Question 1

One week postdelivery, an infant boy becomes extremely irritable and continuously rubs his right eye, which contains a mucopurulent exudate. An examination of the eye shows papillae on the conjunctiva. No bacteria are seen in the exudate. The most likely causative infectious agent is

Accepted Answer

This case of neonatal conjunctivitis is most likely caused by Chlamydophila trachomatis since no bacteria are present and papillae rather than follicles are observed. The mother was probably the source of the infection.

Question 2

A 58-year-old man presents at your office complaining of extreme pain in his right testicle. Physical examination shows considerable swelling. A small amount of urethral exudate could be aspirated. Microscopic examination and Gram staining showed the presence of bacteria. Those bacteria most likely are

Accepted Answer

Both Staphylococcus epidermidis and various Enterobacteriaceae can cause epididymitis in men over the age of 35 years, but Gram-negative rods is not a choice; therefore, Gram-positive cocci is correct.

Question 3

A 22-year-old woman presents with symptoms of vaginitis, including a yellowish discharge. She claims to have not been sexually active for 18 months. When KOH is added to the discharge, a "fishy" odor appears. She is most likely infected with

Accepted Answer

Gardnerella vaginalis and Candida albicans are the non-STD choices. Gardnerella vaginalis is correct because it produces the fishy odor when KOH is added to the discharge.

Question 4

A known alcoholic appears at the emergency department with chest pain, a 40°C/104°F fever, chills, and a productive cough. He has no history of chronic pulmonary disease. There are red blood cells an encapsulated Gramnegative rods in the sputum. The symptoms are most likely caused by

Accepted Answer

Klebsiella pneumoniae is associated with pneumonia in alcoholics. The other Gram-negative rod (Pseudomonas aeruginosa) is associated with chronic pulmonary disease in the immunocompromised.

Question 5

There is an outbreak of gastrointestinal disease involving six children at a day care center. The children all have symptoms of fever, watery stool, and vomiting. Recent activities at the center involved playing with animals including kittens, turtles, birds, and hamsters. What types of bacteria are most likely to be observed in the stool?

Accepted Answer

The most likely bacteria to cause gastrointestinal disease with the symptoms and circumstances provided is a species of Salmonella, which are Gram-negative rods.

Question 6

A 75-year-old man is brought by his daughter to the community health center. He appears confused and has a stiff neck and severe headache. She indicates that the previous week he had a runny nose and other symptoms consistent with sinusitis. What organism would you expect to find in his cerebrospinal fluid?

Accepted Answer

The symptoms of confusion and severe headache point to a case of bacterial meningitis. With preceding sinusitis in an elderly man, Streptococcus pneumoniae is the most likely cause. The other two bacteria are more often observed in infants or young adults.

Question 7

While on winter semester break, a 21-year-old male college student appears at his family physician's office with several skin lesions on his right arm. They consist of a central pustule within a raised erythematous area. He reports that the only recent unusual activities that have involved skin exposure have been hot tub parties at his friend's cabin during the previous two weekends. What is the most likely causative infectious agent?

Accepted Answer

Pseudomonas aeruginosa is associated with an infection known as "whirlpool" or "hot tub" folliculitis. Inappropriate care of whirlpools, hot tubs, and swimming pools can allow this organism to grow and enter the skin through small breaks.

Question 8

In July, you are called to a rural nursing home where several of the residents have developed a gastrointestinal disease consisting of fever, vomiting, and bloody stool. Lab analysis of the stool shows the presence of PMNs and Gram-negative rods. Epidemiological discussions with the residents indicate they all shared the same raw milk brought to one resident by his farmer son. The most likely cause of the infection is

Accepted Answer

The symptoms and lab analysis of the stool are consistent with Campylobacter jejuni infection. The raw milk was most likely the source of the infection.

Question 9

An 18-month-old female infant is brought to the emergency department by her mother. The mother reports an abrupt onset of symptoms consisting of continual crying, high fever (40°C/104°F), and a cough
Producing rusty colored sputum. What would you expect a chest x-ray and lab findings to show?

Accepted Answer

The most common cause of CAP in infants and elderly is Streptococcus pneumoniae. The symptoms in this case are consistent, and the rusty colored sputum is suggestive of this bacteria. It is a Gram-positive cocci with a lobar pneumonia on a chest x-ray.

Quiz 9: Clues for Distinguishing Causative Infectious Agents Systems Approach

One week postdelivery, an infant boy becomes extremely irritable and continuously rubs his right eye, which contains a mucopurulent exudate. An examination of the eye shows papillae on the conjunctiva. No bacteria are seen in the exudate. The most likely causative infectious agent is

A 22-year-old woman presents with symptoms of vaginitis, including a yellowish discharge. She claims to have not been sexually active for 18 months. When KOH is added to the discharge, a "fishy" odor appears. She is most likely infected with

A known alcoholic appears at the emergency department with chest pain, a 40°C/104°F fever, chills, and a productive cough. He has no history of chronic pulmonary disease. There are red blood cells an encapsulated Gramnegative rods in the sputum. The symptoms are most likely caused by

An 18-month-old female infant is brought to the emergency department by her mother. The mother reports an abrupt onset of symptoms consisting of continual crying, high fever (40°C/104°F) , and a cough Producing rusty colored sputum. What would you expect a chest x-ray and lab findings to show?