Alamosa Salmonella Outbreak

Last week I attended the Rocky Mountain Water and Wastewater Plant Operators Advanced School. During this training conference, various experts from public and private institutions spoke to us about new technology, emerging contaminants, and treatment optimization. The recent salmonella outbreak in Alamosa, CO was also a hot topic of discussion.

The salmonella outbreak is believed to have started on March 7th. Since then, there have been over 78 confirmed cases, with as many as 293 people showing signs of illness. Twelve people have been hospitalized.

The source of the outbreak still has not been detected. Alamosa obtains it's water from five deep aquifer wells. According to state officials at the conference, salmonella was not detected at the well heads. Thus, you can eliminate the groundwater as the source. This means that the contamination must have come from the distribution system, and lab results have confirmed that salmonella is in the water system. Two state officials at the conference believed that the contamination came from an underground storage tank that was not on any maps or inventory of the distribution system. However, the latest news still says that the source is unknown.

The strain of salmonella detected in the water is associated with deer and birds such as geese or cranes. Thus, animal droppings or a dead bird in a water tank could be possible explanations for the salmonella. One of the experts at the conference did bring up an interesting observation. According to him, only salmonella had been detected in the water and not any other bacteria, such as e coli that may be associated with a dead animal. Thus, it appears that animal droppings may be the source.

Another reason for the outbreak is that the water in Alamosa was not chlorinated. According to a state official at the conference, Alamosa received a variance "twenty or thirty years ago", allowing them to provide water without chlorination. This was most likely due to the purity of the deep aquifer. However, chlorine is added to water for treatment due to its disinfection and its residual properties. Residual chlorine remains in water after it leaves the water treatment plant, which helps to sanitize the distribution system. The salmonella outbreak may have been prevented if chlorine was added.

Alamosa is now flushing the distribution system with a 25 mg/L dose of chlorine. This should disinfect the pipelines and allow the citizens to use the water for washing, showers, and eventually drinking again. I am pretty certain that the town will have to implement chlorination, and possibly other treatment methods, in the future. Incidents such as this are very rare, but it does remind us of the importance of water treatment.