How worried should you be about Hong Kong’s unusual flu outbreak?

More than 300 severe cases have been reported since May, with a summer peak that has arrived earlier than expected

PUBLISHED : Monday, 24 July, 2017, 3:28pm
UPDATED : Monday, 31 July, 2017, 1:43pm

The rising number of flu cases in Hong Kong this summer has sparked widespread concern, especially with the peak season arriving earlier than in previous years.

More than 300 severe flu cases have been reported since May when the Centre for Health Protection announced the start of the influenza season, and workload at public hospitals has ballooned with occupancy rates at medical wards consistently above 100 per cent.

The Hospital Authority has announced a set of measures to cope with the surge in service demand, including shifting patient load to a private hospital.

Here is what you need to know about the current outbreak:

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Q: How severe is the spread of flu in Hong Kong?

The Centre for Health Protection has increasingly found more patient samples testing positive for flu viruses. According to latest statistics, the positive rate for the viruses rose sharply from 13.5 per cent in mid-May to more than 40.6 per cent in the second week of July.

Meanwhile, the number of severe cases continues to add up. Among the 312 severe cases recorded since early May, 205 adults and three children have died from flu.

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Public medical wards have been overburdened with the intake of more patients with severe flu. Overall occupancy rate has gone beyond 100 per cent since July 17.

Some of the more severely hit hospitals include Queen Elizabeth Hospital in Yau Ma Tei and Prince of Wales Hospital in Sha Tin.

Q: What is unusual about the peak season for flu this summer?

The summer flu peak period arrived earlier this year in May, compared with a comparatively “quiet” summer last year after an extended winter flu season. Two years ago, the peak season for flu in summer started in June.

More than 300 severe flu cases have been recorded since May this summer, compared with 50 in the same period last year, and about 180 between May and July in 2015.

Mutation may be behind surge in flu cases this summer, experts say

Dr Leung Chi-chiu, chairman of the Medical Association’s Advisory Committee on Communicable Diseases, said the exceptional increase in cases this summer might be due to a weaker flu peak in winter, of which the reasons remained unclear. As fewer people contracted the flu in winter, there was a smaller number of people who had developed a natural immunity – the body builds its own protection against a particular flu virus after overcoming it. Therefore come summer, more people are susceptible.

Leung also added that those with weaker immune systems, such as young children aged below three, might easily develop more severe complications when infected.

Q: Are Hongkongers sufficiently protected by flu vaccines?

Professor Yuen Kwok-yung, chair professor in the University of Hong Kong’s microbiology department, said that more than 35 per cent of tested samples of influenza A H3N2 – the dominant flu strain in the city this summer – showed a minor mutation.

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Yuen cited a recent study by Danish researchers stating that a specific type of mutation, which was found in the current strain in Hong Kong, might have rendered vaccines used in the past two years ineffective.

But the Department of Health said no evidence suggested that the minor mutation of the H3N2 virus mentioned in the Danish research led to a rise in the city’s cases this summer.

More studies are also needed to determine if such changes would directly lead to weaker effect of flu vaccines.

Meanwhile, the protection period for people who have received flu vaccines late last year is coming to an end as the shots are only effective for about six months.

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Q: Should travellers be advised against visiting Hong Kong?

Dr Leung said visitors to the city should not be worried about the threat of flu, as the dominant strain is not a new one, and flu viruses are prevalent worldwide. Therefore, most people would have already developed a natural immunity in their bodies if they have been previously exposed to the H3N2 virus, which could have been present across countries in the northern hemisphere during the last winter period.

Q: What can be done to prevent flu?

The Centre for Health Protection suggested for people to avoid going to crowded or poorly ventilated public places. High-risk people such as young children or the elderly should consider wearing masks when visiting such places.

People are also advised to wash their hands with liquid soap and water before touching their mouths, nose or eyes, or after touching public installations such as handrails or door knobs.

Alcohol-based hand sanitisers can also be used.