Flint Residents’ Hygienic Practices Did Not Place Them at Greater Risk of Contracting Shigella Than Surrounding Michigan Residents

The Flint, Michigan, water crisis, which unfolded as a consequence of the State of Michigan’s decision to switch to using the Flint River as the city’s drinking water source, presented multiple alarming health risks to the public. With multiple boil water advisories issued shortly after the switch in 2014, a Safe Drinking Water Act violation for elevated potentially carcinogenic disinfection byproducts (total trihalomethanes, TTHMs), dangerously high levels of lead and copper released into household drinking water owing to pipe corrosion (which resulted from an additional decision to not add anticorrosives to save money), elevated blood lead levels of children and adults across the city, and an outbreak of Legionella, Flint residents experienced an onslaught of disturbing news about the safety and reliability of their drinking water system. With the 2016 outbreak of Shigella in Genesee and Saginaw counties, Michigan, it prompts the question, was the Flint water system the source of the outbreak?

Alternatively, the Shigella outbreak also provided fodder for the narrative that Flint residents were confused, uneducated, and hysterical and thereby responsible for the crisis. In 2015, Brad Wurfel, spokesperson for the Department of Environmental Quality described Mona Hanna-Attisha’s investigation of blood lead levels of children treated at Hurley Medical Center in Flint as fomenting hysteria. Public forums held across the city, with scientific experts and public officials at the helm, dismissed the concerns of residents even as residents presented physical evidence from their homes that something was wrong with the water system. Residents were characterized as confused and reacting emotionally. Ultimately, residents were vindicated by the weight of evidence, and many scientific officials who had dismissed the concerns of residents backtracked on their earlier statements.

However, with the emergence of Shigella, a renewed narrative shifted the blame of the public health crisis to Flint residents. Genesee County’s environmental health supervisor, Jim Henry, told CNN in 2016 that Flint residents were afraid of the water system and had stopped bathing, instead using baby wipes to replace handwashing and personal hygiene. The story was picked up by the national media, and the pathogen’s fecal–oral route of transmission added to the stigmatization of Flint residents.

In this issue of AJPH, McClung et al. (p. 842) present a case–household analysis of 83 households, totaling 158 patients, in Saginaw and Genesee counties, where at least one person in the household was diagnosed between March 1 and October 30, 2016 as having contracted Shigella sonnei. The analysis supports the conclusion that neither of these assertions are true. The researchers used a multimethod approach, including household surveys, a genomic investigation, and a geospatial investigation, to ascertain the relationship between behaviors and cases, the relatedness of cases, and any degree of spatial clustering. The data of this analysis show that during the week preceding their illness, 66% of index cases (the first person in the home to become ill) came into contact with someone in diapers or someone who was known to have had diarrhea. The median age of all 158 patients was 10 years, 59% were African American, and 58% were female. The patients residing in Flint were not statistically different from the rest of the population from Genesee and Saginaw counties on any of these measures.

Importantly, although the results of the survey indicate that Flint residents did report changes in bathing, showering, and handwashing in response to the Flint water crisis, McClung et al. point out that secondary attack rates in households were the same across the cases. Countering the assertion that Flint residents were using baby wipes and hand sanitizer in lieu of bathing with water, none of the Flint patients reported that this was true for them. There was no statistically significant difference in the use of tap water for bathing or showering between the Flint and non-Flint patients. The results of this investigation offer no evidence to show that Flint residents’ efforts to reduce their risks from exposure to Flint municipal water resulted in compromised hygienic practices and an increased risk of contracting Shigella. The authors emphasize that the survey data support the conclusion that the water system was not the likely source of the outbreak because only four of the Flint houses used the Flint water for drinking, and the patients outside Flint did not have paths of travel that would put them in contact with water from the Flint system.

Through a genomic investigation of a random sample of 27 isolates from outbreak patients and 57 isolates from Michigan patients not known to be associated with the outbreak, the investigators found that all 27 outbreak isolates were contained within a single clade (genetic branch with a common ancestor). The analysis showed a high degree of diversity within the clade along with multiple smaller genetic clusters, suggesting diversity that evolves from the spread of the pathogen across the community from person to person. If the outbreak was the result of the contamination of a shared water source, the authors expected to see a high degree of relatedness across the isolates. The results of the genomic investigation point to the gradual spread of Shigella across the counties rather than broadly and acutely from a single contaminated water source. McClung et al. state that these findings are consistent with other outbreaks that were spread from person to person.

Although the genomic analysis does not point to a failure in the treatment system as the cause of Flint’s outbreak, the authors concede that there is the possibility that pipe failures further along in the distribution system could allow infiltration of sewage and subsequent exposure in the household plumbing. The Kulldorff Scan statistic uses a varying window size (of time and space) to check for clustering. The results of this analysis found no spatial or spatial–temporal clusters of cases in Flint. If a main break in a neighborhood allowed the intrusion of sewage into the drinking water distribution system, one would expect to find a statistically significant cluster in that neighborhood. Adequate residual chlorine levels across the city’s monitoring sites make it unlikely that Shigella would be able to survive in the water distribution system. Although McClung et al. were unable to test residual chlorine levels at the point of use (typically the kitchen sink), the authors point out that there was no concurrent outbreak of other chlorine-sensitive pathogens such as Escherichia coli or Salmonella, which would likely be present if there was an intrusion of sewage into household drinking water concurrent with insufficient residual chlorine levels.

McClung et al. underscore that the findings of their analysis indicate that the source of the outbreak was not the city of Flint’s drinking water distribution system. The reader should additionally take away from this article that the results do not provide evidence that Flint residents’ hygiene practices placed them at additional risk of contracting Shigella. These data suggest that the 2016 outbreak of Shigella in Saginaw and Genesee counties was no different from the outbreaks that affect roughly 500 000 people across the United States every year. At least from the data presented in this article, it would seem that the 2016 Shigella outbreak in Flint was a rather unfortunate coincidence compounding all the other challenges the community was facing at the time as a consequence of the water crisis.