Chlamydia pneumoniae (now called Chlamydophila pneumoniae) is one of three Chlamydia species that can cause pneumonia in humans. They are Gram-negative cocci bacteria present throughout nature. Untreated, these infections can become chronic.
The more familiar Chlamydia trachomatis (what most people think of when they hear the word Chlamydia) is associated with sexually transmitted diseases trachoma, pelvic inflammatory disease, and cervicitis, although it can also cause eye, ear, and nose infections and pneumonia in infants and young kids. Chlamydia psittaci, another pneumonia-causing Chlamydia species, is acquired from pet birds (cocatiels, parrots, parakeets, and macaws) and poultry (chicken, ducks, pigeons, turkeys, and sparrows) and causes psittacosis or ornithosis, which can involve severe pneumonia.
Clinically, Chlamydia pneumoniae is the most common of the three and ordinarily the least troublesome species. Along with Mycoplasma pneumoniae and Legionella species (Legionnaires Disease), C. pneumoniae can cause atypical pneumonia or so-called community-acquired, “walking pneumonia.”
About one half to three quarters of people have had C. pneumoniae infection at some point in their lives, most typically when they are adolescents and young adults. The bacteria causes over a quarter of a million cases of pneumonia each year.
Transmission and Microbiology
Most commonly, humans transmit C. pneumoniae by respiratory droplets or by direct contact. It is not transmitted sexually like C. trachomatis. The microorganism is comprised of two bodies: the elementary body (the infectious particle) and the reticulate body, which makes new copies of itself (replicates) within cells. The elementary body has a particular affinity for cells that line the inside of the respiratory tract, heart, and blood vessels. Once the elementary body enters a cell, it becomes a reticulate body and must exist within that cell as a parasite. The bacterium has several protective factors that prevent the host cell from killing it. The immune system does recognize and respond to the bacterium, but the antibodies it produces do not prevent later re-infection.
In the respiratory tract, Chlamydia pneumoniae causes atypical pneumonia, including a non-productive but persistent cough, headache, and generally not feeling well. The bug may also cause infections such as bronchitis, laryngitis, pharyngitis, rhinitis, and sinusitis. Many people who have it experience no symptoms or only mild symptoms, which explains the “walking pneumonia” name. If fever is present, it usually occurs early in the infection. Unlike most other pneumonia-causing pathogens, C. pneumoniae can cause a fairly severe sinusitis.
Most commonly, a blood test is done to measure IgM (acute) and IgG (chronic) titers for C. pneumoniae. But results may not be reliable if the infection is new since the IgM antibody response can take up to 6 weeks to appear in the body and the igG response up to 8 weeks. Chest X-rays, the standard method to diagnosing regular pneumonia, usually show little or nothing for C. pneumoniae.
A promising laboratory diagnostic technique is polymerase chain reaction (PCR) cell culture of throat swab or sputum. However, most doctors’ offices, hospitals, and laboratories don’t offer this test yet.
On standard blood cell tests, white blood cell numbers are not elevated in Chlamydia infections, unlike most other infections. However, alkaline phosphate levels may be higher than normal.
Since diagnosis of C. pneumoniae may be equivocal, treatment is often started when infection is suspected but not confirmed (this is called empiric treatment or treatment by clinical symptoms). Patients will usually be given Doxycycline, Tetracycline, Erythromycin, Azithromycin, Clarithromycin or the newer drug Telithromycin. In the hospital, patients are generally started on intravenous Doxycycline. When diagnosis is in question but atypical pneumonia is suspected, Tetracycline, which also treats Mycoplasma pneumoniae, may be given. Even with successful treatment, cough and a lack of energy may continue for weeks after the organism is gone.
Recent studies have shown that Chlamydia pneumoniae can also cause a number of problems outside the respiratory tract. For example, the microorganism can infect cells of the cardiovascular system and contribute to plaque formation in the blood vessels (atherosclerosis). Other complications of C. pneumoniae infection include:
- ear infection
- infection of the inside walls and valves of the heart (endocarditis)
- skin disease (erythema nodosu)
- neurological weakness (Guillain-Barré syndrome)
- brain inflammation (encephalitis)
Chlamydia pneumoniae may also play a role in Alzheimer’s disease, chronic fatigue syndrome, macular degeneration, multiple sclerosis, and sarcoidosis, although the link is still questionable and this research is in its infancy. There is scientific evidence, however, that supports the role of the bacterium in the development of new-onset asthma.
It is important to note that mixed infections (having more than one microorganism at a time) occur in half of all patients with Chlamydia pneumoniae. This is especially true for Lyme patients, many of whom have a laundry list of co-infections to contend with besides Lyme.
If you’ve got Lyme and are experiencing symptoms that don’t seem to go away with Lyme treatment, you might want to ask your doctor to be tested for Chlamydia pneumonia (and Mycoplasma pneumoniae too).
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