Infectious diseasesepidemiology and surveillance

Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control methods

Victorian statutory requirement

Notification and school exclusion are not required.

Infectious agent

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

Identification

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 which resolve and then a dry cough and low grade fever.

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

Method of 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% 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

The incubation period is approximately 21 days.

Public health significance

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% of cases of community-acquired pneumonia can be attributed to this organism.

Asymptomatic carriage occurs in 2–5% of the population. Only about 10% 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.

Speculation regarding the bacteria’s involvement in the pathogenesis of atherosclerotic arterial disease continues. Seroepidemiologic studies have shown an association between evidence of C. pneumoniae infection and atherosclerosis but the significance of this is not yet established. Studies are ongoing into the effect of prophylactic antibiotic treatment on prevention of atherogenesis.

Possible links with Alzheimer’s disease, arthritis and asthma are also postulated.

Reservoir

Humans.

Mode of transmission

Transmission occurs person to person via respiratory secretions.

Period of communicability

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

Susceptibility & resistance

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% of the population becoming seropositive by 20 years of age. Infection does not produce complete immunity and reinfection can occur.

Control methods

Control of case
Mild to moderate infections are generally treated with roxithromycin or doxycycline. Consult the current version of Therapeutic guidelines: antibiotic (Therapeutic Guidelines Limited). Patients being managed in the community should be reviewed after 24 hours to assess treatment response. Therapy 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.

Special settings
Institutions
Avoid crowding in living and sleeping quarters.