HHS ties pandemic mitigation advice to severity

Feb 1, 2007 (CIDRAP News) – Federal officials today unveiled recommendations for nonpharmaceutical steps to battle pandemic influenza, tying them to a new "Pandemic Severity Index" (PSI), similar to the system for categorizing hurricanes.

Officials predicted that the early, coordinated use of "community mitigation measures" such as isolating patients, sending students home, and canceling public gatherings could make a significant difference in the course of an epidemic.

Relatively disruptive steps such as dismissing classes, changing work schedules, and canceling meetings should be reserved for moderate and severe pandemics, says the 108-page report released by the Department of Health and Human Services (HHS).

In a mild pandemic, the only community mitigation measure recommended is isolating sick people at home, along with using antiviral treatment as available.

In discussing the HHS guidance document today, Dr. Julie Gerberding, director of the Centers for Disease Control and Prevention (CDC), called the five-level PSI "an important and new concept." She said the planners designed the index to mimic hurricane classifications. With recent memories of the Category 5 Hurricane Katrina, "We have embedded in our minds different levels of severity," she said.

Severity level is initially based on case-fatality ratio (CFR), a single criterion that will likely be known even early in a pandemic when small clusters and outbreaks are occurring, the report says. Other measures, such as excess mortality, could be factored in later. Two events would prompt the CDC director to designate a pandemic category: the World Health Organization (WHO) declaring a phase 6 pandemic level and the US government declaring a stage 3, 4, or 5 alert.

The pandemic severity index levels are:

  • Category 1, CFR of less than 0.1%
  • Category 2, CFR 0.1% to 0.5%
  • Category 3, CFR 0.5% to 1%
  • Category 4, CFR 1% to 2%
  • Category 5, CFR 2% or higher

The PSI "has been a missing aspect to pandemic preparedness," said Dr. Marty Cetron, director of the CDC's Division of Global Migration and Quarantine.

The pandemics of 1957 and 1968 both fit into Category 2, whereas the severe pandemic of 1918-19 qualified as a Category 5, according to Cetron and Gerberding.

The new report, titled "Interim Pre-Pandemic Planning Guidance: Community Strategy for Pandemic Influenza Mitigation in the United States—Early, Targeted, Layered Use of Nonpharmaceutical Interventions," is the product of months of work by government agencies and many other stakeholders, officials said.

The current federal pandemic plan contains some general information on community prevention measures, but state and local public health agencies and other groups had asked for more specifics, the CDC has said.

"This was an effort that reflected a huge army of people behind it," said Cetron. "The 9 months or more we spent on it was akin to birthing a child."

In preparing the recommendations, planners looked at the history of the last three pandemics, examined mathematical models, studied seasonal flu transmission, consulted experts from many fields, and conducted citizen focus groups, Gerberding said.

"One important conclusion is the earlier you initiate an intervention, the more likely it is to make a big impact," she said.

The report describes four types of measures for battling a pandemic:

  • Isolation and treatment of people who have suspected or confirmed cases of pandemic influenza in their homes or in healthcare settings, depending on illness severity and medical capacity
  • Voluntary home quarantine of household contacts of those with suspected or confirmed pandemic influenza, along with prophylactic antiviral medication use, if available
  • Dismissing school classes and closing daycare centers, along with other social distancing measures for young people
  • Social distancing for adults through actions such as changing work schedules and environments and canceling large public gatherings

For Category 4 and 5 pandemics, the CDC recommends that all four interventions be used and that school classes be suspended for up to 12 weeks. Category 2 or 3 pandemics would warrant voluntary isolation of sick people, though other measures may be added or modified depending on the recommendations of local health authorities; for example, schools could be closed for 4 weeks instead of 12 weeks.

Regarding school closures, Cetron said one idea under discussion is that while students would be sent home, buildings could be kept open for certain pruposes, such as preparing food for delivery to children depending on the federal school lunch program.

The goals of community interventions are to slow the pandemic in order to buy time for producing an effective vaccine and to lower both the peak number of cases and total cases, the report says. Achieving those things would lighten the burden on hospitals and improve the ability to maintain society in general, Gerberding noted.

Cetron voiced hope that nondrug measures could make a real difference in a pandemic.

In looking at the results of mathematical models, he said, "There was a remarkable confluence around common themes: Earlier is better than later, and second, though a series of partially effective measures might not be effective in and of themselves, when these are layered on top of one another, they have a real additive effect." He added that the common themes emerging from different studies "are reasons for optimism."

The report says the modeling studies indicate that multiple nondrug interventions "may decrease transmission substantially and that even greater reductions may be achieved when such measures are combined with the targeted use of antiviral medications for treatment and prophylaxis."

In response to a question about the use of breathing masks, Gerberding said the CDC would be releasing some updated guidance on citizen use of masks and respirators, though she couldn't predict when. For now, she said it would make sense in a pandemic for people to use simple surgical masks to prevent their own coughing from infecting others.

Gerberding stressed that the new document is not considered final. "We fully expect that as we learn more we're going to have to update our planning tool."

Cetron acknowledged that the recommended interventions will be difficult to plan and carry out. "What we're talking about here is not going to be easy to implement. But it would be much more difficult to try to come up with a solution on the fly in the midst of a pandemic."

CDC officials also announced today the launching of public service announcements designed to educate the public about the threat of a pandemic and how to respond. But they gave no details about where or how often the advertisements will run.

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