Diagnosis and differential diagnosis of chlamydial pneumonia
Abstract The chlamydia family has only one genus, Chlamydia, which includes 4 chlamydial species, namely C. trachomatis ), Chlamydia psittaci (C?psittaci), Chlamydia pneumoniae (C.pneumoniae) and Chlamydia pecorum (C pecorum). Purpose: To discuss the diagnosis and differential diagnosis of chlamydial pneumonia. Methods: Diagnosis was made based on the patient's clinical manifestations and examination results. Conclusion: The clinical manifestations of Chlamydia pneumoniae pneumonia are non-specific, and the diagnosis depends entirely on laboratory tests. Psittacosis pneumonia is mainly diagnosed based on relevant occupational history, contact history, and cell culture of blood and bronchial secretions to discover the pathogen.
Keywords Chlamydia Pneumonia Diagnosis
The chlamydia family has only one genus, Chlamydia, which includes 4 chlamydial species, namely C. trachomatis, Parrot Chlamydia thermophila (C?psittaci), Chlamydia pneumoniae (C.pneumoniae) and Chlamydia pecorum (C pecorum). Chlamydia trachomatis causes human trachoma, inclusion conjunctivitis, nongonococcal urethritis, and cervicitis. If the mother has genital Chlamydia trachomatis infection, the fetus may be infected during delivery, manifesting as neonatal Chlamydia trachomatis pneumonia and inclusion conjunctivitis. Chlamydia psittaci causes psittacosis in humans, which manifests as respiratory infection or systemic infection mainly in the respiratory system. Chlamydia bovis only infects cattle and sheep and has not been reported to cause disease in humans. Chlamydia pneumoniae is a new species of chlamydia identified only in recent years and is an important pathogenic agent of pneumonia, bronchitis and sinusitis. Chlamydia pneumoniae pneumonia is usually milder, but recovery time is longer. Unlike psittacosis, patients infected with Chlamydia pneumoniae have no history of contact with infected birds. Human infections caused by C. pneumoniae are far more common than other chlamydial species.
(1) Chlamydia pneumoniae
1. Overview
Chlamydia pneumoniae (chlamydia pneumoniae) is a newly named chlamydia, which mainly causes respiratory tract and lung diseases. Infect.
2. Epidemiology
Sero-epidemiological surveys show that human Chlamydia pneumoniae infection is universal, and more than half of the cases in the United States and other parts of the world have experienced Chlamydia pneumoniae infection. , that is, the presence of Chlamydia pneumoniae-specific IgG antibodies in the serum. Our research has found that the infection rate of Chlamydia pneumoniae in China increases rapidly with age, and there is no gender difference; the infection rate in children is around 20%, in young adults it can reach 50% to 60%, and in the elderly it is as high as 70% to 80%. Considering the high positive rate of Chlamydia pneumoniae in the population and the gradual decline of antibodies after infection, it is estimated that all people are likely to be infected with Chlamydia pneumoniae at some point in their lives, and reinfection is also common. The annual incidence of Chlamydia pneumoniae is 9% and 6% in the 5-9 and 10-14 age groups respectively, which are the two age groups with the highest incidence rates in the entire population. Chlamydia pneumoniae is a strictly human chlamydia. There is no animal intermediate host. The infection route is from person to person through respiratory secretions. Local epidemics or general epidemics may exist in families, schools, the military, and other work areas where the population is concentrated. Chlamydia pneumoniae infection spreads slowly, even in densely populated areas such as those mentioned above. Other studies have shown that people infected with Chlamydia pneumoniae are not necessarily the source of infection, but asymptomatic carriers may be the source of infection. Chlamydia pneumoniae pneumonia accounts for about 5% to 10% of all community-acquired pneumonia.
Unlike Mycoplasma pneumoniae, most Chlamydia pneumoniae infections are asymptomatic latent infections or mild systemic infections that do not attract the patient's attention. Chlamydia pneumoniae pneumonia is more common in adult and elderly patients. It is less common among teenagers under 20 years old.
3. Cause
Chlamydia pneumoniae is Gram-negative and is a strictly intracellular parasitic pathogen that parasitizes in the cytoplasm and produces inclusion bodies visible under a light microscope. Unlike viruses, it has both DNA and RNA and a cell wall similar to Gram-negative bacteria, and is sensitive to broad-spectrum antibiotics.
Chlamydia pneumoniae (TWAR) (Washington isolate TW-183 in 1983 and Taiwan isolate AR-39 in 1965) is a strictly human pathogen, and there is no animal intermediate host.
Seroepidemiological surveys show that human Chlamydia pneumoniae infection is universal and has a positive relationship with population density.
4. Clinical manifestations
Mild cases may have no obvious symptoms. Teenagers often have hoarseness, dry cough, and sometimes symptoms of pharyngitis, sinusitis, and bronchitis such as fever and sore throat, which can last for several weeks. Pneumonia is usually mild and has clinical manifestations very similar to Mycoplasma pneumoniae infection. Pneumonia in adults can be severe, especially in the elderly, and often requires hospitalization.
As a type of atypical pneumonia, Chlamydia pneumoniae pneumonia has similarities with other atypical pneumonias in X-ray manifestations, namely airspace consolidation sign, ground glass opacity, reticular shadow, Bronchopneumonia and small nodules. HRCT (high-resolution CT) imaging features are lobule-centered shadows, alveolar shadows, airspace consolidation, and lobular-like distribution of ground-glass shadows, while airspace consolidation and bilateral lung disease are common in Chlamydial pneumonia. More common in . Chlamydia pneumoniae pneumonia mainly consists of irregularly distributed interstitial pneumonia and focal pneumonia. The difference is that scattered or small focal foam cell reactions can be seen in Chlamydia pneumoniae pneumonia.
5. Laboratory tests
The count and classification of peripheral blood white blood cells are normal, but 80% of patients have accelerated erythrocyte sedimentation rate. Specific laboratory testing methods include cell culture, serology, and PCR techniques.
1) Cell culture: Nasopharyngeal or posterior pharyngeal wall swabs, tracheal and bronchial aspirates, alveolar lavage fluid and other specimens can be used for chlamydial culture. Recently, it has been reported that the isolation rate of Chlamydia pneumoniae is greatly improved in specimens treated with trypsin and/or sodium ethylenediaminetetraacetic acid (EDTA). Isolates can be identified using C. trachomatis, C. pneumoniae species-specific monoclonal antibodies, and Chlamydia genus-specific monoclonal antibodies.
The HL cell line is the most sensitive to the growth of Chlamydia pneumoniae, and it has also been reported that HEP-2 (human laryngeal epidermal carcinoma) is sensitive to the growth of Chlamydia pneumoniae. Nasopharyngeal or posterior pharyngeal wall swabs are the most commonly used specimens. Tracheal and bronchial aspirates and bronchoalveolar lavage fluid specimens are the most ideal because the specimens contain more pathogens and the results are more clinically meaningful. Sputum specimens often have toxic effects on cell cultures.
Same as collecting specimens for Mycoplasma pneumoniae, hold the swab and wipe off as many cells as possible, because chlamydia is accompanied by cells. The swab should be made of calcium alginate, polyester, or polyester fiber material, and the handle should be plastic or aluminum. Wooden or bamboo cotton swabs should not be used as they may contain potential chlamydial inhibitors. The specimen transport solution is 2SP containing antibiotics (0.2 mol/L sucrose phosphate buffer containing 10% inactivated fetal calf serum). After collection, the specimens should be refrigerated at 4°C. If they cannot be vaccinated within 24 hours, they should be stored at -70°C. The specimen is inoculated into a centrifuge culture tube or culture plate so that the chlamydial particles in the specimen are extruded and adsorbed to the cultured cells under the action of external physical forces, thereby improving sensitivity. Inclusion bodies can be seen in positive specimens within 72 to 96 hours of inoculation. Isolates can be identified using C. pneumoniae species-specific monoclonal antibodies and stained with indirect fluorescence or direct fluorescence. 2) Serological micro-immunofluorescence test (MIF) is currently the most commonly used standard method for chlamydial serology in the world. Its sensitivity is much higher than the complement fixation test (CF) using Chlamydia-specific antigen as the antigen, and it is also superior. Lipopolysaccharide (LPS)-based enzyme immunoassay (EIA).
Serological diagnostic criteria: For any chlamydial species, if MIF test IgG≥1:512 and/or IgM≥1:32, after excluding false positives caused by rheumatoid factor (RF) Recent infection can be diagnosed; a 4-fold or above increase in double serum antibody titer can also be diagnosed as recent infection; IgG≥1:16 but <1:512, and IgM antibody is negative, indicating past infection with Chlamydia pneumoniae.
3) PCR test PCR has been successfully used to detect Chlamydia pneumoniae in specimens, such as throat swab specimens. Studies have shown that PCR technology is 25% more sensitive than traditional culture methods. In addition, the advantage of PCR is that it does not require live Chlamydia pneumoniae, so the death of Chlamydia caused by improper transportation or freezing will not affect the test results.
6. Diagnostic criteria
The clinical manifestations of Chlamydia pneumoniae pneumonia are not specific, and the diagnosis depends entirely on laboratory tests.
Chlamydia pneumoniae is obtained by culture of respiratory specimens; the serum Chlamydia pneumoniae antibody titer changes 4-fold or more (increases or decreases), and the Chlamydia pneumoniae antibody titer (microimmunofluorescence test) is ≥1:32, the diagnosis can be confirmed. Serum Chlamydia pneumoniae IgG antibody titer ≥1:512 or IgM antibody titer ≥1:16 (microimmunofluorescence test) is significant, and Chlamydia pneumoniae infection should be highly suspected.
7. Differential diagnosis
The clinical manifestations of Chlamydia pneumoniae pneumonia are similar to Mycoplasma pneumoniae pneumonia, Legionella pneumonia and some viral pneumonias, and differential diagnosis basically relies on laboratory examinations.
(2) Psittacosis pneumonia
1. Overview
Psittacosis is caused by a Gram-negative, inactive pathogen - Chlamydia psittaci. This pathogen has other chlamydial characteristics and is an obligate intracellular parasite that lives in the tissues, blood and feces of parrots and other birds (such as chickens, ducks, turkeys, pigeons, peacocks, finches). You can get the disease from contact with the above-mentioned poultry or inhaling bird droppings; in the acute stage, it can also occasionally cause human-to-human transmission through the respiratory tract. After a person is infected, they can continue to carry the pathogen for up to ten years. The vast majority of this disease is sporadic.
2. Physiology and pathology
After the pathogen is inhaled, it enters the bloodstream and multiplies in monocytes and macrophages in the liver and spleen, and then spreads to the lungs or other organs through the bloodstream. . Intrapulmonary lesions often begin in the hilus, blood. There is an inflammatory reaction around the target and spreads to the surroundings, causing lobular and interstitial pneumonia, especially in the sagging parts of the lung lobes or lung segments; desquamation and necrosis of the bronchioles and bronchial epithelium; inflammatory cells and edema fluid infiltration in the alveoli. came out with a small amount of bleeding. In severe cases, lung tissue necrosis and hilar lymph node enlargement may occur, and sometimes a pleurisy reaction may occur. Local necrosis may occur in the liver, the spleen may be enlarged, and the heart, kidneys, nervous system, and digestive tract may be affected and cause lesions.
3. Clinical manifestations
The incubation period of this disease is 1 to 2 weeks, and it can reach 4 weeks in the elderly. The onset is often insidious. Symptoms may be similar to influenza, with chills and fever beginning with severe pneumonia. The body temperature gradually rises, reaching over 40°C, with a relatively slow pulse. The patient feels fatigue, myalgia, and joint pain, may have nasal or macular rash, and develops a cough in about 1 week, accompanied by a small amount of sticky sputum or blood in the sputum. In addition, patients may still experience gastrointestinal symptoms such as nausea, vomiting, and abdominal pain, as well as mental symptoms such as drowsiness, delirium, stupor, and convulsions, which are more common in children. Severe cases may have signs of consolidation and occasionally hepatosplenomegaly. X-ray signs show infiltration lesions in both lungs, radiating outward from the hilus, and the lesions may merge into a lobar distribution, with more in the lower lobes. Diffuse bronchopneumonia or interstitial pneumonia is often present, and sometimes miliary or obvious consolidation shadows or a small amount of pleural effusion can be seen. The white blood cell count is normal or slightly elevated.
4. Diagnostic criteria
Diagnosis is mainly based on occupational history, contact history, and cell culture of blood and bronchial secretions to detect pathogens. Although a positive serum complement fixation test cannot distinguish the type of chlamydia, it is still a simple diagnostic method if combined with the contact history. If the antibody titer of the double serum increases 4 times or the single titer is above 1:64, it has diagnostic value. Currently, the direct immunofluorescence method is used to detect specimens using monoclonal fluorescence, which has higher sensitivity and specificity.
References
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[2] Liu Ning; Diagnostic value of Mycoplasma pneumoniae and Chlamydia in children [J]; Laboratory Medicine; Issue 02, 2007
[3] Yu Xinzhong, Wang Zhuoying, Wu Manwu, Xu Ping, Zeng Yan, Zheng Shufang; Analysis of 335 cases of acute lower respiratory tract infection caused by Chlamydia pneumoniae in children[J]; Chinese Journal of Hospital Infection; 2004 Issue 11