**3.3 Treatment of infections due to** *C. psittaci*

*C. psittaci* causes a zoonotic disease called psittacosis, also known as ornithosis. Psittacosis is frequently transmitted to humans predominantly from birds *via* inhalation of dried droppings, feather dust, or respiratory secretions [99, 100]. The disease can manifest clinically in a variety of ways, ranging from asymptomatic disease or non-specific flu-like illness to severe systemic illness with pneumonia [100, 101]. Other complications that may require hospitalization are cardiac infections (such as endocarditis and myocarditis), hepatitis, arthritis, encephalitis, and sepsis [102]. The most typical illness manifestation is an upper respiratory infection. It is assumed that about 1–8% of CAP is caused by psittacosis [101, 103]. The laboratory diagnosis of psittacosis is usually difficult. Clinical application of traditional pathogen culture is uncommon since it takes a long time and requires high-standard laboratory conditions to culture *C. psittaci* in cells. Serological testing is primarily utilized in retrospective research and is not very useful for the earlier detection of severe patients. *C. psittaci* is easily identified by NAAT and metagenomic nextgeneration sequencing; however, these procedures are not routinely utilized in most hospitals [104]. Therefore, a patient with a history of bird contact who exhibits atypical pneumonia symptoms or unexplained fever without localizing signs, clinicians should consider a diagnosis of psittacosis, and treatment should not await a definitive diagnosis.

Beta-lactam antibiotics are not effective in psittacosis, whereas tetracyclines and macrolides are both effective against *C. psittaci*. Tetracyclines and especially doxycycline is the preferred medication for the treatment of *C. psittaci* pneumoniae [104, 105]. As an alternative or in situations where tetracyclines are prohibited, such as in pregnant women or young children under the age of eight, macrolides such as erythromycin and azithromycin may be utilized [106]. Doxycycline 100 mg orally two times a day for 7 to 10 days is the suggested regimen for psittacosis. Also, a 5 to 7-day regimen of azithromycin (if a clinical response is observed) can be used alternatively. The third-line antibiotics for *C. psittaci* are fluoroquinolones, which have less potency than tetracyclines and macrolides [95, 104, 107]. With proper and early treatment overall prognosis is good and death occurs in less than 1% of patients [102, 104].
