29 May 2006
Four criteria in the WHO decision to launch an influenza containment operation once a change occurs from Pandemic Alert Phase 3 to Phase 4
Much concern has been generated over the past two weeks regarding a family cluster in Sumatra, Indonesia of up to eight persons with H5N1 avian influenza. This is not the first such cluster, but it is the largest to date. Nor will this be the last such cluster. Thus, it is worthwhile looking again at the four (4) criteria integral to the decision to launch a containment operation that the WHO articulated in their March 17, 2006 document titled, “WHO pandemic influenza draft protocol for rapid response and containment”.
WHO states (pages 8-9): “An attempt to contain an emerging pandemic virus at its source is a demanding exercise and a resource-intensive operation. Moreover, supplies of antiviral drugs reserved for use to support an operation are finite and not easily replenished, and must therefore be used judiciously. For these reasons the decision to initiate activities aimed at rapid containment should be triggered by compelling evidence that the situation represents a transition in the behavior of the virus likely to result in efficient and sustained human-to-human transmission. Such evidence will derive from a combination of clinical, epidemiological, and virological findings as guided by the following criteria:
1. Moderate-to-severe respiratory illness (or deaths) in three or more health care workers who have no known exposure other than contact with ill patients, and laboratory confirmation of H5N1 infection in at least one of these workers.
2. Moderate-to-severe respiratory illness (or deaths) in 5 to 10 persons with evidence of human-to-human transmission in at least some, and laboratory confirmation of H5N1 infection in more than 2 of these persons.
3. Compelling evidence that more than one generation of human-to-human transmission of the virus has occurred.
4. Isolation of a novel virus combining avian and human material or a virus with an increased number of mutations not seen in avian isolates from one or more persons with moderate-to-severe respiratory illness(acute onset), supported by epidemiological evidence that transmission patterns have changed.
In the current family cluster in Indonesia, criteria # 1 and # 4 are definitely NOT met. Criteria # 2 is probably met, unless a common environmental source (e.g., chickens with H5N1) is identified by the ongoing investigation. Criteria # 3 is only possibly met by the one person who might represent a single instance of a second generation of human-to-human transmission.
IF a containment operation is launched, then WHO delineates a two-phase strategy:
1. Immediate implementation of standard measures aimed at reducing further transmission. In this phase, active case finding and contact tracing are undertaken and antiviral drugs are administered, in a targeted way, to treat persons identified during these activities.
2. Implementation of exceptional measures, including wider prophylactic administration of antiviral drugs, quarantine, and (possibly) the introduction of social distancing measures.
Moreover, WHO emphasizes that throughout these two sequential phases of the containment response “enhanced surveillance at national and international levels is important to guide the continuation of measures and monitor their impact.
These WHO criteria could be updated with future drafts of this protocol that first appeared earlier this year. Room for interpretation and application to specific conditions and epidemiological, clinical, and virological findings for the current cluster in Indonesia and for the highly predictable future clusters in the same and other regions of the world, including Africa, are allowed within the WHO wording of the factors influencing the decision to launch or not launch a containment operation. This is as it should be.
Future media, public health, and political concern about the beginning of the next human flu pandemic should reflexively look back at these four WHO criteria integral to the decision-making process of whether to launch a containment strategy, and thereby declare the transition from the current Phase 3 Pandemic Alert to a Phase 4 (“small clusters”) or Phase 5 (“larger clusters” of persons).
Daniel R. Lucey, MD, MPH
Director, Center for Biologic Counterterrorism and Emerging Diseases
EROne Institutes, Washington Hospital Center
Co-Director, Master of Science Program in Biohazardous Threat Agents and Emerging Infectious Diseases, Georgetown University Medical Center
Washington, DC Website: www.BePast.org