Legionnaires' Disease
- Author: Paul Cochrane at Aerotech Laboratories
- Thu, 13 May 1999
"Electric Water Heaters/Reservoirs for Legionella: IAQ Bioaerosol Tech Tip
#11"
Legionnaires' Disease is most often associated with cooling towers, hot tubs, fountains
and other similar man made water containing devices where "outbreaks" occur.
Typically, under these scenarios there are a number of victims and fatalities occur.
However, these "outbreaks" that garner so much media attention are only a small
percentage of the estimated 15,000+ cases of Legionnaires' Disease that occur
annually. One of the most common amplification sites for Legionella bacteria is the
electric water heater. Factors increasing the chances for amplification include infrequent
use, improper maintenance, adjustment to lower temperatures to prevent scalding and/or
failed heating elements. Temperature stratification and sediment buildup also provide an
ideal breeding ground for Legionella bacteria. Samples of water collected from drains of
water heaters can often exceed 1,000 Colony Forming Units Per Milliliter (CFU per ml) and
occasionally 10,000 CFU per ml or greater. The bacteria can be transported to water pipes,
faucets, shower heads and other point of use devices where direct exposure and/or
additional amplification can occur. Unfortunately, when the disease is transmitted to
humans under this scenario, only one individual is usually affected and the source of the
infection is often never determined.
The good news is that amplification of Legionella bacteria in water heaters is relatively
easy to control through the use of proper maintenance procedures. These include
periodically draining the water heater to eliminate sediment buildup, checking heating
elements to ensure that they are properly functioning and maintaining water heater
temperatures at or above 55 degrees C to inhibit growth of the bacteria.
Contaminated hot water systems can be disinfected by raising the temperature of the
water heater to 70 degrees C and running each distal tap until a temperature of 65 degrees
C is obtained for 5 minutes or more.
- An Update on Legionnaires's Disease: IAQ Tech Tip #25
- 5 April, 2000
Legionnaires' disease is a potentially deadly pneumonia that is contracted by inhaling
airborne water droplets containing Legionella bacteria (legionellae). Legionellae can
proliferate in plumbing systems, cooling towers, humidifiers, whirlpool spas and baths,
and respiratory care devices.
UNDETECTED CASES. Most cases of Legionnaires' are not detected. Even when cases are
detected, the public rarely hears about them, because only a small percentage of
Legionnaires' cases occur as part of the multicase outbreaks that sometimes make the news.
Symptoms of Legionnaires' are similar to those of other types of pneumonia, so undetected
cases end up being classified merely as pneumonia with no apparent cause. Many of these
deaths could be prevented because, unlike most pneumonias, the source (e.g., a plumbing
system) of Legionnaires' cases can be identified.
BIOFILM. Biofilm that coats potable water and cooling tower piping is a primary
contributor to legionellae growth. Biofilm is a slimy structure that is formed as microbes
attach to underwater surfaces. Biofilm and scale that form in valves and fittings and on
pipe walls not only feed legionellae but also protect them from hot water and chemical
disinfectants.
PUBLIC AWARENESS. Last November, CNN & TIME, a TV news magazine, aired a segment on
Legionnaires' disease in hospitals. CNN reported that "every year thousands of
patients contract [Legionnaires'] disease from contaminated hospital water systems."
The show included an interview with Dr. Victor Yu, a Legionnaires' expert from the
VA Medical Center in Pittsburgh: "These outbreaks--they're actually occurring all
through the country every week," said Yu. "It's an explosive problem to realize
that people are dying, to realize that the means are there for preventing all this from
happening, and that those means are not being exercised." Indeed, more people are
learning that Legionnaires' disease is widespread, and that preventive measures are not
implemented in most buildings.
NEW DIAGNOSTIC TEST. A new (clinical) 15-minute test for a common strain of Legionella
makes patient testing easy, which should result in more testing and more diagnoses.
As more cases are detected, more attention will be given to plumbing systems, cooling
towers, and other sources of contamination.
OUTBREAKS. The biggest outbreak of last year--and one of the biggest ever--occurred in the
Netherlands in late February to early March 1999. It involved 242 cases of illness and 28
deaths. The outbreak was blamed on a whirlpool spa displayed at a trade show.
NEW DISINFECTION TECHNOLOGY. In plumbing systems, copper-silver ionization has
outperformed chlorine, partly because of its apparent ability to disinfect systems laden
with biofilm. Studies indicate Chlorine Dioxide is also more effective than chlorine, plus
lower in cost, less harmful to ingest, and less likely to cause pipe leaks. Suppliers
claim it even removes biofilm over time. Chlorine Dioxide may be effective against
legionellae in cooling towers also. Chlorine Dioxide has been used for years in the
UK, but is still uncommon in the USA, partly because of concerns about the safety of
onsite generation. New technology (by Halox, Chalfont, PA) makes the generation process
much safer than before, so it may soon gain acceptance in the USA. Look for reports of
studies on actual cooling towers and plumbing systems, rather than laboratory models.
REGULATIONS. The New York State Department of Health sent a letter of Legionnaires'
recommendations to some 250 hospitals and 650 nursing homes early last year. NYDOH is
recommending routine sampling in hospitals that treat high-risk patients. The State of
Maryland has also begun the process of drafting Legionnaires' guidance.
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