Drug-Resistant Flu Linked With Pneumonia, Norwegian Doctors Say
Email | Print | A A A
By Jason Gale
Dec. 31 (Bloomberg) -- A drug-resistant influenza strain that has spread globally this year needs further study to gauge its virulence, according to doctors in Norway who found the bug was linked with patients suffering more severe symptoms.
A form of the H1N1 seasonal flu virus that evades Roche Holding AG's Tamiflu appeared more likely to cause pneumonia and sinusitis than the H1N1 strain without the resistance-causing mutation, researchers from the Norwegian Institute of Public Health in Oslo and the U.K.'s Health Protection Agency said.
While ``not a statistically significant finding,'' results of the study, involving fewer than 300 patients, ``warrant further investigation,'' the authors said. The study was released online today ahead of publication in the February edition of Emerging Infectious Diseases by the U.S. Centers for Disease Control and Prevention.
Tamiflu-evading influenza has been reported in 50 countries on six continents since widespread resistance to the bestselling antiviral was first reported to the World Health Organization by Norway in January. Its emergence prompted doctors to consider other medicines, such as GlaxoSmithKline Plc's Relenza, to fight a disease the WHO estimates causes 250,000 to 500,000 deaths annually.
In the U.S., doctors prescribing anti-flu treatments should give their patients Relenza, an orally inhaled medicine, or a combination of Tamiflu and an older drug called rimantadine, the CDC said in a Dec. 19 statement. Basel, Geneva-based Roche had worldwide Tamiflu sales of $1.74 billion in 2007 and $2.1 billion in 2006.
Dominant Strain
Of the 65 H1N1 viruses tested in the U.S. since October, 99 percent were resistant to oseltamivir, and all were susceptible to Relenza, rimantadine and amantadine, a similar drug, the CDC said. H1N1 is the dominant flu strain currently circulating in the U.S. this winter. In Europe, the H3N2 seasonal flu strain, which is susceptible to Tamiflu, is more common.
Preliminary data indicate that Tamiflu-resistant H1N1 flu viruses don't cause different or more severe symptoms compared with Tamiflu-sensitive H1N1 viruses, the CDC said in its Dec. 19 health advisory. Flu typically causes fever, joint and muscle ache, cough, sore throat and runny nose.
Of patients infected with the mutant strain in the Norwegian study, 9.2 percent had pneumonia and 6.2 percent had sinusitis. That compares with a pneumonia risk of 2.9 percent and sinusitis risk of 3 percent in patients infected with a non- resistant H1N1 strain. Risk ratios weren't statistically significant after adjusting for age, gender, and predisposing disease, according to the study.
Pandemic Plans
The emergence of Tamiflu-resistance has raised concern that the medicine, stockpiled by governments worldwide, might become a less powerful weapon in the fight against the H5N1 avian strain and any global contagion it spawns because of the potential for bird flu and pandemic flu to exchange genes with drug-resistant seasonal flu.
``Resistance in a more virulent influenza virus can have serious public health implications because of fewer therapeutic and prophylactic options, which may result in more persons being affected by influenza and more severe illness and death in those who become infected,'' Siri H. Hauge and colleagues wrote. ``These findings should be taken into consideration when shaping future strategies for treating and preventing seasonal and pandemic influenza.''
The researchers found the resistant strain occurred in the absence of selective pressure caused by widespread Tamiflu usage. The pill is not available in Norway without a prescription and it is rarely prescribed there, they said.
``Our data indicate that the viruses carrying this resistance mutation are fully capable of persistence and spread in the absence of selective pressure,'' the authors wrote.
