Issue 31 - Update on Pandemic Influenza: The Threat Moves Closer to Reality

_______________________________________________________________________________

Update on Pandemic Influenza: The Threat Moves Closer to Reality
_______________________________________________________________________________

Pandemic influenza is defined as the efficient and sustained transmission of a new influenza A virus which is spread by large droplets (coughing, sneezing). A new strain is usually caused by antigenic drift from animals to humans, i.e., when a human with influenza is also infected by a flu strain from an animal.(1)

According to the World Health Organization, the latest avian flu virus, H5N1, has demonstrated several characteristics that increase the probability of a pandemic.(2) To start with, the H5N1 virus has shown evidence of becoming hardier and lasting longer in the environment. It is easily transmitted in wild ducks and geese, and can infect domestic poultry. In the domestic birds, the disease spreads efficiently and has a high morbidity rate. Since 2003, over 100 million chickens have died in Vietnam, Thailand, Laos, Cambodia, Indonesia, Malaysia, and China.(1) And recent evidence indicates that the virus now spreads from human to human.(3) So far, person to person spread has been limited to only one generation of human-to-human transmission.(1)

Not all avian flu viruses spread to humans. When they do, most do not cause serious illness. Yet the H5N1 has spread from poultry to humans and caused serious disease with an extremely high fatality rate of 62%. As of April 14, 2005, there have been 17 cases, 12 deaths in Thailand; 68 cases, 36 deaths in Vietnam; and 3 cases, 3 deaths in Cambodia.(4)

The course of the H5N1 disease in humans includes diarrhea in addition to influenza symptoms, along with severe ARDS. The only effective anti-viral treatment available is oseltamivir.

A New Role for Syndromic Surveillance
The elements of preparation for, and response to, the potential spread of avian influenza to the U.S. population are of course familiar to the readers of this newsletter, since preparing for pandemic influenza is much like preparing for bioterrorist-caused outbreaks or SARS. This means that surveillance, a crucial component of preparedness, should be ongoing, and not just limited to the October to mid-May influenza season. Surveillance also needs to focus on the earliest possible detection as discussed in the October 2004 issue of the RedBat Alert. Simply documenting the occurrence of influenza, as is now done through the CDC’s sentinel provider system, is not adequate for early detection.

The Pandemic Influenza Preparedness and Response Plan, issued in draft form last August by the Department of Health and Human Services, notes that “efforts are under way to move toward year-round reporting.” It also notes that “Future enhancements will include exploring use of existing electronic datasets to increase the flexibility of the existing system to respond to emergencies, exploring hospital based surveillance for severe respiratory syndromes that may be caused by influenza but also may be related to SARS or other agents.” (5)

This newsletter includes a case study, which shows how one state, with the participation of its major hospitals, has already implemented these enhancements.

Case Study: How North Dakota Uses Syndromic Surveillance to Track Influenza
The North Dakota Department of Health (NDDoH) began monitoring emergency department (ED) visits in the state's major hospitals in 2003, as part of the state's syndromic surveillance plan. Julie Goplin, the Surveillance Epidemiologist who monitors the ED syndromic surveillance data, started tracking influenza-like-illness (ILI) beginning with the 2003-2004 influenza season. As the season progressed, she noted that the ILI syndromic surveillance data closely matched that of their physician-based sentinel providers, who submit reports weekly. She shared the data with the Influenza Branch of the Centers for Disease Control (CDC), which agreed to accept the hospital sites as sentinel surveillance sites for the 2004-2005 influenza season.

Beginning in March of 2004, Goplin started using the in-place syndromic surveillance program for conducting influenza surveillance year-round. According to Goplin, "this is a major goal of the pandemic influenza plan, and our system allows us to meet this goal without expanding the traditional, physician-based sentinel system to a year-round system. And the syndromic system provides us with daily data instead of weekly data." She has also created a web site for making data available to the participating hospitals.

The syndromic surveillance software program used by the NDDoH is the proprietary system, RedBat(r). It is used by ten hospitals in North Dakota, and covers seven of the largest cities and highest populated counties, including over 50 percent of the state's population.

References
(1) Uyeki, Tim, MD, MPH, in a presentation at the Society for
Healthcare Epidemiologists in America annual meeting, April 10, 2005.

(2) World Health Organization. Avian Influenza: Assessing the Pandemic Threat. January 2005. Available at
http://www.who.int/csr/disease/influenza/WHO_CDS_2005_29/en/

(3) Ungchusak K, et al. Probable person-to-person transmission of avian influenza A (H5N1). New England Journal of Medicine. 2005 Jan 27:352(4):333-40.

(4) World Health Organization.Cumulative Number of Confirmed Cases of Avian Influenza. Available at http://www.who.int/csr/disease/avian_influenza/country/cases_table_2005_04_14/en/

(5) U.S. Department of Health and Human Services. Draft: Pandemic Influenza Preparedness and Response Plan. August 2004. Available at
http://www.dhhs.gov/nvpo/pandemicplan/

Annual Syndromic Surveillance Conference Date Finalized
The fourth annual Syndromic Surveillance Conference is now scheduled for September 13-15, 2005, in Seattle, Washington. Abstracts can be submitted between May 2 and July 15, and registration starts May 2. Watch for details at www.syndromic.org.

Back to the top