News
26 June 2009
New influenza (H1N1)v virus (swine influenza): Update 14
On 11 June 2009, the World Health Organization (WHO) raised the worldwide influenza pandemic alert level from phase 5 to phase 6 [1, 2]. This indicates that a global influenza pandemic is occurring; there is sustained human-to-human transmission of influenza A (H1N1)v virus in at least one country of two or more regions of the world. Although the pandemic alert is at level 6, this does not mean that illness with influenza A(H1N1)v has increased in severity. The WHO considers the current influenza pandemic to be of moderate severity, similar to seasonal influenza [3]. They encourage all countries to monitor the outbreak, communicate information about it to the public, roll out sustainable plans for mitigating the health and social impact of influenza, and provide adequate medical care for those who are affected.
Current status of the pandemic
Nearly 60,000 cases of influenza A (H1N1)v have now been confirmed from 116 countries and territories around the world [4]; see Table listing affected countries. In the northern hemisphere, Canada, China, Japan, Mexico, the United Kingdom and the United States have each reported more than 1,000 cases, and in the southern hemisphere, Argentina, Australia and Chile have reported more than 1,000 cases.
The spread of this new influenza virus has been more rapid than in the past; during previous pandemics it took more than six months to spread as widely as this virus has spread in less than six weeks [5]. International travel has facilitated the geographic spread, and cases have tended to initially occur in urban settings before wider spread within countries. As the pandemic has progressed cases are increasingly being locally acquired, although the pattern varies between countries depending upon how recently the virus has been introduced into a country. Patterns vary from imported cases only, to limited local transmission often associated with outbreaks in schools, to widespread and sustained community transmission [5-7]. Estimates of the secondary attack rate within households range from 22% to 33%; this is higher than the attack rates for seasonal influenza [5].
Most confirmed cases have been characterised by an uncomplicated febrile respiratory illness, with fever, cough, sore throat, malaise and headache [5, 6, 8]. However, gastrointestinal symptoms have been seen in nearly a quarter of patients. Two to five percent of persons in the US and Canada have been hospitalised with severe illness characterised by pneumonia and respiratory failure; with an overall case fatality rate of 0.1 to 0.2 [8-10]. Many of those who have died have either been pregnant or had underlying conditions such as asthma or other chronic lung disease, diabetes, immunosuppression, and neurologic or cardiovascular disease.
Approximately 70% of cases have occurred in persons under the age of 30 years [5, 6]. The younger age of cases may be related to increased susceptibility in this age group, exposure that has occurred during travel or in school settings, or delays in spread to older populations [5]. However, there is evidence that adults age 60 and older may have some pre-existing antibody to the influenza A(H1N1)v [11]. The complete implications of this finding are not known.
Advice for travellers
There are no travel restrictions to any country. The current pandemic alert level is at phase 6, indicating widespread global transmission. Consistent with this, the WHO do not recommend closure of borders, nor do they recommend travel restrictions.
Specific advice for travellers is outlined in the NaTHNaC Health Information Sheet: New influenza A (H1N1)v (swine influenza): Advice for travellers.
Further information is available at the following sources:
Foreign and Commonwealth Office. Swine flu outbreak: http://www.fco.gov.uk/en/travelling-and-living-overseas/swine-flu
Health Protection Agency, Swine Influenza: http://www.hpa.org.uk/webw/HPAweb&Page&HPAwebAuto
ListName/Page/1240732817665?p=1240732817665
Health Protection Agency: Algorithm for the management of patients with a flu-like illness. S6. 23 June 2009. [Accessed 26 June 2009]. Available at: http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/124073281
WHO, Influenza A (H1N1): http://www.who.int/csr/disease/swineflu/en/index.html
European Centre for Disease Prevention and Control: http://ecdc.europa.eu/
Centers for Disease Control and Prevention, H1N1 Flu (Swine flu): http://www.cdc.gov/h1n1flu/
NaTHNaC Country Information pages: http://www.nathnac.org/ds/map_world.aspx
NHS Choices: http://www.nhs.uk/Pages/HomePage.aspx
References
1. World Health Organization. World now at the start of 2009 influenza pandemic. 11 June 2009. [Accessed 26 June 2009]. Available at: http://www.who.int/mediacentre/news/statements/2009/h1n1_p
andemic_phase6_20090611/en/index.html
2. World Health Organization. Current WHO phase of pandemic alert. [Accessed 26 June 2009]. Available at: http://www.who.int/csr/disease/avian_influenza/phase/en/index
3. World Health Organization. What is phase 6? 11 June 2009. [Accessed 26 June 2009]. Available at: http://www.who.int/csr/disease/swineflu/frequently_asked_ques
tions/levels_pandemic_alert/en/index.html
4. World Health Organization. Influenza A (H1N1) – update 54. 26 June 2009. [Accessed 26 June 2009]. Available at: http://www.who.int/csr/don/2009_06_26/en/index.html
5. World Health Organization. New influenza A (H1N1) virus: global epidemiological situation, June 2009. Wkly Epidem Rec 84:249-257, 2009. Available at: http://www.who.int/wer/2009/wer8425/en/index.html
6. European Centre for Disease Prevention and Control. Analysis of influenza A(H1N1)v individual data in EU and EEA/EFTA countries. 17 June 2009. Accessed 26 June 2009]. Available at: http://ecdc.europa.eu/en/files/pdf/Health_topics/0906_Influenza_
A(H1N1)_Analysis_of_individual_data_EU_EEA-EFTA.pdf
7. Health Protection Agency. Weekly epidemiologic update. 24 June 2009 (Week 26). [Accessed 26 June 2009]. Available at: http://www.hpa.org.uk/web/HPAweb&HPAwebStandard/HPAweb
8. World Health Organization. Human infection with new influenza A (H1N1) virus: clinical observations from Mexico and other affected countries, May 2009. Wkly Epidem Rec 84:185-189, 2009. Available at: http://www.who.int/wer/2009/wer8421.pdf
9. World Health Organization. Considerations for assessing the severity of an influenza pandemic. Wkly Epidem Rec 84:197-202, 2009. Available at: http://www.who.int/wer/2009/wer8422.pdf
10. Centers for Disease Control and Prevention. Hospitalized patients with novel influenza A (H1N1) virus infection – California, April-May, 2009. MMWR. 58:536-541, 2009. Available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5819a6.htm
11. Centers for Disease Control and Prevention. Serum-cross-reactive antibody response to a novel influenza A (H1N1) virus after vaccination with seasonal influenza vaccine. MMWR 58:521-524. Available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5819a1.htm
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