Symposium on Border Health - February 2007
By Luis Escobedo, MD, SM, MPH
By World Health Organization (WHO) standards, we are halfway to an influenza pandemic. WHO has adopted a six-phase pandemic influenza planning guide:
- Phase 1 is an inter-pandemic phase with no pathogenic circulating avian influenza virus capable of human transmission.
- Phase 2 is an inter-pandemic phase with known avian pathogenic circulating strain, but with no known human disease transmission.
- Phase 3 is a pandemic alert phase with known avian pathogenic strain that has infected humans, but with no sustained human-to-human transmission observed.
- Phase 4 is a pandemic alert phase with isolated clusters of human-to-human transmissions.
- Phase 5 is a pandemic alert phase with continued and more sustained clusters of human-to-human transmission.
- Phase 6 is a pandemic phase with worldwide distribution of sustained human-to-human transmission.
We are currently in phase 3 of this pandemic influenza planning guide.
A global outbreak occurs when an emergent novel influenza virus acquires the ability to infect humans and cause human-to-human transmission. Humans lack the necessary immunity and, through close human interaction, facilitate the rapid worldwide spread of the virus. Three global influenza outbreaks have occurred during the last century, in 1918, 1957, and 1968.
The 1918 pandemic resulted in 40 to 50 million deaths worldwide, with 500,000 in the United States. Unlike other outbreaks, it targeted healthy adults. Mathematical modeling suggests that once human-to-human transmission is established, global disease spread is inevitable.
Without intervention, the first U.S. case would be detected in one to two months. Widespread community outbreaks would ripple through the country in a series of waves lasting two to three months. The expected number of U.S. cases during the pandemic would be 90 million persons, or 30 percent of the population. Of those affected, 45 million (50 percent) would seek medical care, and 128,000 to 1.5 million would require intensive care, including mechanical ventilation. The expected U.S. mortality would be approximately 200,000, but could be as high as 1.9 million for a highly pathogenic strain, as in the 1918 pandemic.
The current pandemic influenza concern stems from a highly virulent influenza A H5N1 virus, which first appeared in birds in 1997, reemerged in domestic and wild fowl in 2004, and has resulted in 220 human cases. The human mortality associated with these cases has been more than 50 percent. Human infection was acquired through close contact with infected domestic fowl. No sustained human-to-human transmission has been documented.
National Response Plans
Sustained human-to-human transmission anywhere in the world will be the triggering event to initiate a pandemic response in the United States. Close collaboration with local and state health departments will be critical to ensure successful containment efforts. Emphasis will be placed on detecting the first few cases and containing their spread as much as possible to allow the production of enough vaccines and antivirals to cover the majority of the population.
Initial detection and containment efforts would include targeted travel restrictions and screening of incoming and outgoing travelers at designated international ports of entry, including land borders. Procedures will be needed to enforce isolation and quarantine of groups of persons who may be the initial cases and contacts. Traffic at U.S.-Mexico ports of entry may be redirected, but total border closure is not likely. Other in-country containment efforts would include targeted quarantine and isolation, social distancing measures, and the judicial use of antivirals to treat cases and contacts.
The two principal vaccine goals are to produce and maintain a vaccine stockpile to vaccinate 20 million responders and support individuals against the strain that presents the pandemic threat, and to expand the manufacturing surge capacity to produce enough vaccine to vaccinate the entire U.S. population within six months.
A stockpile of 75 million doses of antivirals will be established and divided at the state and federal levels. Response planning is a collaborative effort between federal agencies and local and state health departments. Local elected officials in close coordination with the local health authority will guide all planning and response activities through the use of the Incident Command System.
Border Collaboration Efforts
The goal of cross-border collaboration is to develop a comprehensive, coordinated, science-based approach to plan for and manage the threat of human influenza pandemic in border communities and across North America. The United States, Canada, and Mexico are working collaboratively to treat North America as a single epidemiological unit. To accomplish this, binational health authorities from the federal level and from border states and sister-city communities are working together to remove obstacles that prevent effective cross-border assistance for planning and responding to emergency situations. This will necessitate the analysis and revision of appropriate legislation regarding professional licensure and the procedures to facilitate the timely exchange of information and human resources.
A binational communication plan is being developed that incorporates clear, bilingual, and consistent messaging at the community level and at land ports of entry. Active and passive binational surveillance systems using common case definitions will be implemented, and the mechanisms for timely sharing of information and clinical specimens across the border are being established. These systems must incorporate both human and animal surveillance activities.
Mexican and U.S. federal health authorities also are working closely to share procedures, laboratory reagents, and diagnostic technology to enhance laboratory diagnostic capacity.
Both the United States and Mexico have set up nationwide laboratory response systems that ensure rapid H5N1 influenza virus identification capacity at all levels. Procedures are in place to implement needed training for laboratory staff, and systems are being developed to ensure the timely cross-border transference of clinical laboratory specimens and laboratory reagents.
National public health laboratories from Mexico's National Institute of Epidemiological Reference and the Centers for Disease Control and Prevention (CDC) influenza branch have set up the necessary infrastructure and biosafety procedures to isolate, genotype, and cross-confirm pandemic influenza strains and other potential bioterrorism agents. Early detection will require rapid influenza A detection, and pandemic influenza polymerase chain reactions technology (RT-PCR) to detect the presence of a pandemic strain. This will be done through a laboratory referral system that serves all communities. Viral confirmation and isolation can be done through reference state and CDC laboratories.
Public health measures at U.S.-Mexico land ports of entry will need to establish common case definitions and triggers for issuing travel alerts and advisories for countries affected by avian or pandemic influenza. Compatible signage and public information will be developed, and common approaches and screening policies for northbound and southbound border crossers will need to be discussed and agreed upon. There will be a need to share information and coordinate measures to protect the border control personnel, including personal protective equipment and other appropriate risk-reduction measures to support continuity of operations.
The Practicing Physician's Role
Practicing physicians will be critical players in all aspects of community planning and response efforts. Their ability to act as health care givers, patient advisors, and individual and community educators makes them a valuable asset to public health response planners. Physicians who treat immigrant groups will be especially valuable because members of immigrant communities may be less likely to seek early medical care or will do so late in the disease process. By serving as the link to immigrant populations, these physicians can represent the health needs of immigrant groups during a pandemic.
Physicians will need to make sure they and their patients are up to date on all immunization requirements, especially seasonal influenza A. Procedures for early reporting and referral to health departments and hospitals will need to be in place. Physicians should be ready to assist local health departments to promptly implement any needed patient and community infection control practices and social distancing measures. Such measures have never been tested and tried on a widespread scale. Public health authorities are working closely to issue the necessary guidance to ensure that such measures cause the minimum disruption for society. All public health is local, and an effective public health response will require the leadership and support of the physician community. Complacency is the enemy of health protection.
- HHS Pandemic Influenza Plan. Washington, DC: US Health and Human Services; November 2005. Available at: http://www.dhhs.gov/pandemicflu/plan/. Accessed Dec. 15, 2006.
- National Strategy for Pandemic Influenza: Implementation Plan . Washington, DC: Homeland Security Council; May 2006. Available at: http://www.whitehouse.gov/homeland/nspi_implementation.pdf. Accessed Dec. 15, 2006.
- Mexican National Plan for Preparedness and Response for Pandemic Influenza . National Committee for Health Security; June 2006.
- Pandemic Influenza Preparedness Plan . Austin, Texas: Texas Department of State Health Services; October 2005.
Dr. Escobedo is the director of Health Service Regions 9 and 10 for the Texas Department of State Health Services.
An Influenza Primer
Human influenza viruses include three different species, A, B, and C. Influenza A and B variants cause seasonal outbreaks in northern hemisphere countries during the fall and winter. Influenza C can induce mild disease in adults and moderate disease in children. Influenza A viruses cause seasonal disease outbreaks and can cause life-threatening disease among the very young, the elderly, and persons with debilitating medical conditions. These outbreaks are responsible for 6,000 deaths and more than 200,000 hospitalizations per year.
Influenza A is an enveloped RNA virus containing two antigenic glycoproteins: neuraminidase and hemaglutenin. These antigens facilitate host cell entry and egress, and give influenza A virus its species-specific pathogenic characteristics. There have been 15 different hemaglutenin and eight neuraminadase antigen types described. A new influenza A subtype capable of infecting humans can emerge as a result of a dramatic genetic reassortment (antigenic shift) that produces novel viruses containing various combinations of these two antigens. A subtler genetic drift results in a different subtype virus with the same group antigens (antigenic drift). Antigenic drift is responsible for the seasonal variability of circulating influenza A viruses. Antigenic drift creates the need for a unique seasonal influenza vaccine that is likely to contain antibodies against the current virus in circulation. Antigenic shift creates new viruses which can cause pandemics.
Influenza A viruses are transmitted through respiratory droplets and have an incubation period of one to two days. The infectious period is greatest immediately before the onset of symptoms and continues for approximately one week. Onset of symptoms is abrupt, can be severe, and includes high fever, dry cough, myalgia, headache, and malaise. Disease is usually self-limiting lasting approximately 10 days. A common complication among high-risk groups includes secondary bacterial pneumonia. Treatment usually is supportive, and early use of antivirals, osaltamivir or zanamivir, may shorten the course of the disease. A pandemic influenza strain likely will behave similarly, but its pathogenicity may be greater.
February 2007 Texas Medicine Contents
Texas Medicine Main Page