Pregnant women, children under two years of age and people with chronic lung disease are the three groups of people facing the greatest risk of severe or fatal A/H1N1 influenza infection, the World Health Organization (WHO) said on Friday.

A pupil is injected the vaccine against the A/H1N1 flu in Lhasa, capital of southwest China's Tibet Autonomous Region, October 14, 2009. The health ministry already sent 200,000 doses of flu vaccine to Tibet Autonomous Region. Students of primary and middle schools and children in kindergartens started to be given the vaccines on Wednesday. [Xinhua]

The above conclusion was drawn by clinicians, scientists and public health professionals at the end of a three-day meeting in Washington aimed at sharing information about the clinical features and management of the pandemic influenza, the UN agency said in a statement.

Participants at the meeting also agreed that neurological disorders can increase the risk of severe disease in children.

Although the exact role of obesity is poorly understood at present, obesity and especially morbid obesity have been present in a large portion of severe and fatal cases of A/H1N1 infection, the WHO said.

According to the statement, experts confirmed at the meeting that the overwhelming majority of persons worldwide infected with the new H1N1 virus continue to experience uncomplicated influenza-like illness, with full recovery within a week, even without medical treatment.

However, concern is now focused on the clinical course and management of small subsets of patients who rapidly develop very severe progressive pneumonia. In these patients, severe pneumonia is often associated with failure of other organs, or marked worsening of underlying asthma or chronic obstructive airway disease.

Treatment of these patients is difficult and demanding, strongly suggesting that emergency rooms and intensive care units will experience the heaviest burden of patient care during the pandemic.

The WHO said primary viral pneumonia had been the most common finding in severe A/H1N1 cases and a frequent cause of deaths.

Besides, secondary bacterial infections have been found in approximately 30 percent of fatal cases.

Findings presented during the meeting add to a growing body of evidence that prompt treatment with the antiviral drugs, oseltamivir or zanamivir, reduces the severity of illness and improves the chances of survival.

These findings strengthen previous WHO recommendations for early treatment with these drugs for patients who meet treatment criteria, even in the absence of a positive confirmatory test, the WHO statement said.

(Xinhua News Agency October 17, 2009)