eMedicine Specialties > Pulmonology > Infectious Lung Diseases

Chlamydial Pneumonias

Author: Yuji Oba, MD, FCCP, Associate Professor of Clinical Medicine, Division of Pulmonary, Critical Care, and Environmental Medicine, University of Missouri Health Care
Coauthor(s): Vamsi P Guntur, MD, MSc, Assistant Professor of Clinical Medicine, Division of Pulmonary, Critical Care and Environmental Medicine, University of Missouri
Contributor Information and Disclosures

Updated: Oct 15, 2008

Introduction

Background

Three chlamydial organisms are pathogenic to humans: Chlamydophila (formerly Chlamydia) pneumoniae, Chlamydophila (formerly Chlamydia) psittaci, and Chlamydia trachomatis. These are small, gram-negative, obligate intracellular organisms. All 3 species can cause pneumonia in humans.

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 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 susceptible host cells. The organism subsequently produces cytoplasmic inclusions in the infected cells. The cells release the matured inclusions to infect adjacent cells.

The mode of transmission is different between 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.¹ Birds known to cause ornithosis include cockatiels, parrots, parakeets, macaws, 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

United States

• C pneumoniae: Approximately 50% of young adults and 75% of elderly persons have serological evidence of previous infection. The pathogen is estimated to cause 10-20% of community-acquired pneumonia cases among adults.² 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 1988-1998, 813 cases of psittacosis in humans were reported to the US Centers for Disease Control and Prevention (CDC).³ Approximately 70% of the psittacosis cases with a known source of infection resulted from exposure to pet birds. 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/or nasopharyngitis that in some cases develops into neonatal pneumonitis.

Mortality/Morbidity

• C psittaci: The mortality rate from infection with C psittaci was 20% in the preantibiotic era. The mortality rate is 5% with antibiotic treatment; it is less than 1% with early diagnosis and treatment.
• C pneumoniae: The mortality rate from C pneumoniae infection was 9.8% in one meta-analysis.⁴ Secondary infection, such as pneumococcal bacteremia, or the presence of severe underlying disease is associated with increased mortality.⁵ A Canadian study reported a mortality rate of 4.9% with C pneumoniae pneumonia, which is similar to the rate for bacteremic pneumococcal pneumonia (5.4%) and the overall cohort of community-acquired pneumonia (9.4%).⁶
• C trachomatis: Most infants with C trachomatis pneumonia are only moderately ill; if the infection is not treated, respiratory failure and prolonged spells of apnea may occur.

Sex

• C pneumoniae is more common in males (60-90%) than in females; this difference is possibly due to cigarette smoking.

Age

• Anyone exposed to infected birds is at risk for infection with C psittaci.
• The incidence of C pneumoniae pneumonia is highest among elderly persons. Primary infection pneumonia is more common in persons aged 7-40 years, whereas reinfection pneumonia is more common in elderly persons.
• With regard to C trachomatis pneumonia, approximately 11-20% of infants born to infected mothers develop symptomatic pneumonia before age 8 weeks.⁷ Adult cases have been reported in immunocompromised hosts.⁸

Clinical

History

• C psittaci
  • Exposure to birds, especially sick ones, is a clue to the diagnosis in a patient with pneumonia and splenomegaly. Pet shop employees and poultry industry workers are also at risk. Obtain an occupational and avocational history in all patients with community-acquired pneumonia.
  • The incubation period is 5-14 days or longer. Abrupt onset of constitutional symptoms is a common presentation in symptomatic patients.
  • The severity of disease ranges from asymptomatic to severe pneumonia with systemic illness.
  • A nonproductive cough has been observed in 50-80% of patients; however, this symptom is often absent initially. Chest pain is common, but pleuritic pain is rare.
  • Fever is the most common symptom and may reach 103-105°F (39.4-40.5°). Some patients may present with culture-negative endocarditis or fever of unknown origin.
  • Signs of meningitis or encephalitis, including focal neurological deficits and seizures, may develop. Photophobia, epistaxis, tinnitus, deafness, GI symptoms, and arthralgia have been reported in less than half of patients.
• C pneumoniae
  • The incubation period is approximately 3-4 weeks. The onset is usually gradual and may be biphasic. Symptoms of bronchitis or pneumonia follow upper respiratory tract symptoms (rhinitis, laryngitis, pharyngitis, sinusitis) in 1-4 weeks.
  • Most persons with C pneumoniae infections are asymptomatic, and most have relatively mild respiratory illnesses.
  • Sputum is usually scant, but cough is prominent.
  • A history of hoarseness is more common in C pneumoniae infection than in mycoplasmal infection or other pneumonias.
  • Headache occurs in as many as 58% of cases and may be important as a nonclassic pneumonia finding.
  • Patients with C pneumoniae infection are less likely to report fever.
  • Symptoms may be prolonged, with persistent cough and malaise for weeks to months despite appropriate use of antibiotics.
• C trachomatis pneumonia
  • Nasal obstruction and discharge, cough, and tachypnea are present.
  • Infants are usually symptomatic for 3 weeks or more before presentation.

Physical

• C psittaci
  • A pulse-temperature dissociation (fever without elevated pulse), which is also seen in Q fever, typhoid fever, and Legionnaires’ disease⁹ ; somnolence; splenomegaly; and an erythematous, blanching, maculopapular rash (eg, Horder spots) in the presence of pneumonia suggest ornithosis. Rose spots look very similar to Horder spots and are observed in persons with typhoid fever.
  • Auscultatory findings may be sparse and may underestimate the extent of pneumonia.
  • Defervescence is usually slow.
  • Signs of hepatitis, hemolytic anemia, disseminated intravascular coagulation, meningoencephalitis, or reactive arthritis may be observed.
  • Cutaneous manifestations, including Horder spots (rare), splinter hemorrhages, superficial venous thromboses, acrocyanosis, and erythema nodosum, may be observed.
• C pneumoniae
  • Fever is more often present in the first few days than in a week or later. Fever is often absent by the time of examination.
  • Pharyngeal erythema without exudate occurs in various atypical pneumonias; however, sinus percussion tenderness is more common with C pneumoniae pneumonia than with other pneumonias.
  • Rhonchi and rales are present even in mild disease.
• C trachomatis pneumonia
  • Most patients are afebrile and only moderately ill.
  • Scattered crackles with good breath sounds are characteristic. Wheezing is usually absent.
  • Conjunctivitis and middle ear abnormality are present in half the infants with pneumonia.

Causes

All 3 human pathogenic species, including C pneumoniae, C psittaci, and C trachomatis, can cause chlamydial pneumonia.

• Search for CME/CE on This Topic »

• Chlamydia Symptoms
• Sexually Transmitted Diseases Center
• Chlamydia Overview
• Chlamydia Causes
• Chlamydia Treatment