What is public health surveillance?
Public health officials coined the term surveillance to describe the systems they set up to watch out for and control the occurrence of health threats.
Just as the police set up closed-circuit television devices and community watch programmes to detect and prevent crime, public health practitioners set up surveillance systems to detect unwanted health events and prevent them from escalating and damaging population health.
While public health surveillance originated to control the spread of infectious diseases such as plague, cholera or coronavirus, it has evolved to include some non-communicable diseases, occupational health and injuries as well as biological, behavioural and social determinants of these conditions.
- To detect, at an early stage, acute public health threats from all hazards – disease, biological, chemical, radiation, natural disaster and deliberate acts – which require rapid investigation and response;
- To guide control programmes by measuring disease burden, monitoring trends, describing disease distribution and evaluating the effectiveness of public health programmes
The rise of global health surveillance
Today, the world community is working together to control the outbreak and spread of the coronavirus COVID-19. But precedent for such activities was laid over 700 years ago.
When plague ravaged Europe during the fourteenth century authorities understood that international spread of such diseases followed cross-border trade, pilgrimage and war; and so prevention of disease was a national security issue. In the city-state of Venice, authorities instigated quarantine measures – keeping arriving ships in the harbour for 40 days before docking, and holding people in isolation for 40 days at land borders to prevent entry of plague.
In the mid-nineteenth century, governments agreed international conventions aimed at stopping spread of plague and cholera – and two other infectious diseases, yellow fever and smallpox. The conventions required each country to report outbreaks of these diseases to all signatories of the convention, and permitted application of certain public health measures at international borders once a country reported of one of the diseases.
In the early twentieth century, governments in the Americas and in Europe set up regional conventions called International Sanitary Bureaus to coordinate international activities to prevent the transmission of disease across borders.
In 1951, the newly formed World Health Organization (WHO) led establishment of the International Sanitary Regulations (ISR) to foster global cooperation in reporting and acting at international borders to guard against the spread of cholera, plague, yellow fever, and smallpox.
International Health Regulations (IHR)
In 1969, the WHO replaced the ISR with the International Health Regulations (IHR) which required countries to report any cases of cholera, plague, yellow fever, and smallpox to WHO. If a country reported one of these diseases, other countries could apply pre-established control measures at international borders – such as a requirement of proof of vaccination against yellow fever of any passenger arriving from a country that reported yellow fever to WHO.
In 2005, after the 2003 the outbreak of the Severe Acute Respiratory Syndrome (SARS), WHO updated the IHR and published the IHR 2005 as a legal framework to include more diseases, and developed real-time evidence-based recommendations for prevention and control of outbreaks.
The IHR 2005 mandate WHO member countries to report immediately the occurrence of a single case of four diseases (smallpox, poliomyelitis due to wild type poliovirus, human influenza caused by a new subtype, and severe acute respiratory syndrome (SARS)).
The IHR 2005 require countries to develop core capacities in public health, including surveillance systems and epidemiology services, that can analyse and act on surveillance information to detect and respond to diseases where and when they occur so that their potential to spread internationally is decreased.
Public Health Emergency of International Concern
The IHR 2005 defines the term Public Health Emergency of International Concern (PHEIC) as follows:
“an extraordinary event which is determined, as provided in these Regulations:
- to constitute a public health risk to other States through the international spread of disease; and
- to potentially require a coordinated international response.
This definition implies a situation that: is serious, unusual or unexpected; carries implications for public health beyond the affected State’s national border; and may require immediate international action.”
WHO evaluates each newly identified outbreak for its potential to become a PHEIC by the country in which it is occurring.
WHO has declared PHEICs for
- H1N1 (Swine fever) in 2009
- Poliomyelitis in 2014
- The Ebola outbreak in West Africa from August 2014 and 2016
- Zika Virus, Microcephaly and Guillain–Barré syndrome in the Americas from February to November 2016
- The Ebola Outbreak in the Democratic Republic in July 2019
- COVID-19 in January 2019.
Surveillance within countries
Each country has lists of diseases/conditions and events that it requires its health workers to report by law. These can be:
- Reportable diseases of greatest public health threat: health workers or laboratory technicians must report individual cases as they occur. These diseases include those required by the IHR 2005 and, for example, anthrax, cholera, legionellosis, and the plague.
- Notifiable conditions: health workers should report the number of cases that have occurred in a given time period, for example communicable diseases such as measles, pneumonia, HIV/AIDS or diarrhea, or non-communicable conditions such as cancers, diabetes or hypertension.
The structure of government responsibilities for public health surveillance varies. Most often, countries set up dedicated early warning and rapid response surveillance teams that work with or complement surveillance activities of specific control programmes such as malaria, HIV/AIDS or tuberculosis.
- surveillance and response teams detect early stage public health threats.
- Control programmes gather disease (or condition) specific information to plan activities. and share information with surveillance teams as required.
- A national network of public health laboratories, often linked to international reference laboratories, confirms etiologic agents, genetic strains, and antibiotic resistance patterns.
surveillance activities are said to be:
- Active when health workers pro-actively seek out cases, for example when tracing the contacts of a known case
- Passive when the system relies on patients to report themselves to the systems, for example by attending a health facility
Surveillance data to detect outbreaks
Using standard case definitions, health workers report individual cases of reportable and notifiable diseases to the local or national surveillance centre where staff aggregate reports, and clean and analyse the data. In cleaning the data, staff look for coding and classification errors, and for duplicate reports.
Indicator-based data are derived from patients diagnosed – by syndrome description, clinical or laboratory confirmation. The surveillance team identifies them through routine collection or active case search and reports them either as individual or aggregated cases.
Event-based data are about outbreaks, unusual events or changes in human exposure. Rather than wait for official reports, the surveillance team gathers information and rumours through the media, Internet and unusual events occurring reported by the community, and investigates these reports. The team captures abnormal health events in real-time and confirms potential outbreaks by triangulating with indicator-based data.
Epidemiologists analyse the data to determine how many new cases have occurred during the past day or week and their distribution in time, place and by person to see whether the magnitude and pattern of disease under surveillance is changing. They note any changes in frequency, clustering, or distribution and flag them for verification and explanation.
Epidemiologists responsible for surveillance use standard epidemiological methods to analyse trends, identify clusters and suspect of some risk factors. Using increasingly sophisticated technologies for data capture and analysis, surveillance teams can monitor real-time occurrence in time and place of unusual events such as cholera or legionella, or seasonal outbreaks such as malaria.
Once epidemiologists have concluded their analyses, they prepare reports which can trigger immediate action by a rapid response team to visit the site of the events and investigate the situation and contain the outbreak. They also send reports to clinicians in hospitals and local and national programme managers.
Many countries publish weekly disease surveillance reports that are also available to the general public, for example the United States (US) Centers for Disease Control and Prevention (CDC) publish the Morbidity and Mortality Weekly Report (MMWR), the European Centre for Disease Control (ECDC) publishes Eurosurveillance and the WHO publishes the Weekly Epidemiological Record.
Surveillance data to guide control programmes
public health surveillance guides control programmes by:
- Measuring occurrence and burden of a disease or condition, and describing its epidemiological patterns. For example, disease in humans results from interactions between the human host and causative agents or hazards of all types. A surveillance system can closely monitor any changes in these dynamic factors and their consequences.
- Monitoring and forecasting trends in risk behaviour. For example, surveillance of annual per capita cigarette consumption in the US showed an increased trend from 54 cigarettes in 1900 to 4,345 cigarettes in 1963. Researchers related this trend to advertising and an expansion in the number of cigarette companies.
- Evaluating performance of control programme. After they have implemented interventions, health authorities use surveillance data to see if disease incidence declines. For example, when vaccine coverage increases, the number of cases of vaccine-preventable diseases tends to decrease. Raising taxes on cigarettes is one way to reduce consumption. The data would document a correlation between raised taxes and declining trends in cigarette consumption.
To achieve these functions, programmes collect data through patient records, surveys, programme records or informal sources.
Types of data collected include:
- Determinants of the condition, for example socio-economic, demographic or biological determinants
- Behaviours or risk factors associated with the condition, for example tobacco use, drug taking or socio-economic status
- Morbidity and mortality associated with the condition, for example prevalence, incidence and mortality rates
- Programme responses, for example coverage of treatments of prophylatics
- Abnormal or unusual events associated with the condition, for example reports of outbreaks of clusters of events
Evaluation of surveillance systems
Public health authorities regularly review their surveillance activities.
The US Centers for Disease Control and prevention have issued Guidelines for Evaluating Public Health Surveillance Systems which focus on three areas:
- The surveillance system itself, describing the system, its structure, diseases under surveillance, sources of data, and how data are processed, analysed and disseminated;
- The resources used to operate the system, including funding sources, adequately trained staff, and information technology;
- The usefulness and quality of surveillance information, using the following indicators:
Usefulness of the data: Do the data and information disseminated to data providers and users contain comprehensible facts, findings and useful recommendations to improve control measures and guide programme management? Has the system detected outbreaks? How many of the detected outbreaks were investigated and controlled in a timely manner?
Timeliness of the data and other information: Is data dissemination timely and regular? For example, epidemic prone diseases require weekly summary, while other diseases require only monthly or quarterly summaries. Are these requirements met?
Validity and completeness of the data: Much of the data come from clinical diagnoses that do not have laboratory confirmation. It is useful to conduct studies to determine the accuracy of diagnoses using standard laboratory confirmation testing. This helps in preparing estimates of the proportion of confirmed cases among all reported cases. When doing field investigations, investigators can compare the number of actual cases they find with the number of cases reported through the system. This provides an estimate of reporting completeness of the system.
Global public health surveillance is the collection, analysis and use of standardized information about health threats or their risk factors from more than one country, and usually world-wide. surveillance mainly focuses on infectious diseases. But global systems also seek to identify deliberate use of biological agents or toxins to cause harm.
WHO leads the global public health surveillance system. It gathers information from formal and informal sources working through its country and regional offices. WHO extends its reach through various networks:
The Global Outbreak and Response Network (GOARN)
GOARN is a collaboration of existing institutions and networks, constantly alert and ready to respond. The network pools human and technical resources for rapid identification, confirmation and response to outbreaks of international importance. WHO coordinates international outbreak response using resources from GOARN.
The Global Influenza Surveillance and Response System (GISRS)
GISRS is a system fostering global confidence and trust for over half a century, through effective collaboration and sharing of viruses, data and benefits based on Member States’ commitment to a global public health model.
The Global Polio Laboratory Network (GPLN)
GPLN consists of 146 WHO accredited polio laboratories, in 92 countries across the six WHO regions of the world. Its primary responsibility is to distinguish poliovirus as a cause of acute flaccid paralysis (AFP) from AFP caused by other diseases.
The Global Project on Anti-Tuberculosis Drug Resistance Surveillance
The Global Project on Anti-Tuberculosis Drug Resistance Surveillance is a common surveillance platform to which countries can provide data that are then used to monitor the evolution and spread of multi-drug resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB).
The Global Antimicrobial Resistance (AMR) Surveillance System (GLASS)
GLASS develops a standardised strategy to collect, analyse and share clinical, laboratory and epidemiological data globally, and assesses the burden and support local, national and global strategies to control AMR.
Major geographic regions of the world coordinate surveillance activities, for example in the European Union through the European Centre for Disease Prevention and Control, in the United States through the Centers for Disease Control and Prevention. WHO coordinates surveillance not only globally but between countries in its six geographical regions.
Some neighbouring countries cooperate independently to prevent and control infectious diseases occurring in their geographical regions, for example:
The East African Integrated Disease Surveillance Network (EAIDSNet)
EAIDSNet is a regional collaboration between the national ministries responsible for human and animal health of the EAC Partner States (Burundi, Kenya, Rwanda, Uganda and Tanzania). They work with national health research and academic institutions.
The Mekong Basin Disease Surveillance network (MBDS)
MBDS is a regional collaboration between six countries through which the Mekong river flows, that is Cambodia, China (Yunnan and Guangxi Provinces), Lao PDR, Myanmar, Thailand and Vietnam.
The Middle East Consortium on Infectious Disease Surveillance (MECIDS)
MECIDS is a collaboration between Jordan, Palestine and Israel and intends to expand membership to all countries in the region.
The Southeast European Center for Surveillance and Control of Infectious Diseases (SECID )
SECID is a collaboration between the signatories of the Dubrovnik Pledge: Albania, Bosnia and Herzegovina, Bulgaria, Croatia, Romania, Serbia and Montenegro, and The Former Yugoslav Republic of Macedonia.
Connecting Organisations for Regional Disease Surveillance (CORDS)
CORDS coordinates six regional networks working in 28 countries in Africa, Asia, the Middle East and Europe. Its mission is to detect and control the spread of infectious diseases by catalysing exchange and collaboration among regional surveillance networks globally.
ICT based networks
Some ground breaking examples of the use of information and communication technology include:
The Programme for Monitoring Emerging Diseases (ProMed-mail)
ProMed-mail is a fully moderated internet-based listserv, that receives and publishes reports of public health events in humans, animals, wildlife and plants from its subscribers and other traditional and non-traditional information sources.
Global Public Health Intelligence Network (GPHIN)
GPHIN continuously scans the WWW gathering information from multiple source news aggregators in real time. Analysts identify new events and inform subscribers – who are governmental and non-governmental agencies with an established public health mandate.
HealthMap fully-automated application, utilizes online informal sources for disease outbreak monitoring and real-time surveillance of emerging public health threats. HeathMap trawls WWW sources of information displays the events by time, geographic location, and aetiology. Users around the world can use an app to find Outbreaks Near Me.
Flu Near You
Flu Near You invites anyone living North America, over 12 years of age, to report if they have an influenza-like-illness. Once registered, participants are asked weekly by e-mail to complete a brief survey. The survey seeks information on 10 symptoms linked to influenza, and other information such as whether or not the registered participant has had an influenza vaccination.
Participatory Onehealth Disease Detection (PODD)
Changmai University in Thailand has developed PODD as a mobile application which connects 296 volunteers in 71 local governments. When volunteers notice an abnormal event such as poultry dying off or sickness in animals or humans, they notify local authorities who dispatch a surveillance and rapid response team to investigate and contain the event.
Challenges and some solutions
Coordination of national surveillance activities
National surveillance units may have sufficient staff for each disease control programme. But at lower levels of the health system, the same individuals often manage more than one programme and are heavily burdened by reporting requirements. There is also duplication of effort in reporting between the programmes.
WHO supports countries to coordinate surveillance activities across departments, programmes and administrative levels through Integrated Disease Surveillance and Response (IDSR). IDSR links surveillance with other health information activities. It also strengthens overall capacity of countries to maintain public health surveillance.
Building capacity for national surveillance system
The IHR 2005 obligate countries to develop comprehensive disease surveillance, detection and response when and where infectious diseases and other acute public health threats occur. In reality, national surveillance capacity in many countries is still not at expected and necessary levels. This may be, as the Ebola epidemic highlighted in West Africa, that health systems are weak and underfunded, or that the surveillance system itself does not function efficiently. Regular evaluation of the system can identify which components need to be strengthened. An over-riding issue is for the system to deploy and maintain enough professionals throughout the system with the required skills. They need to understand the limitations of the data they work with and interpret analyses of the surveillance data.
Since the US CDC initiated the Epidemic Intelligence Services (EIS) in 1951, other regions of the world have established similar training programmes and are graduating field-based epidemiologists with expertise in surveillance and response. Currently, there are 69 such programs around the world forming the Training Programs in Epidemiology and Public Health Interventions Network (TEPHINET).
Coordinating surveillance across sectors
Approximately 75 per cent of newly identified human diseases are zoonotic in origin and 70 per cent of these diseases have their origins in wildlife. Since the 1997 outbreak of H5N1 Avian Influenza in Hongkong, animal surveillance and human surveillance units have begun to share information and alert each other of unusual events. Environmental factors are also crucial to disease occurrence. For example paralytic shellfish poisoning occurs among people who consume shellfish affected by harmful algae growth in the sea.
The OneHealth approach involves sharing information between multiple health sectors and working together to identify and resolve outbreaks.
Sharing information and ensuring equal benefit
During the 2005 Avian Influenza outbreak, WHO requested all affected countries to share the virus isolated from humans for further study and vaccine development. Some governments expressed concern about potential negative economic consequences of sharing information and about possible inequities in the benefits of sharing.
This led to the 2007 Jakarta Declaration on responsible practices for sharing Avian Influenza viruses and resulting benefits which underlined need for continued open, timely and equitable sharing of information, data and biological specimens related to influenza; it also emphasized need for more equitable sharing of benefits for example in the generation of diagnostics, drugs, and vaccines. This declaration led to the Pandemic Influenza Preparedness Framework (PIP) under which manufacturers of influenza vaccine, diagnostics and pharmaceutical that use GISRS information make annual financial contributions to WHO. WHO uses approximately 70 per cent of these contributions for pandemic preparedness activities and surveillance. It uses 30 per cent for pandemic response including purchase of vaccines and antivirals at the time of a pandemic for developing counties without access to these supplies.
Similar to clinical or public health practice, institutions or agencies responsible for public health surveillance need a set of ethics to guide their operations.
The 2017 WHO guidelines on ethical issues in public health surveillance proposed 17 guidelines. These guidelines can be grouped in three major groups. First, the mandate and broad responsibility of the agency to undertake surveillance and subject it to ethical scrutiny. Second, the obligation to ensure appropriate protection and rights of individuals under surveillance. Third, considerations in making decisions about how to communicate and share surveillance data to pursue common good and equity of population without harm to individual.
The complete chapter on which we based this page:
Lippeveld T., Azim T., Boone D., Dwivedi V., Edwards M., AbouZahr C. (2019) Health Management Information Systems: Backbone of the Health System. In: Macfarlane S., AbouZahr C. (eds) The Palgrave Handbook of Global Health Data Methods for Policy and Practice. Palgrave Macmillan, London.
CDC’s Updated Guidelines for Evaluating Public Health Surveillance Systems These guidelines were developed by the US Centers for Disease Control and Prevention with the purpose of evaluating public health surveillance systems is to ensure that problems of public health importance are being monitored efficiently and effectively.
WHO Guidelines on Ethical Issues in Public Health Surveillance. These guidelines outline 17 ethical guidelines that can assist everyone involved in public health surveillance, including officials in government agencies, health workers, NGOs and the private sector.
Chatham House Guide to Sharing the Data and Benefits of Public Health Surveillance. This guide developed by the Chatham House Centre on Global Health Security project facilitates both informal and formal data sharing. The guide proposes seven principles: building trust, articulating the value, planning, using quality data, understanding the legal context, coming to agreement, and evaluating.