Improving infectious disease surveillance

The advance of human civilization has brought people, plants, animals, and microbes together in otherwise improbable combinations and locations. Today, international travel and commerce (most notably the explosive growth of commercial air transportation during the past 50 years) drives the rapid, global distribution of microbial pathogens, and the organisms that harbor them. These include humans, whose migrations have been implicated in the spread of diseases including SARS, drug-resistant malaria, and chikungunya (a vector-borne viral disease) in Europe. Indeed, it is possible to travel between most places in the world in less time than the incubation period for many infectious diseases. Travel has not only become increasingly rapid, but also more pervasive in once-remote areas that serve as both sources and sinks for emerging infectious diseases.

Newly emerging and re-emerging diseases highlight the need for a systems approach to domestic and global disease surveillance and detection. Since 2003, highly pathogenic avian influenza has spread across 60 countries, killing millions of birds and 238 of 378 infected people. Yet, disease surveillance and detection still rely heavily on the astute individual: the clinician, veterinarian, grower, livestock manager, or agricultural extension agent who notices something “unusual” and brings it to the attention of officials. While most developed countries have some type of national surveillance system and the ability to detect and diagnose human, animal, and plant diseases, many developing countries have insufficient resources or infrastructure to support such activities. In these places, disease detection relies first on the local level and is entirely dependent upon the early recognition of both known and novel infectious diseases. The catch is that there is a dearth of these “astute” individuals in many areas of the world that are incubators for emerging infectious diseases.

Technological advances in disease surveillance and detection–such as regional syndromic surveillance, bioinformatics, and rapid diagnostic methods–have contributed to infectious disease control and prevention. Containing the spread of disease, in a profoundly interconnected world, however, requires active vigilance for signs of an outbreak, rapid characterization of its geographic range, definition of the causative disease agent(s), as well as strategies and resources for an appropriate and efficient response. These challenges–often viewed in terms of human public health–are shared by the plant and animal health communities.

In the United States, disease surveillance is conducted through various state and federal programs. The infectious diseases that require official notification, which vary from state to state, are reported to state health departments, which in turn verify disease reports, monitor disease incidence and prevalence, identify possible outbreaks, and forward their findings to the Centers for Disease Control and Prevention (CDC). The CDC and other federal agencies, including the Food and Drug Administration (FDA), the U.S. Department of Agriculture (USDA), and the Defense Department independently gather and analyze national infectious disease surveillance reports and morbidity and mortality data for humans, plants, livestock, and wildlife. Moreover, the CDC and Defense independently fund and maintain both domestic and international infectious disease diagnostic laboratory networks.

Many cities and states in the United States use syndromic surveillance, which monitors nonspecific, pre-diagnostic indicators for disease outbreaks in near real-time, to provide an early warning of infectious disease outbreaks in their communities. Syndromic surveillance systems monitor descriptive data from clinical diagnoses, chief complaints, and behaviors (e.g. school and work absenteeism, sales of over-the-counter medications, illness-related 911 calls, emergency room admissions for symptoms indicative of infectious disease) to infer patterns suggestive of an outbreak. Syndromic surveillance systems currently in use include the Real-Time Outbreak and Disease Surveillance System (RODS), employed by several states to gather data on the symptoms of emergency room patients; the National Retail Data Monitor (NRDM), which examines sales of over-the-counter medications; the Electronic Surveillance System for the Early Notification of Community-Based Epidemics (ESSENCE), operated by Defense and others, which allows epidemiologists to track, in real time, syndromes reported in daily data feeds from regional hospitals and clinics; ProMED-mail, administered by the International Society for Infectious Diseases, which allows contributors anywhere in the world to report clinical disease observations; the federal BioSense program, which aggregates data relevant to bioterrorist and other public health threats from numerous electronic sources; and the internet-searching Global Public Health Information Network (GPHIN), managed by Health Canada and the World Health Organization (WHO). The global response to SARS, for example, was triggered by the internet-searching capabilities of the GPHIN.

Most traditional global disease surveillance programs target specific diseases (e.g. influenza, polio, guinea worm); infrastructure and support is relatively weak for the more difficult task of tracking emerging and re-emerging microbial threats to human health. This is particularly true in developing countries, where scarce human and material resources may not support even routine surveillance tasks, such as the recording of births and deaths. Recent international initiatives to expand capacity for the detection and surveillance of infectious diseases in developing countries have been largely overshadowed by efforts specifically directed toward HIV/AIDS, malaria, and tuberculosis. This narrow focus is especially worrisome, since infectious diseases–often of animal origin–are a major cause of morbidity and mortality in low-resource populations, and such environments frequently serve as incubators for emerging pathogens.

In recognition of this threat, the World Health Organization (WHO) revised its International Health Regulations (IHRs)–the legal framework for international cooperation on disease surveillance and response. Once limited to a trio of internationally notifiable diseases (plague, cholera, and yellow fever), the revised IHRs became the “world’s first legally binding agreement in the fight against public health emergencies of international concern.” The ambitious goal of the IHRs is early identification, containment, and resolution of such public health emergencies. As of June 2007, when the IHRs came into force and effect, member nations are required to report to the WHO all new and reemerging diseases with epidemic or pandemic potential, irrespective of their origin or source. Furthermore, each state must notify the WHO when an “event that may constitute a public health emergency of international concern” occurs within its borders. Such notifiable events can extend beyond communicable diseases and arise from any origin or source including other public health emergencies that may affect populations across borders, such as chemical spills, leaks, or dumping; or nuclear “events.” This broad notification requirement aims to detect and contain events at their source by providing a coordinated response and expands the regulation’s scope to include any novel or evolving risk to international public health.

Critics argue that unless developing countries experiencing outbreaks are given more resources and training prior to and during an “outbreak,” the new regulations may not significantly increase disease reporting. On the other hand, recent advances in telecommunications can hasten the identification of, and response to, infectious disease threats, as has been seen in the responses to SARS and H5N1 avian influenza. The bigger problem is that despite abundant evidence that we live in a highly interdependent world–where diseases and their hosts are quickly transported from one area of the globe to another–no single agency, either domestically or globally, has the mandate or responsibility for infectious disease surveillance and response. Moreover, no single agency or multilateral organization focuses on infectious diseases in people, plants, and animals; nor does any one body collect and collate data from across the scientific spectrum, to ensure that health solutions are based on the input of professionals working with humans, domestic animals, and wildlife.

The global capacity to respond to microbial threats to health depends on a public health infrastructure that has suffered from years of neglect. Upgrading current public health capacities would require considerably increased, and sustained, investments across all levels of government. Recent increases in funding for bioterrorism preparedness have led to programs and policies intended to both protect against acts of bioterrorism and improve the U.S. public health response to all microbial threats. Some would argue that biodefense spending–focusing on a narrow suite of highly unlikely infectious disease threats to public health and agriculture–has diverted limited resources from more urgent unmet needs in infectious disease surveillance, detection, and response.

Biodefense efforts must complement rather than supplant those addressing the continuum of infectious disease concerns and potential disasters for which public health agencies are already responsible. The only way to achieve the objectives of bioterrorism preparedness is to enhance the public health infrastructure and resource commitments at all levels of government. If domestic and international officials do not enhance and improve their infectious disease preparedness programs, they will miss critical opportunities to “look over the horizon” and protect humans, plants, and animals from a range of naturally-occurring and intentionally introduced infectious disease risks.