Why Legionella survives in pipes
According to the Centers for Disease Control, Legionnaires’ disease is on the rise in the United States. In fact, the rate of reported cases of Legionnaires’ disease has grown by nearly nine times since 2000.
Health departments reported nearly 10,000 cases of Legionnaires’ disease in the United States in 2018. However, because Legionnaires’ disease is likely underdiagnosed, this number may underestimate the true incidence. A recent study estimated that the true number of Legionnaires’ disease cases may be 1.8–2.7 times higher than what is reported. More illness is usually found in the summer and early fall, but it can happen any time of year.
The CDC says it is unclear whether this increase represents artifact (due to increased awareness and testing), increased susceptibility of the population, increased Legionella in the environment, or some combination of factors.
In the pool and spa domain, incidences of Legionnaires’ outbreaks are all too common. One of the largest such outbreaks occurred in 2019 at the North Carolina Mountain State Fair. The outbreak sickened more than 140 people and resulted in four deaths. Health Officials said that the evidence suggested a couple of hot tub displays were the likeliest source of the bacteria.
Later that same year, another Legionnaires’ outbreak linked to hot tub displays at a Texas State Fair prompted the CDC to issue an official Health Alert Network warning regarding hot tub displays at events and trade shows. The outbreak occurred at the East Texas State Fair and resulted in eight confirmed cases and one death.
Although Legionnaires’ is considered rare, every year, numerous Legionnaires’ outbreaks are traced to commercial or public spas, ostensibly cared for to ensure public health. A recent CDC study reported that between 2000 and 2014, it accounted for 31 percent of all hotel-originated waterborne illnesses. That same report stated that hotel water venues account for about a third of all disease outbreaks associated with chlorinated water.
Currently, more than a dozen people are suing the Sands Resort, in Hampton Beach, New Hampshire, for an outbreak that occurred there that sickened 49 people and killed two. The source of the outbreak was linked to the spa.
Outbreaks such as these occur, even in water that appears clean and cared for, occur largely because of biofilm in the plumbing.
When microorganisms such as bacteria, fungi, and algae gather together on a surface and then coat themselves with slimy substances, they have formed biofilm. Biofilms can start with just a couple cells and then grow into huge colonies that contain a wide variety of organisms.
Many bacterial pathogens such as Legionella and Pseudomonas like to live in biofilms and will often thrive and reproduce quickly in a biofilm environment. Once a biofilm becomes established on a surface, it can be very difficult to treat. Although swimming pool and spa sanitizers are very good at killing microorganisms that are free floating in the water, it is difficult for them to get down through the slime layers of biofilm and kill all potentially harmful organisms. If only the top layer of organisms is killed, the cells underneath can continue to grow and reproduce, thereby reforming the biofilm structure in a short time.
That is why it is possible for a spa with adequate chlorination levels to continue to host biofilms and their associated microorganisms.
There are a number of spa purges and jet cleaners that are readily available for the pool and spa industry. Many formulations contain enzymes, which have been demonstrated to break down the organic components that are part of the biofilm matrix such as human skin cells, hair, oils, makeup, sunscreens, dead algae, and more.
To make a biocidal claim, however, the Environmental Protection Agency requires the product to meet specific testing criteria.
Furthermore, they discriminate between the different types of claims that can be made.
For example, a product may claim to remove biofilm without actually killing it. A product may claim to prevent biofilm. A product may claim to control or reduce biofilm. Finally, a product may claim to kill biofilm. There are different testing guidelines for each of these claims.
To our best knowledge, there is only one company that manufactures an EPA-registered biofilm removal product. They make the only products in the spa industry that can claim to remove biofilm according to the EPA.
Manufactured by Unique Solutions, the products are called Hot tub Serum, composed of Alkyl* dimethyl benzyl ammonium chloride, and Ahhsome, composed of Alkyl* dimethyl ethylbenzyl ammonium chloride.
These products are EPA registered effective against both algae and animal pathogenic bacteria (gram positive and negative.)
Legionella on the inner walls of pipes can grow a slimy substance known as biofilm, which encapsulates and protects the colony from disinfectants. Image credit: B. Hayes/NIST.