Keywords: chlamydia, pneumonia, occult infection
1. Pathogens
1,1 Chlamydia trachomatis
It is the most common pathogen of sexually transmitted diseases in the United States and includes at least 15 serotypes, namely B, Ba, D, E, L1, L2 in group B; A, C, H, I, J, K, L3 in group C and F and G in intermediate groups, which can cause multisystem and multiple diseases. Most experts believe that the serotype of Chlamydia trachomatis is one of the main causes of the different types of infections, and that the L3 type can cause pneumonia in mice. Chlamydia trachomatis is a common cause of pneumonia in infants aged 3 to 8 years, while not being the most important in older children and adults with pneumonia.
1,2 Chlamydia psittaci
can infect many animals, but the primary host is avian and can be present in almost all avian species, with secondary hosts being mammals other than humans. Humans are infected only after contact with these animals, especially with poultry or infected with bird droppings, and is an occupational disease of avian breeders, traffickers and slaughterers; human-to-human infections are rare. The question of whether there is a primary parrot fever infection in humans is still under debate. Chlamydia psittaci grows readily in chicken embryo yolk sacs and HeLa cells, monkey kidney cell cultures, and can infect mice with pneumonia, peritonitis or encephalitis and cause death.
1,3 Chlamydia pneumoniae
The first representative strain was isolated from Taiwan Province after 1965, and later different strains were found in 1983 and 1986, respectively. Was thought to be a serotype of Chlamydia psittaci, later confirmed to be a new, independent species and named Chlamydia pneumoniae. Chlamydia pneumoniae has the same genus-specific antigens as Chlamydia psittaci and Chlamydia trachomatis, and other specific antigen serologic features are different. Only humans are known to be hosts of this chlamydia, and the mode of infection may be human-to-human transmission through respiratory secretions [2]. Investigations suggest that at least 40% of adults have been infected with this chlamydia, mostly subclinical; the elderly can be re-infected. Studies have shown that community-acquired pneumonia is caused by Chlamydia pneumoniae in 6-19% of cases, and that Chlamydia pneumoniae pneumonia in children under 5 years of age, although uncommon, still accounts for about 6-9% of cases [3].
2. Pathogenesis
Chlamydia can produce endotoxin that is not heat-resistant and is present in the cell wall of the chlamydia. In addition to the pathogenesis of chlamydia, which is related to the host cell response to the toxin, chlamydia must pass through specific receptors in different cells to exert specific adsorption and uptake of particles [4]. Therefore, various chlamydia exhibit different histophilic and pathogenic properties.
The pathogenicity of Chlamydia is mainly through inhibition of the metabolism of infected cells; lysis and destruction of cells leading to release of lysozyme; and cytotoxic effects of metabolites causing metamorphic and autoimmune reactions.
After infection, Chlamydia first invades the columnar epithelial cells and grows and multiplies within the cells, then enters the cells of the monocyte macrophage system and proliferates, leading to the death of the infected cells, while still evading the host immune defense function and receiving intermittent protection. When the body is infected with chlamydia, specific immunity is produced, but this immunity is weak and short-lived. Therefore, chlamydia is prone to persistent and recurrent infections, as well as latent infections.
3. Clinical manifestations and diagnosis
3.1 Chlamydia trachomatis pneumonia
Mostly transmitted by the infected mother, the onset of the disease is slow. The infection is often first in the eye and then transmitted to the respiratory tract via the nasolacrimal duct. Symptoms appear 2 weeks to 12 weeks after birth and may begin with upper respiratory tract infection, followed by cough and shortness of breath. There is no fever or occasionally a low fever. Physical examination shows that there is often a fine wet inhalation (14).
The peripheral blood leukocyte count is generally normal and eosinophilia is increased. The chest radiograph shows extensive bilateral interstitial and alveolar infiltrates, hyperinflation is common, and occasionally solid changes are seen. Direct fluorescent antibody test (DFA), enzyme immunoassay (EIA) to detect Chlamydia trachomatis antigen in nasopharyngeal specimens; serologic examination for specific antibodies, dichotomous serum with more than 4-fold elevated antibody titers or IgM > 1:32 and IgG > 1:512; and PCR technique for direct detection of Chlamydia DNA can be used as diagnostic basis [5].
3, 2 Chlamydia psittaci pneumonia
The pathogen enters the body through the respiratory tract, multiplies in mononuclear cells and releases toxins, which are disseminated to the lungs and systemic tissues via the blood stream. Immunity is weakened after the disease and can recur, with a reported recurrence rate of 21% and a reinfection rate of about 10%.
The incubation period is 6 to 14 days, with early flu-like symptoms, mostly accompanied by moderate to high fever. The fever subsides in 3 to 7 days in children with mild type; about 8 to 14 days in common type; and 20 to 25 days in heavy type. The initial cough is dry, followed by sputum and progressively mild or severe dyspnea. There is a relatively slow pulse, myalgia, and chest pain. Occasionally, there are gastrointestinal symptoms such as nausea, vomiting, and loss of appetite. It may be accompanied by hepatomegaly and splenomegaly. Jaundice is occasionally seen. In case of systemic infection, central nervous system symptoms or myocarditis may be present.
Chest radiographs mostly suggest hairy glass-like shadows from the lung hilum to the periphery, especially downward in the lung field, with dotted shadows in the middle; peripheral blood leukocyte count is normal; blood sedimentation is slightly increased in the early stage. The diagnosis is confirmed by the presence of Chlamydia psittaci inclusions in the phagocytes of the alveolar exudate.
3.3 Chlamydia pneumoniae pneumonia
The clinical presentation is nonspecific and is very similar to mycoplasma pneumonia. infection is rare in children under 5 years of age, but children and young people over 8 years of age are susceptible and easily infected. The disease has a slow onset, long duration, and mild general symptoms, with pharyngitis, laryngitis, and sinusitis as its characteristic manifestations. In adolescents, there is often hoarseness and dry cough; fever may occasionally be present and may last for several weeks; pneumonia is usually mild; some may be accompanied by extrapulmonary manifestations such as erythema nodosum, thyroiditis, encephalitis and Green-Barre syndrome. Pneumonia is more severe in adults, especially in the elderly, and hospitalization and respiratory support are often necessary. The agent is seen in 5-10% of older adults with community-acquired pneumonia with severe symptoms requiring hospitalization; it is also seen in 5-10% of hospital-acquired pneumonia.
The peripheral blood leukocyte count is mostly normal on laboratory tests. Chest radiographic changes are nonspecific, mostly unilateral infiltrates in the lower lobes, showing segmental pneumonia, or in severe cases, extensive bilateral pneumonia or even extensive solid changes.
The pathogenic examination is the same as for Chlamydia trachomatis pneumonia, but the test with pharyngeal swab specimens is not as sensitive as the serological test.
4. Treatment
The principles of treatment are generally the same as those for general pneumonia.
4.1 General treatment
Strengthen care and rest, keep the room air fresh and appropriate room temperature and humidity. Keep the respiratory tract unobstructed. Ensure supply.
4.2 Pathogenic treatment
4,2,1 Macrolide antibiotics
Azithromycin: one of the antibiotics of choice for chlamydial pneumonia. 5mg/kg, d, dose, double the first dose. The first dose is doubled. If you cannot take it orally or if your condition is severe, you can use it intravenously. The course of treatment is 10 to 21 days depending on the severity of the disease.
Erythromycin: The dosage is 50mg/kg, d, divided into 3-4 times, orally or intravenously, the course of treatment is 2-3 weeks. 30mg-50mg/kg, d for children under 8 years old.
Clarithromycin: Treatment amount: 0,5g/time, 2 times/d for 21 days. children over 12 years old are treated as adults. However, it is contraindicated for pregnant women and cautioned for lactating women.
4,2,2 Quinolone antibiotics
Gatifloxacin: It belongs to fluoroquinolones and has strong antibacterial effect on Chlamydia, its activity is equivalent to sparfloxacin and tolclofloxacin, which are 4 times and 16 times of levofloxacin and ciprofloxacin respectively, but lower than clarithromycin and minocycline. Usage: 400mg/d for 2-3 weeks, with 89% efficiency.
Moxifloxacin: It is a new type of fluoroquinolone antibacterial drug with broad-spectrum and rapid bactericidal effect, better than ciprofloxacin and erythromycin.
In addition, temafloxacin, trovafloxacin, gepafloxacin and clindamycin also have good antibacterial activity against Chlamydia, but their use is strictly limited due to serious adverse reactions.
4,2,3 Tetracyclines
Tetracycline, doxycycline, erythromycin, ciprofloxacin, methylpyrimethamine, sulfamethoxazole in vitro studies have shown that doxycycline and tetracycline are the most sensitive. Tetracycline has been used less often in clinical practice because of its more side effects and its tendency to produce drug resistance. Doxycycline: 50mg/dose, 2 times/d, the first dose can be doubled; children 2mg/kg, d, divided into 2 times. Minocycline: 100mg/dose, 2 times/d, the first dose can be doubled.
4.2.4 Sulfonamides
Sulfonamides have been reported to have similar efficacy to macrolides, quinolones, tetracyclines and other anti-chlamydial agents.
4,2,5 Rifampicin
In vitro tests have shown that rifampicin is highly active against Chlamydia, but it is used only in special cases or in combination with other classes of drugs in critical or resistant cases [6].
4,2,6 Other
Antibiotics such as β-lactams, lincomycins, and aminoglycosides are not effective against Chlamydia.
4,3 Supportive and symptomatic treatment
Plasma, or gammaglobulin, can be applied in severe, prolonged, frail or malnourished cases. Symptomatic treatment such as antipyretic and sedation can be given to those with fever and irritability as appropriate.
4.4 Immunotherapy and its prospects
DNA vaccine is a promising new approach for immunoprophylaxis of Chlamydia pneumoniae, however, the development of genetic vaccine is a very complicated process and further research is needed.
5. Prognosis
Chlamydia pneumonia has a long course, and there is a tendency for symptoms to recur if treatment is stopped prematurely. Young people or those with mild symptoms are generally well treated, while the mortality rate in the elderly is about 5-10% [7].