TABLE. Environmental testing results of a Shiga toxin–producing Escherichia coli O157:H7 outbreak investigation — city A, Utah, July–August 2023.
| Site* | Grab water samples (MPN/100 mL) |
Dead-end ultrafiltration water samples |
||
|---|---|---|---|---|
| Total coliforms† | E. coli† | Microbial source tracking§ | E. coli O157:H7 | |
| Exposure site A |
<1 |
<1 |
Avian: detected |
Detected |
| Ruminant: ND | ||||
| Human: ND | ||||
| Exposure site C |
344.8 |
5.1 |
Avian: detected |
Detected |
| Ruminant: detected | ||||
| Human: ND | ||||
| Exposure site D |
866.4 |
8.5 |
Avian: detected |
Detected |
| Ruminant: ND | ||||
| Human: ND | ||||
| Exposure sites E and F |
5.2 |
<1 |
Avian: detected |
ND |
| Ruminant: ND | ||||
| Human: ND | ||||
| Exposure site G |
NC |
NC |
Avian: detected |
Detected |
| Ruminant: detected | ||||
| Human: detected | ||||
| Exposures site H |
686.7 |
3.1 |
Avian: detected |
ND |
| Ruminant: detected | ||||
| Human: ND | ||||
| Exposure site I |
<1 |
<1 |
Avian: detected |
Detected |
| Ruminant: detected | ||||
| Human: ND | ||||
| Exposure site J |
285.1 |
4.1 |
Avian: detected |
ND |
| Ruminant: detected | ||||
| Human: ND | ||||
| Exposure site K |
228.2 |
10.8 |
Avian: detected |
ND |
| Ruminant: detected | ||||
| Human: ND | ||||
| City A UPMIW reservoir |
Grab #1: 33.1 |
Grab #1: 2.0 |
Avian: detected |
ND |
| Grab #2: 613.1 |
Grab #2: 9.6 |
Ruminant: ND |
||
| Human: ND | ||||
| City A UPMIW reservoir sediment #1 |
NA |
NA |
Avian: detected |
ND |
| Ruminant: ND | ||||
| Human: ND | ||||
| City A UPMIW reservoir sediment #2 | NA | NA | Avian: detected |
Detected |
| Ruminant: ND | ||||
| Human: ND | ||||
Abbreviations: E. coli = Escherichia coli; MPN = most probable number; NA = not applicable; NC = not collected; ND = not detected; UPMIW = untreated, pressurized, municipal irrigation water.
* Exposure sites A–K were named based on the location of each ill person’s reported UPMIW exposure.
† Total coliforms and E. coli (fecal indicator bacteria) were measured using Environmental Protection Agency standard methods, IDEXX Colilert-18 or Enterolert, on 100-mL grab water samples paired with dead-end ultrafiltration water samples. Sediment was not tested for total coliforms and E. coli.
§ Microbial source tracking assays were conducted using methods described in https://journals.asm.org/doi/10.1128/aem.04137-13, https://academic.oup.com/jambio/article/108/3/974/6720002?login=true, and https://www.frontiersin.org/articles/10.3389/fsufs.2019.00124/full.
¶ Detection of E. coli O157:H7 in environmental samples was determined using methods from https://assets.publishing.service.gov.uk/media/5be99537ed915d6a203046fd/SCA_Blue_Book_236.pdf, https://assets.publishing.service.gov.uk/media/5be9964e40f0b667b363e25d/MoDWPart4-223MAYh.pdf, and https://pubmed.ncbi.nlm.nih.gov/19363065/.
** A grab water sample was not collected at exposure site G.