Legionnaires’ disease, also known as Legionnaires’ illness, is a respiratory infection caused by Legionella bacteria. Patients may experience symptoms such as fever, cough, chest pain, dyspnea, and myalgias. The disease is primarily treated with medication, with erythromycin being the preferred drug. Early and aggressive treatment generally results in a good prognosis.
Clinical classification
According to the 2007 World Health Organization (WHO) guidelines, Legionnaires’ disease is divided into three subtypes: pneumonic Legionnaires’ disease, extrapulmonary syndrome, and Pontiac fever.
Epidemiology
Contagious
Legionnaires’ disease is contagious.
Source of infection
The main source of pollution that poses a potential threat to humans is artificial water systems, such as air conditioning cooling towers, water supply systems, shower heads, hot spring swimming pools, fountains, etc. In addition, contaminated medical devices such as ultrasonic atomizers and respiratory tubes can also cause hospital-acquired infections.
Transmission routes
Legionella can infect humans in a variety of ways, including respiratory, waterborne, and nosocomial transmission. Currently, there have been no reports of human-to-human transmission.
1. Transmission through the respiratory tract
Experts currently believe that aerosol inhalation is the primary route of infection for community-acquired Legionnaires’ pneumonia. Aerosol particles with a diameter of less than 5 μm can directly enter the respiratory bronchioles and alveoli, causing infection. Inhalation of aerosol particles contaminated with Legionella can cause Legionnaires’ disease. Aerosols primarily originate from various devices, such as nebulizers, humidifiers, showerheads, artificial fountains, and central air conditioning cooling towers. Furthermore, inhalation of dust containing Legionella at construction or landscaping sites can also cause the pathogen to enter the lungs, leading to infection.
2. Waterborne transmission
Direct consumption of Legionella-contaminated water can cause Legionella bacteria, which have colonized the oropharyngeal mucosa, to enter the respiratory tract through breathing, leading to infection. In addition, accidentally inhaling contaminated water into the lungs while brushing or rinsing the mouth can also cause infection.
3. Nosocomial transmission
When performing certain medical operations, if the rules, regulations and operating procedures are not strictly followed, Legionella can enter the human body through contaminated ultrasonic nebulizers, respiratory intubation, bronchoscope or artificial airway suction, and cause infection.
Incidence
This disease is relatively common worldwide. According to the epidemiological survey results on the pathogen spectrum of community-acquired pneumonia conducted by Liu Youning and He Lixian from 2002 to 2005, Legionella is not uncommon in my country, accounting for 5.1% and 4.0% of community pneumonia respectively.
mortality rate
The mortality rate of this disease is generally about 15%; the mortality rate of those with delayed treatment or no treatment is about 10%~30%; the mortality rate of those with weakened immune function can be as high as about 80%.
Incidence trend
With the improvement of living standards and the gradual popularization of facilities such as air conditioning and hot water bathing, the incidence and outbreak of Legionnaires’ disease may be on the rise.
High-risk population
Men are more likely to get the disease than women, and the elderly are more likely to get the disease.
High-incidence areas
The main outbreak sites are concentrated in places where young and middle-aged people gather, such as boot camps, schools, and factories.
High incidence season
The disease occurs in all seasons, but is more common in summer and autumn.
Causes
Overview
This disease is caused by infection with Legionella bacteria. The primary causative agent of Legionnaires’ disease is Legionella pneumophila serotype 1, which naturally inhabits various water bodies, including lakes, streams, and ponds. The pathogen enters the human body through the respiratory tract and waterborne transmission, leading to infection. Currently, there have been no confirmed reports of human-to-human transmission.
Basic cause
1. Legionella are a type of Gram-negative aerobic bacteria that require specialized nutrients. They contain multiple endotoxins and exotoxins, and the combined effects of these toxins are pathogenic. Legionella concentrations in natural water bodies are typically low, making them less likely to cause Legionnaires’ disease. However, once Legionella enter a water system, such as a municipal water supply, they colonize the pipe walls. Under suitable conditions, they can form a Legionella biofilm, evading the inhibitory effects of disinfectants and allowing them to grow and multiply in large numbers.
Whether or not Legionella develops disease after inhalation is closely related to the virulence of the pathogen and the body’s cellular immune function. The pathogen can adhere to cells in the lower respiratory tract and invade lung tissue via specific adhesins, damaging phagocytes and multiplying within them, causing cytopathic effects. In immunocompromised individuals, multiple lobes of the lungs may be affected. The bacteria often enter the pulmonary vasculature through the intrathoracic lymphatic system and circulate throughout the body, affecting multiple organs.
Risk factors
Risk factors for Legionnaires’ disease include male sex, smoking, chronic diseases (such as chronic cardiopulmonary disease, diabetes, end-stage renal failure, tumors, etc.), and immunodeficiency (such as HIV infection, use of corticosteroids or tumor necrosis factor-α).
symptom
Overview
The clinical manifestations of this disease vary depending on the type of disease. Pneumonic Legionnaires’ disease is mainly characterized by pneumonia; extrapulmonary syndrome is mainly characterized by manifestations of other systems; and Pontiac fever is mainly manifested by acute fever, and the course of the disease is self-limited.
Typical symptoms
1. Legionnaires’ disease
(1) The incubation period is 2 to 10 days, with an average of 5.5 days. Mild cases only present with low-grade fever and mild cough; severe cases may present with high fever and multiple organ failure.
(2) Prodromal symptoms include fatigue, low-grade fever, headache, myalgia, general malaise, and poor appetite. After 1 to 2 days, a sudden high fever occurs, accompanied by chills and shivering, and the fever is of the protracted fever type, with muscle aches all over the body.
(3) Some patients experience nausea, vomiting, abdominal pain, and watery diarrhea.
(4) Dry cough, chest pain, and shortness of breath gradually worsen, with a small amount of mucous sputum coughed up, which may contain blood and some may contain purulent sputum. Dyspnea worsens as the condition worsens.
2. Extrapulmonary syndrome
(1) Urinary system: manifested as oliguria or anuria.
(2) Digestive system: Symptoms include nausea, vomiting, abdominal pain, diarrhea, and black stools in severe cases.
(3) Nervous system: manifested as confusion, mental disorder, coma, epilepsy, etc.
(4) Cardiovascular system: manifested as heart discomfort and chest tightness.
3. Pontiac Fever
After a prodromal phase of headache, myalgia, and malaise, fever, chills, cough, and sore throat rapidly develop, resembling influenza. This acute, self-limited illness lasts 2-5 days, with rapid recovery. Other manifestations include diarrhea, nausea, tinnitus, photophobia, and extrapulmonary manifestations such as pericarditis and pyelonephritis.
complication
Common complications include lung abscess, empyema, respiratory distress syndrome (ARDS), disseminated intravascular coagulation (DIC), shock, etc.
examine
Scheduled inspection
Patients experiencing symptoms such as fever, cough, chest pain, and difficulty breathing should seek medical attention promptly. Doctors will first perform a physical examination to gain a preliminary understanding of the patient’s condition. They may then recommend routine blood tests, urine tests, liver and kidney function tests, pathogen testing, serum-specific antibody testing, and chest X-rays to further understand the patient’s condition and confirm the diagnosis.
Physical examination
The doctor will conduct a detailed physical examination using visual, palpation, percussion, and auscultation techniques. The patient may experience tachypnea, dry and wet rales in the lungs, and signs of pulmonary consolidation.
Laboratory tests
1. Blood routine test
Leukocytes and neutrophils increased with left shift of nuclei.
2. Urinalysis
A small number of patients may have proteinuria and microscopic hematuria.
3. Liver and kidney function
Some patients may have abnormal liver function.
4. Pathogen inspection
Culturing pathogens from specimens such as secretions, blood, sputum, and pleural effusions is difficult, resulting in a low positive rate and requiring more than a week, making timely diagnosis difficult. If the specimen is sputum, the addition of polymyxins, vancomycin, and other agents to the culture medium and acidification of the sputum are necessary to increase the positive rate. Tracheal aspirates have the highest positive rate, and a positive result confirms the diagnosis.
5. Serum-specific antibody detection
After infection, two specific antibodies (IgG and IgM) appear in serum. Specific IgM antibodies can be detected approximately one week after infection, while IgG antibodies begin to rise around two weeks after infection. Indirect blood fluorescence assay (IFA) is currently the most widely used method in China.
Imaging examinations
Chest X-ray examination: multi-segment and multi-lobe consolidation shadows mainly in the middle and lower lung fields, which may be accompanied by a small amount of pleural effusion.
diagnosis
Diagnostic principles
A clear diagnosis can generally be made based on the patient’s medical history, as well as clinical manifestations such as fever, cough, chest pain, and difficulty breathing, combined with the results of pathogen testing, serum-specific antibody testing, chest X-ray, and other examinations.
Differential diagnosis
1. Streptococcus pneumonia
Pneumococcal pneumonia is a common community-acquired pneumonia caused by Streptococcus pneumoniae. Typical symptoms include sudden onset of high fever, chills, chest pain, and cough with rusty sputum. Compared with Legionnaires’ disease, pneumococcal pneumonia typically progresses more rapidly and is often accompanied by significant pleural involvement. Radiographic findings often demonstrate lobar pneumonia, whereas Legionnaires’ disease more often presents with multilobar or patchy infiltrates.
2. Klebsiella pneumoniae pneumonia
Klebsiella pneumoniae pneumonia is more common in immunocompromised or chronically hospitalized patients, particularly alcoholics and those with diabetes. Its typical manifestations are acute onset, high fever, and cough with brick-red, gelatinous sputum. Radiographic findings often include right upper lobe consolidation with cavitation. Compared with Legionnaires’ disease, Klebsiella pneumoniae pneumonia is associated with more pronounced sputum characteristics and rapid progression, often complicated by empyema or lung abscesses. Legionnaires’ disease presents more frequently with systemic symptoms (eg, headache, myalgia) and gastrointestinal symptoms (eg, diarrhea), and is less likely to develop cavitation on radiographic examinations.
3. Mycoplasma pneumonia
Mycoplasma pneumonia is an atypical pneumonia caused by Mycoplasma pneumoniae, commonly occurring in adolescents and young adults. Symptoms are typically mild, with progressive fever, dry cough, headache, and fatigue, often accompanied by pharyngitis or otitis. Compared with Legionnaires’ disease, mycoplasma pneumonia presents with milder systemic symptoms and is less likely to present with gastrointestinal symptoms. Radiologically, mycoplasma pneumonia often presents as interstitial pneumonia or patchy infiltrates, while Legionnaires’ disease is more likely to present with multilobar consolidation.
4. Chlamydia pneumonia
Chlamydial pneumonia, primarily caused by Chlamydia pneumoniae, commonly affects young and elderly adults. Symptoms are similar to those of mycoplasmal pneumonia, presenting with mild fever, dry cough, and fatigue, but the disease progresses more slowly. Compared with Legionnaires’ disease, chlamydial pneumonia is associated with fewer systemic and gastrointestinal symptoms and often presents with interstitial pneumonia or lobular infiltrates on imaging. Legionnaires’ disease is more often characterized by acute onset, high fever, and multisystem involvement.
treat
Treatment principles
Legionnaires’ disease is primarily treated with anti-infective medications, with erythromycin being the preferred treatment. Azithromycin and clarithromycin are also options. However, penicillins, cephalosporins, and aminoglycosides are ineffective. In addition to medications, general treatment and symptomatic therapy can be used to improve symptoms.
Symptomatic treatment
Pay attention to the treatment of water and electrolyte imbalance, keep the respiratory tract open, and prevent and treat complications.
General treatment
Rest in bed and avoid overexertion.
Drug treatment
1. Erythromycin is the first choice for treatment. If oral administration is ineffective, intravenous drip is required. Rifampicin can be added to patients with immunodeficiency or severe disease.
2. Antibiotics such as azithromycin, clarithromycin, roxithromycin, and cyclic erythromycin (such as Guansha) can also be used.
Related drugs
Erythromycin, rifampin, azithromycin, clarithromycin, roxithromycin, erythromycin cyclic (such as Guansha)
Surgical treatment
This disease generally does not require surgical treatment.
Treatment cycle
The treatment cycle of this disease is affected by factors such as the severity of the disease, treatment plan, treatment timing, age and physical condition, and may vary from person to person.
Treatment costs
There may be significant individual differences in treatment costs, and the specific costs are related to the selected hospital, treatment plan, medical insurance policy, etc.
Prognosis
General prognosis
With active treatment in the early stages of the disease, the prognosis is generally good, and patients can usually achieve clinical recovery. However, some patients with severe disease, weakened immune system, delayed treatment, or no treatment may face life-threatening consequences, with death often caused by respiratory failure or multiple organ failure.
Hazards
1. Legionella can cause outbreaks and pose a serious threat to human health. Furthermore, the disease can cause fever, cough, and breathing difficulties in patients, affecting their quality of life.
2. If not treated in time, it may cause the patient’s death.
Self-healing
Pontiac fever, a type of Legionnaires’ disease, usually resolves on its own.
Curative
With early and active treatment, it can generally be cured.
daily
Overview
Patients should maintain a good attitude in daily life, actively cooperate with treatment, and pay attention to self-management to promote recovery from the disease.
Medication care
1. Follow the doctor’s instructions, use the medicine correctly, and do not stop taking the medicine at will.
2. Pay attention to the adverse reactions of the drug. If you experience any discomfort frequently, you need to inform your doctor for appropriate treatment.
Life Management
1. Keep the indoor air fresh and flowing.
2. Pay attention to rest and ensure adequate sleep to promote body recovery.
3. Pay attention to hygiene. Patients should wash their hands, rinse their mouths, take a bath, and clean frequently.
4. Keep the shower water clean and clean and disinfect the air conditioner regularly.
5. Keep warm.
diet
Dietary adjustment
A scientific and reasonable diet can ensure the normal functioning of the body, help control the disease, maintain the treatment effect, and promote recovery from the disease.
Dietary recommendations
1. Ensure regular diet and eat at regular times and in regular amounts.
2. Eat more fresh fruits and vegetables, and pay attention to supplementing vitamin C to enhance the patient’s immunity.
3. Strengthen nutrition supply and eat foods that are easy to digest, contain sufficient calories and are rich in protein.
Dietary taboos
1. No smoking or drinking.
2. Avoid eating raw, cold, spicy and irritating foods.
3. Eat less animal offal, fried and greasy foods.
prevention
Preventive measures
1. Avoid drinking raw water.
2. Strengthen exercise, improve the body’s immunity and prevent the occurrence of diseases.
3. It is recommended that people with low immunity try to avoid crowded places such as hospitals and hotels.
4. Keep the indoor environment clean and tidy, and open windows regularly for ventilation.
Medical Guide
Outpatient indications
1. Symptoms of fever and cough appear.
2. Symptoms such as abdominal pain, diarrhea, confusion, and mental disorder occur.
3. Accompanied by symptoms of fatigue, headache, and myalgia.
4. Other severe, persistent or progressive symptoms and signs occur.
All of the above require timely medical consultation.
Treatment department
This disease falls under the diagnosis and treatment category of infectious diseases, and patients can go to the infectious diseases department for treatment.
Medical preparation
1. Make an appointment in advance and bring your ID card, medical insurance card, medical card, etc.
2. A comprehensive physical examination may be performed, and it is recommended that you wear clothing that is easy to put on and take off.
3. If you have had medical treatment recently, please bring relevant medical records, examination reports, laboratory test results, etc.
4. If you have taken some medicine to relieve symptoms recently, you can bring the medicine box with you.
5. Family members can be arranged to accompany the patient to seek medical treatment.
6. Patients can prepare a list of questions they want to ask in advance.
Questions your doctor may ask
1. What’s wrong with you?
2. Are there any factors that make your symptoms worse or better?
3. What tests have you undergone? What were the results?
4. Have you ever been treated before? How was it treated? What was the effect?
5. Do you have any underlying diseases?
6. Do any of your family members have similar symptoms?
What questions can patients ask?
1. What disease do I have? What causes it?
2. What tests do I need to do?
3. Is my condition serious? Can it be cured?
4. What treatment options are available? Does hospitalization require treatment?
5. Are there any risks associated with these treatments?
6. How long does it take to be cured? Will it recur after being cured?
7. How should I take care of myself after returning home?
8. Do I need a follow-up check? How often?