The 2018-2019 FoodNet Population Survey: A tool to estimate risks and behaviors associated with enteric infections.

The FoodNet Population Survey is a periodic survey of randomly selected residents in 10 US sites on exposures and behaviors that may be associated with acute diarrheal infections and the health care sought for those infections. This survey is used to estimate the true disease burden of enteric illness in the United States and to estimate rates of exposure to potential sources of illness. Unlike previous FoodNet Population Surveys, this cycle used multiple sampling frames and administration modes, including cell phone and web-based questionnaires, that allowed for additional question topics and a larger sample size. It also oversampled children to increase representation of this population. Analytic modeling adjusted for mode effects when estimating the prevalence estimates of exposures and behaviors. This report describes the design, methodology, challenges, and descriptive results from the 2018-19 FoodNet Population Survey.

Observed face mask use outside retail chain stores during the COVID-19 pandemic in two cities in the state of Idaho, USA.

During the COVID-19 pandemic, public health authorities have encouraged the use of face masks to minimize transmission within the community. To assess mask wear during a COVID-19 surge and guide public health response efforts, including public messaging on mask recommendations, we compared observed mask use in the largest city in each of Idaho's 2 most populous counties, both without a current mask mandate. We recorded mask usage by every third person exiting stores of 5 retail chains in Boise and Nampa during November 8-December 5, 2021. Observations were conducted during three time periods (morning, afternoon, and evening) on weekday and weekend days. A multivariable model with city, retail chain, and city-chain interaction was used to assess mask wear differences by city for each chain. Of 3021 observed persons, 22.0% wore masks. In Boise, 31.3% (430/1376) of observed persons wore masks; in Nampa, 14.3% (236/1645) wore masks. Among all persons wearing masks, > 94% wore masks correctly; cloth and surgical masks were most common. By retail chain, observed individuals at Boise locations were 2.3-5.7 times as likely to wear masks than persons at respective Nampa locations. This study provided a rapid, nonconfrontational assessment of public use of mitigation measures in 2 Idaho cities during a COVID-19 surge.

Evaluation of SaTo pans as a new latrine technology in Kisumu County healthcare facilities, Kenya.

OBJECTIVES: Innovations to improve public sanitation facilities, especially in healthcare facilities (HCFs) in low-income countries, are limited. SaTo pans represent novel, largely untested, modifications to reduce odour and flies and improve acceptability of HCF sanitation facilities. We conducted a pilot project to evaluate acceptability, cleanliness, flies and odour within latrines in 37 HCFs in Kisumu, Kenya, randomised into intervention (SaTo pan modifications) and control arms by sub-county and HCF level. METHODS: At baseline (pre-intervention) and endline (>3 months after completion of SaTo pan installations in latrines in intervention HCFs), we surveyed users, cleaners and in-charges, observed odour and cleanliness, and assessed flies using fly tape. Unadjusted difference-in-difference analysis compared changes from baseline to endline in patient-reported acceptability and observed latrine conditions between intervention and control HCFs. A secondary assessment compared patient-reported acceptability following use of SaTo pan versus non-SaTo pan latrines within intervention HCFs. RESULTS: Patient-reported acceptability of latrines was higher following the intervention (baseline: 87%, endline: 96%, p = 0.05). However, patient-reported acceptability was also high in the control arm (79%, 86%, p = 0.34), and the between-arm difference-in-difference was not significant. Enumerator-observed odour declined in intervention latrines (32%-14%) compared with controls (36%-51%, difference-in-difference ratio: 0.32, 95% confidence interval: 0.12-0.84), but changes in flies, puddling of urine and visible faeces did not differ between arms. In the secondary assessment, fewer intervention than control latrines had patient-reported flies (0% vs. 26%) and odour (18% vs. 50%), and reported satisfaction was greater. Most cleaners reported dropholes and floors were easier to clean in intervention versus controls; limited challenges with water for flushing were reported. CONCLUSIONS: Our results suggest SaTo pans may be acceptable by cleaners and users and reduce odour in HCF sanitation facilities, though challenges exist and further evaluation with larger sample sizes is needed.

Multistate reptile- and amphibian-associated salmonellosis outbreaks in humans, United States, 2009-2018.

Non-typhoidal Salmonella cause an estimated 1.4 million human illnesses, 26,000 hospitalizations and 400 deaths annually in the United States. Approximately 11% of these infections are attributed to animal contact. Reptiles and amphibians are known sources of salmonellosis; young children (aged <5 years) are disproportionately affected by reptile- and amphibian-associated salmonellosis (RAAS) outbreaks. We describe multistate RAAS outbreaks to characterize illnesses and inform prevention efforts. RAAS outbreaks were defined as ≥2 culture-confirmed human Salmonella infections with similar pulsed-field gel electrophoresis patterns and epidemiologic, laboratory or traceback evidence linking them to a common reptile/amphibian exposure. Data sources included the Animal Contact Outbreak Surveillance System; CDC Outbreak Response and Prevention Branch's outbreak management database; PulseNet, the national molecular subtyping network for foodborne disease surveillance in the United States; and the National Antimicrobial Resistance Monitoring System. Twenty-six RAAS outbreaks were reported during 2009-2018, resulting in 1465 illnesses and 306 hospitalizations. The outbreaks were associated with turtles (19), lizards (5), snakes (1) and frogs (1). Sixteen (61.5%) outbreaks were linked to small turtles (<4 inches), resulting in 914 illnesses. Forty-nine percent of outbreak-associated patients were aged <5 years. Of 362 patients/caregivers interviewed, 111 (30.7%) were aware that reptiles/amphibians can carry Salmonella. Among 267 patient isolates with antimicrobial susceptibility information, 20 (7.5%) were non-susceptible to ≥1 antibiotic used to treat human salmonellosis. RAAS outbreaks result in considerable morbidity, particularly among young children. Illnesses linked to small turtles are preventable through education, targeted outreach to caregivers and paediatricians, and when appropriate, enforcement. Historically, individual states and jurisdictions have enforced existing or promulgated new authorities to address outbreaks. Preventing future RAAS outbreaks requires addressing challenges related to the illegal sale/distribution of small turtles; and for legal reptile sales, providing information on RAAS risk to consumers at point of sale to support informed pet ownership decisions.

Increasing Incidence of Invasive Group A Streptococcus Disease, Idaho, USA, 2008-2019.

We investigated invasive group A Streptococcus epidemiology in Idaho, USA, during 2008-2019 using surveillance data, medical record review, and emm (M protein gene) typing results. Incidence increased from 1.04 to 4.76 cases/100,000 persons during 2008-2019. emm 1, 12, 28, 11, and 4 were the most common types, and 2 outbreaks were identified. We examined changes in distribution of clinical syndrome, patient demographics, and risk factors by comparing 2008-2013 baseline with 2014-2019 data. Incidence was higher among all age groups during 2014-2019. Streptococcal toxic shock syndrome increased from 0% to 6.4% of cases (p = 0.02). We identified no differences in distribution of demographic or risk factors between periods. Results indicated that invasive group A Streptococcus is increasing among the general population of Idaho. Ongoing surveillance of state-level invasive group A Streptococcus cases could help identify outbreaks, track regional trends in incidence, and monitor circulating emm types.

Pediatric Medicaid Visits for Soil-Transmitted Helminth Infections in the Black Belt Region-Alabama, 2010-2018.

Areas of rural Alabama may be at risk for re-emergence of soil-transmitted helminthiasis (STH) where environmental conditions are favorable for STH transmission, including in the agricultural Black Belt region. We describe pediatric Medicaid STH visits in Alabama and compare STH visit rates in Black Belt counties with those of non-Black Belt counties. Alabama Medicaid visit claims among children aged 0-18 years who received an STH diagnosis during January 2010-December 2018 were examined. STH-related pediatric visits were uncommon, but several counties with higher STH rates were identified. Visit rates did not differ meaningfully when comparing Black Belt with non-Black Belt region counties (rate ratio: 1.10; 95% CI: 0.73-1.64). Additional studies examining STH prevalence among children living in communities at risk for STH in Alabama can further clarify STH burden and identify communities experiencing environmental and sanitation conditions favorable to STH endemicity.

Agritourism and Kidding Season: A Large Outbreak of Human Shiga Toxin-Producing Escherichia coli O157 (STEC O157) Infections Linked to a Goat Dairy Farm-Connecticut, 2016.

The objective of this study was to determine sources of Shiga toxin-producing Escherichia coli O157 (STEC O157) infection among visitors to Farm X and develop public health recommendations. A case-control study was conducted. Case-patients were defined as the first ill child (aged <18 years) in the household with laboratory-confirmed STEC O157, or physician-diagnosed hemolytic uremic syndrome with laboratory confirmation by serology, who visited Farm X in the 10 days prior to illness. Controls were selected from Farm X visitors aged <18 years, without symptoms during the same time period as case-patients. Environment and animal fecal samples collected from Farm X were cultured; isolates from Farm X were compared with patient isolates using whole genome sequencing (WGS). Case-patients were more likely than controls to have sat on hay bales at the doe barn (adjusted odds ratio: 4.55; 95% confidence interval: 1.41-16.13). No handwashing stations were available; limited hand sanitizer was provided. Overall, 37% (29 of 78) of animal and environmental samples collected were positive for STEC; of these, 62% (18 of 29) yielded STEC O157 highly related by WGS to patient isolates. STEC O157 environmental contamination and fecal shedding by goats at Farm X was extensive. Farms should provide handwashing stations with soap, running water, and disposable towels. Access to animal areas, including animal pens and enclosures, should be limited for young children who are at risk for severe outcomes from STEC O157 infection. National recommendations should be adopted to reduce disease transmission.

Trends in Racial and Ethnic Disparities in COVID-19 Hospitalizations, by Region - United States, March-December 2020.

Persons from racial and ethnic minority groups are disproportionately affected by COVID-19, including experiencing increased risk for infection (1), hospitalization (2,3), and death (4,5). Using administrative discharge data, CDC assessed monthly trends in the proportion of hospitalized patients with COVID-19 among racial and ethnic groups in the United States during March-December 2020 by U.S. Census region. Cumulative and monthly age-adjusted COVID-19 proportionate hospitalization ratios (aPHRs) were calculated for racial and ethnic minority patients relative to non-Hispanic White patients. Within each of the four U.S. Census regions, the cumulative aPHR was highest for Hispanic or Latino patients (range = 2.7-3.9). Racial and ethnic disparities in COVID-19 hospitalization were largest during May-July 2020; the peak monthly aPHR among Hispanic or Latino patients was >9.0 in the West and Midwest, >6.0 in the South, and >3.0 in the Northeast. The aPHRs declined for most racial and ethnic groups during July-November 2020 but increased for some racial and ethnic groups in some regions during December. Disparities in COVID-19 hospitalization by race/ethnicity varied by region and became less pronounced over the course of the pandemic, as COVID-19 hospitalizations increased among non-Hispanic White persons. Identification of specific social determinants of health that contribute to geographic and temporal differences in racial and ethnic disparities at the local level can help guide tailored public health prevention strategies and equitable allocation of resources, including COVID-19 vaccination, to address COVID-19-related health disparities and can inform approaches to achieve greater health equity during future public health threats.

Impact Of Supply- and Demand-Side Interventions Integrated with Antenatal Care on Use of Maternal Health Services-Western Kenya, 2013‒2014.

We evaluated whether antenatal supply-side and demand-side interventions in 10 public health care facilities (HCFs) increased the percentage of women who had four or more antenatal care (ANC4+) visits and HCF deliveries from baseline to follow-up compared with women in 10 public control HCFs in Kenya. We compared maternal registry data during baseline and follow-up periods between public intervention and public control HCFs; we added seven private intervention HCFs and five private control HCFs to evaluate an unanticipated pilot insurance program that enabled women to use private intervention HCFs. From baseline to follow-up, ANC4+ visits and HCF deliveries in public intervention HCFs were 1.64 and 1.19 times greater, respectively, than in public control HCFs. Health care facility deliveries were 1.5 times higher in private intervention HCFs than public intervention HCFs. Results suggested that the combined antenatal and insurance interventions motivated increased ANC4+ visits and HCF deliveries. Women appeared to prefer private HCFs for delivery.

Estimate of Burden and Direct Healthcare Cost of Infectious Waterborne Disease in the United States.

Provision of safe drinking water in the United States is a great public health achievement. However, new waterborne disease challenges have emerged (e.g., aging infrastructure, chlorine-tolerant and biofilm-related pathogens, increased recreational water use). Comprehensive estimates of the health burden for all water exposure routes (ingestion, contact, inhalation) and sources (drinking, recreational, environmental) are needed. We estimated total illnesses, emergency department (ED) visits, hospitalizations, deaths, and direct healthcare costs for 17 waterborne infectious diseases. About 7.15 million waterborne illnesses occur annually (95% credible interval [CrI] 3.88 million-12.0 million), results in 601,000 ED visits (95% CrI 364,000-866,000), 118,000 hospitalizations (95% CrI 86,800-150,000), and 6,630 deaths (95% CrI 4,520-8,870) and incurring US $3.33 billion (95% CrI 1.37 billion-8.77 billion) in direct healthcare costs. Otitis externa and norovirus infection were the most common illnesses. Most hospitalizations and deaths were caused by biofilm-associated pathogens (nontuberculous mycobacteria, Pseudomonas, Legionella), costing US $2.39 billion annually.

Geographic Range of Recreational Water-Associated Primary Amebic Meningoencephalitis, United States, 1978-2018.

Naegleria fowleri is a free-living ameba that causes primary amebic meningoencephalitis (PAM), a rare but usually fatal disease. We analyzed trends in recreational water exposures associated with PAM cases reported during 1978-2018 in the United States. Although PAM incidence remained stable, the geographic range of exposure locations expanded northward.

Estimating the Incubation Period of Salmonella Urinary Tract Infections Using Foodborne Outbreak Data.

Urinary tract infections (UTIs) are common and may occur in foodborne Salmonella outbreaks. Using data from PulseNet, the U.S. national molecular subtyping network for foodborne disease surveillance, we analyzed the 9781 Salmonella isolates associated with the 110 outbreaks from 2004 to 2013 that included at least one urine isolate. Within each outbreak, we calculated standardized isolation dates, using these dates in a linear mixed model to estimate the difference in incubation period for infections yielding stool versus urine isolates. We estimate that the incubation period for Salmonella UTIs is on average 10.6 (95% confidence interval 6.0-15.2) days longer than for gastrointestinal illness, suggesting that outbreak investigators should interview UTI patients about a longer time period before illness onset to identify sources of infection.

Risk Factors for Epidemic Cholera in Lusaka, Zambia-2017.

On October 6, 2017, the Zambia Ministry of Health declared a cholera outbreak in Lusaka. By December, 1,462 cases and 38 deaths had occurred (case fatality rate, 2.6%). We conducted a case-control study to identify risk factors and inform interventions. A case was any person with acute watery diarrhea (≥ 3 loose stools in 24 hours) admitted to a cholera treatment center in Lusaka from December 16 to 21, 2017. Controls were neighbors without diarrhea during the same time period. Up to two controls were matched to each case by age-group (1-4, 5-17, and ≥ 18 years) and neighborhood. Surveyors interviewed cases and controls, tested free chlorine residual (FCR) in stored water, and observed the presence of soap in the home. Conditional logistic regression was used to generate matched odds ratios (mORs) based on subdistricts and age-groups with 95% CIs. We enrolled 82 cases and 132 controls. Stored water in 71% of case homes had an FCR > 0.2 mg/L. In multivariable analyses, those who drank borehole water (mOR = 2.4, CI: 1.1-5.6), had close contact with a cholera case (mOR = 6.2, CI: 2.5-15), and were male (mOR = 2.5, CI: 1.4-5.0) had higher odds of being a cholera case than their matched controls. Based on these findings, we recommended health education about household water chlorination and hygiene in the home. Emergency responses included providing chlorinated water through emergency tanks and maintaining adequate FCR levels through close monitoring of water sources.

A Tale of Two Healthcare-associated Infections: Clostridium difficile Coinfection Among Patients With Candidemia.

Candidemia and Clostridium difficile infection (CDI) are important healthcare-associated infections that share certain risk factors. We sought to describe candidemia-CDI coinfection using population-based surveillance data. We found that nearly 1 in 10 patients with candidemia had CDI coinfection.

Association of water quality with soil-transmitted helminthiasis and diarrhea in Nueva Santa Rosa, Guatemala, 2010.

Improved water quality reduces diarrhea, but the impact of improved water quality on Ascaris and Trichuris, soil-transmitted helminths (STH) conveyed by the fecal-oral route, is less well described. To assess water quality associations with diarrhea and STH, we conducted a cross-sectional survey in households of south-eastern Guatemala. Diarrhea was self-reported in the past week and month. STH was diagnosed by stool testing using a fecal parasite concentrator method. We explored associations between Escherichia coli-positive source water (water quality) and disease outcomes using survey logistic regression models. Overall, 732 persons lived in 167 households where water was tested. Of these, 79.4% (581/732) had E. coli-positive water, 7.9% (58/732) had diarrhea within the week, 14.1% (103/732) had diarrhea within the month, and 6.6% (36/545) tested positive for Ascaris or Trichuris, including 1% (6/536) who also reported diarrhea. Univariable analysis found a statistically significant association between water quality and STH (odds ratio [OR] = 5.1, 95% confidence interval [CI] = 1.1-24.5) but no association between water quality and diarrhea. Waterborne transmission and effects of water treatment on STH prevalence should be investigated further. If a causal relationship is found, practices such as household water treatment including filtration might be useful adjuncts to sanitation, hygiene, and deworming in STH control programs.

Water, Sanitation, and Hygiene Characteristics among HIV-Positive Households Participating in the Global Enteric Multicenter Study in Rural Western Kenya, 2008-2012.

Diarrheal illness, a common occurrence among people living with human immunodeficiency virus (PLHIV), is largely preventable through access to safe drinking water quality, sanitation, and hygiene (WASH) facilities. We examined WASH characteristics among households with and without HIV-positive residents enrolled in the Global Enteric Multicenter Study (GEMS) in rural Western Kenya. Using univariable logistic regression, we examined differences between HIV-positive and HIV-negative households in regard to WASH practices. Among HIV-positive households, we explored the relationship between the length of time knowing their HIV status and GEMS enrollment. No statistically significant differences were apparent in the WASH characteristics among HIV-positive and HIV-negative households. However, we found differences in the WASH characteristics among HIV-positive households who were aware of their HIV status ≥ 30 days before enrollment compared with HIV-positive households who found out their status < 30 days before enrollment or thereafter. Significantly more households aware of their HIV-positive status before enrollment reported treating their drinking water (odds ratio [OR] confidence interval [CI]: 2.34 [1.12, 4.86]) and using effective water treatment methods (OR [CI]: 9.6 [3.09, 29.86]), and had better drinking water storage practices. This suggests that within this region of Kenya, HIV programs are effective in promoting the importance of practicing positive WASH-related behaviors among PLHIV.

Clinical, environmental, and behavioral characteristics associated with Cryptosporidium infection among children with moderate-to-severe diarrhea in rural western Kenya, 2008-2012: The Global Enteric Multicenter Study (GEMS).

BACKGROUND: Cryptosporidium is a leading cause of moderate-to-severe diarrhea (MSD) in young children in Africa. We examined factors associated with Cryptosporidium infection in MSD cases enrolled at the rural western Kenya Global Enteric Multicenter Study (GEMS) site from 2008-2012. METHODOLOGY/PRINCIPAL FINDINGS: At health facility enrollment, stool samples were tested for enteric pathogens and data on clinical, environmental, and behavioral characteristics collected. Each child's health status was recorded at 60-day follow-up. Data were analyzed using logistic regression. Of the 1,778 children with MSD enrolled as cases in the GEMS-Kenya case-control study, 11% had Cryptosporidium detected in stool by enzyme immunoassay; in a genotyped subset, 81% were C. hominis. Among MSD cases, being an infant, having mucus in stool, and having prolonged/persistent duration diarrhea were associated with being Cryptosporidium-positive. Both boiling drinking water and using rainwater as the main drinking water source were protective factors for being Cryptosporidium-positive. At follow-up, Cryptosporidium-positive cases had increased odds of being stunted (adjusted odds ratio [aOR] = 1.65, 95% CI: 1.06-2.57), underweight (aOR = 2.08, 95% CI: 1.34-3.22), or wasted (aOR = 2.04, 95% CI: 1.21-3.43), and had significantly larger negative changes in height- and weight-for-age z-scores from enrollment. CONCLUSIONS/SIGNIFICANCE: Cryptosporidium contributes significantly to diarrheal illness in young children in western Kenya. Advances in point of care detection, prevention/control approaches, effective water treatment technologies, and clinical management options for children with cryptosporidiosis are needed.

Cholera Epidemic - Lusaka, Zambia, October 2017-May 2018.

On October 6, 2017, an outbreak of cholera was declared in Zambia after laboratory confirmation of Vibrio cholerae O1, biotype El Tor, serotype Ogawa, from stool specimens from two patients with acute watery diarrhea. The two patients had gone to a clinic in Lusaka, the capital city, on October 4. Cholera cases increased rapidly, from several hundred cases in early December 2017 to approximately 2,000 by early January 2018 (Figure). In collaboration with partners, the Zambia Ministry of Health (MoH) launched a multifaceted public health response that included increased chlorination of the Lusaka municipal water supply, provision of emergency water supplies, water quality monitoring and testing, enhanced surveillance, epidemiologic investigations, a cholera vaccination campaign, aggressive case management and health care worker training, and laboratory testing of clinical samples. In late December 2017, a number of water-related preventive actions were initiated, including increasing chlorine levels throughout the city's water distribution system and placing emergency tanks of chlorinated water in the most affected neighborhoods; cholera cases declined sharply in January 2018. During January 10-February 14, 2018, approximately 2 million doses of oral cholera vaccine were administered to Lusaka residents aged ≥1 year. However, in mid-March, heavy flooding and widespread water shortages occurred, leading to a resurgence of cholera. As of May 12, 2018, the outbreak had affected seven of the 10 provinces in Zambia, with 5,905 suspected cases and a case fatality rate (CFR) of 1.9%. Among the suspected cases, 5,414 (91.7%), including 98 deaths (CFR = 1.8%), occurred in Lusaka residents.

Association of maternal KIR gene content polymorphisms with reduction in perinatal transmission of HIV-1.

The role of killer cell immunoglobulin-like receptors (KIRs) in the transmission of HIV-1 has not been extensively studied. Here, we investigated the association of KIR gene content polymorphisms with perinatal HIV-1 transmission. The KIR gene family comprising 16 genes was genotyped in 313 HIV-1 positive Kenyan mothers paired with their infants. Gene content polymorphisms were presented as presence of individual KIR genes, haplotypes, genotypes and KIR gene concordance. The genetic data were analyzed for associations with perinatal transmission of HIV. There was no association of infant KIR genes with perinatal HIV-1 transmission. After adjustment for gravidity, viral load, and CD4 cell count, there was evidence of an association between reduction in perinatal HIV-1 transmission and the maternal individual KIR genes KIR2DL2 (adjusted OR = 0.50; 95% CI: 0.24-1.02, P = 0.06), KIR2DL5 (adjusted OR = 0.47; 95% CI: 0.23-0.95, P = 0.04) and KIR2DS5 (adjusted OR = 0.39; 95% CI: 0.18-0.80, P = 0.01). Furthermore, these maternal KIR genes were only significantly associated with reduction in perinatal HIV transmission in women with CD4 cell count ≥ 350 cells/ µl and viral load <10000 copies/ml. Concordance analysis showed that when both mother and child had KIR2DS2, there was less likelihood of perinatal HIV-1 transmission (adjusted OR = 0.44; 95% CI: 0.20-0.96, P = 0.039). In conclusion, the maternal KIR genes KIR2DL2, KIR2DL5, KIR2DS5, and KIR2DS2 were associated with reduction of HIV-1 transmission from mother to child. Furthermore, maternal immune status is an important factor in the association of KIR with perinatal HIV transmission.

Shiga Toxin-Producing E. coli Infections Associated with Flour.

BACKGROUND: In 2016, a multijurisdictional team investigated an outbreak of Shiga toxin-producing Escherichia coli (STEC) serogroup O121 and O26 infections linked to contaminated flour from a large domestic producer. METHODS: A case was defined as infection with an outbreak strain in which illness onset was between December 21, 2015, and September 5, 2016. To identify exposures associated with the outbreak, outbreak cases were compared with non-STEC enteric illness cases, matched according to age group, sex, and state of residence. Products suspected to be related to the outbreak were collected for STEC testing, and a common point of contamination was sought. Whole-genome sequencing was performed on isolates from clinical and food samples. RESULTS: A total of 56 cases were identified in 24 states. Univariable exact conditional logistic-regression models of 22 matched sets showed that infection was significantly associated with the use of one brand of flour (odds ratio, 21.04; 95% confidence interval [CI], 4.69 to 94.37) and with tasting unbaked homemade dough or batter (odds ratio, 36.02; 95% CI, 4.63 to 280.17). Laboratory testing isolated the outbreak strains from flour samples, and whole-genome sequencing revealed that the isolates from clinical and food samples were closely related to one another genetically. Trace-back investigation identified a common flour-production facility. CONCLUSIONS: This investigation implicated raw flour as the source of an outbreak of STEC infections. Although it is a low-moisture food, raw flour can be a vehicle for foodborne pathogens.