Aug 29, 2006 (CIDRAP News) – The World Health Organization (WHO) today released a list of case definitions for human H5N1 avian influenza infection to improve reporting and tracking of the disease.
The WHO said the use of standard definitions will help national and international authorities report and classify human cases, promote better communication, and allow the comparison of data across time and between places. The agency worked with several partners to develop the definitions.
Officials listed several caveats about using the terminology. The case definitions apply only to the current phase of pandemic alert (phase 3, no or very limited human-to-human transmission) and may change as new information emerges about the disease or its epidemiology. National authorities should notify the WHO only about probable or confirmed H5N1 cases. The definitions are not intended to provide complete case descriptions, but to standardize case reporting.
Clinical decisions about the care of patients who may have H5N1 infection should be based on clinical judgment and epidemiologic reasoning, not on the case definitions, the WHO said. The agency said that although most patients with H5N1 infection have had fever and lower respiratory symptoms, the clinical spectrum is broad.
The case definitions include:
Person under investigation: A person whom public health authorities are investigating for possible H5N1 infection.
Suspected H5N1 case: A patient who has unexplained acute lower respiratory illness with a fever greater than 38°C (100.4°F) and cough, shortness of breath, breathing difficulty, and one or more of the following exposures 7 days before symptom onset:
- Close contact within 1 meter (eg, caring for, speaking with, or touching) with a person who is a suspected, probable, or confirmed H5N1 case
- Exposure to (eg, handling, slaughtering, defeathering, butchering, or preparing for consumption) poultry or wild birds, their remains, or their feces where H5N1 infections in animals or humans have been suspected or confirmed in the last month
- Consumption of raw or undercooked poultry where H5N1 infections in animals or humans have been suspected or confirmed in the last month
- Close contact with a confirmed H5N1-infected animal other than poultry or wild birds (eg, cat or pig)
- Handling human or animal samples suspected of containing the H5N1 virus in a laboratory or other setting.
Probable H5N1 case (notify WHO):
- Definition 1: A person who meets the criteria for a suspected case and has either (1) evidence of acute pneumonia on a chest radiograph plus respiratory failure (hypoxemia, severe tachypnea) or (2) laboratory confirmation of influenza A but insufficient laboratory evidence for H5N1
- Definition 2: A person dying of an unexplained respiratory illness who is epidemiologically linked by time, place, and exposure to a probable or confirmed H5N1 case.
Confirmed H5N1 case (notify WHO): A patient who meets the criteria for a suspected or probable case and has had one of the following test results from a national, regional, or international influenza laboratory whose H5N1 test results are accepted by the WHO:
- Isolation of an H5N1 virus
- Positive H5 polymerase chain reaction (PCR) results from tests using two different PCR targets (eg, primers specific for influenza A and H5 hemagglutinin)
- A fourfold or greater rise in neutralization antibody titer for H5N1 based on testing of an acute serum specimen (collected 7 days or less after symptom onset) and a convalescent serum specimen. The convalescent neutralizing antibody titer must be 1:80 or higher
- A microneutralization antibody titer for H5N1 of 1:80 or greater in a single serum specimen collected at day 14 or later after symptom onset and a positive result using a different serologic assay, such as a horse red blood cell hemagglutination inhibition titer of 1:160 or more or an H5-specific Western blot positive result.
Aug 29 WHO statement on case definitions for human H5N1 infections