Legionnaires' disease

Introduction to Legionnaires' Disease Legionnaires' disease is a pneumonia-based infection caused by legionellosis, also known as legionelladisease. The pathogens are mainly from contaminated water sources and invade from the respiratory tract. In addition, pathogenic bacteria may cause another clinical type with fever, headache, and myalgia. The condition is mild, called Pontiacfever. basic knowledge The proportion of illness: 0.003% Susceptible people: no special people Mode of transmission: airborne Complications: pneumonia, respiratory failure, shock, brain edema, pancreatitis, pancreatitis, peritonitis

Legionnaire's disease

Legionella is an aerobic multi-sex gram-negative bacterium that is widely found in the natural environment. Its source of infection is human, water and air-conditioning systems that are transmitted through the air.

(1) Causes of the disease

According to the cell wall composition, biochemical reaction and DNA hybridization research, Legionella is not related to the pathogens known in the past, so it constitutes a single family. Legionellaceae has only one genus, Legionella. 42 species and 64 serotypes have been found, of which about 19 are isolated from patients (Table 1); the rest are isolated from the environment. There are Lp1, Lp3, Lp5, Lp6, Lp9, etc. in China, and the main cause is disease. L. pneumophila (Lp) and P. micdadei; 15 serotypes of Legionella pneumophila, about 90% are serotype I, Legionella is Gram-negative bacilli, (0.3~ 0.9) m × (2 ~ 4) m, occasionally filamentous, flagellate, mostly one, located at the top, aerobic, motility, the bacteria do not grow in ordinary medium, the most suitable medium for medicine Using charcoal-yeast extract agar (BCYE), the colonies grow after 2 to 4 days, with a diameter of 1-2 mm, flat or slightly convex, and the edges are neat, and can be seen in FG (Feeley-Gorman) agar medium for 3 to 5 days. Needle-sized colonies that emit yellow fluorescence under ultraviolet light, most species are peroxygenated Hydrogenase weakly positive, nitrate enzyme and urease negative, only use starch instead of other sugars, biochemical identification is generally not useful for identification of the bacteria, often based on growth and morphology, and finally serological identification, the bacteria The cell wall contains 14 to 17 carbon branched fatty acids, which, unlike other bacteria, can be detected by gas chromatography.

Legionella can produce a variety of enzymes and toxins, including proteases, phosphonates, deoxyribonuclease, beta lactamase, and cytotoxins, which may be related to virulence. The bacteria have both internal and external toxins, their structure and others. Gram-negative bacilli are slightly different, do not contain hydroxy fatty acids, but contain 2-keto-3-deoxyoctanoic acid and special branched-chain fatty acids. The bacteria live in fresh water in the natural environment, and the biofilm can survive in distilled water. 4 months, 3 months in river water, 1 year in tap water, Legionella growth can be supported by some free living protozoa, or parasitic in its body, such as amoeba, protozoa and Legionella, and Protozoa can alter the virulence of Legionella.

(two) pathogenesis

The damage caused by Legionella pneumophila (Lp) can be divided into indirect damage and direct damage. The indirect damage begins with the action of alveolar macrophages (M). It is found that after Lp is swallowed by M, It can inhibit the fusion of phagosomes and lysosomes, and can regulate the pH value of mononuclear phagocytic cells to optimize their survival and reproduction. Lp captures M by interfering with the depolarization of cells, successfully completes immune escape, and utilizes M. The nutritional factors continue to survive and multiply, and then cleave M, leading to acute damage of alveolar epithelium and endothelium, accompanied by edema and fibrous exudation. Legionella can also cause damage by inducing apoptosis, and the direct damage of Lp is mainly It is the action of hemolysin, cytotoxins and enzymes. The inhaled pathogen is swallowed by macrophages and propagates in its phagocytic vacuoles, producing cytotoxins, killing macrophages, and invading other macrophages. The presence of antibodies does not prevent the growth of pathogens, while cell-mediated immunity plays an important role in anti-infective effects. Cytokines produced by lymphocytes stimulated by antigens can be inhibited. The bacteria multiply in macrophages. After that, antibodies, complements and polynuclear cells can eliminate the pathogens. Most patients are confined to the lungs. The consolidation lesions are mostly large-leaf, and a small part is focal or plaque. The deaths were generally affected by both lungs. There was no significant difference in the chances of involvement of the upper and lower leaves. The lungs in the consolidation zone were congested, edematous and focal hemorrhage, often accompanied by a small amount of fibrinous pleurisy. Microscopic examination was mainly fiber. Plain suppurative pneumonia, a large number of neutrophil infiltration in the alveoli, and a large number of phagocytic cells.

Fibrin and moderate amounts of red blood cells and protein debris, some patients have acute diffuse alveolar damage, manifested as hyaline membrane formation, alveolar epithelial necrosis, shedding and regeneration, vascular endothelial cell swelling and degeneration, and a small number of inflammatory cells in the interstitial Infiltration, electron microscopic observation of capillary and epithelial cell basement membrane is still intact, suggesting that normal structure and function can be restored, bronchial often no significant involvement, so patients with cough and sputum are not many, using modified Dieterle saturated silver staining, Giemsa staining, pathogens Can be seen in phagocytic cells, neutrophils and extracellular, but non-specific, direct fluorescent antibody staining positive bacteria are specific, abscesses outside the chest are rarely seen, the pathogenesis of Pontiac fever is still unknown According to epidemiological and bacteriological data, most people in the same building unit are inhaled by aerosols from air-conditioning systems. The water in the air-conditioning system is contaminated by Legionella and other bacteria. The incubation period of this disease is 12 ~36h, this period is too short, it is difficult to explain with bacterial invasion and reproduction, may be a variety of bacterial toxins in the water Cause; or an immune response to a variety of microorganisms in the water.

Legionnaires' disease prevention

The mortality rate of Legionnaires' disease is about 15%. The older the age, the higher the mortality rate. The mortality rate of patients with underlying diseases or immunodeficiency is also high. The cause of death is mostly respiratory failure, followed by shock and acute renal failure. Diagnosis and effective treatment can reduce the mortality rate.

There are currently no effective preventive measures.

(1) Disinfection of drinking water: adding chlorine or boiling can kill the bacteria.

(2) The air-conditioning system should be shut down, disinfected and cleaned, and sanitized for water supply systems, wet equipment, sprayers, etc. to control the outbreak.

(3) The immune vaccine is under development.

Preventive measures can be used to address public health threats caused by Legionnaires' disease, although it is not possible to eradicate the source of infection, but it can significantly reduce risks. Legionnaires' disease prevention relies on good management of possible sources of infection, including regular cleaning and disinfection, and the use of other physics ( Temperature) or chemical measures (biocides) to minimize growth. For example, the cooling tower can be cleaned and disinfected regularly, and biocides are added frequently or continuously; sufficient levels of chlorine and other organisms are killed in the hot spring pool. And completely drain the system at least once a week to clean the entire system; keep the hot and cold water system clean, keep the hot water at 60 degrees Celsius, keep the cold water below 20 degrees Celsius, or use a suitable biocide to limit Growth, especially in hospitals, industrial sites, hotels, leisure centers, etc., will greatly reduce the possibility of Legionella contamination and prevent the occurrence of sporadic cases. The current method is chlorination (1 × 10 ^{- 6)} high or intermittent chlorination process (50 × 10 ^-6), but the law corrosive pipe, having reduced once the degree of chlorination, and Legionella Re is detected, it is ideal for disinfection measures, remains to be further studied.

Legionnaires' disease complications Complications pneumonia respiratory failure shock cerebral edema pancreatitis pancreatitis peritonitis

The condition is rapid and violent. If not treated in time, it will die of pneumonia and other complications.

The most common complication of Legionnaires' disease is respiratory failure, shock, acute kidney failure and multiple organ failure, requiring antibiotic treatment to recover without exception, and usually only after weeks or months to fully recover, occasionally severe progressive pneumonia Or pneumonia treatment is ineffective, and in rare cases, brain sequelae can occur.

The mortality caused by Legionnaires' disease depends on the severity of the disease, the suitability of the initial antimicrobial treatment, the environment in which Legionnaires' disease is infected, and the host factors (in patients with suppressed immune response, the disease is usually more severe), and the case fatality Up to 4080% of patients who do not receive treatment to suppress the immune response, can be reduced to 530% by appropriate case management and depending on the severity of clinical symptoms and signs, and can die for those who can form an immune response The rate is usually in the range of 10-15%.

In addition, it can also be complicated by peritoneal and pancreatitis, pulmonary infarction, and brain edema.

Legionnaires' disease symptoms Common symptoms Muscle soreness, respiratory failure, cyanosis, high heat, muscle pain, unconsciousness, nausea, fatigue, shock, vertigo

Legionnaires' disease is mainly manifested in two clinical types, Legionnaires' disease and Pontiac fever.

1. The latency of Legionnaires' disease is 2 to 10 days, with an average of 5.5 days. The clinical manifestations are difficult to distinguish from pneumonia caused by pneumococcal disease. The severity of the disease is different. The typical cases in this section are fatigue, low fever and loss of appetite. After about 12~48h, the protrusion is hot, the body temperature is continuous, it can be as high as 40°C or more, accompanied by recurrent chills, body muscle soreness, about 20% of patients have nausea and vomiting, sometimes with abdominal pain (10%~20%), 25% ~50% have watery diarrhea, dry cough 2 to 3 days after the disease, sometimes cough a small amount of sticky, even with bloodshot, rarely purulent, 30% to 40% have chest pain, often due to cough, breathing Exacerbation, with the increase of pneumonia, patients with shortness of breath, physical examination of patients with acute disease, sweat more, breathing faster, about half of the patients have relatively slow pulse, the lungs have a fine wet voice, and then the lungs appear obvious consolidation Signs (25%), severe cases have cyanosis, a few may have respiratory failure, about 20% can be conscious, mentally disordered, paralyzed, unconscious, etc., a small number of patients may have hallucinations, individual patients have shock, about 10% can occur Acute renal failure.

Severe cases showed oliguria or no urine, lighter only mild creatinine and urea nitrogen increased, digestive tract hemorrhage can be seen, as the disease progresses, the shadow expands into large leaves, the density deepens, at the peak of the disease, about 65% of patients have bilateral multilobular lesions. Although pleural effusion is not uncommon, it is generally not large. Most patients have a gradual decline in body temperature over the course of 8-10 days. The respiratory symptoms and general conditions are improved, but other diseases such as patients Or immunocompromised, the condition is heavier, prone to respiratory failure, the course of disease can also be delayed, and may be complicated by lung abscess or delayed absorption, etc., the mortality rate of patients without specific treatment is 10% to 30%; and the mortality rate of immunodeficiency patients Up to 80%, most of the causes of death are respiratory and multiple organ failure, extrapulmonary Legionella infection is extremely rare, including dialysis channel infection, sinusitis, pericarditis and brain, skin, intestinal abscess, prosthetic valve endocarditis, peritonitis Wait.

2. Pontiac fever: the incubation period is about 24 to 48 hours. More than 90% of the buildings can be affected by the same pathogen. The onset is urgent. The patient has chills, chills, fever, fatigue, myalgia and headache. Some patients have dry cough, discomfort in the throat and sternum, nausea, diarrhea and dizziness, individual patients have conscious convulsions, memory loss, nightmares, insomnia, etc. Physical examination, except for elevated body temperature and accelerated heart rate, no abnormalities, no lungs Department of inflammation, chest X-ray examination is also negative, the course of 2 to 5 days, the condition recovered smoothly, is a self-limiting disease.

Because the disease is difficult to distinguish from pneumonia caused by other causes, clinical diagnosis is difficult, and the diagnosis depends on pathogens and immunological examination.

1. Epidemiological data: incidence in summer and autumn, the use of air conditioning humidification system, spray shower and other history, age 40 years and older, smoking, chronic lung disease or heart disease, the application of adrenocortical hormone, and occurred in the hospital If you have a respiratory therapy device, you should consider this disease.

2. Clinical data: patients with pneumonia and the first symptom of diarrhea, although the systemic symptoms are serious and the respiratory symptoms are not obvious, pneumonia with neurological symptoms, pneumonia and respiratory secretions are generally culture-negative, antibiotics treated with beta lactam Patients with ineffective pneumonia should consider this disease.

3. Laboratory examination: the total number of white blood cells in Legionnaires patients is between (10 ~ 20) × 109 / L, between the proportion of neutrophils increased, there is a nuclear left shift phenomenon, ESR increased, urine test about 10% protein and Microscopic hematuria, a small number of patients have elevated blood creatinine and urea nitrogen, liver function test can have alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, bilirubin increased, muscle It is not uncommon for acid phosphate kinase (MM isoenzyme) to be elevated. Hyponatremia and hypophosphatemia can also be seen. Individual patients have myosinuria, renal failure or disseminated intravascular coagulation, and cerebrospinal fluid examination is often negative. A small number of increased pressure, mononuclear cells increased to (25 ~ 100) × 106 / L, sputum and intratracheal aspiration Gram staining only a small number of neutrophils can not find the dominant bacteria, ordinary culture failed to separate For pathogens, specific diagnosis requires isolation of pathogens from clinical specimens.

Legionnaires' disease check

The total number of white blood cells in Legionnaires patients is between (10 ~ 20) × 109 / L, the proportion of neutrophils increases, there is a nuclear left shift phenomenon, ESR increases, urine test about 10% protein and microscopic hematuria, a small number of patients have blood Increased creatinine and urea nitrogen, liver function tests can have alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase, elevated bilirubin, creatine phosphokinase (MM co-workers Elevation of enzymes is not uncommon, hyponatremia, hypophosphatemia can also be seen, individual patients have myosinuria, renal failure or disseminated intravascular coagulation, cerebrospinal fluid examination is often negative, a few have increased pressure, single core The cells were elevated to (25-100)×106/L, and only a small amount of neutrophils were found in the sputum and tracheal extracts. Gram-negative bacteria could not be found, and the common culture failed to isolate pathogenic bacteria. Isolation of pathogens from clinical specimens confirms the presence of pathogens or their antigens in tissues or body fluids, and the growth of specific antibodies by more than four times. Legionella can be isolated from sputum, pleural effusion or lung tissue in BCYE medium.

Serological examination:

(1) Indirect fluorescent antibody method.

(2) Direct fluorescent antibody method for early diagnosis.

X-ray chest examinations mostly involve unilateral ones, which are characterized by rounded shadows or flaky bronchial pneumonia with blurred edges.

Legionnaires disease diagnosis and identification

(1) Early should be associated with lobar pneumonia, bronchial pneumonia, viral pneumonia, mycoplasma pneumonia, rickettsial disease (such as Q fever), parrot fever, bacillary dysentery, Yersinia enteritis and certain Vibrio Enteritis and other identification.

(B) The late stage should be differentiated from chronic emphysema, liver and kidney and other organic diseases and certain nervous system infections.

The diagnosis of Pontiac fever is based on clinical manifestations, epidemiology and serological tests.

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