Swine flu is most dangerous when it causes the lungs to become inflamed, flood with fluid and fail to function, doctors in Australia and New Zealand found.
While a majority of people infected with the virus have a mild illness, a small number develop life-threatening disease, intensive-care specialists Steven Webb and Ian Seppelt said. The doctors described the most common of three main complications from the pandemic strain as flu A-associated acute respiratory disease syndrome, or “flaards.”
“Flaards -- sometimes with associated multiple organ failure -- is the most common syndrome and has the highest attributable mortality,” Webb and Seppelt wrote in an editorial in the September issue of the medical journal Critical Care and Resuscitation.
The new H1N1 influenza strain has killed at least 3,917 people and spread to 191 countries and territories since its discovery in Mexico and the U.S. in April. Hospitals in the Northern Hemisphere are bracing for a surge in flu cases in coming weeks, spurred by colder weather that promotes its spread. In Australia, flu patients occupied a quarter of beds in intensive-care units last winter and 178 died.
Cases may be peaking in Hong Kong. Average daily attendance at the city’s accident and emergency departments rose from 6,354 in the last week of August to 7,086 last week, according to a government statement on Sept. 25. The virus has killed at least 23 people in Hong Kong, including Alan Dick, principal of the Canadian International School, according to Natalia Leung, a department of health spokeswoman.
Intensive-care doctors in Australia and New Zealand are pooling data on more than 400 swine flu cases to describe disease patterns and treatment strategies, and inform the Northern Hemisphere countries about what to expect this winter.
‘Canary in the Coal Mine’
“ICUs are the ‘canary in the coal mine’,” Webb and Seppelt wrote in the editorial. “It is only by documenting the severe cases requiring intensive care that it is possible to get an idea of the overall impact of this new disease.”
In Victoria, Australia’s second most-populous state, the pandemic virus sickened about 5 percent of the population, with 0.3 percent of infected patients being hospitalized, health officials said in a study yesterday in the Medical Journal of Australia. One in five people admitted to the hospital were transferred to ICU, mostly because of severe respiratory failure.
Eighty-five percent of critically ill patients survived after staying an average of nine days in ICU. Almost three- quarters of these patients required mechanical ventilation to breathe and 7 percent needed to have their blood pumped through an artificial lung in a procedure known as extracorporeal membrane oxygenation, or ECMO.
In most cases, flu remains in the nose, throat and bronchi, where it causes a runny nose, sore throat and cough until the body’s immune systems eliminates it, usually within a week.
The new H1N1 strain may be at least 1,000 times more adept than seasonal flu at infiltrating the lower branches of the airway, said Yoshihiro Kawaoka, a virologist at the University of Tokyo, who has studied the viruses in non-human primates.
In severe cases, influenza can damage the capillaries surrounding the tiny grape-like sacs, known as alveoli, where gas is exchanged through the blood. Damaged alveoli can bleed, causing pulmonary hemorrhage and blood clots.
Inflammatory chemicals are produced by the immune system to fight the infection and repair the damage. An over-exuberant response can worsen the effect by filling the lungs with fluid and cause permanent scarring that restricts the lungs.
Besides flaards, the other predominant disease patterns associated with the pandemic flu virus are community-acquired bacterial pneumonia and an exacerbation by the virus of airflow limitation, Webb and Seppelt said.
Life-threatening infection may be more common in people with underlying health conditions, including morbid obesity, type-2 diabetes, cancer, a weakened immune system and chronic lung disease, they said. Pregnant women and those who recently gave birth also appear at higher risk.
Still, “many patients with flaards are young and previously well,” they said. In Australia, the median age of people dying from seasonal flu is 83. With the novel H1N1 virus, it is 51 years, the health department said in a report last week.