Question

Case #1

Three individuals from a military unit involved in a large training exercise in a very remote area of the western US developed mild fevers, headaches and dry coughs. During subsequent days, the three individuals began to produce small amounts of thin, clear sputum. The small field hospital unit performed CBCs, sputum Gram stains, and chest x‐rays on the 3 patients. The CBCs were normal. The sputum gram stains showed a few neutrophils but no bacteria. The chest x‐rays of the three showed a patchy infiltrate. The patients did not improve after 3 days of penicillin treatment. The conditions of two had in fact worsened.

The small laboratory was limited to performing basic testing. However, one MLS decided to retrieve the EDTA tube which she placed in a glass of chipped ice. Within a few minutes, she noted that the blood cells began to agglutinate into small clumps that could be seen with the naked eye. When she warmed the blood back to room temperature, the clumps disappeared.

a. Based only on the information provided by the history and laboratory information, what is the most likely infectious agent? (1 point)

b. Why were no bacteria seen on the sputum Gram stain? Why can a gram stain still be of value in this situation? (2 points)

c. What was the significance of the erythrocyte clumping when the tube of blood was placed on ice? (2 points)

Answer 1

a. Based on the information provided the most likely infectious agent is Mycoplasma pneumoniae.

b. In this type of pneumonia the bacteria can be differentiated with other infections because it shows slow progression of symptoms. Lack of growth on blood agar and lack of bacteria in gram-stain are significant diagnostic results for the possibility of Mycoplasma pneumoniae.

c. The cold agglutination test is used to determine if the autoantibodies that agglutinate the erythrocytes at less then 37degrees Celsius are present or not as these IgM antibodies with I antigen are present in blood during the Mycoplasma pneumoniae infection.