Legionellosis: Legionnaires' disease and Pontiac fever

Legionellosis is an infection caused by the bacteria Legionella pneumophila. The disease has two forms: Legionnaires' disease, the more severe form which includes pneumonia, and Pontiac fever, a milder illness. Legionnaires' disease acquired its name in 1976 when an outbreak of pneumonia occurred among persons attending a convention of the American Legion in Philadelphia. Later the bacterium causing the illness was named Legionella.

How common is Legionellosis in the U.S.?

Of the 2.4 million cases of pneumonia that occur each year in the United States, an estimated 10,000 to 100,000 are actually cases of Legionnaires' disease. 5% - 15% of these cases are fatal. An additional unknown number are infected but have mild or no symptoms. It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms alone, other tests are required for diagnosis.

How is Legionellosis spread?

Outbreaks of Legionellosis have occurred after persons have inhaled aerosols that come from a water source (i.e. air conditioning, cooling towers, whirlpool spas, showers, sinks and bathtubs) contaminated with the bacteria. Persons may be exposed to these aerosols in homes, workplace, hospitals or public places. Infection can not be transmitted from one person to another. Source: Center for Disease Control and Prevention, Atlanta, GA.

Prevention in domestic and commercial hot water systems

It is actually very simple to minimize Legionella and other bacteria from growing in a hot water system. Water temperatures must be kept above 140F (60C) in tanks and 122F (50C) at all taps (faucets and showers). (from Legionellae Control in Health Care Facilities - A Guide for Minimizing Risk by Matthew R. Freije ).

As you can see, the current trend in the United States that recommends reducing the temperature of the hot water heater to prevent scalding is dangerous and misguided. Scalding may be prevented, but dangerous bacteria can grow rampant.

The solution to scalding in the shower

The problem of scalding in the shower can be easily addressed. There are two technologies that when combined are effective in controlling the temperature fluctuations at the outlet to 2F (1C). One is the thermostat and the other a pressure balancing mechanism. FM Mattsson AB of Sweden has developed the world's first Thermostatic and Pressure Balanced shower and in-line valves to address the problem. Models are available for any type of installation be it for hospitals, apartment buildings, schools, homes or ships.

Traditional "anti-scald" valves alone are not adequate for this application. The reason is that it takes a combination of the thermostat and pressure balancing shuttle to prevent temperature fluctuations in modern water systems. Valves that just contain a thermostat can not compensate for changes in pressure in a water system. On the other hand a pressure balancing valve with no thermostat isn't fast enough to compensate for changes in temperature.

The FM Mattsson valve adds another measure of safety ~ automatic shut-down. If the valve all of a sudden encounters a situation where the hot or the cold water supply is interrupted, it will automatically shut-down until the situation is corrected. This added safety feature avoids injury or discomfort due to a sudden blast of either cold or hot water.


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