Surveillance of Waterborne Disease Outbreaks Associated with Drinking Water - United States, 2015-2020.

Problem/Condition: Public health agencies in U.S. states, territories, and freely associated states investigate and voluntarily report waterborne disease outbreaks to CDC through the National Outbreak Reporting System (NORS). This report summarizes NORS drinking water outbreak epidemiologic, laboratory, and environmental data, including data for both public and private drinking water systems. The report presents outbreak-contributing factors (i.e., practices and factors that lead to outbreaks) and, for the first time, categorizes outbreaks as biofilm pathogen or enteric illness associated. Period Covered: 2015-2020. Description of System: CDC launched NORS in 2009 as a web-based platform into which public health departments voluntarily enter outbreak information. Through NORS, CDC collects reports of enteric disease outbreaks caused by bacterial, viral, parasitic, chemical, toxin, and unknown agents as well as foodborne and waterborne outbreaks of nonenteric disease. Data provided by NORS users, when known, for drinking water outbreaks include 1) the number of cases, hospitalizations, and deaths; 2) the etiologic agent (confirmed or suspected); 3) the implicated type of water system (e.g., community or individual or private); 4) the setting of exposure (e.g., hospital or health care facility; hotel, motel, lodge, or inn; or private residence); and 5) relevant epidemiologic and environmental data needed to describe the outbreak and characterize contributing factors. Results: During 2015-2020, public health officials from 28 states voluntarily reported 214 outbreaks associated with drinking water and 454 contributing factor types. The reported etiologies included 187 (87%) biofilm associated, 24 (11%) enteric illness associated, two (1%) unknown, and one (<1%) chemical or toxin. A total of 172 (80%) outbreaks were linked to water from public water systems, 22 (10%) to unknown water systems, 17 (8%) to individual or private systems, and two (0.9%) to other systems; one (0.5%) system type was not reported. Drinking water-associated outbreaks resulted in at least 2,140 cases of illness, 563 hospitalizations (26% of cases), and 88 deaths (4% of cases). Individual or private water systems were implicated in 944 (43%) cases, 52 (9%) hospitalizations, and 14 (16%) deaths.Enteric illness-associated pathogens were implicated in 1,299 (61%) of all illnesses, and 10 (2%) hospitalizations. No deaths were reported. Among these illnesses, three pathogens (norovirus, Shigella, and Campylobacter) or multiple etiologies including these pathogens resulted in 1,225 (94%) cases. The drinking water source was identified most often (n = 34; 7%) as the contributing factor in enteric disease outbreaks. When water source (e.g., groundwater) was known (n = 14), wells were identified in 13 (93%) of enteric disease outbreaks.Most biofilm-related outbreak reports implicated Legionella (n = 184; 98%); two nontuberculous mycobacteria (NTM) (1%) and one Pseudomonas (0.5%) outbreaks comprised the remaining. Legionella-associated outbreaks generally increased over the study period (14 in 2015, 31 in 2016, 30 in 2017, 34 in 2018, 33 in 2019, and 18 in 2020). The Legionella-associated outbreaks resulted in 786 (37%) of all illnesses, 544 (97%) hospitalizations, and 86 (98%) of all deaths. Legionella also was the outbreak etiology in 160 (92%) public water system outbreaks. Outbreak reports cited the premise or point of use location most frequently as the contributing factor for Legionella and other biofilm-associated pathogen outbreaks (n = 287; 63%). Legionella was reported to NORS in 2015 and 2019 as the cause of three outbreaks in private residences (2). Interpretation: The observed range of biofilm and enteric drinking water pathogen contributing factors illustrate the complexity of drinking water-related disease prevention and the need for water source-to-tap prevention strategies. Legionella-associated outbreaks have increased in number over time and were the leading cause of reported drinking water outbreaks, including hospitalizations and deaths. Enteric illness outbreaks primarily linked to wells represented approximately half the cases during this reporting period. This report enhances CDC efforts to estimate the U.S. illness and health care cost impacts of waterborne disease, which revealed that biofilm-related pathogens, NTM, and Legionella have emerged as the predominant causes of hospitalizations and deaths from waterborne- and drinking water-associated disease. Public Health Action: Public health departments, regulators, and drinking water partners can use these findings to identify emerging waterborne disease threats, guide outbreak response and prevention programs, and support drinking water regulatory efforts.

Healthcare Provider Confidence and Perceived Barriers to Diagnosing Illness Associated with Harmful Algal Blooms.

Introduction: Illnesses caused by harmful algal blooms can vary in clinical presentation and severity depending on the types of algae, cyanobacteria, or toxins involved as well as the route and extent of exposure. These illnesses are primarily diagnoses of exclusion owing to lack of access to clinical testing for harmful algal bloom toxins. We used a national survey of healthcare providers to explore self-reported confidence and perceived barriers to diagnosing harmful algal bloom-associated illnesses. Methods: We conducted a descriptive analysis (SAS 9.4) of 2 questions from a national survey of healthcare providers administered September 14-October 26, 2020 (N=1,503). Chi-square tests were used to assess differences between groups, with statistical significance defined as p<0.05. Results: Most (68%) providers reported little to no confidence in their ability to identify illnesses caused by harmful algal blooms, 17% were confident or very confident, and 15% reported not seeing patients with these illnesses. Responses differed by specialization, work setting, sex, experience, whether pediatric patients were seen, and number of patients seen. Respondents regularly using resources such as newspapers (31%), professional societies (29%), and government health agencies (26%) reported increased confidence. Of 1,283 (85%) respondents who were asked about barriers to accurately diagnosing patients with these illnesses, 71% selected lack of knowledge about harmful algal bloom-associated illnesses as a barrier. Conclusions: Provider confidence in identifying harmful algal bloom-associated illnesses was low, and lack of knowledge was identified as a primary barrier, suggesting that more outreach and education are needed. Tailoring information for specific provider audiences and providing it through highly frequented channels could increase providers' confidence in identifying and diagnosing harmful algal bloom-associated illnesses.