Since passage of the Safe Drinking Water Act and its amendments by EPA 
, community-wide drinking water outbreaks in the U.S. are rare 
. The Salmonella
outbreak that occurred in Alamosa, Colorado in 2008 was one of the largest drinking water-associated outbreaks reported in the U.S. since the 1993 Cryptosporidium
outbreak in Milwaukee, which sickened an estimated 400,000 people 
. The estimated economic impact of the Alamosa outbreak totaled over $2.6 million. An unanticipated consequence of the outbreak was the loss of trust in the public water system after the outbreak.
Despite our comprehensive approach, this outbreak cost estimate is lower than previous epidemiologic studies of outbreaks in public water systems, perhaps due to our conservative methodological approach and the differences in the size of the affected population or duration of the outbreak. Harrington et al. estimated the economic impact of a 1984 waterborne outbreak of giardiasis in a Pennsylvania county at $18.2–133.3 million (in 2008 dollars) and did not include the cost of the outbreak response or the impact on local businesses 
. The outbreak occurred in a community of 25,000 households, resulted in 370 cases of giardiasis and a boil water advisory that lasted at least 99 days (270 days for half of those affected). Corso et al. estimated that the massive 1993 cryptosporidiosis outbreak in Milwaukee, Wisconsin (population ~ 1.6 million) affecting 403,000 individuals cost an estimated $143.4 million (in 2008 dollars) in direct healthcare expenditures and productivity losses 
; the cost of using an alternate water source during the outbreak, costs to local businesses, and the cost of the outbreak response were not included. Despite these differences, the limited number of cost analyses for waterborne outbreaks underscores the need to conduct these analyses for future outbreak investigations and the utility of including longer follow-up investigations to capture long-term costs.
In our assessment, 31% of households and 21% of survey respondents became ill during the outbreak. Approximately one-third of those who became sick reported a potential long-term health consequence following their diarrheal illness and, of those, 26% were still experiencing symptoms 18 months after the outbreak. Because all symptoms were based on self-report, and may have been coincidental to, rather than caused by the Salmonella
outbreak, we included only symptoms that began within 30 days of diarrheal illness. In addition, similar frequencies of post-Salmonella
infection joint pain 
and other symptoms 
have been observed in previous studies, including a Canadian study that found that such symptoms can persist for three years post-infection 
. Although they were rare, we also found that 2% of cases experienced a more serious complication of infection such as bowel perforation, peritonitis, septic arthritis, or endocarditis, complications from Salmonella
infection that have been reported elsewhere 
. Unfortunately, we were unable to estimate the direct and indirect costs associated with these long-term sequelae. However, the time and costs associated with these are likely to have been substantial. For instance, patients with arthritis and other rheumatologic conditions had average annual medical care expenditures of $1,891 and earned $1,590 less than individuals without these conditions in 2003 
. Additionally, urinary tract infections cost an estimated $1.6 billion per year in 1994 in direct and indirect costs 
Over 90% of households reported that municipal water was their main drinking water source at home prior to the outbreak. After the outbreak, 38% of respondents mainly drank bottled water and only 30% of households continued to primarily drink tap water; an additional 15% purchased a new filter or filtration system. The purchase of bottled water and installation and maintenance of filters cost City of Alamosa residents approximately $273,000 during the outbreak. Almost half (45%) of survey respondents cited safety concerns as a reason for switching from tap to bottled water. This lack of trust was also apparent in survey participants’ comments, such as: “I will never again fully trust the system or drink any tap water without some concern…” and “I still don’t feel safe drinking or cooking with the city water… I have spent a lot of money buying bottled water.”
The economic impact of the outbreak on the sample of businesses was one of the largest expenses, totaling $626,000 and accounting for 24% of the total outbreak costs. Approximately half of businesses that responded indicated that they lost money and approximately one-third had to close temporarily during the outbreak. Only 60% reported ever returning to pre-outbreak financial levels, including one that noted that “it took 2–3 months to get back to previous levels.” Because the survey was sent 18 months after the outbreak, it could have failed to reach businesses that might have been forced to close because of the outbreak. Household survey responses corroborated this; one respondent noted that “we couldn’t pay our mortgage [and] lost our restaurant. We now both work for someone else for not as much pay. We had our restaurant for 25 years.”
This assessment was subject to several limitations. First, our outbreak cost estimate is likely an underestimate. It does not include health care costs for individuals who sought care outside of Alamosa (either because some ill individuals may not have responded to the survey or because we were only able to obtain hospital-associated costs from one local hospital). We also were unable to assign an estimate for the one death associated with the outbreak. Alamosa is the geographic and commercial center of the San Luis Valley, and many people from surrounding areas work and dine in Alamosa but the survey did not capture business-related costs or health impact for people who live outside of Alamosa or for businesses that either did not receive a survey or did not respond. Additionally, outbreak response costs incurred by the federal government and by local organizations or municipalities outside the City of Alamosa that contributed to the outbreak response are likely incomplete. Household survey respondents also mentioned various costs not covered in the questionnaire, such as the cost of gas, disposable plates/utensils, or pet care associated with the outbreak. Additionally, direct and indirect costs associated with the long-term health consequences of Salmonella infection were not assessed. Outbreak-associated costs were also limited to those incurred during the outbreak, even though it is likely that many costs have been incurred since the outbreak.
Second, we assumed that the survey respondents were a representative sample of the City of Alamosa population, yet our survey respondents differed by age, sex, ethnicity, and socioeconomic status 
. In addition, our survey was conducted 18 months after the outbreak, and persons who responded to the survey may have been more likely to be sick during the outbreak and therefore to respond to the survey, although the attack rate estimated from our household survey is similar to the estimate found in a survey of Alamosa residents immediately after the outbreak (CDPHE, unpublished data). Third, our indirect cost estimates were based on assumptions (see Supporting Information in File S1 for details) about the value of caretakers’ and ill people’s time. However, the wages reported in our survey were similar to that reported for the Colorado non-Metropolitan Statistical Area that includes Alamosa 
. Finally, our relatively low response rate (~ 30%), although similar to that of other mailed surveys 
, may mean that the results of the household and business surveys are not reflective of the experiences of all City of Alamosa households and businesses.
The likely source of the outbreak was determined to be animal contamination of a storage tank that had numerous cracks and entry points 
. This outbreak highlights the critical importance of robust inspection of public drinking water storage facilities, identification of system deficiencies during required sanitary surveys, and maintaining staffing and resources for adequate follow-up for any deficiencies identified. Although it is now being chlorinated, the City of Alamosa’s water prior to the outbreak was derived from an unchlorinated ground water source. The recently promulgated Ground Water Rule (GWR) 
requires most community water systems to complete initial sanitary surveys by 2012. Once fully implemented, it should help reduce the risk for similar outbreaks in the future. Nevertheless, a deficiency in the distribution system (i.e., storage tank contamination) was the primary cause of this outbreak. Maintaining the integrity of the nation’s drinking water systems is a fundamental safeguard to protecting public health and preventing economic damage from waterborne disease outbreaks and should be a top public policy imperative.