A 20-year-old female college student presents with a 5-day history of cough and low-grade fever ...

A 20-year-old female college student presents with a 5-day history of cough, low-grade fever (temperature 100°F), sore throat, and coryza.
On examination, there is mild conjunctivitis and pharyngitis. Tympanic membranes are inflamed, and one bullous lesion is seen. Chest exam shows few basilar rales.
Laboratory findings are as follows:
Hct: 38
WBC: 12,000/μL
Lymphocytes: 50%
Mean corpuscular volume (MCV): 83 nL
Reticulocytes: 3% of red cells
CXR: bilateral patchy lower lobe infiltrates


The sputum Gram stain is likely to show
a. Gram-positive diplococci
b. Tiny gram-negative coccobacilli
c. White blood cells without organisms
d. Acid-fast bacilli

Answer:
c. White blood cells without organisms

This patient is likely to have
a. High titers of adenovirus
b. High titers of IgM cold agglutinins
c. A positive silver methenamine stain
d. A positive blood culture for Streptococcus pneumoniae

Answer: b. High titers of IgM cold agglutinins

Treatment of choice is
a. Erythromycin
b. Supportive therapy
c. Trimethoprim-sulfamethoxazole
d. Cefuroxime

Answer: a. Erythromycin

Discussion: This young woman presents with symptoms of both upper and lower respiratory infection. The combination of sore throat, bullous myringitis, and infiltrates on chest x-ray is consistent with infection due to M. pneumoniae. This minute organism is not seen on Gram stain. Neither S. pneumoniae nor H. influenzae would produce this combination of upper and lower respiratory tract symptoms. The patient is likely to have high titers of IgM cold agglutinins. The low hematocrit and elevated reticulocyte count reflect a hemolytic anemia that can occur from mycoplasma infection. These IgM class antibodies are directed to the I antigen on the erythrocyte membrane.
The treatment of choice for mycoplasma infection is erythromycin.