March 31, 2005

H5N1 flu virus toll rises to 74 patients with 49 dead:  Pandemic Prodrome?

 

Today the WHO updated the total number of lab-confirmed persons with H5N1 infection to 74 of whom 49 (66%) have died. These figures include 2 patients in Cambodia, both of whom have died, 55 patients in Vietnam of whom 35 have died, and 17 patients in Thailand, of whom 12 have died. Yesterday the WHO confirmed bird flu “outbreaks involving large numbers of poultry… including one in Pyongyang Province”, North Korea. Confirmatory testing for H5N1 is still pending. WHO has volunteered to send the anti-influenza drug, oseltamivir to North Korea, since H5N1 as well as other strains of influenza are susceptible to this drug.

 

Today’s South China Morning Post (SCMP) newspaper (www.scmp.com) reports that North Korea has killed hundreds of thousands of chickens in an attempt to control the bird flu outbreak and that no human cases have been reported. They also report that influenza experts from China, Australia, and the veterinary expert from the UN/WHO will arrive in North Korea soon.  A Reuters Alertnews article March 28^th cited South Korean officials offering to help control the bird flu outbreak in the North Korean capital of Pyongyang if asked to do so, as well as taking precautions to prevent spread of the disease into South Korea.

 

This SCMP article also commented on recent reports of clusters of patients in Vietnam with proven or suspected H5N1 infection. A WHO report March 29 also cited the ongoing investigations into these clusters in Vietnam to determine the epidemiologic risk factors for infection. Analysis of the virus genetic sequence can assist in determining whether or not mutations have occurred that could increase the risk of sustained person-to-person transmission.

 

The true case fatality rate of H5N1 is likely lower than 66% because of the fact that only the most ill, usually hospitalized, patients have been tested and reported to the WHO. Vietnam recently reported two asymptomatic patients infected with H5N1. Enserink and Normile  (Science 2005 (March 25); 307:1865) discuss in detail the issues surrounding the lack of data on the actual spread of H5N1.  This situation is due in part to the lack of large-scale testing of asymptomatic contacts of patients, as was done in 1997 in Hong Kong during their H5N1 outbreak involving 18 symptomatic patients and six fatalities. 

 

Until sustained transmission of H5N1 from person-to-person is proven we will not know for sure whether the month-by-month increase in H5N1 cases represents the prodrome of the next influenza pandemic. Having more data from expanded testing for H5N1 would surely increase the odds of identifying the start of the pandemic, however, and accelerate the global response.  The effect that the first H5N1-infected returning travelers from Vietnam, Thailand, or Cambodia will have in the USA or European countries can be anticipated, even if the route of transmission is linked to poultry rather than human contact. 

 

 Daniel R. Lucey, MD, MPH