Community Congregate Settings

Amra Uzicanin and Joanna Gaines


Settings and patterns of human congregation are risk factors and determinants for infectious and other diseases in communities because they can modulate the scope and extent of spread through modes of exposure and transmission (e.g., person-to-person, airborne, foodborne, waterborne, and vectorborne). Except for households, which are the elemental unit of human congregation, among the most notable community settings associated with regular, nonrandom congregation are educational institutions and workplaces. Other community congregate settings include places where people gather occasionally or without a prevailing pattern in terms of time, place, or membership (e.g., entertainment and mass gathering venues, such as movie theaters and concert halls, or commercial venues, such as shopping malls). Some congregate settings accommodate larger groups of people with limited access to the surrounding community (e.g., jails, prisons, and other detention facilities).

Comprehensively enumerating all congregate settings and congregation behaviors that could become relevant in a field investigation is difficult; therefore, this chapter reviews field investigations in four types of congregate settings: (1) educational institutions, (2) workplaces, (3) mass gatherings, and (4) detention facilities. For investigations in each setting, practical and legal implications are discussed, followed by a summary of one or more illustrative investigations.

Educational Institutions

Educational institutions are virtually ubiquitous and are the key settings where children and youth regularly congregate in large numbers. For example, 75.2 million students were enrolled in schools and colleges in the United States in 2014; of these, an estimated 55 million were elementary and secondary school students (pre-kindergarten through grade 8, and grades 9–12, respectively) (1). These institutions and facilities also employ many adults; for example, in 2014, almost 10 million teachers and other staff worked in educational institutions (1).

The intense social density that characterizes schools, combined with age-related biological, behavioral, and environmental factors, can facilitate infectious disease transmission within schools and lead to secondary spread into households and the wider community. School-based outbreaks have involved a multitude of infectious pathogens, and correlation between school opening dates and communitywide disease activity has been reported for influenza and other seasonally occurring respiratory infections (2–4). Educational institutions are therefore important venues for epidemiologic field investigations of disease outbreaks in communities and priority settings for encouraging appropriate disease prevention measures, such as vaccination, environmental hygiene, and healthy behaviors. Educational institutions also can be settings for implementing or evaluating some public health interventions (e.g., vaccination).

Implications for Field Investigations

  • Practical:
    • School-based records can provide information useful for field investigations, and school nurses might be able to assist the public health team.
    • Since some case-patients may seek care elsewhere rather than contact a school nurse, investigators may need to work simultaneously with the affected schools and the local healthcare providers to evaluate a school-based outbreak and obtain relevant case-based information.
    • The fact that some school nurses serve on a part-time basis in multiple schools can pose a logistical challenge for collaboration with investigators.
    • School-based investigations can interfere with routine educational activities and processes; accordingly, public health teams should strive to minimize that interference by coordinating thoroughly with education officials.
  • Legal:
    • In addition to general legal requirements (see Chapter 13), public health staff preparing to conduct an investigation in schools should be aware of the privacy protection laws that apply in schools. The federal Family Educational Rights and Privacy Act protects the privacy of student education records (5), including school attendance records, which might be relevant in some investigations.
    • School nurses are particularly important for data collection that must adhere to requirements of both the Health Insurance Portability and Accountability Act of 1996 (6) and the Family Educational Rights and Privacy Act.
    • Because educational institutions employ staff, legal considerations pertinent for worksites might apply.

Illustrative Field Investigation

Because school-based outbreaks often herald wider disease spread, school-based investigation may yield critical early insights into wider community outbreaks and even major epidemics. In April 2009, an investigation of a febrile respiratory illness outbreak was initiated in a New York City high school comprising 2,686 students and 228 staff, days after Centers for Disease Control and Prevention (CDC) confirmation of an initial eight cases of human infection with a novel swine-origin influenza A(H1N1) virus, subsequently termed influenza A(H1N1)pdm09, in Texas and California. During April 22–24, a total of 222 students visited the school nursing office because of fever and respiratory symptoms and subsequently left school. Because of suspicion that the new influenza A virus might have caused the outbreak, public health officials visited the school on April 24 and collected nasopharyngeal swab samples from five newly symptomatic students identified by the school nurse and from an additional four students at a nearby physician’s office. On April 26, CDC confirmed seven of these nine initial samples as the new influenza A(H1N1) virus. Nasopharyngeal swab collection kits were provided to local physicians’ offices and emergency departments. During April 26–28, they collected an additional 42 samples, of which 37 (88%) subsequently tested positive for the new virus, bringing the total number of confirmed cases in this cluster to 44—approximately half of all US cases of this novel influenza A(H1N1) virus detected by April 28. Field investigators conducted telephone interviews with these 44 persons with laboratory-confirmed illness, which helped determine that the clinical presentation in this cluster (in a population known to be at low risk for severe disease from seasonal influenza) appeared to be similar to seasonal influenza (7). An enhanced surveillance for self-reported influenza-like illness (ILI) was subsequently launched, including two online surveys to all students and staff administered on April 26 and May 2, which identified that approximately 800 students and staff (35% of student respondents and 10% of employee respondents) had ILI during that period. A link with travel to Mexico, where the new virus was known to be circulating widely, was established for five students with ILI and symptom onset during April 20–23; one of these students also had laboratory-confirmed infection. The data on laboratory-confirmed cases collected through this school-based investigation helped describe the natural history of the 2009 outbreak of a novel influenza A(H1N1) in New York City (8). The new virus subsequently spread throughout the United States and worldwide, causing the first influenza pandemic of the twenty-first century.

During the response to the 2009 influenza A(H1N1) pandemic in the United States, school-aged children were designated as one of the priority groups for the monovalent pandemic vaccine. An estimated 85% of local health departments held school-located vaccination clinics starting in October 2009. Approximately one-third of all US children aged 5–17 years who received pandemic vaccine were vaccinated at school (9). School-based field evaluations undertaken in 2010 in Maine by public health officials in close collaboration with schools, most notably with school nurses, helped to document that the vaccine was effective in preventing laboratory-confirmed pandemic influenza and in reducing student and teacher absenteeism (10,11).


In 2015, of 81.4 million families in the United States, 80% had at least one employed member (12). Places of employment range from small family-owned businesses with few or no employees to large companies with tens of thousands of employees in offices, production plants, or other facilities. Availability of workplace-based employee services also varies and can include employee cafeterias, occupational health clinics, and other on-site health and wellness facilities. Epidemiologic field investigations in workplaces most frequently involve occupational disease and injury issues (see Chapter 21). However, workplaces may be associated with occurrence of nonoccupational diseases, most notably infectious disease outbreaks that prompt field investigations. Initial case-patients in workplace-associated infectious disease outbreaks frequently are identified by the local healthcare facilities where employed adults receive primary care or by emergency departments. Information about the place of employment obtained from adult patients with an infectious disease is the key piece of the puzzle in identifying and investigating workplace-related outbreaks.

Implications for Field Investigations

  • Practical:
    • Preparatory steps include gathering information about the workplace setting of the investigation and identifying opportunities for collaboration with an on-site occupational health team (if available), as well as with local healthcare providers and facilities where affected employees might have sought care.
    • Because epidemiologic investigations in a workplace can interfere with, or even interrupt, business processes, coordination with the workplace leadership can help avert or minimize disruption and ensure compliance with business-specific rules and regulations.
    • At the onset of workplace-based investigations, field teams should determine which business records might aid the investigation and what additional information should be collected about worksites, employees, and/or clients. In addition, on-site occupational health clinics might be able to assist with conducting field investigations and implementing outbreak responses.
  • Legal: In addition to legal requirements (see Chapter 13), field investigators should be aware of rules and regulations that apply to investigations in a workplace setting (see Chapter 21).

Illustrative Field Investigations

Although workplaces are not commonly thought of as venues for spread of infectious diseases that are prevented through routine childhood vaccination, under some circumstances clusters of vaccine-preventable disease can occur among adults in work settings and spread into surrounding communities. In 1999, a 29-year-old man sought treatment in three healthcare facilities for what he thought was a sexually transmitted disease. At his third visit, he was noted to have a maculopapular rash, low-grade fever, and lymphadenopathy, and he subsequently tested IgM positive for rubella. He was employed at a meat-packing plant in a county that had no cases of rubella reported for the previous 9 years and had high rubella vaccination rates among children. In the following 2 months, 83 confirmed rubella cases occurred in the county, all among unvaccinated persons. Of those cases, 52 (63%) were in meat-packing plant employees or their household contacts, mainly foreign-born Hispanic men from countries without childhood rubella vaccination at the time they were born. The meat-packing plant had an attack rate of 14.4/1,000 persons, compared with the countywide attack rate of 0.19/1,000 persons. Field investigation documented that vaccine failure was not associated with this outbreak originating in a workplace but rather lack of rubella vaccination among some of the employees. Crowded working and living conditions further facilitated rubella transmission. During outbreak response, vaccination campaigns targeted seven meat-packing plants with 3,000 workers (13). In this example, the workplace was the setting where many unprotected (unvaccinated) adults congregated and acquired rubella infection after the virus was introduced in that setting despite little rubella circulation in the surrounding community. The workplace component of this field investigation helped elucidate the actual risk factors associated with this outbreak.

The built environment of community congregate settings, including workplaces, may be an important determinant for disease exposure. After reports of illness of unknown etiology among several military base employees, Legionnaires’ disease (LD) was confirmed in two persons. An epidemiologic field investigation identified 67 cases of Legionella-related disease, including LD and Pontiac fever. Cases clustered on the base’s eastern office complex. Subsequently, Legionella colonies grew from environmental samples collected from two cooling towers serving the eastern office complex; isolates from one of two towers matched the same species and serogroup as clinical isolates. A retrospective cohort indicated that the risk for Legionella infection was associated with occupancy in the building closest to that cooling tower (14). This example illustrates how understanding a workplace layout and distribution of cases can help epidemiologists develop and test a hypothesis during a field investigation in workplaces and other settings.

Mass Gatherings

Mass gatherings range in size and purpose; no minimum number of people constitutes a “mass gathering.” The World Health Organization defines a mass gathering as any event during which people gather at a specific place for a set time in sufficient numbers to strain the resources or infrastructure (including healthcare) of the host community or country (15). Medical and public health efforts in advance of mass gatherings focus primarily on preparedness and response. Risk assessment is a critical component in planning for mass gatherings and should follow an iterative process in which feedback informs the focus of public health surveillance and response efforts (15).

Implications for Field Investigations

  • Practical:
    • The multiplicity of factors associated with different mass gatherings (e.g., location, number of venues, number and mobility of participants, length of planning time, indoor or outdoor setting, weather and seasonal considerations, number of government jurisdictions) directly influence public health preparations and potential epidemiologic field investigations.
    • Potential partners for public health surveillance and response include traditional public health systems (e.g., health departments, hospitals) and agencies and event-specific entities (e.g., Olympic organizing committees).
    • The public health risks associated with a mass gathering include environmental health issues, infectious diseases, and other domains (16,17).
    • Because existing public health surveillance systems sometimes are of limited value for timely detection of outbreaks associated with mass gatherings, retrospective surveys often are needed to complete epidemiologic field investigations involving mass gathering attendees. For that reason, enhancement of existing surveillance systems to ensure timeliness and accuracy might be required for some mass gatherings (18,19). These enhanced systems typically increase the speed of reporting of existing surveillance systems (20).
  • Legal: Multiple government and administrative levels (e.g., local, state, federal, multinational) might have jurisdiction in mass gatherings, and their response roles will depend on such factors as their capacities and legal authorities.

Illustrative Field Investigation

Surveillance systems using preestablished criteria can expedite the speed of outbreak detection and response. A syndromic surveillance system was used in 2005 for a camping event in Virginia attended by approximately 43,000 youths and adults. Public health personnel screened arriving attendees for symptoms such as vomiting, diarrhea, rash, fever, pinkeye or red eyes, and cough. If any group of arriving attendees (e.g., a bus) had three or more persons with symptoms associated with communicable disease during the previous 48 hours, the entire group was referred for additional screening. Public health personnel also established a syndromic surveillance system to quickly identify communicable disease outbreaks. These screening processes rapidly identified four clusters of gastrointestinal illness, and symptomatic persons were restricted from handling food for the remainder of their time in camp. Screening on the hottest day of the event identified a surge in heat-related illnesses, leading to rescheduling of an event and provision of additional shade structures, cooling stations, and water sources. These efforts to mitigate heat-related illnesses resulted in one of the lowest rates of heat-related exhaustion and heatstroke during the entire 10-day event (21). These rapid public health responses demonstrate the value of syndromic surveillance at a mass gathering event. Health risks were quickly and effectively identified through judicious planning and use of resources, and steps were taken to reduce the risk to other attendees.

Detention Facilities

Disease surveillance and outbreak response in detention facilities require collaboration and coordination between public health agencies and the criminal justice system, sometimes at multiple jurisdictional levels. Prisons, jails, and other detention facilities involve tight regulation of populations, with special protections to ensure the population’s vulnerability is not exploited. The US Department of Health and Human Services defines a prisoner as “any individual involuntarily confined or detained in a penal institution”—such persons include those detained pending arraignment, trial, or sentencing (22). Oversight of prisoners depends on jurisdiction of incarceration. For example, at the federal level, the federal Bureau of Prisons operates federal facilities; provides essential medical, dental, and psychiatric services; and monitors for infectious disease outbreaks (23). State and local detention facilities—including prisons and jails—usually are operated at respective levels of jurisdiction.

Implications for Field Investigations

  • Practical:
    • Health officials have limited access to prisoners. They might be able to speak with prisoners only within sight of guards. Prisoners might be distrustful and unwilling to disclose possible exposures, particularly if an exposure was related to a prohibited activity (e.g., brewing alcohol) (24,25).
    • Field investigators may be able to closely track points of contact for prisoners because of their controlled movements; however, many prisons have large populations and therefore many opportunities for contact among prisoners.
    • In some detention settings, limitations in access to medical records for prisoners and workers also can complicate outbreak detection and response.
    • Workers in detention facilities can share exposures with prisoners (e.g., environmental conditions or person-to-person contact), adding an additional layer of complexity to the response as the two populations are treated differently within detention facility systems.
    • Investigations in these settings require collaboration between criminal justice authorities and public health officials, sharing resources and information when appropriate to identify and mitigate public health threats (26).
  • Legal:
    • Public health practitioners need to be aware of the unique regulations for prison populations and ensure that their efforts comply with applicable rules and laws.
    • Specific regulations provide additional protections to prisoners involved as subjects in Department of Health and Human Services– conducted or – supported research (27). These regulations also apply if a person becomes a prisoner during the course of an investigation (27).
    • Law enforcement officials also should be consulted to ensure prisoners are adequately protected.

Illustrative Field Investigation

Public health investigations in prison populations pose unique challenges and require close collaboration between public health entities and the criminal justice systems. For example, consumption of prison-made alcohol, known as pruno, was related to multiple outbreaks of botulism among prison inmates during 2011 and 2012 (24,25). Botulism, a potentially life-threatening illness, is caused by a toxin produced by the bacterium Clostridium botulinum. In previous outbreaks, prisoners have been hospitalized and intubated (25). Pruno is made primarily from fruit, sugar, and water; root vegetables sometimes are added. An investigation of a cluster of eight prisoners sickened in Utah found that they had added to their pruno a baked potato saved from a meal, which was the likely source of the C. botulinum (24). Partnership with law enforcement officials and prison authorities enabled epidemiologists to understand patient connections and identify possible exposures.


The systematic approach to conducting an epidemiologic field investigation (see Chapter 3) applies to epidemiologic investigations of congregate settings. However, investigations involving congregate settings also can face unique challenges, such as the potential for interference with normal business processes, limits on data availability and access, and additional legal and confidentiality requirements. Field investigations of congregate settings can be aided by the following:

  • Online information can help investigators learn about community and congregate settings affected by the public health issue under investigation.
  • Initial meetings with local public health officials can verify and supplement information found online and facilitate contact with key persons responsible for congregate settings of interest.
  • Understanding setting-specific legal and practical implications is important at the onset of investigations of congregate settings.
  • Depending on the situation, field investigators might need to research and document the characteristics of the congregate settings, including physical layout, environmental aspects (e.g., air, water, sanitation), on-site ancillary services (e.g., food and healthcare), relevant schedules, and attendance and/or absenteeism.
  • A field investigation in a congregate setting must take into consideration behaviors and other potentially relevant factors for disease exposure or transmission within that setting and community.
  • Close coordination and collaboration with officials responsible for the congregate setting during all investigation stages—from planning to completion—are critical to ensure the investigation’s efficiency and minimizing disruptions of the gathering.
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