Snapshot A 26-year-old woman presents to her primary care physician for a nonproductive cough of 1-week duration. She reports that the cough started quite suddenly, along with subjective fevers. She denies having any headaches, any upper respiratory symptoms, chest pain, or shortness of breath. She has a past medical history of polycystic ovarian syndrome and anxiety. She lives at home with her parents and a 10-year-old parrot. A chest radiograph shows left lower lobe consolidation and bilateral small pleural effusions. Given her risk factors, she is started on doxycycline for suspected atypical pneumonia. Introduction Classification Chlamydiae obligate intracellular bacteria Chlamydophila pneumoniae atypical (interstitial) pneumonia Chlamydophila psittaci psittacosis, which presents as an atypical (interstitial) pneumonia or fever of unknown origin Chlamydia trachomatis sexually transmitted disease, trachoma, or lymphogranuloma venereum Pathogenesis cannot make own ATP and are obligate intracellular (Chlamys = cloak, as in cloaked inside a cell!) the bacteria has 2 forms: elementary body and reticulate body the elementary body (the infectious form) attaches to the outer membrane of host cells and enters through endocytosis to become intracellular they produce cytoplasmic inclusions (reticulate bodies) the reticulate body replicates inside the cell using fission and reorganizes into elementary bodies, which then goes on to infect more cells Studies detection of DNA via polymerase chain reaction (PCR) or nucleic acid amplification test (NAAT) detection of immunoglobulin using microimmunofluorescence Giemsastain reticulate bodies seen in cytoplasm diagnosis is made via serologic testing and clinical findings Chlamydophila pneumoniae Introduction clinical syndrome atypical pneumonia transmission via aerosols demographics primarily in adolescents and young adults atypical organisms uncommon in patients >65 years of age, but C. pneumoniae is the most common atypical pathogen in the elderly risk factors smoking Presentation upper respiratory symptoms (initial) nasal congestion sore throat sinus pressure pneumonia (after 1-4 weeks) fever and malaise cough with minimal sputum hoarse voice headache sinus percussion tenderness Imaging chest radiography findings diffuse patchy infiltrates in interstitial areas generally involves more than 1 lobe Treatment azithromycin first-line doxycycline avoid in children and pregnant women Complications erythema nodosum Guillain-Barré syndrome Chlamydophila psittaci Introduction clinical syndrome presents as an atypical (interstitial) pneumonia or fever of unknown origin transmission via aerosols reservoir is birds (parrots) risk factors exposure to birds, especially pet birds that are sick pet shop employees occupational exposure to poultry Presentation acute onset of symptoms high fever nonproductive cough may have splenomegaly Imaging chest radiography findings unilateral single lower lobe consolidation can have small pleural effusions Treatment doxycycline or tetracycline first-line azithromycin Complications endocarditis myocarditis multi-organ failure