Incorporating COVID-19 into Acute Febrile Illness Surveillance Systems, Belize, Kenya, Ethiopia, Peru, and Liberia, 2020-2021.

Existing acute febrile illness (AFI) surveillance systems can be leveraged to identify and characterize emerging pathogens, such as SARS-CoV-2, which causes COVID-19. The US Centers for Disease Control and Prevention collaborated with ministries of health and implementing partners in Belize, Ethiopia, Kenya, Liberia, and Peru to adapt AFI surveillance systems to generate COVID-19 response information. Staff at sentinel sites collected epidemiologic data from persons meeting AFI criteria and specimens for SARS-CoV-2 testing. A total of 5,501 patients with AFI were enrolled during March 2020-October 2021; >69% underwent SARS-CoV-2 testing. Percentage positivity for SARS-CoV-2 ranged from 4% (87/2,151, Kenya) to 19% (22/115, Ethiopia). We show SARS-CoV-2 testing was successfully integrated into AFI surveillance in 5 low- to middle-income countries to detect COVID-19 within AFI care-seeking populations. AFI surveillance systems can be used to build capacity to detect and respond to both emerging and endemic infectious disease threats.

Global Disease Detection-Achievements in Applied Public Health Research, Capacity Building, and Public Health Diplomacy, 2001-2016.

The Centers for Disease Control and Prevention has established 10 Global Disease Detection (GDD) Program regional centers around the world that serve as centers of excellence for public health research on emerging and reemerging infectious diseases. The core activities of the GDD Program focus on applied public health research, surveillance, laboratory, public health informatics, and technical capacity building. During 2015-2016, program staff conducted 205 discrete projects on a range of topics, including acute respiratory illnesses, health systems strengthening, infectious diseases at the human-animal interface, and emerging infectious diseases. Projects incorporated multiple core activities, with technical capacity building being most prevalent. Collaborating with host countries to implement such projects promotes public health diplomacy. The GDD Program continues to work with countries to strengthen core capacities so that emerging diseases can be detected and stopped faster and closer to the source, thereby enhancing global health security.

Evaluation of the Use of Zero-Augmented Regression Techniques to Model Incidence of Campylobacter Infections in FoodNet.

The Foodborne Diseases Active Surveillance Network (FoodNet) is currently using a negative binomial (NB) regression model to estimate temporal changes in the incidence of Campylobacter infection. FoodNet active surveillance in 483 counties collected data on 40,212 Campylobacter cases between years 2004 and 2011. We explored models that disaggregated these data to allow us to account for demographic, geographic, and seasonal factors when examining changes in incidence of Campylobacter infection. We hypothesized that modeling structural zeros and including demographic variables would increase the fit of FoodNet's Campylobacter incidence regression models. Five different models were compared: NB without demographic covariates, NB with demographic covariates, hurdle NB with covariates in the count component only, hurdle NB with covariates in both zero and count components, and zero-inflated NB with covariates in the count component only. Of the models evaluated, the nonzero-augmented NB model with demographic variables provided the best fit. Results suggest that even though zero inflation was not present at this level, individualizing the level of aggregation and using different model structures and predictors per site might be required to correctly distinguish between structural and observational zeros and account for risk factors that vary geographically.

Infection with Pathogens Transmitted Commonly Through Food and the Effect of Increasing Use of Culture-Independent Diagnostic Tests on Surveillance--Foodborne Diseases Active Surveillance Network, 10 U.S. Sites, 2012-2015.

To evaluate progress toward prevention of enteric and foodborne illnesses in the United States, the Foodborne Diseases Active Surveillance Network (FoodNet) monitors the incidence of laboratory-confirmed infections caused by nine pathogens transmitted commonly through food in 10 U.S. sites. This report summarizes preliminary 2015 data and describes trends since 2012. In 2015, FoodNet reported 20,107 confirmed cases (defined as culture-confirmed bacterial infections and laboratory-confirmed parasitic infections), 4,531 hospitalizations, and 77 deaths. FoodNet also received reports of 3,112 positive culture-independent diagnostic tests (CIDTs) without culture-confirmation, a number that has markedly increased since 2012. Diagnostic testing practices for enteric pathogens are rapidly moving away from culture-based methods. The continued shift from culture-based methods to CIDTs that do not produce the isolates needed to distinguish between strains and subtypes affects the interpretation of public health surveillance data and ability to monitor progress toward prevention efforts. Expanded case definitions and strategies for obtaining bacterial isolates are crucial during this transition period.

Foodborne Diseases Active Surveillance Network-2 Decades of Achievements, 1996-2015.

The Foodborne Diseases Active Surveillance Network (FoodNet) provides a foundation for food safety policy and illness prevention in the United States. FoodNet conducts active, population-based surveillance at 10 US sites for laboratory-confirmed infections of 9 bacterial and parasitic pathogens transmitted commonly through food and for hemolytic uremic syndrome. Through FoodNet, state and federal scientists collaborate to monitor trends in enteric illnesses, identify their sources, and implement special studies. FoodNet's major contributions include establishment of reliable, active population-based surveillance of enteric diseases; development and implementation of epidemiologic studies to determine risk and protective factors for sporadic enteric infections; population and laboratory surveys that describe the features of gastrointestinal illnesses, medical care-seeking behavior, frequency of eating various foods, and laboratory practices; and development of a surveillance and research platform that can be adapted to address emerging issues. The importance of FoodNet's ongoing contributions probably will grow as clinical, laboratory, and informatics technologies continue changing rapidly.

Bacterial enteric infections detected by culture-independent diagnostic tests--FoodNet, United States, 2012-2014.

The increased availability and rapid adoption of culture-independent diagnostic tests (CIDTs) is moving clinical detection of bacterial enteric infections away from culture-based methods. These new tests do not yield isolates that are currently needed for further tests to distinguish among strains or subtypes of Salmonella, Campylobacter, Shiga toxin-producing Escherichia coli, and other organisms. Public health surveillance relies on this detailed characterization of isolates to monitor trends and rapidly detect outbreaks; consequently, the increased use of CIDTs makes prevention and control of these infections more difficult. During 2012-2013, the Foodborne Diseases Active Surveillance Network (FoodNet*) identified a total of 38,666 culture-confirmed cases and positive CIDT reports of Campylobacter, Salmonella, Shigella, Shiga toxin-producing E. coli, Vibrio, and Yersinia. Among the 5,614 positive CIDT reports, 2,595 (46%) were not confirmed by culture. In addition, a 2014 survey of clinical laboratories serving the FoodNet surveillance area indicated that use of CIDTs by the laboratories varied by pathogen; only CIDT methods were used most often for detection of Campylobacter (10%) and STEC (19%). Maintaining surveillance of bacterial enteric infections in this period of transition will require enhanced surveillance methods and strategies for obtaining bacterial isolates.

Preliminary incidence and trends of infection with pathogens transmitted commonly through food - Foodborne Diseases Active Surveillance Network, 10 U.S. sites, 2006-2014.

Foodborne illnesses represent a substantial, yet largely preventable, health burden in the United States. In 10 U.S. geographic areas, the Foodborne Diseases Active Surveillance Network (FoodNet) monitors the incidence of laboratory-confirmed infections caused by nine pathogens transmitted commonly through food. This report summarizes preliminary 2014 data and describes changes in incidence compared with 2006-2008 and 2011-2013. In 2014, FoodNet reported 19,542 infections, 4,445 hospitalizations, and 71 deaths. The incidence of Shiga toxin-producing Escherichia coli (STEC) O157 and Salmonella enterica serotype Typhimurium infections declined in 2014 compared with 2006-2008, and the incidence of infection with Campylobacter, Vibrio, and Salmonella serotypes Infantis and Javiana was higher. Compared with 2011-2013, the incidence of STEC O157 and Salmonella Typhimurium infections was lower, and the incidence of STEC non-O157 and Salmonella serotype Infantis infections was higher in 2014. Despite ongoing food safety efforts, the incidence of many infections remains high, indicating that further prevention measures are needed to make food safer and achieve national health objectives.

Bacterial Enteric Infections Among Older Adults in the United States: Foodborne Diseases Active Surveillance Network, 1996-2012.

BACKGROUND: A growing segment of the population-adults aged ≥65 years-is more susceptible than younger adults to certain enteric (including foodborne) infections and experience more severe disease. MATERIALS AND METHODS: Using data on laboratory-confirmed infections from the Foodborne Diseases Active Surveillance Network (FoodNet), we describe trends in the incidence of Campylobacter spp., Escherichia coli O157, Listeria monocytogenes, and nontyphoidal Salmonella infections in adults aged ≥65 years over time and by age group and sex. We used data from FoodNet and other sources to estimate the total number of illnesses, hospitalizations, and deaths in the United States caused by these infections each year using a statistical model to adjust for underdiagnosis (taking into account medical care-seeking, stool sample submission, laboratory practices, and test sensitivity). RESULTS: From 1996 to 2012, 4 pathogens caused 21,405 laboratory-confirmed infections among older adults residing in the FoodNet surveillance area; 49.3% were hospitalized, and 2.6% died. The average annual rate of infection was highest for Salmonella (12.8/100,000) and Campylobacter (12.1/100,000). Salmonella and Listeria led as causes of death. Among older adults, rates of laboratory-confirmed infection and the percentage of patients who were hospitalized and who died generally increased with age. A notable exception was the rate of Campylobacter infections, which decreased with increasing age. Adjusting for underdiagnosis, we estimated that these pathogens caused about 226,000 illnesses (≈600/100,000) annually among U.S. adults aged ≥65 years, resulting in ≈9700 hospitalizations and ≈500 deaths. CONCLUSIONS: Campylobacter, E. coli O157, Listeria, and Salmonella are major contributors to illness in older adults, highlighting the value of effective and targeted intervention.

Incidence and trends of infection with pathogens transmitted commonly through food--Foodborne Diseases Active Surveillance Network, 10 U.S. sites, 2006-2013.

Foodborne disease continues to be an important problem in the United States. Most illnesses are preventable. To evaluate progress toward prevention, the Foodborne Diseases Active Surveillance Network (FoodNet) monitors the incidence of laboratory-confirmed infections caused by nine pathogens transmitted commonly through food in 10 U.S. sites, covering approximately 15% of the U.S. population. This report summarizes preliminary 2013 data and describes trends since 2006. In 2013, a total of 19,056 infections, 4,200 hospitalizations, and 80 deaths were reported. For most infections, incidence was well above national Healthy People 2020 incidence targets and highest among children aged <5 years. Compared with 2010-2012, the estimated incidence of infection in 2013 was lower for Salmonella, higher for Vibrio, and unchanged overall.† Since 2006-2008, the overall incidence has not changed significantly. More needs to be done. Reducing these infections requires actions targeted to sources and pathogens, such as continued use of Salmonella poultry performance standards and actions mandated by the Food Safety Modernization Act (FSMA). FoodNet provides federal and state public health and regulatory agencies as well as the food industry with important information needed to determine if regulations, guidelines, and safety practices applied across the farm-to-table continuum are working.

A toolkit for planning and implementing acute febrile illness (AFI) surveillance.

Acute febrile illness (AFI) is a broad clinical syndrome with a wide range of potential infectious etiologies. The lack of accessible, standardized approaches to conducting AFI etiologic investigations has contributed to significant global gaps in data on the epidemiology of AFI. Based on lessons learned from years of supporting AFI sentinel surveillance worldwide, the U.S. Centers for Disease Control and Prevention developed the toolkit for planning and implementing AFI surveillance, described here. This toolkit provides a comprehensive yet flexible framework to guide researchers, public health officials, and other implementers in developing a strategy to identify and/or monitor the potential causes of AFI. The toolkit comprises a cohesive set of planning aids and supporting materials, including an implementation framework, generic protocol, several generic forms (including screening, case report, specimen collection and testing, and informed consent and assent), and a generic data dictionary. These materials incorporate key elements intended to harmonize approaches for AFI surveillance, as well as setting-specific components and considerations for adaptation based on local surveillance objectives and limitations. Appropriate adaptation and implementation of this toolkit may generate data that expand the global AFI knowledge base, strengthen countries' surveillance and laboratory capacity, and enhance outbreak detection and response efforts.

Toward a Continuum of Measures to Mitigate Primary and Secondary Impacts of COVID-19 and Other Public Health Emergencies.

The global COVID-19 response focused heavily on nonpharmaceutical interventions (NPIs) until vaccines became available. Even where vaccination coverage is low, over time governments have become increasingly reluctant to use NPIs. Inequities in vaccine and treatment accessibility and coverage, differences in vaccine effectiveness, waning immunity, and immune-escape variants of concern of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinforce the long-term need for mitigation. Initially, the concept of NPIs, and mitigation more broadly, was focused on prevention of SARS-CoV-2 transmission; however, mitigation can and has done more than prevent transmission. It has been used to address the clinical dimensions of the pandemic as well. The authors propose an expanded conceptualization of mitigation that encompasses a continuum of community and clinical mitigation measures that can help reduce infection, illness, and death from COVID-19. It can further help governments balance these efforts and address the disruptions in essential health services, increased violence, adverse mental health outcomes, and orphanhood precipitated by the pandemic and by NPIs themselves. The COVID-19 pandemic response revealed the benefits of a holistic and layered mitigation approach to public health emergencies from the outset. Lessons learned can inform the next phases of the current pandemic response and planning for future public health emergencies.

Calculating a measure of overall change in the incidence of selected laboratory-confirmed infections with pathogens transmitted commonly through food in the Foodborne Diseases Active Surveillance Network (FoodNet), 1996-2010.

To measure overall change in the incidence of illness, we combined data for infections caused by 6 bacterial pathogens monitored by the Foodborne Diseases Active Surveillance Network for which >50% of illnesses are estimated to be transmitted by food. The overall incidence for these pathogens was 23% lower in 2010 than during the period 1996-1998. This estimate provides a summary of changes in incidence of infection for these pathogens.

Increasing rates of vibriosis in the United States, 1996-2010: review of surveillance data from 2 systems.

BACKGROUND: The Centers for Disease Control and Prevention monitors vibriosis through 2 surveillance systems: the nationwide Cholera and Other Vibrio Illness Surveillance (COVIS) system and the 10-state Foodborne Diseases Active Surveillance Network (FoodNet). COVIS conducts passive surveillance and FoodNet conducts active surveillance for laboratory-confirmed Vibrio infections. METHODS: We summarized Vibrio infections (excluding toxigenic V. cholerae O1 and O139) reported to COVIS and FoodNet from 1996 through 2010. For each system, we calculated incidence rates using US Census Bureau population estimates for the surveillance area. RESULTS: From 1996 to 2010, 7700 cases of vibriosis were reported to COVIS and 1519 to FoodNet. Annual incidence of reported vibriosis per 100,000 population increased from 1996 to 2010 in both systems, from 0.09 to 0.28 in COVIS and from 0.15 to 0.42 in FoodNet. The 3 commonly reported Vibrio species were V. parahaemolyticus, V. vulnificus, and V. alginolyticus; both surveillance systems showed that the incidence of each increased. In both systems, most hospitalizations and deaths were caused by V. vulnificus infection, and most patients were white men. The number of cases peaked in the summer months. CONCLUSIONS: Surveillance data from both COVIS and FoodNet indicate that the incidence of vibriosis increased from 1996 to 2010 overall and for each of the 3 most commonly reported species. Epidemiologic patterns were similar in both systems. Current prevention efforts have failed to prevent increasing rates of vibriosis; more effective efforts will be needed to decrease rates.

Relative risk of listeriosis in Foodborne Diseases Active Surveillance Network (FoodNet) sites according to age, pregnancy, and ethnicity.

BACKGROUND: Quantitative estimates of the relative risk (RR) of listeriosis among higher-risk populations and a nuanced understanding of the age-specific risks are crucial for risk assessments, targeted interventions, and policy decisions. METHOD: The RR of invasive listeriosis was evaluated by age, pregnancy status, and ethnicity using 2004-2009 data from the Foodborne Diseases Active Surveillance Network (FoodNet). Nonparametric logistic regression was used to characterize changes in risk with age and ethnicity. Adjusted RRs and 95% confidence intervals (CIs) were evaluated using negative binomial generalized linear models. RESULTS: Among non-pregnancy-associated cases, listeriosis incidence rates increased gradually with age (45-59 years: RR, 4.7; 95% CI, 3.3-6.8; >85 years: RR, 53.8; 95% CI, 37.3-78.9; reference: 15-44 years). The RR was significantly higher for Hispanics than for non-Hispanics (RR, 1.8; 95% CI, 1.3-2.5). Among women of reproductive age (15-44 years), pregnant women had a markedly higher listeriosis risk (RR, 114.6; 95% CI, 68.9-205.1) than nonpregnant women. The RR was higher for Hispanic than non-Hispanic women, regardless of pregnancy status, and this increased during the study period (2004-2006: RR, 1.9; 95% CI, 1.0-3.3; 2007-2009: RR, 4.8; 95% CI, 3.1-7.1). CONCLUSIONS: This study quantifies the increases in risk of listeriosis among older persons, pregnant women, and Hispanics in the United States. Additional research is needed to better describe the independent effects of age on risk while accounting for underlying conditions. These estimates are needed both to optimize risk assessment models and to inform targeted interventions and policy decisions.

Sex-based differences in food consumption: Foodborne Diseases Active Surveillance Network (FoodNet) Population Survey, 2006-2007.

BACKGROUND: This analysis used data from the most recent Foodborne Diseases Active Surveillance Network (FoodNet) Population Survey (May 2006 through April 2007) to examine differences in the consumption of various types of foods between men and women. METHODS: Participants were surveyed by telephone and asked whether or not they had consumed certain foods in the past 7 days, including the following "high-risk" foods commonly associated with foodborne illness: pink hamburger, raw oysters, unpasteurized milk, cheese made from unpasteurized milk, runny eggs, and alfalfa sprouts. Data were weighted to adjust for survey design and to reflect the age and sex distribution of the population under FoodNet surveillance. RESULTS: A total of 14 878 persons ≥ 18 years were interviewed, of whom 5688 (38%) were men. A higher proportion of men reported eating meat and certain types of poultry than women, whereas a higher proportion of women ate fruits and vegetables. A higher proportion of men than women reported consuming runny eggs (12% versus 8%), pink hamburger (7% versus 4%), and raw oysters (2% versus 0.4%). A higher proportion of women than men ate alfalfa sprouts (3% versus 2%). No differences by sex were observed for consumption of unpasteurized milk or cheese. CONCLUSIONS: Data from the FoodNet Population Surveys can be useful in efforts to design targeted interventions regarding consumption of high-risk foods. Moreover, understanding the background rates of food consumption, stratified by sex, may help investigators identify the kinds of foods likely to be associated with outbreaks in which a preponderance of cases occur among members of one sex.

Invasive listeriosis in the Foodborne Diseases Active Surveillance Network (FoodNet), 2004-2009: further targeted prevention needed for higher-risk groups.

BACKGROUND: Listeriosis can cause severe disease, especially in fetuses, neonates, older adults, and persons with certain immunocompromising and chronic conditions. We summarize US population-based surveillance data for invasive listeriosis from 2004 through 2009. METHODS: We analyzed Foodborne Diseases Active Surveillance Network (FoodNet) data for patients with Listeria monocytogenes isolated from normally sterile sites. We describe the epidemiology of listeriosis, estimate overall and specific incidence rates, and compare pregnancy-associated and nonpregnancy-associated listeriosis by age and ethnicity. RESULTS: A total of 762 listeriosis cases were identified during the 6-year reporting period, including 126 pregnancy-associated cases (17%), 234 nonpregnancy-associated cases(31%) in patients aged <65 years, and 400 nonpregnancy-associated cases (53%) in patients aged ≥ 65 years. Eighteen percent of all cases were fatal. Meningitis was diagnosed in 44% of neonates. For 2004-2009, the overall annual incidence of listeriosis varied from 0.25 to 0.32 cases per 100,000 population. Among Hispanic women, the crude incidence of pregnancy-associated listeriosis increased from 5.09 to 12.37 cases per 100,000 for the periods of 2004-2006 and 2007-2009, respectively; among non-Hispanic women, pregnancy-associated listeriosis increased from 1.74 to 2.80 cases per 100,000 for the same periods. Incidence rates of nonpregnancy-associated listeriosis in patients aged ≥ 65 years were 4-5 times greater than overall rates annually. CONCLUSIONS: Overall listeriosis incidence did not change significantly from 2004 through 2009. Further targeted prevention is needed, including food safety education and messaging (eg, avoiding Mexican-style cheese during pregnancy). Effective prevention among pregnant women, especially Hispanics, and older adults would substantially affect overall rates.

Deaths associated with bacterial pathogens transmitted commonly through food: foodborne diseases active surveillance network (FoodNet), 1996-2005.

BACKGROUND: Foodborne diseases are typically mild and self-limiting but can cause severe illness and death. We describe the epidemiology of deaths associated with bacterial pathogens using data from the Foodborne Diseases Active Surveillance Network (FoodNet) in the United States. METHODS: We analyzed FoodNet data from 1996-2005 to determine the numbers and rates of deaths occurring within 7-days of laboratory-confirmation. RESULTS: During 1996-2005, FoodNet ascertained 121,536 cases of laboratory-confirmed bacterial infections, including 552 (.5%) deaths, of which 215 (39%) and 168 (30%) were among persons infected with Salmonella and Listeria, respectively. The highest age-specific average annual population mortality rates were in older adults (≥65 years) for all pathogens except Shigella, for which the highest age-specific average annual population mortality rate was in children <5 years (.2/1 million population). Overall, most deaths (58%; 318) occurred in persons ≥65 years old. Listeria had the highest case fatality rate overall (16.9%), followed by Vibrio (5.8%), Shiga toxin-producing Escherichia coli O157 (0.8%), Salmonella (0.5%), Campylobacter (0.1%), and Shigella (0.1%). CONCLUSIONS: Salmonella and Listeria remain the leading causes of death in the United States due to bacterial pathogens transmitted commonly through food. Most such deaths occurred in persons ≥65 years old, indicating that this age group could benefit from effective food safety interventions.

Incidence of acute gastroenteritis and role of norovirus, Georgia, USA, 2004-2005.

Approximately 179 million cases of acute gastroenteritis (AGE) occur annually in the United States. However, lack of routine clinical testing for viruses limits understanding of their role among persons seeking medical care. Fecal specimens submitted for routine bacterial culture through a health maintenance organization in Georgia, USA, were tested with molecular diagnostic assays for norovirus, rotavirus, astrovirus, sapovirus, and adenovirus. Incidence was estimated by using national health care utilization rates. Routine clinical diagnostics identified a pathogen in 42 (7.3%) of 572 specimens; inclusion of molecular viral testing increased pathogen detection to 15.7%. Community AGE incidence was 41,000 cases/100,000 person-years and outpatient incidence was 5,400/100,000 person-years. Norovirus was the most common pathogen, accounting for 6,500 (16%) and 640 (12%) per 100,000 person-years of community and outpatient AGE episodes, respectively. This study demonstrates that noroviruses are leading causes of AGE among persons seeking medical care.

Methods for monitoring trends in the incidence of foodborne diseases: Foodborne Diseases Active Surveillance Network 1996-2008.

Foodborne illnesses are a substantial health burden in the United States. The Foodborne Diseases Active Surveillance Network (FoodNet) is the principal foodborne disease component of the Centers for Disease Control and Prevention's Emerging Infections Program. FoodNet is a collaborative project among Centers for Disease Control and Prevention, Emerging Infections Program sites, the U.S. Department of Agriculture, and the U.S. Food and Drug Administration. One of FoodNet's main objectives is to monitor changes in the incidence of selected foodborne pathogens. In 1996, FoodNet began active, population-based surveillance for laboratory-diagnosed cases of Campylobacter, Listeria, Salmonella, Shiga toxin-producing E. coli O157, Shigella, Vibrio, and Yersinia infection. Surveillance for cases of Cryptosporidium and Cyclospora infection was added in 1997 and surveillance for non-O157 Shiga toxin-producing E. coli was added in 2000. From 1997 to 2008, the FoodNet surveillance population increased, primarily through the addition of new sites. The increase in the number of FoodNet sites and the size of the population under surveillance as well as the variation in the incidence of infections among sites posed challenges in the selection of the most appropriate method to monitor changes in incidence. To account for variation introduced by changes in population size, a main-effects, log-linear Poisson (negative binomial) regression model was adopted to estimate the magnitude of changes in the incidence of pathogens by comparing current year incidence to reference periods. The article explains how FoodNet uses the negative binomial model to examine changes in incidence over time, describes the reference periods used, explains the graphics used to display results, and discusses future directions in the analysis of trends over time.

The effect of different recall periods on estimates of acute gastroenteritis in the United States, FoodNet Population Survey 2006­2007.

BACKGROUND: A number of countries have estimated the prevalence of acute gastroenteritis by asking survey respondents to recall past episodes of diarrhea; however, the recall period used varies between studies. We conducted a survey to examine the effects of 7-day and 1-month recall periods on the estimated annual episodes of acute gastroenteritis. Further, we examine whether asking first about illness in the previous 7 days affects a person's response to a 1-month recall period. METHODS: The Foodborne Diseases Active Surveillance Network (FoodNet) conducted a population-based telephone survey that included asking respondents about the occurrence of gastrointestinal symptoms. From February through April 2007, we randomly split respondents into two groups to examine effect of recall periods and question order. One group was first asked about symptoms in the 7 days before interview and then asked about symptoms in the month before interview. The other group was asked only about symptoms in the month before interview. RESULTS: Overall, the monthly prevalence of acute diarrheal illness (≥3 loose stools in 24-hours, lasting >1 day, or restricting daily activities) was 7.7%. This proportion was consistent among the respondents who were first asked about a 7-day recall period (n=1436) and those asked only about symptoms in the past month (n=2132). Extrapolation from the reported 7-day prevalence of 3.1% to an annual rate of 1.6 episodes per person, however, was almost twice the rate of episodes estimated when extrapolating from the month recall period. Similar findings were found with acute gastroenteritis (acute diarrheal illness or vomiting without respiratory symptoms). CONCLUSIONS: First asking respondents about a 7-day recall period did not affect the prevalence of acute gastroenteritis reported for a 1-month recall period. Recall period length did, however, have a major impact on estimates of acute gastroenteritis. Retrospective studies using different recall periods may not be comparable.