Excerpt from Chlamydia Pneumonia

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C pneumoniae causes mild pneumonia or bronchitis in adolescents and young adults. Older adults may experience more severe disease and repeated infections.

C psittaci causes psittacosis or ornithosis after exposure to infected birds. Ornithosis is the preferred term because almost any bird except psittacine birds (eg, parakeets, parrots) can transmit the organism. The clinical spectrum of C psittaci infection ranges from an asymptomatic infection to a fulminant toxic syndrome. Patients with ornithosis most commonly present with pneumonia or fever of unknown origin.

C trachomatis is an important cause of sexually transmitted diseases, including trachoma, pelvic inflammatory disease, and cervicitis. C trachomatis can also cause pneumonia, primarily in infants and young children. Reports document cases of pneumonia due to C trachomatis in immunocompromised adults and laboratory workers.

Pathophysiology: Chlamydiae initiate infection by attaching to the outer membrane of the susceptible host cells. The organism subsequently produces cytoplasmic inclusions in infected cells. The cells release the matured inclusions to infect adjacent cells.

The mode of transmission is different for the 3 species, but all can cause systemic disease by hematogenous spread. Respiratory secretions transmit C pneumoniae from human to human, whereas infected birds transmit C psittaci to humans via the respiratory route through direct contact or aerosolization. Birds known to cause ornithosis include parrots, parakeets, chickens, ducks, turkeys, pigeons, and sparrows, among others.

When pregnant women have a C trachomatis infection of the cervix, the organism is transmitted when the infant passes through the infected birth canal. C trachomatis infection may cause neonatal conjunctivitis, nasopharyngitis, otitis media, and pneumonitis. The tendency to chronic inflammation is typical, and chronic persistent infection may occur if neonatal infections remain untreated.

Frequency:

• In the US:
  
  
  • C pneumoniae: Approximately 50% of young adults and 75% of elderly persons have serological evidence of previous infection. The pathogen is estimated to cause 3-10% of community-acquired pneumonia cases among adults. The estimated number of cases of C pneumoniae pneumonia is 300,000 cases per year. Although C pneumoniae infections occur every year, epidemiological studies suggest a 4-year cycle in the incidence of C pneumoniae pneumonia.

  • C psittaci: Cases of ornithosis declined after the introduction of antibiotic-laced bird feed and a quarantine period of 30 days for imported birds. From 1987-1996, 619 cases of psittacosis in humans were reported to the US Centers for Disease Control and Prevention (CDC), which is approximately 50-100 cases per year. Since 1996, fewer than 50 confirmed cases have been reported in the United States each year. The diagnosis of psittacosis can be difficult, and many more cases may occur that are not correctly diagnosed or reported.

  • C trachomatis: In infants, an estimated 12,000 cases of pneumonia due to C trachomatis occur each year. Approximately 5-22% of pregnant women are thought to have C trachomatis infection of the cervix, and 30-50% of neonates born to infected mothers show culture evidence of infection. Of infected neonates, 15-25% present with clinical conjunctivitis and nasopharyngitis that in some cases develops into .....

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