What is Legionnaire's Disease?

Legionella is a clinical syndrome caused by bacteria of the genus Legionella. In 1976, when the United States Philadelphia held a veterans conference, the outbreak became popular. Pathogens come mainly from soil and sewage, are transmitted by the air, and invade from the respiratory tract. According to the 2007 World Health Organization (WHO) guidelines, legionellosis is divided into three subtypes: Legionella pneumoniae (LD) Legionella infection with pneumonia as the main clinical manifestation, also known as Legionella pneumonia; Extrapulmonary Syndrome refers to the spread of infection from the lungs to other systems outside the lungs; Pontiac fever is mainly manifested by acute fever with a self-limited course of disease. The main pathogen of Legionella is Legionella pneumophila serotype 1. More men than women. The elderly, smokers and alcoholics, and those with low immune function are susceptible to the disease.

Basic Information

nickname

Legionella pneumonia

English name

legionnaires disease

English alias

legionellosis

Visiting department

Respiratory Medicine

Multiple groups

More men than women, pregnant women, the elderly, and immunocompromised persons are at high risk

Common locations

lung

Common causes

Gram-negative Legionella pneumophila infection

Common symptoms

Abdominal pain, watery stools, anxiety, nervous retardation, delirium, etc.

Causes of Legionella

Legionella bacteria are aerobic polygram-negative bacteria that are widely present in the natural environment. The source of infection is water and air conditioning systems, which are transmitted through the air. According to cell wall composition, biochemical reactions and DNA hybridization studies, Legionella is not related to previously known pathogenic bacteria, so it constitutes a separate family. There is only one genus of Legionellaceae, namely Legionella. Those who have been finalized in China include Lp1, Lp3, Lp5, Lp6, Lp9 and so on.

The disease-causing patients are mainly Legionella pneumophila (Lp) and Legionella mellitus; there are 15 serotypes of Legionella pneumophila, about 90% of which are serotype I. Legionella is a gram-negative bacillus. Legionella can produce a variety of enzymes and toxins, including proteases, phosphatases, deoxyribonucleases, -lactamase, and cytotoxins, which may be related to virulence. The growth of Legionella can be supported by some free-living protozoa, or parasitic in its body, such as amoeba. Protozoa interact with Legionella, and protozoa can alter the virulence of Legionella.

Clinical manifestations of legionellosis

Pneumonia type

The incubation period is generally 2 to 10 days. The prodromal symptoms are fatigue, headache, and sore muscles throughout the body. Sudden fever can reach 40 ° C or higher within 1 to 2 days. Symptoms of multiple system involvement can occur early in the course of the disease. The vast majority of patients have a cough, which is initially a dry cough. Half of the patients turn to non-purulent sticky sputum or slightly purulent sputum. The sputum often contains a small amount of blood, and some may have hemoptysis.

A few patients have chest pain, and dyspnea is more common. Fine wet rales can be heard in the lungs. Followed by obvious signs of pulmonary consolidation. About 25% have gastrointestinal symptoms such as nausea, vomiting and diarrhea, and some are the only first symptoms. Neurological symptoms are more common in the acute phase, including varying degrees of disturbance of consciousness, increased muscle tone or paroxysms, gait instability, etc. There may be temporary limb paralysis and no signs of localization of the nervous system. In most cases, the body temperature dropped from 8 to 10 days, and systemic symptoms such as pneumonia improved. However, in severe cases, heart, liver, and kidney functions may be impaired, or even death may result from functional failure, and lung abscesses may be delayed.

2. Non-pneumonia type (Pontiac fever)

This type is a mild type of the bacterial infection, with an incubation period of 5 to 66 hours and half of which is about 36 hours. Cold and fever onset, body temperature generally does not exceed 39.5 , with headache, myalgia and so on. Respiratory symptoms were not severe. Half of the patients had mild dry cough and chest pain, and some had dry throat. Individuals may have neurological manifestations such as diarrhea, watery stools, or insomnia, dizziness, memory loss, confusion, neck rigidity, and tremor, all of which are mild. The course of non-pneumonia type heals for 3 to 5 days.

Legionnaires disease check

Laboratory inspection

Peripheral blood elephant white blood cell count increased, mostly between (10-20) × 10 ⁹ / L, neutrophils increased, nuclear shift left was visible; respiratory secretions (sputum or endotracheal aspirate) Gram staining could not be found A large number of dominant flora, only a small number of neutrophils were seen.

2. Serological examination

(1) The antibody titer of the double serum antibody by the indirect fluorescent antibody method is increased by more than 4 times and 1: 128, or the single serum titer of the recovery period 1: 956 can diagnose the disease, more than 3 weeks (a few 6 weeks ) Serum antibody titer can reach diagnostic criteria. The positive rate of this method is about 80%.

(2) Direct fluorescent antibody method Detection of pathogenic bacteria in patients' respiratory secretions by known antibodies, the positive rate can reach 50%, which can be used for early diagnosis.

Diagnosis of Legionella

The clinical diagnosis of Legionella bacillus infection is difficult, and its clinical manifestations are difficult to distinguish from chest infections caused by other pathogens. Therefore, serological or pathogenic examinations must be performed to confirm the diagnosis.

Legionnaires disease treatment

Macrolides or fluoroquinolones are preferred. Tetracyclines and rifazone are also effective. Penicillins, aminoglycosides, and cephalosporins have no significant effect on the disease.

In addition, maintaining water and electrolyte balance, the application of respirators in respiratory failure, vasoactive drugs and other anti-shock measures during shock, and dialysis therapy in acute renal failure are all important treatment measures.

Prognosis of Legionella

The case fatality rate of Legionnaires' disease is about 15%. The older the case, the higher the case fatality rate. The case fatality rate is also higher in those with underlying diseases or immunodeficiency. Most of the causes of death were respiratory failure, followed by shock and acute renal failure. If early diagnosis and effective treatment can be given, the mortality rate can be reduced.