Prevalence and Genetic Diversity of Adenovirus 40/41, Astrovirus, and Sapovirus in Children with Acute Gastroenteritis in Kansas City 2011-2016.

BACKGROUND: Most U.S. acute gastroenteritis (AGE) episodes in children are attributed to norovirus, whereas very little information is available on adenovirus 40/41 (AdV40/41), astrovirus or sapovirus. The New Vaccine Surveillance Network (NVSN) conducted prospective, active, population-based AGE surveillance in young children. METHODS: We tested and typed stool specimens collected between December 2011 to June 2016 from one NVSN site in Kansas City for the three viruses, and calculated hospitalization and emergency department (ED) detection rate. RESULTS: Of 3,205 collected specimens, 2,453 (76.5%) were from AGE patients (339 inpatients and 2,114 ED patients) and 752 (23.5%) were from healthy controls (HC). In AGE patients, astrovirus was detected in 94 (3.8%), sapovirus in 252 (10.3%) and AdV40/41 in 101 (4.5%) of 2249 patients. In HC, astrovirus was detected in 13 (1.7%) and sapovirus in 15 (2.0%) specimens. Astrovirus type 1 (37.7%) and genogroup I sapoviruses (59.3%) were most prevalent.Hospitalization rates were 5 (AdV40/41), 4 (astrovirus) and 8 (sapovirus) per 100,000 children <11 years old, whereas ED rates were 2.4 (AdV40/41), 1.9 (astrovirus) and 5.3 (sapovirus) per 1000 children <5 years old. CONCLUSIONS: Overall, AdV40/41, astrovirus, and sapovirus were detected in 18.6% of AGE in a large pediatric hospital in Kansas City.

Acute Gastroenteritis Outbreak Among Colorado River Rafters and Backpackers in the Grand Canyon, 2022.

INTRODUCTION: From April 1 to May 31, 2022, Grand Canyon National Park received increased acute gastroenteritis reports. Pooled portable toilet specimens identified norovirus genogroups I and II. We sought to determine outbreak transmission contributors and individual risk factors while rafting or backpacking in the park. METHODS: Grand Canyon rafters and backpackers were surveyed online from June 13-July 8, 2022, and a Cox proportional hazards model was used to identify predictors associated with illness and adjusted for potential confounding factors. RESULTS: Among 762 surveys, 119 cases and 505 well persons submitted complete survey data. Illness among rafters was associated with interaction with ill persons during the trip (adjusted hazard ratio [adjHR] = 3.4 [95%CI 2.3-5.0]) and lack of any hand hygiene (1.2 [0.7-1.9]) or use of only sanitizer or water (1.6 [1.04-2.6]) before snacks. Younger rafters had higher illness rates compared to those ≥60 y (1.5 [1.2-1.8] for ages 40-59 and 2.2 [1.4-3.5] for ages <40 y). CONCLUSIONS: Person-to-person transmission likely accounted for the widespread outbreak. Future outbreak mitigation efforts on river trips could focus on symptom screening before the trip starts, prompt separation of ill and well passengers, strict adherence to hand hygiene with soap and water, minimizing social interactions among rafting groups, and widespread outbreak notices and education to all park users.

Spatiotemporal Trends in Norovirus Outbreaks in the United States, 2009-2019.

BACKGROUND: Globally, noroviruses cause infections year-round but have recognized winter seasonality in the Northern Hemisphere and yearly variations in incidence. With candidate norovirus vaccines in development, understanding temporal and geographic trends in norovirus disease is important to inform potential vaccination strategies and evaluate vaccine impact. METHODS: We analyzed data from the National Outbreak Reporting System (NORS) and CaliciNet on single-state norovirus outbreaks that occurred during August 2009-July 2019 in the contiguous United States. We defined norovirus season onset and offset as the weeks by which 10% and 90% of norovirus outbreaks in a surveillance year occurred, respectively, and duration as the difference in weeks between onset and offset. We compared norovirus seasons across surveillance years and geographic regions. RESULTS: During August 2009-July 2019, 24 995 single-state norovirus outbreaks were reported to NORS and/or CaliciNet. Nationally, the median norovirus season duration was 24 weeks, with onset occurring between October and December and offset occurring between April and May. Across all years combined, we observed a west-to-east trend in seasonality, with the earliest onset (October) and latest offset (May) occurring in western regions and the latest onset (December) and earliest offset (April) occurring in northeastern regions. CONCLUSIONS: Timing and duration of the US norovirus season varied annually but generally occurred during October-May. Norovirus wintertime seasonality was less distinct in western regions and was progressively more pronounced moving east. Further understanding the drivers of spatiotemporal dynamics of norovirus could provide insights into factors that promote virus transmission and help guide future interventions.

A Comparison of Pathogen Detection and Risk Factors among Symptomatic Children with Gastroenteritis Compared with Asymptomatic Children in the Post-rotavirus Vaccine Era.

OBJECTIVE: To describe demographics, pathogen distribution/seasonality, and risk factors in children seeking care for acute gastroenteritis (AGE) at a midwestern US emergency department during 5 postrotavirus vaccine years (2011-2016), and further, to compare the same data with matched healthy controls (HC). STUDY DESIGN: AGE and HC participants <11 years old enrolled in the New Vaccine Surveillance Network study between December 2011 to June 2016 were included. AGE was defined as ≥3 diarrhea episodes or ≥1 vomiting episode. Each HC's age was similar to an AGE participant's age. Pathogens were analyzed for seasonality effects. Participant risk factors for AGE illness and pathogen detections were compared between HC and a matched subset of AGE cases. RESULTS: One or more organisms was detected in 1159 of 2503 children (46.3%) with AGE compared with 99 of 537 HC (17.3%). Norovirus was detected most frequently among AGE (n = 568 [22.7%]) and second-most frequently in HC (n = 39 [6.8%]). Rotavirus was the second most frequently detected pathogen among AGE (n = 196 [7.8%]). Children with AGE were significantly more likely to have reported a sick contact compared with HC, both outside the home (15.6% vs 1.4%; P < .001) and inside the home (18.6% vs 2.1%; P < .001). Daycare attendance was higher among children with AGE (41.4%) compared with HC (29.5%; P < .001). The Clostridium difficile detection rate was slightly higher among HC (7.0%) than AGE (5.3%). CONCLUSIONS: Norovirus was the most prevalent pathogen among children with AGE. Norovirus was detected in some HC, suggesting potential asymptomatic shedding among HC. The proportion of AGE participants with a sick contact was approximately 10 times greater than that of HC.

Predicting norovirus and rotavirus resurgence in the United States following the COVID-19 pandemic: a mathematical modelling study.

BACKGROUND: To reduce the burden from the COVID-19 pandemic in the United States, federal and state local governments implemented restrictions such as limitations on gatherings, restaurant dining, and travel, and recommended non-pharmaceutical interventions including physical distancing, mask-wearing, surface disinfection, and increased hand hygiene. Resulting behavioral changes impacted other infectious diseases including enteropathogens such as norovirus and rotavirus, which had fairly regular seasonal patterns prior to the COVID-19 pandemic. The study objective was to project future incidence of norovirus and rotavirus gastroenteritis as contacts resumed and other NPIs are relaxed. METHODS: We fitted compartmental mathematical models to pre-pandemic U.S. surveillance data (2012-2019) for norovirus and rotavirus using maximum likelihood estimation. Then, we projected incidence for 2022-2030 under scenarios where the number of contacts a person has per day varies from70%, 80%, 90%, and full resumption (100%) of pre-pandemic levels. RESULTS: We found that the population susceptibility to both viruses increased between March 2020 and November 2021. The 70-90% contact resumption scenarios led to lower incidence than observed pre-pandemic for both viruses. However, we found a greater than two-fold increase in community incidence relative to the pre-pandemic period under the 100% contact scenarios for both viruses. With rotavirus, for which population immunity is driven partially by vaccination, patterns settled into a new steady state quickly in 2022 under the 70-90% scenarios. For norovirus, for which immunity is relatively short-lasting and only acquired through infection, surged under the 100% contact scenario projection. CONCLUSIONS: These results, which quantify the consequences of population susceptibility build-up, can help public health agencies prepare for potential resurgence of enteric viruses.

Enteric Illness Outbreaks Reported Through the National Outbreak Reporting System-United States, 2009-2019.

BACKGROUND: The National Outbreak Reporting System (NORS) captures data on foodborne, waterborne, and enteric illness outbreaks in the United States. This study describes enteric illness outbreaks reported during 11 years of surveillance. METHODS: We extracted finalized reports from NORS for outbreaks occurring during 2009-2019. Outbreaks were included if caused by an enteric etiology or if any patients reported diarrhea, vomiting, bloody stools, or unspecified acute gastroenteritis. RESULTS: A total of 38 395 outbreaks met inclusion criteria, increasing from 1932 in 2009 to 3889 in 2019. Outbreaks were most commonly transmitted through person-to-person contact (n = 23 812; 62%) and contaminated food (n = 9234; 24%). Norovirus was the most commonly reported etiology, reported in 22 820 (59%) outbreaks, followed by Salmonella (n = 2449; 6%) and Shigella (n = 1171; 3%). Norovirus outbreaks were significantly larger, with a median of 22 illnesses per outbreak, than outbreaks caused by the other most common outbreak etiologies (P < .0001, all comparisons). Hospitalization rates were higher in outbreaks caused by Salmonella and Escherichia coli outbreaks (20.9% and 22.8%, respectively) than those caused by norovirus (2%). Case fatality rate was highest in E. coli outbreaks (0.5%) and lowest in Shigella and Campylobacter outbreaks (0.02%). CONCLUSIONS: Norovirus caused the most outbreaks and outbreak-associated illness, hospitalizations, and deaths. However, persons in E. coli and Salmonella outbreaks were more likely to be hospitalized or die. Outbreak surveillance through NORS provides the relative contributions of each mode of transmission and etiology for reported enteric illness outbreaks, which can guide targeted interventions.

Norovirus Outbreaks in Long-term Care Facilities in the United States, 2009-2018: A Decade of Surveillance.

BACKGROUND: In the United States, norovirus is the leading cause of healthcare-associated gastroenteritis outbreaks. To inform prevention efforts, we describe the epidemiology of norovirus outbreaks in long-term care facilities (LTCFs). METHODS: The Centers for Disease Control and Prevention (CDC) collect epidemiologic and laboratory data on norovirus outbreaks from US health departments through the National Outbreak Reporting System (NORS) and CaliciNet. Reports from both systems were merged, and norovirus outbreaks in nursing homes, assisted living, and other LTCFs occurring in 2009-2018 were analyzed. Data from the Centers for Medicare and Medicaid Services and the National Center for Health Statistics were used to estimate state LTCF counts. RESULTS: During 2009-2018, 50 states, Washington D.C., and Puerto Rico reported 13 092 norovirus outbreaks and 416 284 outbreak-associated cases in LTCFs. Participation in NORS and CaliciNet increased from 2009 to 2014 and median reporting of LTCF norovirus outbreaks stabilized at 4.1 outbreaks per 100 LTCFs (interquartile range [IQR]: 1.0-7.1) annually since 2014. Most outbreaks were spread via person-to-person transmission (90.4%), and 75% occurred during December-March. Genogroup was reported for 7292 outbreaks with 862 (11.8%) positive for GI and 6370 (87.3%) for GII. Among 4425 GII outbreaks with typing data, 3618 (81.8%) were GII.4. LTCF residents had higher attack rates than staff (median 29.0% vs 10.9%; P < .001). For every 1000 cases, there were 21.6 hospitalizations and 2.3 deaths. CONCLUSIONS: LTCFs have a high burden of norovirus outbreaks. Most LTCF norovirus outbreaks occurred during winter months and were spread person-to-person. Outbreak surveillance can inform development of interventions for this vulnerable population, such as vaccines targeting GII.4 norovirus strains.

Understanding Variation in Rotavirus Vaccine Effectiveness Estimates in the United States: The Role of Rotavirus Activity and Diagnostic Misclassification.

BACKGROUND: Estimates of rotavirus vaccine effectiveness (VE) in the United States appear higher in years with more rotavirus activity. We hypothesized rotavirus VE is constant over time but appears to vary as a function of temporal variation in local rotavirus cases and/or misclassified diagnoses. METHODS: We analyzed 6 years of data from eight US surveillance sites on 8- to 59-month olds with acute gastroenteritis symptoms. Children's stool samples were tested via enzyme immunoassay (EIA); rotavirus-positive results were confirmed with molecular testing at the US Centers for Disease Control and Prevention. We defined rotavirus gastroenteritis cases by either positive on-site EIA results alone or positive EIA with Centers for Disease Control and Prevention confirmation. For each case definition, we estimated VE against any rotavirus gastroenteritis, moderate-to-severe disease, and hospitalization using two mixed-effect regression models: the first including year plus a year-vaccination interaction, and the second including the annual percent of rotavirus-positive tests plus a percent positive-vaccination interaction. We used multiple overimputation to bias-adjust for misclassification of cases defined by positive EIA alone. RESULTS: Estimates of annual rotavirus VE against all outcomes fluctuated temporally, particularly when we defined cases by on-site EIA alone and used a year-vaccination interaction. Use of confirmatory testing to define cases reduced, but did not eliminate, fluctuations. Temporal fluctuations in VE estimates further attenuated when we used a percent positive-vaccination interaction. Fluctuations persisted until bias-adjustment for diagnostic misclassification. CONCLUSIONS: Both controlling for time-varying rotavirus activity and bias-adjusting for diagnostic misclassification are critical for estimating the most valid annual rotavirus VE.

Outbreak of Acute Gastroenteritis Among Rafters and Backpackers in the Backcountry of Grand Canyon National Park, April-June 2022.

On May 11, 2022, the National Park Service (NPS) Office of Public Health (OPH) and Coconino County Health and Human Services (CCHHS) in Flagstaff, Arizona contacted CDC about a rising number of acute gastroenteritis cases among backcountry visitors to Grand Canyon National Park (Grand Canyon). The agencies reviewed illness report forms, assessed infection prevention and control (IPC) practices, and distributed a detailed survey to river rafters and hikers with backcountry permits (backpackers) who visited the Grand Canyon backcountry. During April 1-June 17, a total of 191 rafters and 31 backpackers reported symptoms consistent with acute gastroenteritis. Specimens from portable toilets used by nine river rafting trip groups were tested using real-time reverse transcription-polymerase chain reaction and test results were positive for norovirus. Norovirus-associated acute gastroenteritis is highly transmissible in settings with close person-to-person contact and decreased access to hand hygiene, such as backpacking or rafting. IPC assessments led to recommendations for regular disinfection of potable water spigots throughout the backcountry, promotion of proper handwashing with soap and water when possible, and separation of ill persons from those who are not ill. Prevention and control of acute gastroenteritis outbreaks in the backcountry requires rapid reporting of illnesses, implementing IPC guidelines for commercial outfitters and river rafting launch points, and minimizing interactions among rafting groups.

Outbreaks of Acute Gastrointestinal Illness Associated with a Splash Pad in a Wildlife Park - Kansas, June 2021.

In June 2021, Kansas state and county public health officials identified and investigated three cases of shigellosis (a bacterial diarrheal illness caused by Shigella spp.) associated with visiting a wildlife park. The park has animal exhibits and a splash pad. Two affected persons visited animal exhibits, and all three entered the splash pad. Nonhuman primates are the only known animal reservoir of Shigella. The splash pad, which sprays water on users and is designed so that water does not collect in the user area, was closed on June 19. The state and county public health codes do not include regulations for splash pads. Thus, these venues are not typically inspected, and environmental health expertise is limited. A case-control study identified two distinct outbreaks associated with the park (a shigellosis outbreak involving 21 cases and a subsequent norovirus infection outbreak involving six cases). Shigella and norovirus can be transmitted by contaminated water; in both outbreaks, illness was associated with getting splash pad water in the mouth (multiply imputed adjusted odds ratio [aORMI] = 6.4, p = 0.036; and 28.6, p = 0.006, respectively). Maintaining adequate water disinfection and environmental health expertise and targeting prevention efforts to caregivers of splash pad users help prevent splash pad-associated outbreaks. Outbreak incidence might be further reduced when U.S. jurisdicitons voluntarily adopt CDC's Model Aquatic Health Code (MAHC) recommendations and through the prevention messages: "Don't get in the water if sick with diarrhea," "Don't stand or sit above the jets," and "Don't swallow the water."†.

Impact of Nonpharmaceutical Interventions for Severe Acute Respiratory Syndrome Coronavirus 2 on Norovirus Outbreaks: An Analysis of Outbreaks Reported By 9 US States.

In April 2020, the incidence of norovirus outbreaks reported to the National Outbreak Reporting System dramatically declined. We used regression models to determine if this decline was best explained by underreporting, seasonal trends, or reduced exposure due to nonpharmaceutical interventions (NPIs) implemented for severe acute respiratory syndrome coronavirus 2 using data from 9 states from July 2012 to July 2020. The decline in norovirus outbreaks was significant for all 9 states, and underreporting and/or seasonality are unlikely to be the primary explanation for these findings. These patterns were similar across a variety of settings. NPIs appear to have reduced incidence of norovirus, a nonrespiratory pathogen.

Rotavirus Genotype Trends and Gastrointestinal Pathogen Detection in the United States, 2014-2016: Results From the New Vaccine Surveillance Network.

BACKGROUND: Following the implementation of rotavirus vaccination in 2006, severe acute gastroenteritis (AGE) due to group A rotavirus (RVA) has substantially declined in US children. We report the RVA genotype prevalence as well as coinfection data from 7 US New Vaccine Surveillance Network sites during 3 consecutive RVA seasons, 2014-2016. METHODS: A total of 1041 stool samples that tested positive for RVA by Rotaclone enzyme immunoassay were submitted to the Centers for Disease Control and Prevention (CDC) for RVA genotyping and multipathogen testing. RESULTS: A total of 795 (76%) samples contained detectable RVA when tested at the CDC. Rotavirus disease was highest in children < 3 years of age. Four G types (G1, G2, G9, and G12) accounted for 94.6% of strains while 2 P types (P[4] and P[8]) accounted for 94.7% of the strains. Overall, G12P[8] was the most common genotype detected in all 3 seasons. Stepwise conditional logistic analysis found year and study site were significant predictors of genotype. Twenty-four percent of RVA-positive specimens contained other AGE pathogens. CONCLUSIONS: G12P[8] predominated over 3 seasons, but strain predominance varied by year and study site. Ongoing surveillance provides continuous tracking and monitoring of US genotypes during the postvaccine era.

The Changing Landscape of Pediatric Viral Enteropathogens in the Post-Rotavirus Vaccine Era.

BACKGROUND: Acute gastroenteritis (AGE) is a common reason for children to receive medical care. However, the viral etiology of AGE illness is not well described in the post-rotavirus vaccine era, particularly in the outpatient (OP) setting. METHODS: Between 2012 and 2015, children 15 days through 17 years old presenting to Vanderbilt Children's Hospital, Nashville, Tennessee, with AGE were enrolled prospectively from the inpatient, emergency department, and OP settings, and stool specimens were collected. Healthy controls (HCs) were enrolled and frequency matched for period, age group, race, and ethnicity. Stool specimens were tested by means of reverse-transcription real-time quantitative polymerase chain reaction for norovirus, sapovirus, and astrovirus RNA and by Rotaclone enzyme immunoassay for rotavirus antigen, followed by polymerase chain reaction verification of antigen detection. RESULTS: A total of 3705 AGE case patients and 1563 HCs were enrolled, among whom 2885 case patients (78%) and 1110 HCs (71%) provided stool specimens that were tested. All 4 viruses were more frequently detected in AGE case patients than in HCs (norovirus, 22% vs 8%, respectively; rotavirus, 10% vs 1%; sapovirus, 10% vs 5%; and astrovirus, 5% vs 2%; P < .001 for each virus). In the OP setting, rates of AGE due to norovirus were higher than rate for the other 3 viruses. Children <5 years old had higher OP AGE rates than older children for all viruses. CONCLUSIONS: Norovirus remains the most common virus detected in all settings, occurring nearly twice as frequently as the next most common pathogens, sapovirus and rotavirus. Combined, norovirus, sapovirus, rotavirus, and astrovirus were associated with almost half of all AGE visits and therefore are an important reason for children to receive medical care.

Characteristics of GII.4 Norovirus Versus Other Genotypes in Sporadic Pediatric Infections in Davidson County, Tennessee, USA.

BACKGROUND: Norovirus is a leading cause of epidemic acute gastroenteritis (AGE), with most outbreaks occurring during winter. The majority of outbreaks are caused by GII.4 noroviruses; however, data to support whether this is true for sporadic medically attended AGE are limited. Therefore, we sought to compare the clinical characteristics and seasonality of GII.4 vs non-GII.4 viruses. METHODS: Children aged 15 days -17 years with AGE symptoms were recruited from the outpatient, emergency department, and inpatient settings at Vanderbilt Children's Hospital, Davidson County, Nashville, Tennessee, from December 2012 -November 2015. Stool specimens were tested using qRT-PCR for GI and GII noroviruses and subsequently genotyped by sequencing a partial region of the capsid gene. RESULTS: A total of 3705 patients were enrolled, and stool specimens were collected and tested from 2885 (78%) enrollees. Overall, 636 (22%) samples were norovirus-positive, of which 567 (89%) were GII. Of the 460 (81%) genotyped GII-positive samples, 233 (51%) were typed as GII.4 and 227 (49%) as non-GII.4. Compared with children with non-GII.4 infections, children with GII.4 infections were younger, more likely to have diarrhea, and more likely to receive oral rehydration fluids. Norovirus was detected year-round and peaked during winter. CONCLUSIONS: Approximately 40% of sporadic pediatric norovirus AGE cases were caused by GII.4 norovirus. Children infected with GII.4 had more severe symptoms that required more medical care. Seasonal variations were noticed among different genotypes. These data highlight the importance of continuous norovirus surveillance and provide important information on which strains pediatric norovirus vaccines should protect against.

Non-Norovirus Viral Gastroenteritis Outbreaks Reported to the National Outbreak Reporting System, USA, 2009-2018.

During 2009-2018, four adenovirus, 10 astrovirus, 123 rotavirus, and 107 sapovirus gastroenteritis outbreaks were reported to the US National Outbreak Reporting System (annual median 30 outbreaks). Most were attributable to person-to-person transmission in long-term care facilities, daycares, and schools. Investigations of norovirus-negative gastroenteritis outbreaks should include testing for these viruses.

Continued Evidence of the Impact of Rotavirus Vaccine in Children Less Than 3 Years of Age From the United States New Vaccine Surveillance Network: A Multisite Active Surveillance Program, 2006-2016.

BACKGROUND: Since 2006, the New Vaccine Surveillance Network has conducted active, population-based surveillance for acute gastroenteritis (AGE) hospitalizations and emergency department (ED) visits in 3 United States counties. Trends in the epidemiology and disease burden of rotavirus hospitalizations and ED visits were examined from 2006 to 2016. METHODS: Children < 3 years of age hospitalized or visiting the ED with AGE were enrolled from January 2006 through June 2016. Bulk stool specimens were collected and tested for rotavirus. Rotavirus-associated hospitalization and ED visit rates were calculated annually with 2006-2007 defined as the prevaccine period and 2008-2016 as the postvaccine period. Rotavirus genotype trends were compared over time. RESULTS: Over 11 seasons, 6954 children with AGE were enrolled and submitted a stool specimen (2187 hospitalized and 4767 in the ED). Comparing pre- and postvaccine periods, the proportion of children with rotavirus dramatically declined for hospitalization (49% vs 10%) and ED visits (49% vs 8%). In the postvaccine era, a biennial pattern of rotavirus rates was observed, with a trend toward an older median age. G1P[8] (63%) was the predominant genotype in the prevaccine period with a significantly lower proportion (7%) in the postvaccine period (P < .001). G2P[4] remained stable (8% to 14%) in both periods, whereas G3P[8] and G12P[8] increased in proportion from pre- to postvaccine periods (1% to 25% and 17% to 40%), respectively. CONCLUSIONS: The epidemiology and disease burden of rotavirus has been altered by rotavirus vaccination with a biennial disease pattern, sustained low rates of rotavirus in children < 3 years of age, and a shift in the residual genotypes from G1P[8] to other genotypes.

Validation of Acute Gastroenteritis-related International Classification of Diseases, Clinical Modification Codes in Pediatric and Adult US Populations.

International Classification of Diseases diagnostic codes are used to estimate acute gastroenteritis (AGE) disease burden. We validated AGE-related codes in pediatric and adult populations using 2 multiregional active surveillance platforms. The sensitivity of AGE codes was similar (54% and 58%) in both populations and increased with addition of vomiting-specific codes.

Characterizing Norovirus Transmission from Outbreak Data, United States.

Norovirus is the leading cause of acute gastroenteritis outbreaks in the United States. We estimated the basic (R0) and effective (Re) reproduction numbers for 7,094 norovirus outbreaks reported to the National Outbreak Reporting System (NORS) during 2009-2017 and used regression models to assess whether transmission varied by outbreak setting. The median R0 was 2.75 (interquartile range [IQR] 2.38-3.65), and median Re was 1.29 (IQR 1.12-1.74). Long-term care and assisted living facilities had an R0 of 3.35 (95% CI 3.26-3.45), but R0 did not differ substantially for outbreaks in other settings, except for outbreaks in schools, colleges, and universities, which had an R0 of 2.92 (95% CI 2.82-3.03). Seasonally, R0 was lowest (3.11 [95% CI 2.97-3.25]) in summer and peaked in fall and winter. Overall, we saw little variability in transmission across different outbreaks settings in the United States.

Outbreaks Associated with Untreated Recreational Water - California, Maine, and Minnesota, 2018-2019.

Outbreaks associated with fresh or marine (i.e., untreated) recreational water can be caused by pathogens or chemicals, including toxins. Voluntary reporting of these outbreaks to CDC's National Outbreak Reporting System (NORS) began in 2009. NORS data for 2009-2017 are finalized, and data for 2018-2019 are provisional. During 2009-2019 (as of May 13, 2020), public health officials from 31 states voluntarily reported 119 untreated recreational water-associated outbreaks, resulting at least 5,240 cases; 103 of the outbreaks (87%) started during June-August. Among the 119 outbreaks, 88 (74%) had confirmed etiologies. The leading etiologies were enteric pathogens: norovirus (19 [22%] outbreaks; 1,858 cases); Shiga toxin-producing Escherichia coli (STEC) (19 [22%]; 240), Cryptosporidium (17 [19%]; 237), and Shigella (14 [16%]; 713). This report highlights three examples of outbreaks that occurred during 2018-2019, were caused by leading etiologies (Shigella, norovirus, or STEC), and demonstrate the wide geographic distribution of such outbreaks across the United States. Detection and investigation of untreated recreational water-associated outbreaks are challenging, and the sources of these outbreaks often are not identified. Tools for controlling and preventing transmission of enteric pathogens through untreated recreational water include epidemiologic investigations, regular monitoring of water quality (i.e., testing for fecal indicator bacteria), microbial source tracking, and health policy and communications (e.g., observing beach closure signs and not swimming while ill with diarrhea).

The Norovirus Epidemiologic Triad: Predictors of Severe Outcomes in US Norovirus Outbreaks, 2009-2016.

BACKGROUND: Noroviruses are the leading cause of acute gastroenteritis outbreaks worldwide. Clarifying the viral, host, and environmental factors (epidemiologic triad) associated with severe outcomes can help target public health interventions. METHODS: Acute norovirus outbreaks reported to the National Outbreak Reporting System (NORS) in 2009-2016 were linked to laboratory-confirmed norovirus outbreaks reported to CaliciNet. Outbreaks were analyzed for differences in genotype (GII.4 vs non-GII.4), hospitalization, and mortality rates by timing, setting, transmission mode, demographics, clinical symptoms, and health outcomes. RESULTS: A total of 3747 norovirus outbreaks were matched from NORS and CaliciNet. Multivariable models showed that GII.4 outbreaks (n = 2353) were associated with healthcare settings (odds ratio [OR], 3.94 [95% confidence interval {CI}, 2.99-5.23]), winter months (November-April; 1.55 [95% CI, 1.24-1.93]), and older age of cases (≥50% aged ≥75 years; 1.37 [95% CI, 1.04-1.79]). Severe outcomes were more likely among GII.4 outbreaks (hospitalization rate ratio [RR], 1.54 [95% CI, 1.23-1.96]; mortality RR, 2.77 [95% CI, 1.04-5.78]). Outbreaks in healthcare settings were also associated with higher hospitalization (RR, 3.22 [95% CI, 2.34-4.44]) and mortality rates (RR, 5.65 [95% CI, 1.92-18.70]). CONCLUSIONS: Severe outcomes more frequently occurred in norovirus outbreaks caused by GII.4 and those in healthcare settings. These results should help guide preventive interventions for targeted populations, including vaccine development.