Key messages

  • Chlamydophila pneumoniae infection is often mild.
  • C. pneumoniae is emerging as a frequent cause of both upper and lower respiratory tract infections, including bronchitis and pneumonia.
  • Asymptomatic carriers may be an important source of infection.
  • Outbreaks of C. pneumoniae have been reported in closed populations.

Notification requirement for Chlamydophila pneumoniae infection

Notification is not required.

Primary school and children’s services centre exclusion for Chlamydophila pneumoniae infection

School exclusion is not required.

Infectious agent of Chlamydophila pneumoniae infection

The infectious agent is Chlamydophila pneumoniae, an obligate intracellular bacterium (previously named Chlamydia pneumoniae).

Identification of Chlamydophila pneumoniae infection

Clinical features

Chlamydophila pneumoniae infection is often mild. The initial infection appears to be the most severe with reinfection often asymptomatic. A spectrum of illness from pharyngitis and sinusitis to pneumonia and bronchitis may occur. Sometimes there is a biphasic illness, with initial upper respiratory tract infection symptoms that resolve and give rise to a dry cough and low-grade fever.

The organism may be an infectious precipitant of asthma and is implicated in about 5 per cent of episodes of acute bronchitis. Cough occasionally persists for some weeks, despite appropriate antibiotic therapy.

Diagnosis

Chest x-ray may show small infiltrates. Most cases of pneumonia are mild, but the illness can be severe in otherwise debilitated patients.

Laboratory diagnosis is made with serology or culture:

  • Serological diagnosis is made by detecting a four fold rise in antibody titre using microimmunofluorescence (MIF). MIF is the only serological test that can reliably differentiate chlamydial species. A single antibody titre is of little diagnostic value on its own as the seroprevalence of antibodies to C. pneumoniae approaches 50 per cent in the adult population. Seroconversion may take up to eight weeks in an initial infection but it tends to occur much more quickly in reinfection (one to two weeks). False positive antibody tests can occur in the presence of a positive rheumatoid factor.
  • Culture of nasopharyngeal aspirates, throat swabs or bronchial lavage fluid is possible. Swabs should be placed in chlamydia transport medium whilst other specimens can be collected in the usual containers. All samples should be kept refrigerated.

Diagnosis by PCR is available through the Victorian Infectious Diseases Reference Laboratory (VIDRL) but it is currently only being used in investigation of outbreaks of respiratory illness where conventional testing has not revealed the cause of infection.

Incubation period of Chlamydophila pneumoniae

The incubation period is approximately 21 days.

Public health significance of Chlamydophila pneumoniae infection

C. pneumoniae is emerging as a frequent cause of both upper and lower respiratory tract infections. It appears to be a common cause of mild pneumonia, especially in school age children. Up to 10 per cent of cases of community-acquired pneumonia can be attributed to this organism.

Asymptomatic carriage occurs in 2–5 per cent of the population. Only about 10 per cent of infections result in pneumonia. Epidemics of respiratory illness can occur and these usually occur in institutional settings such as military barracks or nursing homes.

Reservoir of Chlamydophila pneumoniae

Humans are the reservoir.

Mode of transmission of Chlamydophila pneumoniae

Transmission occurs person-to-person via respiratory secretions.

Period of communicability of Chlamydophila pneumoniae infection

Asymptomatic carriers may be an important source of infection. Symptomatic patients can carry the bacteria in the nasopharynx for months after illness.

Susceptibility and resistance to Chlamydophila pneumoniae infection

Everyone is susceptible to infection, with the risk of clinical disease increasing in patients with a chronic medical condition. Immunosuppressed patients do not seem to be more susceptible, but older debilitated patients may develop severe disease.

Initial infection occurs in school-age children with up to 50 per cent of the population becoming seropositive by 20 years of age. Infection does not produce complete immunity and re-infection can occur.

Control methods for Chlamydophila pneumoniae infection

Control of case

Mild to moderate infections are generally treated with doxycycline or clarithromycin or roxithromycin. Consult the current version of Therapeutic guidelines: antibiotic. Therapy rarely may need to be continued for up to 14 days.

Isolation is not necessary, but the patient should be counselled on good respiratory hygiene, such as coughing into disposable tissues.

Outbreak measures for Chlamydophila pneumoniae infection

Outbreaks of C. pneumoniae have been reported in closed populations, including among families, university students, military trainees and in schools. Outbreaks have also been reported among the elderly population in institutional settings. In all such closed settings, C. pneumoniae should be considered in the differential diagnosis so that prompt identification and management can occur.

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