Hong Kong - tobacco smokers may be prone to developing life-threatening complications from swine flu,..

August 24, 2009 - Smokers may be prone to developing life-threatening complications from swine flu, according to patient data from Hong Kong, where tobacco use was noted in almost half of severe cases.

Twelve of 27 swine flu patients who developed pneumonia and other serious illnesses were either current or former smokers and some had no other known risk factors, Thomas Tsang, acting controller of Hong Kong’s Centre for Health Protection, told a medical meeting in Beijing yesterday, August 23rd. “The proportion of smokers among the serious cases is pretty high,” Tsang said in an interview. “So far this is just one observation that stands out and we need to investigate it.”

Tsang’s findings may shed more light on a mystery that doctors are grappling with: why the new flu remains mild for a majority of people and is severe enough to kill in others. Worldwide, about 1,800 people infected with H1N1 have died since the virus was discovered in April.

In Hong Kong, about 1 in 200 people who tested positive for swine flu developed severe disease, with some needing weeks of intensive-care treatment. About 13 percent of adults in the city smoke, Tsang said at a meeting on influenza over the weekend organized by the Lancet medical journal, China’s health ministry and the World Health Organization.

As drugmakers race to make vaccines to fight the pandemic, health officials are trying to identify vulnerable groups in order to prioritize who should get immunized first.

In Hong Kong, three-quarters of H1N1 patients with serious disease had medical factors that made them more susceptible, Tsang said. Chronic lung conditions such as asthma and emphysema, as well as diabetes, cardiovascular disease, morbid obesity and pregnancy, can put people at risk. Smoking might be linked with one or more of these factors, according to Tsang. “Smokers tend to have poorer lung function and smoking is also associated with some other chronic diseases,” Tsang said. “It could be those factors that explain the association rather than smoking per se.”

Smoking is the biggest preventable cause of death and claims 4.9 million lives a year globally, according to the WHO. The habit is also the leading cause of illness and premature deaths in Hong Kong, according to a statement on the city- state’s Tobacco Control Office Web site. An estimated 5,500 deaths a year result from smoking, the agency said.

Nicotine, the addiction-causing chemical in tobacco, interferes with the immune response to seasonal flu, said John Mackenzie, a Melbourne-based virologist who studied the interaction in mouse models more than 30 years ago. “Smoking is interesting,” Mackenzie said in an interview in Beijing yesterday. “It initially enhances the immune system, but then it depresses it. If you smoke, you become much more susceptible to straight viral pneumonia.”

By impeding the body’s defense mechanisms, smoking may enable the virus to replicate undetected for longer and invade more of the respiratory tract, said Frederick Hayden, professor of clinical virology at the University of Virginia School of Medicine in Charlottesville, in an interview yesterday. “There are some epidemiologic observations to show that smokers have a more serious illness from seasonal influenza,” he said. “Some of these factors have been recognized in the past, and I think we’re seeing them reaffirmed. I’d be surprised if it didn’t eventually turn out to be a risk factor.”

The pandemic strain may have a greater predilection than seasonal flu for infecting the lungs, where it can cause viral pneumonia, said Stephen Toovey, a senior research fellow at London’s Royal Free and University College Medical School. It’s possible bad luck and a person’s genetics may also play a role, Toovey said in an interview in Beijing. Taking a deep breath or yawning immediately after an infected person nearby coughs or sneezes could enable large amounts of airborne viral particles to reach the lower branches of the airway, he said. “It could be that if you do get enough virus by whatever route into the lower respiratory tract, you are more likely to have severe disease than you would with, say, a seasonal virus,” Toovey said.

Toovey: researchers are studying whether certain genetic flaws hamper the so-called early innate immune response, giving the virus an advantage over the body’s defenses.

Reference: Smokers Risk Swine Flu Complications Like Pneumonia, Data Show by Jason Gale (j.gale@bloomberg.net), Bloomberg.com, 8/24/2009.

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