1 20% clue cells
          2 pH 4.5 or greater
          3 Positive Whiff Test (yum), Just add KOH and it smells like fish (Perfect party trick or great topping for
any salad)
          4 Discharge: Homogenous greyish fluid
          5 Gram stain for any change in vaginal flora
This infection is of particular concern in which patient population? Why?
          Sexually active women of child bearing age - Transfer to fetus (kudos to Amy)
3. For what other infectious agents should she be tested given her medical history?
          STDs, and HIV
What types of tests are typically used to diagnose these agents? (e.g., culture, serology, molecular testing such
as PCR)
          STDs: Bacterial Culture (except Chalmydia via PCR); HIV: ELISA and Western
4. What type of infection does this patient have?
          UTI: Cystitis; Vaginosis/Vaginitis
Name the organism causing her infection?
          E. coli
What factors predispose her to this infection?
          Multiple sexual partners
Why are these infections more common in young women than men of the same age?
          No prostate, shorter urethra (anatomical), and receptors for the organism

5. What virulence factors does this organism produce and what role do they play in the pathogenesis of her
         Ability to bind uroepithelial cells; Type 1 fimbriae=recognize mannose containing receptor

6. This patient has had previous infections with this organism. How will this information affect your
therapeutic approach?
        1 Resistance to antibiotics
        2 Infection by the same or different stain
What other information gleaned from your physical examination will also influence that approach?
         No Pyelonephritis since no flank pain or costovertebral/abdominal guarding therefore shorter treatment
with antibiotics.

Case 195
The patient is a 66 year-old male who presents to the clinic complaining of back pain of two weeks duration,
compounded by abdominal pain during the past week. The pain in his back was below the right scapula and was
very sharp in nature. He complained of being short of breath due to an inability to breathe deeply as a result of the
pain. He reported that his back pain was relieved by lying down. Three days prior to admission, his temperature
went to 38.0°C and he experienced a shaking chill, which was relieved with TylenolÒ . His medical history also
includes a diagnosis of colon cancer which metastasized to the liver three and a half years ago
During his current physical examination, his temperature was 36.3°C, his pulse was 107, and his blood pressure was
68/46. A chest radiograph was consistent with a right lower lobe pneumonia. His white blood cell count was 9,100
cells/ul. A Gram stain of a sputum sample from this patient is seen in Figure 1. Two sets of blood cultures (four
bottles) obtained at the time of admission were positive for the organism seen in Figure 2 and Figure 3.

1. What is the organism causing this patient's bacteremia?
Do you think the same organism is causing his pneumonia? Explain.
2. With what clinical syndrome are his vital signs consistent?
What virulence factor does this organism produce which is associated with this clinical syndrome?
3. Explain possible ways in which this patient might have become infected with this organism.
4. This organism causes chronic lung infections in patients with cystic fibrosis. How do the strains causing chronic
lung infections in CF patients differ from the isolate causing this patient's infection? (Hint: refer to Figure 2)
5. What role does the immune system play in the chronic lung disease caused by this organism in CF patients?

Case 177
The patient is a four year-old female with an unremarkable past medical history and a vaccination status appropriate
for her age. During the past week, she and her fraternal twin and two younger siblings have all had upper respiratory
tract infections with nasal congestion. On the night prior to admission, she developed fever and left ear pain. The
following day, she was examined and found to have a bulging left eardrum consistent with otitis media. She was
begun on oral amoxicillin/clavulanic acid. Early the next afternoon, she continued to have fever and was irritable.
Later that afternoon, she also complained of a headache and neck pain and she was brought to the emergency
department. On physical examination, she had a stiff neck and was lethargic and listless. There were no focal
neurologic findings but it was noted that she had a rash on her right cheek which the physician thought might be an
early stage of a petechial rash. He performed a spinal tap. The fluid was cloudy with 6750 white blood cells/ml
(95% being neutrophils) and 189 red blood cells/m l. Her CSF protein was 170 mg/dl (normal is 15-45) and her CSF
glucose was 25 mg/dl (normal is 50-75). A Gram stain of the CSF is seen in Figure 1. The culture of the organism
recovered from her CSF is shown in Figure 2. Of note, her serum immunoglobulin levels (IgG. IgA, IgM) were

1. What organism do you think is infecting this patient? What is the significance of her having otitis media in
the development of her infection?
        Haemophilus Influenza; 1st stage of infection usually begin as URI

2. What is the major virulence factor produced by this organism? When this organism does not produce this
virulence factor, what types of infections does it typically cause?
        The Capsule. Other infections are of mucous membranes: otitis media, sinusitis, bronchitis

3. What is the significance of her developing a petechial rash? What organism that causes bacterial
meningitis is frequently associated with this type of rash? What are the pathophysiologic events responsible
for the formation of this rash?
        Sepsis/systemic infection; Neisseria Menningitis; Endotoxin(LPS) causes Disseminated Intravascular

4. How has the epidemiology of infection with this organism changed in the past ten years?
        Vaccine fot type B H. Flu= Hib has reduced incidence of infection

5. How does her vaccination status and immunoglobulin levels help you understand this case?
        Vaccine failure or infection from another strain of H. Influenza (type F)

Case 175
The patient is a 23 month-old female referred to the pediatric walk-in clinic because of cramping abdominal pain
and persistent crying. She has a five day history of intermittent fever and diarrhea, with no history of vomiting. Her
mother noted that two stools the previous day were "real mucousy." During the 45 minutes preceding her admission
she had three non-bloody bowel movements. When walking from the car the child began to scream/cry
inconsolably, while repeatedly drawing up her left leg. Her past medical history is significant for recurrent otitis
media treated two months previously by bilateral myringotomy with placement of tubes.
On physical examination, her abdomen was soft without masses and she had normal bowel sounds. A rectal
examination revealed nothing abnormal and a test for heme in her stool was indeterminate although she
subsequently had a stool characterized by the mother as "bloody." Laboratory findings were significant for a white
blood cell count of 13,900 cells/m l with other values (including electrolyte and urinalysis results) within normal
limits. The surgical residents believed that the child did not have appendicitis. A stool culture was set up and the
enteric pathogen recovered from this patient is seen in Figure 1. On Gram stain, the organism was a curved, pink

1. After assessment by the surgical resident ruled out appendicitis, how would you have treated the child?
          Fluid replacement therapy. In severe cases, use erythromycin. Otherwise, let the infection run its course.
2. What enteric pathogen can frequently mimic appendicitis?
          Yersinia enterocolitica frequently mimics appendicitis.
          How do you explain the similarities between the abdominal pain caused by this enteric pathogen and
          Mesenteric adenitis mimics appendicitis. It infect primarily the ileum and leads to watery diarrhea in
infants less than 5 months old.
3. What bacterial pathogens can cause individuals to have bloody stools?
          p. 135 in notes: Shigella, Salmonella, Yersinia, Campylobacter, Enteroinvasive E. coli, EHEC, C. difficile
can all lead to bloody stools.
          What organism is causing her infection?
          Her infection is Campylobacter jejuni.

4. Explain the special growth conditions needed to recover the pathogen causing her gastrointestinal
         Microaerophilic (6% oxygen, 10% carbon dioxide), special agar at 42 celcius.
5. Once the identity of the pathogen was known, would you have changed your treatment strategy? Explain.
         Yes, no antibiotics are necessary in most cases, and erythromycin is used in severe cases.
6. An increased number of infections with this organism often occur after Thanksgiving in the US. Why?
         Birds, including turkeys, are a major source of campylobacter.
7. This organism is a frequent cause of diarrheal disease in HIV-infected patients.
Explain two problems related to infection with this organism which mainly occur in HIV-infected individuals.
         I. 20% of HIV infected develop chronic diarrhea from campylobacter.
         II. oral quinolone or macrolides induce drug resistance in vivo which causes relapse of campylobacter.
         III. bacteremia is common in immunocompromised with campylobacter.

Case 181
The patient is an eight year-old female who presents with a three day history of vomiting which evolved into
diarrhea and fevers to 38.5°C. Two weeks previously she underwent minor plastic surgery for which she received a
dose of oral cephalexin as surgical prophylaxis. The night prior to her current admission she had six bowel
movements with associated abdominal pain. On admission, she was orthostatic with a blood pressure of 123/61. Her
temperature was 37.2° C, her pulse was 96 beats/minute and her respiratory rate was 32 respirations/minute. Her
physical exam was also significant for some abdominal tenderness and a positive stool guaiac. Her white blood cell
count was 9,000cells/m l. A stool sample was cultured and examined for white blood cells. The fecal leukocyte
exam was graded as 4+ for PMNs. Culture of the organism recovered from her stool is shown in Figure 1 on
MacConkey and blood agar plates. Additional biochemical tests demonstrated that the causative organism was a
motile H2S producer, which was urease negative.

1. What is the organism most likely causing her infection?
         Organism = Salmonella (probably S. Enteriditis) - 2 Buckets + Hydrogen
Sulfide = Salmonella

2. What may have been an important predisposing factor in her development of this infection? Explain why.
What are some other important predisposing factors with this organism?
Predisposing Factors:
     a. Cephalexin - clear out normal gut flora
     b. Anything that reduces stomach acidity - Pepto Bismol; Pot Smoking

3. Bacteremia occurs fairly frequently with the organism causing this patient's diarrhea. In particular,
bacteremia is common in patients with sickle cell anemia. Briefly describe the events which lead to
bacteremia with this organism and explain why patients with sickle cell disease are at increased risk for
infection with this organism.
Events leading to bacteremia:
     a. - Colonization of intestinal tract after ingestion of a large
number of organisms
     b. - Invasion of intestinal epithelium and then incorporation into
     c. - Macrophages travel to spleen, liver, lymph nodes and
salmonella slowly proliferates
     d. - Eventually organism burst into bloodstream, thus causing

Sickle Cell causes "sludging" in liver and spleen which are the main organs
involved in clearing the blood. Because it can't be cleared quickly enough,
sickle cell is a predisposing factor for bacteremia.

4. Describe the epidemiology of infections with this organism. Describe a major outbreak of infection with
this organism that has occurred in the US in the past two years.
         Epidemiology - chicken, turkey, eggs, reptiles. **Salmonella is one of
the most common zoonotic infections. In past two years their was some out break in Nebraska with some turtle or

5. What is the current status of antimicrobial resistance in isolates of this organism recovered in the US?
Resitance - fluoroquinolones and trimethoprim.

What animal husbandry practice may result in increasing frequency of antimicrobial resistance in this
organism? Hint: a visit the CDC website at or Medline may be helpful in answering this

Case 111
The patient is a three month-old male with a three week history of progressive coughing. Over the past two weeks
the patient has been having 20 to 30 coughing episodes per day, each of which lasts for as long as 25 minutes.
During these coughing spells, this child has had difficulty catching his breath and has occasionally vomited. At the
beginning of his illness, he was thought to have otitis media and received a seven day course of amoxicillin. His
history also includes a DPT vaccination at two months. During this most recent examination, a specimen was
obtained with a nasopharyngeal swab. The organism causing his illness was detected in this specimen.

1. What is the most likely organism causing this patient's illness?
          Bordetella pertussis
2. Why is a nasopharyngeal swab the specimen of choice for detecting this organism?
          Higher yield because there are more ciliated epithelial cells to which Pertussis binds.
3. Besides culture, what other detection technique is used? What are its advantages over culture? What are
its disadvantages?
          PCR--faster, more likely to recover due DNA amplification. Disadvantage? Detects dead bugs also cost
and skill can be limiting.
          Antigen detection with direct fluorescent antibody testing, rapid but not as sensitive.
          Serology--problem: requires two specimens, retrospective diagnosis.
4. Given the impressive clinical presentation, no other laboratory procedures were requested. However if
other lab work had been performed, a very striking finding would have been seen on a complete blood count.
What is this finding? What virulence factor of this organism is believed to be responsible for this finding?
          Increase in lymphocytes (70%). Lymphocytosis promoting factor (aka pertussis toxin)
5. Many infectious diseases are unusual in three month-old children. Why? Why wasn't this child protected
from the organism with which he was infected?
          IgG and IgA from the mother. Not high enough level to protect him since vaccination is not lifelong. May
not have had booster shots
6. If this child was in group day care, what action would be necessary to protect his classmates from infection
with this organism?
          Child must stay home until negative cultures. Prophylactic antibiotics? Erythromycin is usual treatment
but resistance starting to be seen (very rare). Second choice is TMP + SMX (ex. Bactrim or other).

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