Case Study 1
A 64-year old male with fever, malaise, and cough.
There are six questions to answer in this case study

Patient's history A 64-year old urbanite male reports to your practice with fever, malaise and a cough. His vaccinations are up-to-date, including DPT. His condition worsens over several days, with his temperature increasing to 40.4C and development of dyspnea (difficulty of breathing.) You have him admitted to a nearby hospital, where laboratory analysis reveals abnormal liver and kidney function. His lungs show signs of mild inflammation with thin, watery secretion.
The patient is given antibiotics and Gram stains are made of a bronchial lavage.


Question 1 of 6
What do you know about the organism from examination of the Gram stain?
A. Gram-positive
B. Gram-negative




ans in bold:
A. Gram-positive
Bacteria with a thick murein cell wall retain crystal violet even when washed with acidified ethanol. Bacteria with this type of cell wall are called Gram-positive and appear purple.
B. Gram-negative
Gram-negative bacteria can be stained with safranin, making them look pink.




Question 2 of 6

What is the shape of the infecting organism?
A. Coccus
B. Coccoid rod
C. Rod


ans in bold:

Bacteria are referred to by their shape.
A. Coccus
Round bacteria are referred to as cocci


B. Coccoid rod
Short rods are often referred to as coccoid rods


C. Rod
Long bacteria are referred to as rod shaped bacteria




"His vaccinations are up-to-date, including DPT."

Question 3 of 6

What does DPT stand for?

A. Diphtheria, Pertussis, Trichomonas

B. Diphtheria, Pseudomonas, Tetanus
C. Damsela, Pertussis, Tetanus
D. Diphtheria, Pertussis, Tetanus

ans:
C. Diphtheria, Pertussis, Tetanus
This vaccination protects against infections by Corynebacterium diphtheriae, Bordetella pertussis (which causes wooping cough), and Clostridium tetani.





Nothing of clinical significance is isolated when the bronchial lavage fluid is cultured on blood agar plates. However, the organism grows well on charcoal yeast extract agar with blood.



Despite antimicrobial and supportive therapy, the patient subsequently develops multiorgan failure and dies after a protracted course.


Question 4 of 6

Which organism caused this disease?

A. Legionella pneumophila

B. Pseudomonas aeruginosa
C. Bordetella pertussis
D. Escherichia coli



ans in bold:
A. Legionella pneumophila
This organism grows well on charcoal yeast extract agar with blood.
B. Pseudomonas aeruginosa
Like Escherichia coli, Pseudomonas aeruginosa can cause this sort of infection, but both should grow on blood agar.
C. Bordetella pertussis
Bordetella pertussis is an uncommon cause of bronchopneumonia, but usually has an acute course unlike the one described in this case. Furthermore, as the patient has been vaccinated (DPT) he is probably immune to infections caused by Bordetella pertussis.
D. Escherichia coli
Escherichia coli like Pseudomonas aeruginosa can cause this sort of infection, but both should grow on blood agar.



Question 5 of 6

What is the most likely source of Legionella pneumophila?

A. Exposure to water containing Legionella pneumophila
B. Contact with another infected person
C. Exposure to an infected animal



ans in bold:

A. Exposure to water containing Legionella pneumophila

Patients are usually infected by inhalation of contaminated water. The concentration of Legionella usually has to exceed 1000 /milliliter to be infectious. Typical sources of contaminated water include cooling systems, shower heads, potable or domestic water systems, respiratory therapy devices, industrial coolants, and whirlpool spas.

B. Contact with another infected person
Humans are dead end hosts. Legionellosis is infectious for humans but not transmissible from person to person.
C. Exposure to an infected animal
Lower animals are rarely affected by exposure to Legionella pneumophila and are an unlikely source of infection. Also, the patient reported no contact with animals.




The patient's disease had been caused by Legionella pneumophila.

Question 6 of 6

Are these organisms primarily human pathogens?

A. Yes
B. No



ans:

B. No
The natural environment of Legionella pneumophila is water. It can also be found in small numbers in the soil. Legionella thrives in warm, stagnant water at temperatures of 25-42o C and reach greater numbers if scale or sediment is present. The presence of Amoebae is also important as they are capable of supporting growth of Legionella.