Young healthy adults are more likely to develop severe human swine flu complications, a study by the Chinese University of Hong Kong shows.

The study was conducted between mid-2009 and early 2010, the peak seasons of the human swine flu pandemic.

The study analyzed the clinical profiles, treatment responses and virus characteristics of 382 patients hospitalized in the New Territories East Cluster. Among them, 70 percent, with an average age of 47, developed severe complications, with 9-13 percent falling into "critical conditions", the research team said at a news conference Thursday at Prince of Wales Hospital.

Among swine flu cases reported, 12.4 percent of patients aged between 35 and 65 developed "critical illness" and were placed in intensive care units (ICU), compared to only 3.2 percent of patients in the same age group who develop critical conditions with a common influenza infection, Nelson Lee, head of the Division of Infectious Diseases at the Faculty of Medicine at the university, said at the conference.

"Young healthy adults have a lower possibility to be infected by the human swine flu, but once they do, they are more likely to develop severe conditions," Lee said. "As we are getting into another peak season for human swine flu, young adults should be especially cautious," he said.

The study also found that conventional antigens tests may be inaccurate in diagnosing human swine flu. The hallmark of the disease is diffuse pneumonitis caused by a high-level viral replication in the lungs with excessive inflammatory response, which might go undetected by testing of upper respiratory tract secretion alone.

"The conventional test has a 46 percent accuracy rate at best. We suggest using the polymerase chain reaction (PCR) test, which so far has proved to be 100 percent accurate," Lee said.

During the outbreak period of human swine flu in the second half of 2009, PCR testing was used on every flu patient, aided by special funding from the Hospital Authority, but now it is used only on selective patients, since the funding program has ended, said Paul Chan at the Department of Microbiology at the university.

Chan, in separate research, detected a mutant virus of the human swine flu. The mutant virus replicated more efficiently in the lower respiratory tract and caused severe pneumonia in all infected patients.

"Citizens needn't worry too much, because the mutant virus proved to be less transmissible than the original virus," Chan said.

The study team pointed out the conventional five-day antiviral treatment is inadequate when patients develop severe conditions with complications.

Within the last two to three weeks, there have been over 30 patients hospitalized at the Prince of Wales Hospital for human swine flu infection, most of whom recovered after treatment, with only one patient still in ICU, Lee said.

China Daily

(HK Edition 01/28/2011 page1)