Description

Chlamydiae are obligate intracellular organisms classified as bacteria but which possess qualities of both bacteria and viruses. They cause a variety of infections from the respiratory to the urogenital tract. The genus has been divided into Chlamydia (Chlamydia trachomatis, others) and Chlamydophila (Chlamydophila pneumoniae, Chlamydophila psittaci, others). Three species are known to affect humans:

• C. trachomatis: a leading cause of sexually transmitted infections in the United States, which can be vertically transmitted during childbirth
• C. psittaci: a rare zoonosis
• C. pneumoniae: an important cause of respiratory infections in the school-aged child; will be the focus of this chapter

Epidemiology

• Spread person to person by respiratory droplets; no seasonal trend
• Asymptomatic carriage and prolonged nasopharyngeal shedding occurs.
• Peak ages of infection are 5 to 15 years.
• Coinfection with other respiratory pathogens is common.
• Serum antibodies are positive in about 50% of adults by age 20 years, and reinfection commonly occurs in adults.

Risk Factors

School-aged children are at highest risk.

General Prevention

Cough etiquette (coughing into elbow or tissue) and proper hand hygiene are important control measures.

Pathophysiology

• Chlamydiae exist in two forms:
  • Elementary body (EB): infectious form
  • Reticulate body (RB): reproductive form
• Life cycle:
  • EB is taken into cell by endocytosis and reorganizes into an RB to replicate.
  • After replication, RB transformed to EB and are released by exocytosis or cytolysis.
  • Cycle between endocytosis and release is 2 to 3 days.