|Week 3 Hospital Admissions - Credit Flu Express|
While Hong Kong is known for having a biphasic or `double peaked’ flu season, their heaviest activity usually occurs between February and April with a less severe season in mid to late summer (see Seasonality of Influenza A(H3N2) Virus: A Hong Kong Perspective (1997–2006).
Last summer hong Kong was hit hard by an unusually severe H3N2 epidemic that easily eclipsed their regular winter/spring epidemic of 2017 (see chart above).Less than six months since its peak, Hong Kong is once again embroiled in a rapidly growing, apparently severe flu season; this time heavily dominated by Influenza B. Some of the press releases over the past 24 hours from Hong Kong's CHP help tell the tale.
- DH procures additional seasonal influenza vaccines from vaccine suppliers
- CHP investigates case of severe paediatric influenza B infection and three outbreaks of influenza B at kindergartens
- CHP investigates three cases of severe paediatric influenza B infection
This week's Flu Express report describes local influenza activity - which literally began in earnest less than 3 weeks ago - as `increased markedly to a high level'.Severe cases of influenza are getting off to an unusally fast start, with `92 severe influenza cases among all ages have been reported, including 47 deaths' since the start of Epi Week 2. Some excerpts from this week's Flu Express follow:
Flu Express is a weekly report produced by the Respiratory Disease Office of the Centre for Health Protection. It monitors and summarizes the latest local and global influenza activities.
Local Situation of Influenza Activity (as of Jan 24, 2018)(SNIP)
Reporting period: Jan 14 – 20, 2018 (Week 3)
- The latest surveillance data showed that the local influenza activity increased markedly to a high level. Currently the predominating virus is influenza B.
- Influenza can cause serious illnesses in high-risk individuals and even healthy persons. Given that seasonal influenza vaccines are safe and effective, all persons aged 6 months or above except those with known contraindications are recommended to receive influenza vaccine to protect themselves against seasonal influenza and its complications, as well as related hospitalisations and deaths.
- Apart from adopting personal, hand and environmental hygiene practices against respiratory illnesses, those members of the public who have not received influenza vaccine are urged to get vaccinated as soon as possible for personal protection.
Laboratory surveillance, 2014-18
Among the respiratory specimens received in week 3, the positive percentage of seasonal influenza viruses was 23.56%, which was above the baseline threshold of 10.7% and higher than 16.83% recorded in the previous week (Figure 2). The 1691 influenza viruses detected last week included 179 (2.49%) influenza A(H1), 118 (1.64%) influenza A(H3), 1340 (18.67%) influenza B and 54 (0.75%) influenza C.
Surveillance of severe influenza cases
(Note: The data reported are provisional figures and subject to further revision.)
Surveillance for intensive care unit (ICU) admissions/deaths with laboratory confirmation of influenza among adult patients (Aged 18 years or above)
Since 2018, the Centre for Health Protection (CHP) has collaborated with the Hospital Authority and private hospitals to monitor ICU admissions and deaths with laboratory confirmation of influenza among adult patients regularly. For surveillance purpose, the cases refer to laboratory-confirmed influenza patients who required ICU admission or died within the same admission of influenza infection. Their causes of ICU admission or death may be due to other acute medical conditions or underlying diseases.
- In week 3, 39 adult cases of ICU admission/death with laboratory confirmation of influenza were recorded, in which 18 of them were fatal. Eight of the 39 severe adult cases were known to have received the 2017/18 influenza vaccine. In the first 4 days of week 4 (Jan 21 to 24), 26 cases were recorded, in which 13 of them were fatal.
In week 3 and the first 4 days of week 4 (Jan 21 to 24), there were three cases of severe paediatric influenza-associated complication.
Global Situation of Influenza Activity
Influenza activity continued to increase in the temperate zone of the northern hemisphere while in the temperate zone of the southern hemisphere activity was at inter-seasonal levels. Worldwide, influenza A accounted still for the majority of influenza detections (62%) but influenza B (mostly from the Yamagata lineage) has increased proportionally.
- In the United States (week ending Jan 13, 2018), influenza activity increased. The proportion of outpatient visits for ILI was 6.3%, which was above the national baseline of 2.2%. The most frequently identified influenza virus type reported by public health laboratories in the week ending Jan 13, 2018 was influenza A (H3).
- In Canada (week ending Jan 13, 2018), the overall influenza activity remained high. The proportion of tests positive for influenza increased slightly from 29% in week 1 to 30% in week 2. The proportion of influenza detections that are influenza B has been increasing since week 43 last year. In week 2, 63% of detections were influenza A and 37% influenza B.
- In the United Kingdom (week ending Jan 14, 2018), influenza activity continues to increase across several surveillance indicators although there are signs that some are stabilising. Influenza A and B are co-circulating. The positivity of influenza detection was 27.3% in the week ending Jan 14, 2018, above the baseline threshold of 8.6%.
- In Europe (week ending Jan 14, 2018), influenza activity was increasing in countries in northern, southern and western Europe. Both influenza A and B viruses were co-circulating. 46% of sentinel specimens were tested positive for influenza virus, similar to the previous weeks (42-50%).
- In Mainland China (week ending Jan 14, 2018), the influenza activity in both southern and northern provinces was at the seasonal level for winter influenza season, but the increasing trend slowed down. In southern provinces, the proportion of ILI cases in emergency and outpatient departments reported by sentinel hospitals was 6.0%, same as that reported in the previous week but higher than that in the corresponding period in 2015-2017 (2.9%, 3.2%, 3.1%). In northern provinces, that proportion was 5.5%, lower than that reported in the previous week (5.7%) but higher than that in the corresponding period in 2015-2017 (3.5%, 3.2%, 3.6%). The proportion of influenza detections in the week ending January 14, 2018 was 45.2%. The most common influenza virus detected currently was influenza B.
- In Macau (week ending Jan 13, 2018), the proportions of ILI cases in emergency departments among adults decreased, while that among children increased. The proportion of influenza detections was 38.4%, higher than 33.9% in the previous week.
- Taiwan (week ending Jan 20, 2018) was at the peak of the influenza season. In the week ending January 20, the proportion of ILI cases in emergency department was 14.32% which was above the threshold of 11.4%. The predominating virus was influenza B.
- In Japan (week ending Jan 14, 2018), the influenza season has started in late November 2017. The average number of reported ILI cases per sentinel site increased to 26.44 in the week ending January 14, 2018, which was higher than the baseline level of 1.00. The most frequently identified influenza virus type in the past five weeks was influenza A(H1N1)pdm09, followed by influenza B and A(H3N2).
Despite its fast start, it remains to be seen how long Hong Kong's winter epidemic will last. The impact of last summer's H3N2 outbreaks was due not only to its severity, but to its roughly 12 week duration.