The flu season will be more severe this year than when swine flu surfaced in humans in the city in 2009 because of a colder, longer and drier winter, University of Hong Kong doctors predict.
And lack of certain antibodies in some people is making swine flu deadlier than other flu strains this year, with patients more vulnerable to other bacterial infections.
These were among the major findings of HKU doctors who yesterday announced the results of their study of flu cases in 2009.
Unlike in 2009 when the swine flu virus was not the major source of flu infections, this year more than 90 per cent of cases are attributed to the swine flu strain.
People who had human swine flu in 2009 should not believe that they were safe because their immunity would have weakened two to four times by now, doctors said.
Swine flu surfaced in humans in Mexico in March 2009, and according to World Health Organisation statistics, the virus has killed more than 18,000 people since.
As of 2pm yesterday, four more swine flu patients were in critical condition in public hospitals, taking the total number of patients in intensive care in Hong Kong to 38. Nine patients have died of swine flu since January 24.
Ivan Hung Fan-ngai, clinical assistant professor with HKU's medicine department, said human swine flu was different from other flu strains, as infected patients would have lower levels of an antibody called IgG2. This increases the chance of contracting other bacterial infections after admission, such as streptococcus pneumoniae, which is a common cause of bacterial meningitis, and staphylococcus aureus, also known as golden staph.
'This is a double attack to their condition and will take longer to heal,' said Kelvin To Kwai-wang, a clinical assistant professor of microbiology.
The Centre for Health Protection reminded parents not to let children with flu symptoms attend school.