Southern Colorado Science Update #1: Alamosa Salmonella outbreak report released

The region of southern Colorado on either side of the Sangre de Cristo Mountains is quite special to the Pharmboy family. The high plains to the east and San Luis Valley to the west are sparsely populated, stunningly beautiful with a veritable mine of geological treasures, and are unlikely to be built up in the PharmKid's lifetime. In fact, most counties down there have fewer people now than they did in 1900.

It is also rugged and you can easily die out there. Which gets you in touch with what matters.

For the blogeratti, the most informative blog I've discovered about the San Luis Valley is SLV Dweller. However, I still haven't found a dedicated blog for the east side, but Sangres.com has the most comprehensive information available for the Scenic Highway of Legends area.

So, you can see why I might enjoy paying attention to news out yonder. Plus, stories that emanate from out there often have an interesting science slant, suitable for consumption by ScienceBlogs readers.

In March and April 2008, 442 people in the town of Alamosa, Colorado (2008 pop. 8,745), were sickened with Salmonella bacteria that was traced to the municipal water supply. Epidemiological estimates are that over 1,300 residents may have been striken. One death was reported. The story made national US news back then and we posted some details back then. I wrote then that "like many bacteria that enjoy the gastrointestinal tract, Salmonella causes diarrhea but can be fatal in small children, the elderly population, or anyone else with a compromised immune system."

Alamosa's water supply system had in the process of being upgraded, in part due to new state controls on arsenic content, but it was still operated under a water disinfection waiver from the state. Over 100 Colorado municipalities were absolved from chlorination requirements especially, in the case of Alamosa, where the water source came from deep artesian sources and would be unlikely to be contaminated like lake or stream sources. However, according to Kyle Clark at 9News in Denver, 76 of these waivers have been revoked.

In a report released last week, state officials have formally cited animal waste contamination in a deteriorating concrete storage tank as the likely cause. Seems that the inside area stays at about 65-75°F year-round. Alamosa is often the nation's icebox (it's 7°F/-14°C as I write) and all manner of birds and mammals take refuge wherever they can. The USGS National Wildlife Health Center describes that Salmonella is frequently shed in the feces of such animals and is often a cause of avian transmission at birdfeeders. (I also noted a couple of years ago that pet turtles are often the source of domestic Salmonella infections in kids.)

David Olinger in The Denver Post wrote that the Alamosa outbreak resulted from a "'perfect storm' of woes."

The 65-page report was written by engineers Ron Falco and Sharon Israel Williams (PDF) and, call me a geek, I spent much of last Saturday night reading it.

Really - I learned a lot about municipal water quality is regulated (and how one goes about disinfecting 50 miles of water lines) and how state and federal disease surveillance works - while not as glamorous as a CSI script, the document engagingly describes how an outbreak actually plays out under multiple jurisdictions. Falco and Williams did some great work here in making a highly-technical report very readable to diverse audiences.

I also learned that the Centers for Disease Control and Prevention routinely performs subtype analysis of infectious organisms by pulsed-field gel electrophoresis (PFGE) through a network of laboratories called PulseNet:

PulseNet is a national network of public health and food regulatory agency laboratories coordinated by the Centers for Disease Control and Prevention (CDC). The network consists of: state health departments, local health departments, and federal agencies (CDC, USDA/FSIS, FDA).

PulseNet participants perform standardized molecular subtyping (or "fingerprinting") of foodborne disease-causing bacteria by pulsed-field gel electrophoresis (PFGE). PFGE can be used to distinguish strains of organisms such as Escherichia coli O157:H7, Salmonella, Shigella, Listeria, or Campylobacter at the DNA level. DNA "fingerprints," or patterns, are submitted electronically to a dynamic database at the CDC. These databases are available on-demand to participants--this allows for rapid comparison of the patterns.

The PulseNet analysis enabled investigators to determine that there was likely to be one source of the contamination:

One initial clue came from laboratory testing that indicated that the serotype and pulsed-field gel electrophoresis (PFGE) pattern of Salmonella associated with the outbreak was rare. This rare pattern matched samples from the Alamosa drinking water and affected patients during the outbreak confirming drinking water as the source of exposure to Salmonella. According to data from the CDC national reporting database, PulseNet, before the outbreak this serotype and PFGE pattern had been identified 31 times in Colorado starting in 2000 when 12 cases were identified around the state. One of the 12 cases was a child from Alamosa whose source of infection was not identified. In the United States this serotype and PFGE pattern has been primarily reported from patients in Colorado, Wyoming and Texas. Seven non-human specimens were identified in a national database during the period 2005-2008 from Wyoming and Oregon. Four were from birds, one a mule deer, one feline, and one unknown. This information confirms the likelihood of the particular strain of Salmonella existing in the natural environment in the western United States. This also indicates that there was likely a single source of contamination into Alamosa's water system, as opposed to multiple sources.

This CDC page describes and links to their 2001 paper in Emerging Infectious Diseases about the establishment of the PulseNet network (direct PDF link here).

I'm currently unable to find any of the original data on the analysis but hope that my colleague drdrA at Blue Lab Coats might be able to help us out. A PubMed search for Alamosa Salmonella returns only one relevant paper, a story on the investigation from the Journal of Environmental Health.

Other documents and some YouTube slide shows are available on the Alamosa Salmonella outbreak site at the Colorado Department of Public Health and Environment.

Well, over and out for now - I've got another bit of southern Colorado news later this weekend.