Primer on Global Disease Surveillance and Response

We identified the basic components of surveillance and response programs and defined them:

• Surveillance: Systematic monitoring for a case (or cases) of an unusual disease and/or an unusual cluster of disease—the stimuli for the initial disease outbreak report
• Reporting: An account of the of initial disease outbreak that reflects an assessment of credibility and of potential public health significance
• Verification: Inquiry to affected country and the initial investigation to verify the disease outbreak
• Response: Intervention and containment of the disease outbreak.

An Unusual Case or An Unusual Cluster of Disease Cases
Knowledge of an infectious disease outbreak conventionally begins in surveillance systems with the recognition and reporting of a case (or cases) of an unusual disease of an unusual cluster of disease. An unusual case may be initially determined through clinical observations using a case definition. A case definition is a group of signs and symptoms that characterize, but may not exclusively belong to, a disease. Some surveillance systems monitor laboratory test results (e.g., serology); some use analysis of patient samples routinely collected by sentinel clinicians; some derive data from routine computer-based searches of patient or public health records; and some use media reports of disease outbreaks.

An unusual cluster of disease cases is an outbreak of a “common disease or syndrome” that is unusual with respect to season, location, demographics or morbidity/ mortality.  For example, based on historical analyses of influenza pandemics, abnormal clusters of influenzalike illness may be the first warning of the emergence of a strain with pandemic potential. Possible signals include an early or an extended flu season, severe illness in younger people, increased mortality, or changes in mortality patterns (i.e., seasonal or demographics of fatal cases). Recognition of such trends is difficult without making comparisons with historical population-based data.

Role of Health Facilities
After infection, onset of illness may be fast or slow; self-recognition of illness depends on the severity of signs and symptoms, which may range from unnoticeable to mild, moderate, or severe. A person who recognizes that s/he is sick may or may not seek health care.  Some reasons for not seeking care include: health care is unavailable or unaffordable, the healthcare system is not trusted, illness may be very mild, the disease is stigmatized, and/or severe illness prevents healthcare seeking. If a disease outbreak is not recognized in the health facility, it may be detected by other societal elements, such as schools (increases in absenteeism), first responders (increases in emergency rescues), or pharmacies/traditional healers (increases in medicine sales).
 
Role of Diagnostic Tests
If a sick person seeks healthcare, the provider may diagnose a common or an unusual disease, and, if one is available, may order a diagnostic test. To be useful in the primary or emergency care facility, such diagnostic tests must be simple, affordable, and accurate. When performed on patients who have signs and symptoms of disease, the test results must also provide actionable information for: care of the patient, infection control in the health care facility, outbreak reporting, investigation, and rapid containment. If the test results are available before the patient leaves the health facility, it may be possible to provide appropriate treatment. If the laboratory test confirms the sick person has a disease that is vaccine preventable (e.g., polio), then screening for asymptomatic carriers and vaccination campaigns may be initiated.

Reporting a Disease Outbreak
If an unusual case of disease is recognized, particularly if it meets the case definition (e.g., watery diarrhea) for diseases of concern (e.g., cholera) one or more notification processes may begin. The healthcare provider may discuss the case with other clinicians, and hospital infection control may be notified. The ministry of health may be notified.  The news media may report on disease outbreaks using information gleaned from a variety of information sources, including societal sources, health care providers, and/or other people who work in hospitals, health departments, or other government departments.

Provisions of the International Health Regulations 2005 for Reporting Outbreaks to WHO
Historically, concerns about the impact of the disease outbreak on international trade and travel responses dissuaded some countries from reporting it or requesting assistance from the World Health Organization (WHO). Such delays affected the size of the outbreak as well as regional or international spread of the disease.  However, as of June 2007 new international regulations are in place. Member States of the World Health Assembly that have agreed to IHR 2005 are now responsible for reporting outbreaks of seven diseases (smallpox, plague, yellow fever, cholera, polio, SARS, or influenza caused by a new strain of human virus), as well as any unusual disease outbreaks and unusual clusters of disease cases with potential for international public health impact to the World Health Organization within 24 hours, regardless of the location of the outbreak.

Verification of a Disease Outbreak
The World Health Organization is responsible for investigations of disease outbreak reports that appear to be credible and that may have international public health significance. WHO staff reviews disease outbreak reports daily, and several questions are considered before WHO takes action on the report: 

• Is the disease one of the seven specified by the IHR 2005?
• Is it an unknown disease?
• Is there potential for spread beyond national borders?
• Is there a serious health impact or unexpectedly high rates of illness or death?
• Is there potential for interference with international trade or travel?
• Does the country have the capacity to contain the outbreak?
• Is the outbreak suspected of being caused by a laboratory accident, or a deliberate act?

If the report seems credible and the outbreak could potentially be a threat of international public health significance, a request for verification is relayed from WHO headquarters to the appropriate WHO regional office.  The affected country is asked to conduct an epidemiological investigation to determine whether or not the outbreak has occurred and to establish the interventions and assistance necessary for containment.

Initial Response to a Disease outbreak
WHO offers assistance to the affectedcountry/s for the investigation of the reported disease outbreak. Assistance includes, but is not limited to, information, diagnostic tests, and field staff. In most cases, the involved country must request the assistance. The type and amount of assistance reflect the disease, the size of the outbreak, and the national resources of involved countries. 

Response to a Disease Outbreak of International Public Health Importance
If the outbreak is verified, WHO will provide additional resources, such as therapeutics and vaccines, maintain situational awareness, and coordinate any and all aspects of the response, including the involvement of WHO’s Global Outbreak Alert and Response Network (GOARN). GOARN is a voluntary technical partnership of approximately 140 institutions coordinated by WHO to support countries in disease outbreak response, primarily through the deployment of multidisciplinary teams of experts. The response to the outbreak will occur on multiple levels within the involved country.  If the outbreak has spread beyond the borders of the involved country, responses of countries in the region and/or the international community may occur simultaneously.  All funds required for international response to disease outbreaks are donated at the discretion of World Health Assembly Member States.