Legionnaires’ disease—46 years on

According to Fox News New York, in May this year, an outbreak of Legionnaires' disease broke out in the Bronx, New York City, and investigators tested positive for Legionnaires' bacteria in four cooling towers there. The fact that a disease is named after "Legion" inevitably leads people to speculate about its connection with the military. This story really started with a group of American veterans.

In 1976, on the occasion of the 200th anniversary of the founding of the United States, a group of veterans held a "Veterans Convention" at the "Stratford View" Hotel in Philadelphia. However, only two days later, more than 180 people developed symptoms such as high fever, headache, vomiting, coughing, and general fatigue. Even 36 residents near the hotel had similar symptoms, as if they had encountered a flu, but 90% of the patients showed signs of pneumonia in their chest X-rays. In the end, there were 221 confirmed cases of this unknown disease and 34 patients died. This explosive news cast a thick shadow on the joyful and peaceful atmosphere at the time.

At the time, the headlines on the front pages of major newspapers were "Mysterious Philadelphia Epidemic", but no laboratory could find the cause. Initially, the researchers targeted influenza, and after ruling out influenza as a suspect, they tested 17 metals for possible involvement; later, health officials also checked for the possibility of other toxins or toxic gases. Some scientists called for a suspension of all work in microbiological laboratories because they were worried that these laboratories might be the source. Government officials warned: "A devastating epidemic could strike without any warning." To this end, the Ford government in the United States is preparing to vaccinate every American with a new influenza vaccine, the swine flu vaccine.

Six months after the outbreak, medical scientists isolated a pathogenic bacteria from the lung tissue of the deceased, but it had never been found before. Later studies confirmed that it was a pathogenic microorganism present in faucets and sinks. Laboratory studies have shown that high water temperature is a favorable factor for the growth and reproduction of this bacteria. Investigators turned their attention to the air conditioning system of the "Stratford View" Hotel and found that although the water in its cooling tower was supplemented by municipal tap water, the water quality had deteriorated after continuous circulation and evaporation. The outbreak occurred in summer, when air conditioners were frequently used, generating a lot of heat, and the water temperature of the cooling tower rose. The bacteria grew and reproduced actively, and after entering the air conditioning system, they were blown out with the cold air, infecting a group of people.

Since most patients are members of the Legion, the bacteria was named "Legionella", and the disease was also called "Legionnaires' disease", or "Legionnaires' disease". In 1978, the US Centers for Disease Control and Prevention and the World Health Organization officially named it "Legionella pneumophila" at the 1st International Symposium on Legionnaires' Disease.

Legionella mainly comes from soil and sewage, and can be spread in the air through respiratory droplets produced by coughing, sneezing, talking, etc., which can cause two types of diseases. One is pneumonia, which is manifested by fever, cough and lung inflammation, and in the later stage, coma, delirium, and even shortness of breath and respiratory failure; the other is non-pneumonia, which is milder and only manifests clinical symptoms such as fever, headache, muscle aches, etc., also known as Pontiac fever.

Since the first discovery, there have been many Legionnaires' disease outbreaks in the United States, such as the outbreak in Flint, Michigan, in 2014-2015. Nearly 100 citizens were infected and 12 died; in November 2019, two air-conditioning cooling towers in a Disneyland in California, USA, carried Legionnaires' bacteria, causing 15 tourists to contract Legionnaires' disease and 2 deaths. Legionnaires' disease has also been reported in many countries, including the United Kingdom, France, Australia, Singapore, and Canada. From 1995 to 2005, the U.S. Centers for Disease Control and Prevention reported a total of 23,076 cases of Legionnaires' disease; from 2011 to 2015, the European Center for Disease Prevention and Control reported 30,532 cases of Legionnaires' disease. It can be seen that Legionnaires' disease is widely spread.

In 1982, the first case of Legionnaires' disease was discovered in Nanjing, my country. Since then, reports have been made in Fujian, Zhejiang, Sichuan, Guangdong, Shandong, Heilongjiang, Hebei, Liaoning, Xinjiang and other places. In 1989, Legionnaires' disease broke out in the suburbs of Beijing. In 1994, cases also appeared in Shanghai. After the occurrence of Legionnaires' disease, Legionella bacteria can often be detected in the air conditioning systems of related hospitals, shopping malls, subway stations, cinemas, hotels and office buildings, surface algae-containing water and forest bathing facilities.

Legionnaires' disease can occur all year round, especially in summer and autumn. The elderly, children and people with weakened immune function are more susceptible. However, the treatment of Legionnaires' disease is still a world problem, and no effective treatment measures have been found. For individuals, it is very important to regularly inspect and disinfect the air conditioning system, especially before turning on the air conditioner for the first time in summer. In addition, it is necessary to strengthen physical exercise, pay attention to food hygiene, develop good living habits, and enhance the body's immunity. (Song Tianli)▲