A 19-year-old man comes to the office due to a week of persistent dry cough that disturbs his sleep. He has also had a sore throat, headaches, and fatigue. Yesterday, he noticed a rash on his arms and legs. The patient has no known medical problems and takes no medications. He has not had any sick contacts. Temperature is 37.8 C (100 F), blood pressure is 115/78 mm Hg, pulse is 86/min, and respirations are 16/min. Mild pharyngeal erythema is present. There is no cervical lymphadenopathy. Cardiopulmonary examination is normal. A faint macular rash is present on the extremities. Chest x-ray reveals increased interstitial markings and a small right-sided pleural effusion. Which of the following organisms is most likely causing this patient's condition?
Mycoplasma pneumonia | |
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Mycoplasma pneumoniae is a highly infectious, low-virulence bacterium that is spread by direct contact with respiratory droplets. Outbreaks are common among young individuals who share close quarters (eg, school children, college students, military recruits), with peak prevalence in the fall and winter. Many infections are subclinical, but patients may develop illness in the upper or lower respiratory tract.
M pneumoniae is the most common cause of atypical pneumonia. Symptoms are indolent and include headache, malaise, fever, and incessant dry cough. Nonpurulent pharyngitis, macular skin rash, and subclinical hemolytic anemia (due to cold agglutinins) may occur. White blood cell count is usually normal. Chest x-ray typically reveals interstitial infiltrates; a serous pleural effusion may be present in approximately 25% of patients. Diagnosis is usually made with clinical and radiographic findings; laboratory testing is not generally needed in the outpatient setting. Empiric treatment with oral antibiotics (eg, azithromycin) is almost universally effective.
(Choice A) Epstein-Barr virus causes infectious mononucleosis with symptoms of headache, malaise, fever, exudative pharyngitis/tonsillitis, lymphadenopathy, and splenomegaly. This patient does not have lymphadenopathy or exudative pharyngitis and has prominent respiratory symptoms, making Mycoplasma more likely.
(Choice B) Influenza tends to present with abrupt (eg, malaise, myalgia, fever, headache), not indolent, symptoms.
(Choice C) Legionella pneumophila usually causes high fever with prominent gastrointestinal (eg, vomiting, diarrhea) and systemic (eg, headache, confusion, malaise) symptoms. Pulmonary manifestations (eg, cough, dyspnea) tend to evolve slowly over days. This patient has upper and lower respiratory symptoms, no gastrointestinal symptoms, and low-grade fever, making L pneumophila less likely.
(Choice D) Moraxella catarrhalis primarily causes otitis media (in children) and chronic obstructive pulmonary disease exacerbations; it is an uncommon cause of pneumonia in healthy adults.
(Choice F) Parvovirus B19 may cause influenza-like symptoms (eg, myalgias, fever, malaise) and a malar rash. Prominent pulmonary symptoms and an interstitial infiltrate are not typical.
(Choice G) Streptococcus pneumoniae is the most common cause of community-acquired pneumonia and typically presents abruptly (not indolently) with fever, productive cough, dyspnea, and lobar (not interstitial) infiltrate on chest x-ray. Upper respiratory symptoms (eg, pharyngitis) and skin rash are uncommon.
Educational objective:
Mycoplasma pneumoniae causes atypical pneumonia with indolent symptoms of headache, malaise, low-grade fever, incessant cough, and nonexudative pharyngitis. Chest x-ray often reveals interstitial infiltrate with or without a small, serous pleural effusion. Empiric oral antibiotics (eg, azithromycin) usually resolve the infection completely.