Legionellosis is an important cause of community- and hospital-acquired pneumonia, and although uncommon, it may cause outbreaks of public health significance.
As of 11 September 2023, a total of 166 cases of legionellosis, including 23 deaths, have been reported from Poland. This observed increase in confirmed cases, and associated hospitalizations and deaths seen since mid-August, is unusual, considering that the number of cases is higher than the annual number reported in Poland since 2016. Investigations are still ongoing to find the source of the outbreak.
Sporadic outbreaks of Legionnaires' disease have been reported previously in Poland. Between 2017 and 2021, Poland reported between 38 to 74 cases of Legionnaires’ disease annually to the European Surveillance System. In 2022, this increased to 111 reported cases.
On 18 August 2023, public health authorities in Rzeszów, Poland, announced the detection of a cluster of 158 suspected community-acquired pneumonia cases, including 15 laboratory-confirmed cases of legionellosis among patients admitted to several hospitals in Rzeszów. Between 18 August and 11 September 2023, a total of 166 laboratory-confirmed cases, all hospitalized, and 23 associated deaths (14%) have been reported.
Preliminary results from an ongoing epidemiological investigation indicate that the first cases developed symptoms on 30 July, while most cases developed symptoms between 12-16 August. Adults between 60 and 90 years are the most affected age group. The most recently reported case has an onset date of 29 August. All 23 related deaths had underlying comorbidities and were between the ages of 53 and 98 (11 females and 12 males).
Legionellosis is an infection caused by Legionella bacteria. The Legionella bacteria can cause a mild illness, Pontiac fever, non-pneumonic form of the disease, and Legionnaires’ disease, a severe pneumonia form of illness that can be fatal.
The bacterium Legionella pneumophila is responsible for most cases of Legionnaires' disease. Outdoors, legionella bacteria survive in soil and water, but rarely cause infections. However, legionella bacteria can multiply in water systems made by humans, such as air conditioners.
Although it's possible to get Legionnaires' disease from home plumbing, most outbreaks have occurred in large buildings, perhaps because complex systems allow the bacteria to grow and spread more easily. Also, home and car air conditioning units don't use water for cooling.
Not everyone exposed to legionella bacteria becomes sick. Smoking damages the lungs, making the smokers more susceptible to all types of lung infections. The risk increases with age, but some people are at higher risk including people over 45 years of age, heavy drinkers, people suffering from chronic respiratory or kidney disease, diabetes, lung and heart disease, and anyone with an impaired immune system.
Legionnaires' disease can be a problem in hospitals and nursing homes, where germs can spread easily, and people are vulnerable to infection.
Legionella occurs naturally in freshwater environments, like lakes and streams. It can become a health concern when it grows and spreads in human-made building water systems.
One transmission route in humans is the inhalation of contaminated aerosols (water droplets suspended in the air) from aquatic environments. After inhalation, the bacteria can reach the pulmonary alveoli. They invade immune cells known as macrophages and ultimately destroy them. People can also contract the disease by aspiration of contaminated water.
Some specific cases are worth mentioning newborn babies born in birthing pools, hospital patients via contaminated water and ice cubes.
People with Legionnaires' disease are not contagious. Only one case of human-to-human transmission has been reported to date. The case involved very close proximity between the two people in a confined space for a long time.
The incubation period for Legionnaires' disease is most commonly 5 to 6 days from the time of exposure to symptom onset, with a range of 2 to 14 days, but public health officials have reported incubation periods up to 26 days under rare circumstances.
Initially, symptoms are fever, mild cough, loss of appetite, headache, malaise, and lethargy, with some patients also experiencing muscle pain, diarrhea, and confusion.
The severity of Legionnaires’ disease ranges from a mild cough to rapidly fatal pneumonia. Untreated Legionnaires’ disease usually worsens during the first week.
Pontiac fever is a milder infection than Legionnaires’ disease. Symptoms are primarily fever and muscle aches. Symptoms can begin between a few hours to 3 days after being exposed to the bacteria and usually last less than a week. Pontiac fever is different from Legionnaires’ disease because someone with Pontiac fever does not have pneumonia.
Mortality from Legionnaires’ disease depends on the severity of the disease, the use of antibiotic treatment, the setting where Legionella was acquired, and whether the patient has underlying conditions, including immunosuppression. The death rate may be as high as 40–80% in untreated immunosuppressed patients and can be reduced to 5–30% through appropriate case management, depending on the severity of the clinical signs and symptoms. Overall, the death rate is usually between 5–10%.
Legionnaires' disease can lead to a number of life-threatening complications, including respiratory failure, septic shock, and acute kidney failure. When not treated promptly, Legionnaires' disease can be fatal.
The long-term side effects of Legionnaires' disease include fatigue, neurologic symptoms, neuromuscular symptoms , and posttraumatic stress disorder .
There are no vaccines that can prevent Legionnaires’ disease. Instead, the key to preventing Legionnaires’ disease is to reduce the risk of Legionella growth and spread.
Outbreaks of Legionnaires' disease are preventable, but prevention requires water management systems in buildings that ensure that water is monitored and cleaned regularly. To lower your personal risk, avoid smoking.