To examine trends in US drinking water outbreaks from 1920 to 2020, we evaluated US drinking water outbreaks documented in the National Outbreak Reporting System and from 4 historic publications dating back to 1920. Before the drinking water regulations of the 1970s, enteric pathogens were the most reported (n = 393; 52%) etiologies. Most outbreaks occurred in individual or private water systems (n = 245; 32%). After major regulations, biofilm-associated outbreaks emerged (n = 343; 32%), and most outbreaks (n = 600; 55%) occurred in community water systems. Biofilm-associated pathogens are an emerging concern in water systems. These findings highlight the importance of drinking water regulations, routine inspections of private wells, and building water management programs. Waterborne disease outbreak investigations and reporting to surveillance systems are essential to identifying factors contributing to outbreaks that can be addressed to improve drinking water policy, practices, and public understanding. As pathogens, drinking water distribution systems, and environmental factors change, identifying etiologic agents and contributing factors in waterborne outbreaks can guide future drinking water policies. (Am J Public Health. 2026;116(9): 1387-1396. https://doi.org/10.2105/AJPH.2026.308475).

BACKGROUND:Low pressure events (LPEs), defined as a water service disruption that presumably lowers system water pressure, can cause drinking water contamination, resulting in increased illness risk to consumers. OBJECTIVES:This study sought to examine whether LPEs increase the risk for highly credible acute gastrointestinal illness (HCGI) and acute respiratory illness (ARI) and to compare water quality in exposed and unexposed areas in the United States. METHODS:A matched cohort study was conducted during the period 2015-2019. For each LPE, household survey exposed areas were matched 1:2 with unexposed areas based on water-main size and material at the point of repair, as well as the housing type and demographic characteristics of the local population from the most recent census tract data. Water samples were collected to monitor physicochemical and microbiological water quality parameters. Households (HHs) were surveyed about water use and illness during the 2 wk after the LPE. Multivariable log-binomial models clustered on utility and LPE number were used to investigate associations between LPE exposure and HCGI and ARI. RESULTS:Five water utilities reported 58 LPEs, including planned maintenance (76%) and emergency (24%) events. Controlling for livestock near home, private well presence, number of people in HH, and travel away from home, exposed HHs were at higher risk of HCGI in comparison with unexposed HHs (risk ratio=1.20; 95% confidence interval: 1.05, 1.37). No associations between LPE and ARI were detected. Certain LPEs characteristics like pipe material, size, and depth were associated with an increased HH HCGI risk. HHs experiencing LPEs where low disinfectant residual, high adenosine triphosphate, or general Bacteroidales were detected in water following an LPE repair were also at a higher risk for HCGI. CONCLUSIONS:LPEs were associated with 20% higher risk of HCGI in HHs. Planned improvements to water distribution system infrastructure, adherence to industry standard distribution repair practices, and water monitoring following pipe repairs could supplement community alert systems to reduce illnesses from LPEs. https://doi.org/10.1289/EHP15564.

IntroductionFreshwater sources (eg, lakes, ponds, rivers, or streams) can be contaminated by pathogens. Ingesting water from these sources can cause illness if the water is insufficiently treated.MethodThe Waterborne Disease and Outbreak Surveillance System (WBDOSS) collects data on waterborne disease outbreaks associated with drinking water, recreational water, other nonrecreational water, and undetermined exposures to water. We analyzed outbreaks reported to WBDOSS that involved ingesting water from freshwater sources in outdoor settings.ResultFrom 2000 through 2022, public health officials in 16 jurisdictions reported 32 outbreaks associated with ingesting water from insufficiently treated freshwater sources. These outbreaks resulted in 437 illnesses, 4 hospitalizations, and no reported deaths. Giardia was implicated in 69% of outbreaks, and Campylobacter was implicated in 28% of total cases. Water from rivers or streams was implicated in 75% of outbreaks. In half the reported outbreaks, water treatment was not attempted. Individuals were primarily exposed in outdoor recreational areas (eg, public outdoor areas, state parks, campgrounds), with most illnesses occurring in those aged 10-19 years.ConclusionThis is the first summary dedicated to outbreaks associated with ingesting freshwater. These outbreaks can be mitigated using potable water sources, when available, or appropriate water treatment. Public health and provider efforts could include engaging the public-especially those who spend time in the backcountry-regarding health risks and encouraging hygiene, safe disposal of feces, and recommended water treatment methods. Healthcare providers should be encouraged to ask individuals about potential exposure to water from outdoor freshwater sources when presenting with gastrointestinal illness.

As part of the response to the highly pathogenic avian influenza A(H5N1) virus outbreak in U.S. cattle and poultry and the associated human cases, CDC and partners are monitoring influenza A virus levels and detection of the H5 subtype in wastewater. Among 48 states and the District of Columbia that performed influenza A testing of wastewater during May 12-July 13, 2024, a weekly average of 309 sites in 38 states had sufficient data for analysis, and 11 sites in four states reported high levels of influenza A virus. H5 subtype testing was conducted at 203 sites in 41 states, with H5 detections at 24 sites in nine states. For each detection or high level, CDC and state and local health departments evaluated data from other influenza surveillance systems and partnered with wastewater utilities and agriculture departments to investigate potential sources. Among the four states with high influenza A virus levels detected in wastewater, three states had corresponding evidence of human influenza activity from other influenza surveillance systems. Among the 24 sites with H5 detections, 15 identified animal sources within the sewershed or adjacent county, including eight milk-processing inputs. Data from these early investigations can help health officials optimize the use of wastewater surveillance during the upcoming respiratory illness season.

Problem/Condition:Splash pads are recreational interactive water venues that spray or jet water on users. Splash pads are intended for children aged <5 years and designed so that water typically does not collect in areas accessible to users, thereby minimizing the risk for drowning. Splash pads were first found to be associated with waterborne disease outbreaks in 1997. Period Covered:1997-2022. Description of System:Since 1971, waterborne disease outbreaks have been voluntarily reported to CDC by state, local, and territorial health departments using a standard paper form via the Waterborne Disease and Outbreak Surveillance System (WBDOSS). Beginning in 2009, WBDOSS reporting was made available exclusively through the National Outbreak Reporting System, a web-based platform. This report characterizes waterborne disease outbreaks associated with splash pads reported to CDC that occurred during 1997-2022. Results:During 1997-2022, public health officials from 23 states and Puerto Rico reported 60 waterborne disease outbreaks associated with splash pads. These reported outbreaks resulted in 10,611 cases, 152 hospitalizations, 99 emergency department visits, and no reported deaths. The 40 (67%) outbreaks confirmed to be caused, in part, by Cryptosporidium resulted in 9,622 (91%) cases and 123 (81%) hospitalizations. Two outbreaks suspected to be caused by norovirus resulted in 72 (73%) emergency department visits. Interpretation:Waterborne pathogens that cause acute gastrointestinal illness can be transmitted by ingesting water contaminated with feces from infected persons. Chlorine is the primary barrier to pathogen transmission in splash pad water. However, Cryptosporidium is tolerant to chlorine and is the most common cause of reported waterborne disease outbreaks associated with splash pads. Public Health Action:Public health officials and the aquatics sector can use the findings in this report to promote the prevention of splash pad-associated outbreaks (e.g., recommended user behaviors) and guide the construction, operation, and management of splash pads. Public health practitioners and the aquatics sector also can collaborate to voluntarily adopt CDC's Model Aquatic Health Code recommendations to prevent waterborne illness associated with splash pads.

In September 2021, eight campylobacteriosis cases were identified in a town in Nebraska, USA. We assessed potential exposures for a case-control analysis. We conducted whole-genome sequencing on Campylobacter isolates from patients' stool specimens. We collected large-volume dead-end ultrafiltration water samples for Campylobacter and microbial source tracking testing at the Centers for Disease Control and Prevention. We identified 64 cases in 2 waves of illnesses. Untreated municipal tap water consumption was strongly associated with illness (wave 1 odds ratio 15.36; wave 2 odds ratio 16.11). Whole-genome sequencing of 12 isolates identified 2 distinct Campylobacter jejuni subtypes (1 subtype/wave). The town began water chlorination, after which water testing detected coliforms. One dead-end ultrafiltration sample yielded nonculturable Campylobacter and avian-specific fecal rRNA genomic material. Our investigation implicated contaminated, untreated, municipal water as the source. Results of microbial source tracking supported mitigation with continued water chlorination. No further campylobacteriosis cases attributable to water were reported.

Consumption of raw water (water that has not been disinfected or filtered) has become an emerging trend in the United States and could pose serious health consequences (1).Drinking water collected directly from outdoor freshwater sources such as lakes, rivers, and streams that has not been adequately treated (i.e., to remove pathogens) can cause disease and outbreaks (2).This report describes how a community in Western Montana responded to an outbreak of 19 cases of diarrheal illness associated with consuming untreated surface water.On May 9, 2022, Sanders County, Montana, reported to the state health department six active cases of Campylobacter infection in their community; this case count represented a substantial increase above the 5-year average of six reported cases annually during 2017-2021.All infected persons reported drinking water from watering point A, an outlet of surface water from a creek near Paradise, Montana (Figure ), before their onset of symptoms, which began on or after May 4.During the next 6 weeks, 13 additional cases of Campylobacter jejuni infection among persons exposed to the same water source were identified through laboratory testing (two by culture-independent confirmation and four by culture confirmation) or epidemiologic linkage (seven).One person was hospitalized, and no deaths were reported.On May 16, Sanders County Public Health environmental health staff members collected 23 liters of water from watering point A. The Montana Laboratory Services Bureau performed membrane filtration on 15 liters of the water sample, using four separate filters (0.45 μm [44 mm] pore size).The filters were then plated on media for Campylobacter culture and isolation following standard methods (3); investigators did not culture for or find any other pathogens.On May 24, the water sample was confirmed positive for Campylobacter by culture.On June 3, staff members performed whole genome sequencing on one Campylobacter isolate from the water sample and isolates from two human outbreak specimens; sequences were compared by both core genome multilocus sequence typing and whole genome multilocus sequence typing (4).Campylobacter isolates from the human specimens and water samples were highly genetically related (0-1 allele apart).Together, whole * https://www.cdc.gov/healthywater/drinking/travel/backcountry_water_treatment.html

More than 7.15 million cases of domestically acquired infectious waterborne illnesses occurred in the United States in 2014, causing 120,000 hospitalizations and 6,600 deaths. We estimated disease incidence for 17 pathogens according to recreational, drinking, and nonrecreational nondrinking (NRND) water exposure routes by using previously published estimates. In 2014, a total of 5.61 million (95% credible interval [CrI] 2.97-9.00 million) illnesses were linked to recreational water, 1.13 million (95% CrI 255,000-3.54 million) to drinking water, and 407,000 (95% CrI 72,800-1.29 million) to NRND water. Recreational water exposure was responsible for 36%, drinking water for 40%, and NRND water for 24% of hospitalizations from waterborne illnesses. Most direct costs were associated with pathogens found in biofilms. Estimating disease burden by water exposure route helps direct prevention activities. For each exposure route, water management programs are needed to control biofilm-associated pathogen growth; public health programs are needed to prevent biofilm-associated diseases.

This study examined 184 legionellosis outbreaks in the United States reported to the Centers for Disease Control and Prevention's Waterborne Disease and Outbreak Surveillance System, from 2001 to 2017. Drinking water characteristics examined include source water type, disinfectant type, exposure setting, geographical distribution by U.S. Census Divisions, and the public water system size (population served). This study found that most of the reported drinking water-associated legionellosis outbreaks occurred in eastern United States, including 35% in the South Atlantic, 32% in the Middle Atlantic, and 16% in the East North Central Census Divisions were linked with building water systems in healthcare and hotel settings; and were associated with buildings receiving drinking water from public water systems serving >10,000 people. Targeted evaluations and interventions may be useful to further determine the combination of factors, such as disinfectant residual type and drinking water system size that may lead to legionellosis outbreaks.

Households in the United States Virgin Islands (USVI) heavily rely on roof-harvested rainwater stored in cisterns for their daily activities. However, there are insufficient data on cistern water microbiological and physicochemical characteristics to inform appropriate cistern water management. Cistern and kitchen tap water samples were collected from 399 geographically representative households across St. Croix, St. Thomas, and St. John and an administered survey captured household site and cistern characteristics and water use behaviors. Water samples were analyzed for Escherichia coli by culture, and a subset of cistern water samples (N = 47) were analyzed for Salmonella, Naegleria fowleri, pathogenic Leptospira, Cryptosporidium, Giardia, and human-specific fecal contamination using real-time polymerase chain reaction (PCR). Associations between E. coli cistern contamination and cistern and site characteristics were evaluated to better understand possible mechanisms of contamination. E. coli was detected in 80% of cistern water samples and in 58% of kitchen tap samples. For the subset of samples tested by PCR, at least one of the pathogens was detected in 66% of cisterns. Our results suggest that covering overflow pipes with screens, decreasing animal presence at the household, and preventing animals or insects from entering the cisterns can decrease the likelihood of E. coli contamination in USVI cistern water.

On September 6 and 20, 2017, Hurricanes Irma and Maria made landfall as major hurricanes in the US Caribbean Territories of the Virgin Islands and Puerto Rico with devastating effects. As part of the initial response, a public health team (PHT) was initially deployed as part of the US Department of Health and Human Services Incident Response Coordination Team. As a result of increased demands for additional expertise and resources, a public health branch (PHB) was established for coordinating a broad spectrum of public health response activities in support of the affected territories. This paper describes the conceptual framework for organizing these activities; summarizes some key public health activities and roles; outlines partner support and coordination with key agencies; and defines best practices and areas for improvement in disaster future operations.

Hand drying is the critical, final step of handwashing. A cross-sectional survey of U.S. adults assessed self-reported hand drying practices in public bathrooms and found increased preference for using electric hand dryers, wiping hands on clothing, and shaking hands and decreased preference for using paper towels during the COVID-19 pandemic relative to before. Respondents expressed concerns about contacting SARS-CoV-2 when touching surfaces in public bathrooms which may be influencing self-reported drying method preference.

Background. Primary amebic meningoencephalitis (PAM) is a rapidly progressive and often fatal condition caused by the free-living ameba Naegleria fowleri. To estimate the global occurrence, characterize the epidemiology, and describe the clinical features of PAM, we report a series of PAM cases published in the international literature and reported to the Centers for Disease Control and Prevention (CDC). Methods. We performed a literature search of PAM case reports published through 2018. Additionally, we included cases reported through the CDC's Free-Living Ameba surveillance or diagnosed via CDC's Free-Living and Intestinal Amebas Laboratory. Cases were classified as confirmed, probable, or suspect on the basis of confirmatory testing, presentation, exposure, and disease course. Results. A total of 381 PAM cases were identified. Seven reported survivors were classified as confirmed. The most commonly reported exposure associated with PAM was swimming/diving, and the most common class of water source was lakes/ponds/reservoirs. Patients were predominantly male (75%), with a median age of 14 years. Confirmed and probable cases were similar in their survival, course of illness, and cerebrospinal fluid (CSF) findings. Conclusions. PAM is a rare but deadly disease with worldwide occurrence. Improved clinician awareness, resulting in earlier diagnosis and treatment, may contribute to increased survival among PAM patients. The case definition of probable used in this study appears to capture cases of PAM, as evidenced by similarities in outcomes, clinical course, and CSF profile to confirmed cases. In the absence of confirmatory testing, clinicians could use this case definition to identify cases of PAM.

COVID-19 vaccination remains the most effective means to achieve control of the pandemic. In the United States, COVID-19 cases and deaths have markedly declined since their peak in early January 2021, due in part to increased vaccination coverage (1). However, during June 19-July 23, 2021, COVID-19 cases increased approximately 300% nationally, followed by increases in hospitalizations and deaths, driven by the highly transmissible B.1.617.2 (Delta) variant* of SARS-CoV-2, the virus that causes COVID-19. Available data indicate that the vaccines authorized in the United States (Pfizer-BioNTech, Moderna, and Janssen [Johnson & Johnson]) offer high levels of protection against severe illness and death from infection with the Delta variant and other currently circulating variants of the virus (2). Despite widespread availability, vaccine uptake has slowed nationally with wide variation in coverage by state (range = 33.9%-67.2%) and by county (range = 8.8%-89.0%).† Unvaccinated persons, as well as persons with certain immunocompromising conditions (3), remain at substantial risk for infection, severe illness, and death, especially in areas where the level of SARS-CoV-2 community transmission is high. The Delta variant is more than two times as transmissible as the original strains circulating at the start of the pandemic and is causing large, rapid increases in infections, which could compromise the capacity of some local and regional health care systems to provide medical care for the communities they serve. Until vaccination coverage is high and community transmission is low, public health practitioners, as well as schools, businesses, and institutions (organizations) need to regularly assess the need for prevention strategies to avoid stressing health care capacity and imperiling adequate care for both COVID-19 and other non-COVID-19 conditions. CDC recommends five critical factors be considered to inform local decision-making: 1) level of SARS-CoV-2 community transmission; 2) health system capacity; 3) COVID-19 vaccination coverage; 4) capacity for early detection of increases in COVID-19 cases; and 5) populations at increased risk for severe outcomes from COVID-19. Among strategies to prevent COVID-19, CDC recommends all unvaccinated persons wear masks in public indoor settings. Based on emerging evidence on the Delta variant (2), CDC also recommends that fully vaccinated persons wear masks in public indoor settings in areas of substantial or high transmission. Fully vaccinated persons might consider wearing a mask in public indoor settings, regardless of transmission level, if they or someone in their household is immunocompromised or is at increased risk for severe disease, or if someone in their household is unvaccinated (including children aged <12 years who are currently ineligible for vaccination).

Tap water that is safe to consume may cause respiratory illness (e.g., Legionnaires’ disease) when water conditions allow for proliferation and aerosolization of biofilm-associated pathogens. This study assessed household tap water consumption, exposure to aerosolized tap water, and associated demographics. A nationally representative FallStyles survey administered by Porter Novelli Public Services was sent to 4,677 US adult panelists in October 2019. There were 3,624 adults who completed the survey (77.5% response rate). Respondents were asked about self-reported use of household tap water for consumption (i.e., drinking, rinsing produce, or making ice) and use through water-aerosolizing devices (e.g., showerheads, humidifiers). Demographics included gender, age, race/ethnicity, education, income, region, and health status. Weighted analyses using complex sample survey procedures were used to assess tap water exposure by route and demographics. Most US adults are exposed to aerosolized tap water through showering (80.6%), and one in five are exposed through other water-aerosolizing devices (20.3%). Consumption and showering were greatest among older, White, higher educated, and higher-income adults. Aerosolized tap water can transmit waterborne pathogens and cause respiratory illness, especially among older age groups and people with weakened immune systems. These results will help target health messages for using water-aerosolizing devices safely.

Although severe COVID-19 illness and hospitalization are more common among adults, these outcomes can occur in adolescents (1). Nearly one third of adolescents aged 12-17 years hospitalized with COVID-19 during March 2020-April 2021 required intensive care, and 5% of those hospitalized required endotracheal intubation and mechanical ventilation (2). On December 11, 2020, the Food and Drug Administration (FDA) issued Emergency Use Authorization (EUA) of the Pfizer-BioNTech COVID-19 vaccine for adolescents aged 16-17 years; on May 10, 2021, the EUA was expanded to include adolescents aged 12-15 years; and on August 23, 2021, FDA granted approval of the vaccine for persons aged ≥16 years. To assess progress in adolescent COVID-19 vaccination in the United States, CDC assessed coverage with ≥1 dose* and completion of the 2-dose vaccination series† among adolescents aged 12-17 years using vaccine administration data for 49 U.S. states (all except Idaho) and the District of Columbia (DC) during December 14, 2020-July 31, 2021. As of July 31, 2021, COVID-19 vaccination coverage among U.S. adolescents aged 12-17 years was 42.4% for ≥1 dose and 31.9% for series completion. Vaccination coverage with ≥1 dose varied by state (range = 20.2% [Mississippi] to 70.1% [Vermont]) and for series completion (range = 10.7% [Mississippi] to 60.3% [Vermont]). By age group, 36.0%, 40.9%, and 50.6% of adolescents aged 12-13, 14-15, and 16-17 years, respectively, received ≥1 dose; 25.4%, 30.5%, and 40.3%, respectively, completed the vaccine series. Improving vaccination coverage and implementing COVID-19 prevention strategies are crucial to reduce COVID-19-associated morbidity and mortality among adolescents and to facilitate safer reopening of schools for in-person learning.

Wastewater surveillance, the measurement of pathogen levels in wastewater, is used to evaluate community-level infection trends, augment traditional surveillance that leverages clinical tests and services (e.g., case reporting), and monitor public health interventions (1). Approximately 40% of persons infected with SARS-CoV-2, the virus that causes COVID-19, shed virus RNA in their stool (2); therefore, community-level trends in SARS-CoV-2 infections, both symptomatic and asymptomatic (2) can be tracked through wastewater testing (3-6). CDC launched the National Wastewater Surveillance System (NWSS) in September 2020 to coordinate wastewater surveillance programs implemented by state, tribal, local, and territorial health departments to support the COVID-19 pandemic response. In the United States, wastewater surveillance was not previously implemented at the national level. As of August 2021, NWSS includes 37 states, four cities, and two territories. This report summarizes NWSS activities and describes innovative applications of wastewater surveillance data by two states, which have included generating alerts to local jurisdictions, allocating mobile testing resources, evaluating irregularities in traditional surveillance, refining health messaging, and forecasting clinical resource needs. NWSS complements traditional surveillance and enables health departments to intervene earlier with focused support in communities experiencing increasing concentrations of SARS-CoV-2 in wastewater. The ability to conduct wastewater surveillance is not affected by access to health care or the clinical testing capacity in the community. Robust, sustainable implementation of wastewater surveillance requires public health capacity for wastewater testing, analysis, and interpretation. Partnerships between wastewater utilities and public health departments are needed to leverage wastewater surveillance data for the COVID-19 response for rapid assessment of emerging threats and preparedness for future pandemics.

Background. Giardiasis is the most common intestinal parasitic disease of humans identified in the United States (US) and an important waterborne disease. In the United States, giardiasis has been variably reportable since 1992 and was made a nationally notifiable disease in 2002. Our objective was to describe the epidemiology of US giardiasis cases from 1995 through 2016 using National Notifiable Diseases Surveillance System data. Methods. Negative binomial regression models were used to compare incidence rates by age group (0-4, 5-9, 10-19, 20-29, 30-39, 40-49, 50-64, and >= 65 years) during 3 time periods (1995-2001, 2002-2010, and 2011-2016). Results. During 1995-2016, the average number of reported cases was 19 781 per year (range, 14 623-27 778 cases). The annual incidence of reported giardiasis in the United States decreased across all age groups. This decrease differs by age group and sex and may reflect either changes in surveillance methods (eg, changes to case definitions or reporting practices) or changes in exposure. Incidence rates in males and older age groups did not decrease to the same extent as rates in females and children. Conclusions. Trends suggest that differences in exposures by sex and age group are important to the epidemiology of giardiasis. Further investigation into the risk factors of populations with higher rates of giardiasis will support prevention and control efforts.