Description

• Chlamydophila pneumoniae (also known as Chlamydia pneumoniae) is an obligate intracellular gram-negative bacterium causing atypical pneumonia in adolescents and young adults. Other reported manifestations include pharyngitis, laryngitis, otitis media, and bronchitis (1).
• C. pneumoniae is thought to be transmitted from person to person via respiratory droplets and small particle aerosolization (2).

Epidemiology

• It is estimated that about 50–85% of worldwide respiratory tract infections caused by C. pneumoniae are asymptomatic.
• C. pneumoniae infections are known to have long incubation periods with symptoms beginning 3 to 4 weeks after exposure (2).

Incidence

• The overall incidence is unknown. Rates of C. pneumoniae in adults with community-acquired pneumonia (CAP) vary widely among studies, ranging from <1% to 20% in adults and up to 44% of pediatric cases (depending on diagnostic methods used).
• The estimated incidence of C. pneumoniae lower respiratory tract infection among children and adults is 100 cases per 100,000.

Prevalence

• Serologic evidence of previous infection found in <10% of children <10 years, up to 50% of adults after the age of 20 years, and ~75% of the elderly.
• C. pneumoniae is estimated to cause about 10% of CAP cases and 5% of bronchitis cases (3).

Etiology and Pathophysiology

• The elementary body (EB) is the infectious form.
  • A rigid cell wall and relative metabolic inactivity allows the organism to survive outside of the host cell for a limited time.
• The EB infects the host cell by attaching to the respiratory mucosa, entering the respiratory epithelial cells through receptor-mediated endocytosis to become a reticulate body (RB).
• RBs divide intracellularly, forming intracytoplasmic inclusions that divide and release chlamydial antigens. This elicits a host immune response leading to mucus production in the nasal passages, sinuses, bronchial tree, and alveoli, along with nasopharyngeal and airway inflammation and bronchospasm.
• After 48 to 72 hours, the RBs become elementary bodies and are released by cell lysis or exocytosis. The EBs are then ready to infect other cells.

Risk Factors

• The incidence of C. pneumoniae increases with age (highest among 65- to 79-year-olds and is associated with more severe, persistent, latent infections).
• Outbreaks reported in persons living in close quarters including military recruits, college students, prisoners, hospital patients, and nursing home residents (2)
• Chronic obstructive pulmonary disease (COPD) and smoking are risk factors for infection by C. pneumoniae.

General Prevention

• C. pneumoniae is transmitted from person to person, although the precise mode of transmission is not known.
• The Centers for Disease Control and Prevention (CDC) recommends standard precautions and infection control measures (e.g., droplet precautions) during outbreaks. Because fomite transmission is possible, hand hygiene is a key preventive strategy.
• Antibiotics to prevent C. pneumoniae infection are not recommended for close contacts (including household members), unless the exposed person is at increased risk for developing serious complications (2).

Commonly Associated Conditions

An association between C. pneumoniae and certain conditions has been described:

• Lung cancer
• Cerebrovascular disease
• Cardiovascular disease
• Schizophrenia
• Obesity
• Reactive arthritis
• Alzheimer disease
• Chronic uncontrolled asthma
• Preeclampsia