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Chlamydia Pneumoniae

Description of Medical Condition

Chlamydia pneumoniae an obligate intracellular bacteria, has been established as an important cause of adult respiratory disease including pneumonia, bronchitis, sinusitis and pharyngitis. There is no animal reservoir.

System(s) affected: Pulmonary

Genetics: No known genetic predisposition

Incidence/Prevalence in USA: Estimated incidence of 100 to 200 cases of pneumonia/100,000/ year. Accounts for 6 to 12% of pneumonias and 3 to 6% of bronchitis cases. Numbers do not necessarily apply to all areas. Incidence of subclinical infection much greater.

Predominant age: Less common in children under 5 years. Pneumonia more common in elderly.

Predominant sex: Male > Female (10-25% more)

Chlamydia Pneumoniae

Medical Symptoms and Signs of Disease

  • 70% to 90% of infections are mild or subclinical
  • Onset often gradual with delayed presentation
  • Sore throat and hoarseness may precede cough by a week or more, giving biphasic appearance to illness
  • Cough (often prominent with scant sputum)
  • Fever (usually early in illness)
  • Sore throat
  • Rhinitis
  • Headache
  • Malaise
  • Hoarseness
  • Sinus congestion
  • Rales, rhonchi or wheezing
  • Pharyngeal erythema
  • Retropharyngeal lymphoid granulation
Chlamydia Pneumoniae

What Causes Disease?

Infection with C. pneumoniae

Risk Factors

  • Outbreaks have occurred among groups of military recruits, university students, students and nursing home residents. Incubation period is approximately 30 days. Sporadic cases often have no apparent source of exposure. No known animal hosts.
  • Serologic evidence of acute and chronic C. pneumoniae infection found in approximately 1/3 of patients admitted to hospital with acute COPD exacerbation, often together with other concurrent bacterial infection
  • Associated with acute respiratory exacerbation in children with cystic fibrosis

Diagnosis of Disease

Differential Diagnosis

Consider other common bacterial respiratory pathogens, including Streptococcus, Bordetella, Haemophilus. Klebsiella, Mycoplasma and Legionella species


  • Leukocyte count usually normal or low
  • Sedimentation rate often moderately elevated
  • Sputum usually negative by gram stain and routine culture

Drugs that may alter lab results: Early treatment with tetracycline may blunt IgG antibody response

Disorders that may alter lab results: None known

Pathological Findings

Not usually available

Special Tests

  • C. pneumoniae can be identified from clinical specimens (not sputum) by culture in HL or HEp2 and by polymerase chain reaction (PCR). Both culture and PCR require a sophisticated laboratory and are not widely available.
  • Serologic testing with microimmunofluorescence (MIF) antibody and enzyme immunoassay (EIA) antibody are both commercially available. Testing with MIF is recommended by the CDC. EIA is less specific. Testing acute and convalescent (at least 3 weeks after disease onset) sera is preferable.


  • Chest radiograph may be abnormal even in clinically mild disease
  • Variable radiographic abnormalities include unilateral and bilateral infiltrates and pleural effusions. Single, subsegmental infiltrate is common.

Diagnostic Procedures

Definite diagnosis of acute infection requires a positive culture or PCR or a four-fold rise in antibody titer. Very high antibody titer or antibody in the IGM fraction suggests a recent infection.

Treatment (Medical Therapy)

Appropriate Health Care

  • Usually outpatient
  • Patients with severe pneumonia or coexisting illness may require hospitalization

General Measures

No specific general measures


Usually reduced during illness


No special diet

Patient Education

  • Griffith HW: Instructions for Patients; Philadelphia, W.B. Saunders Co.
  • For a listing of sources for patient education materials favorably reviewed on this topic, physicians may contact: American Academy of Family Physicians Foundation, P.O. Box 8418, Kansas City, MO 64114. (800)274-2237, ext. 4400

Medications (Drugs, Medicines)

Drug(s) of Choice

  • Azithromycin (Zithromax) 500 mg on day 1, then 250 mg a day on days 2 through 5
  • Clarithromycin (Biaxin) 500 mg po every 12 hours for 10-14 days
  • Tetracycline 500 mg po qid for at least 14 days
  • Doxycycline 100 mg po q 12 hours for at least 14 days


  • Tetracycline not for use in pregnancy or children < 8 years.


Tetracycline may cause photosensi-tivity; sunscreen recommended.

Significant possible interactions:

  • Tetracyclines may increase the anticoagulant effect of warfarin
  • Broad-spectrum antibiotics may reduce the effectiveness of oral contraceptives; barrier method recommended.

Alternative Drugs

  • Erythromycin base 250-500 mg qid for 14-21 days
  • Levofloxacin 250-500 mg qd PO or IV
  • Beta-lactam (penicillin based) antibiotics and sulfisoxa-zole not effective

Patient Monitoring

Weekly until well for response to treatment and resolution of radio-graphic abnormalities

Prevention / Avoidance

  • Transmission presumably via respiratory secretions. Avoid infected persons.
  • Hand washing

Possible Complications

  • Reactive airway disease
  • Erythema nodosum
  • Otitis media
  • Endocarditis
  • Myocarditis
  • Pericarditis
  • Sarcoidosis
  • Meningitis/encephalitis
  • Reactive arthritis
  • Acute chest syndrome in sickle cell disease

Expected Course / Prognosis

  • Resolution of cough and malaise often requires several weeks or longer
  • Chronic bronchospastic disease has been reported following acute infection
  • Persistent or relapsed symptoms may respond to second course of antibiotics


Associated Conditions

  • Chronic obstructive pulmonary disease
  • HIV infection
  • Cystic fibrosis

Age-Related Factors


Usually milder disease in children


Usually more severe in older adults


Associated with atherosclerotic disease-effect of treatment unknown


  • No known special risks
  • Tetracyclines contraindicated


  • TWAR

International Classification of Diseases

078.88 Other specified diseases due to Chlamydiae

See Also

Pneumonia, mycoplasma Psittacosis

Other Notes

  • No significant seasonal variation
  • Most cases occur sporadically, though intrafamilial spread also occurs
  • Infection in debilitated or hospitalized patients can be severe
  • Reinfection is possible
  • Individuals have been reported who are persistently culture positive despite antibiotic treatment
  • Country-wide epidemics of C. pneumoniae infections have been documented in the Scandinavian countries
  • Found in atherosclerotic plaque in coronary arteries, carotid arteries and the aorta. Also associated with Ml and stroke in seroepidemiologic studies. Role in athero-genesis in humans not established. Clinical significance not known.
  • Associated with atherosclerotic disease — effect of treatment unknown
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