The answer to whether Chlamydia can cause pneumonia is yes, but the situation is complex. Chlamydia refers to a genus of bacteria, and different species cause distinct types of infections. These bacteria are characterized as obligate intracellular pathogens, meaning they must invade a host cell to reproduce and survive. The specific species involved, along with the age of the infected person, determines the route of infection and the resulting clinical picture of pneumonia.
Clarifying the Chlamydia Family
The confusion surrounding chlamydial infections stems from the existence of several species that affect humans, each with a different primary site of infection. The species most commonly associated with sexually transmitted infections, Chlamydia trachomatis, is what the public usually refers to as “Chlamydia,” though it primarily causes urogenital infections and conjunctivitis.
A separate species, Chlamydia pneumoniae, is a dedicated respiratory pathogen responsible for causing community-acquired pneumonia in people of all ages. A third species, Chlamydia psittaci, is a zoonotic pathogen transmitted to humans from infected birds, causing a rare but serious condition known as psittacosis or ornithosis, which often presents as pneumonia.
Chlamydial Pneumonia in Adults
Pneumonia in adults caused by this genus is overwhelmingly due to Chlamydia pneumoniae, spread through the inhalation of aerosolized respiratory droplets. This illness is classified as an “atypical pneumonia” because its symptoms are often milder and its presentation differs from traditional bacterial pneumonia. The infection frequently begins with non-pulmonary symptoms, giving it a characteristic biphasic pattern.
The incubation period for C. pneumoniae is long, often taking three to four weeks from exposure until symptoms appear. Initial signs can include a sore throat, hoarseness, pharyngitis, or a low-grade fever, suggesting an upper respiratory tract infection. The pneumonia phase then develops gradually, characterized by a persistent, non-productive cough that can last for several weeks or even months.
While the infection is often mild and referred to as “walking pneumonia,” it can lead to more severe illness in older adults and individuals with compromised immune systems. C. pneumoniae is estimated to be responsible for up to 10% of all community-acquired pneumonia cases annually. It can also cause chronic respiratory issues, including exacerbations of asthma.
Neonatal Chlamydial Pneumonia
A distinct form of chlamydial lung infection occurs in infants, caused by the sexually transmitted species, Chlamydia trachomatis. This involves vertical transmission, where the newborn acquires the bacterium while passing through the mother’s infected birth canal. Approximately 30% to 50% of infants born to mothers with untreated cervical C. trachomatis infection will become infected during delivery.
Pneumonia does not develop immediately; symptoms typically appear subacutely between four and twelve weeks after birth. The clinical presentation is unique, frequently involving a characteristic repetitive, short, forceful cough known as a staccato cough. Infants with this condition are typically afebrile, meaning they do not have a fever, which distinguishes it from many other types of bacterial pneumonia.
A history of chlamydial conjunctivitis, or ophthalmia neonatorum, is often present, though it may have resolved by the time the pneumonia develops. The infection manifests as a subacute pneumonitis, often accompanied by nasal congestion and rapid breathing. Early diagnosis is important for timely treatment, as this form of pneumonia can lead to significant respiratory distress.
Diagnosis and Treatment
Diagnosing chlamydial pneumonia is challenging because the symptoms are often non-specific and overlap with other atypical pathogens. Since Chlamydia species are obligate intracellular bacteria, they cannot be grown using standard laboratory culture techniques, necessitating specialized testing. Diagnosis relies heavily on molecular methods, such as Nucleic Acid Amplification Tests (NAATs), which detect the bacteria’s genetic material in respiratory secretions or nasopharyngeal swabs.
Serology, or antibody testing, can also be used to confirm infection by measuring the level of specific antibodies in the blood, particularly for C. pneumoniae in adults. The intracellular nature of the bacteria dictates treatment, as cell wall-targeting antibiotics like penicillin are ineffective. Preferred first-line treatments are antibiotics that can penetrate the host cell to reach the bacterium.
Macrolides, such as azithromycin or erythromycin, and tetracyclines, like doxycycline, are the classes of antibiotics used to treat chlamydial pneumonias. For adult C. pneumoniae infections, a macrolide or doxycycline is typically prescribed. However, for neonatal C. trachomatis pneumonia, erythromycin or azithromycin is used because tetracyclines are contraindicated in infants and young children due to potential effects on bone and tooth development.